ISSN 1000-0526
CN 11-2282/P
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    2024,50(4):393-406, DOI: 10.7519/j.issn.1000-0526.2023.123001
    Abstract:
    Based on the hourly precipitation data from national meteorological stations of China and the definition method of extreme precipitation with percentile threshold, this paper makes a statistical study of the spatio-temperal distribution and diurnal variation of hourly precipitation in China from April to October in 1951-2021. The results show that the hourly precipitation thresholds of the main rainy season in China are large in the southeast but small in the northwest, and there are four large threshold value centers lo-cated in South China, the Circum-Bohai Region, the middle and lower reaches of the Yangtze River and the Sichuan Basin. With the increasing extremeness, the hourly precipitation threshold in northern China increases more significantly than that in southern China, and the large threshold center moves northward. On the monthly time scale, from the south to north of China, the month with the highest frequency of hourly precipitation is postponed from May to August and the latest month is in West China (September-October). As the extremeness increases, the month with the highest frequency of precipitation is postponed from June-July to July-August, and the regional differences are reduced. In terms of diurnal variation characteristics, the frequency proportion of hourly precipitation of China presents a main valley-peak cycle from afternoon to night and a sub-cycle from midnight to morning. With the increasing extremeness, the amplitude of the main cycle increases and the peak value of the sub-cycle decreases. From the perspective of different geographical locations, the peak time of extreme hourly precipitation in Sichuan Basin is in the early morning, while the peak time in other three areas is consistent with the mean of whole China. The diurnal variation amplitude declines gradually from south to north of China, with the largest amplitude in weastern China. The peak time of hourly precipitation has the characteristics of spatial concentration. The night peak is mainly concentrated in North China, Northeast China and southern coastal areas of China, while the morning-to-forenoon peak is concentrated in the central, east, southwest and the parts of northwest of China. And the gradual delay and abrupt change in spatial distribution of precipitation peak time are closely related to land-sea distribution and large topography. The diurnal variation characteristics of the spatial proportion and frequency proportion of hourly precipitation peak time are similar, both featured with gentle peak in the morning and steep peak at night. This is because the time of the night peak is close to the time at different stations, but the time of the morning peak is not so. Furthermore, with the increasing extremeness, the main peak of frequency proportion at night increases significantly, but the main peak of spatial proportion at night is almost unchanged. This difference is because the change of frequency is mainly caused by the change of frequency at the same stations, rather than the difference between different stations.
    2024,50(4):407-419, DOI: 10.7519/j.issn.1000-0526.2024.022001
    Abstract:
    This article aims to understand the short-time severe rainfall events in the area of Sichuan and Chongqing more comprehensively, and provide references for improving operational forecast skills and numerical weather forecast skills. Based on a convection-scale ensemble forecast system, a short-time severe rainfall event that occurred in the area of Sichuan and Chongqing is selected, and then the ensemble sensitivity analyses of the average precipitation in the target region to the model initial values are carried out and the corresponding dynamic mechanisms are discussed. The results show that the distribution characteristics of sensitive areas correspond well with the synoptic systems that play a key role in the precipitation forecast of the target regions. The sensitive areas around the southwest vortex at 850 hPa and 700 hPa show positive and negative distribution characteristics, the left (right) side of the 500 hPa trough shows negative (positive) sensitive area, the high-level southwest jet area at 250 hPa (south side) shows positive (negative) sensitive area, and the corresponding areas corresponding with the front (back) of the front zone of the middle and low layers show positive (negative) sensitive area. These findings indicate that the stronger the northwest (southeast) wind in the negative (positive) sensitive area around the southwest vortex, the stronger the northwest (southeast) wind on the left (right) side of the trough, the stronger the southwest (northeast) wind in the upper jet stream zone (south), and the higher (lower) the pre-frontal (post-frontal) temperature is, the more favorable they are to the convergence upward movement in the southwest vortex, to the strengthening of the 500 hPa trough, to the strengthening of the 250 hPa divergence, to the increase of the temperature gradient in the frontal zone and to the strengthening of the frontal uplift, which finally result in positive impacts on the precipitation in the target regions.
    2024,50(4):420-433, DOI: 10.7519/j.issn.1000-0526.2023.103001
    Abstract:
    The stability of forecast refers to the consistency of multiple timeliness forecast conclusions issued at different times in the same period. It is an important aspect of the model system, and the large instability will cause trouble to users. In order to understand the stability of common operational models, the relative standard deviation index is used to calculate the magnitude of precipitation fluctuation, and the Flip-Flop index (FFnorm) is improved to measure the reversal degree of precipitation forecast trend in this paper. Besides, the stability of precipitation forecast in two global models (ECMWF, NCEP-GFS) and three regional models (CMA-MESO, CMA-SH9, HHUPS-ST) in six climate zones in China, is discussed on the basis of the two cases of the observed precipitation and the rainstorm and the above. The results are as follows. When there is precipitation, the relative standard deviation of multiple timeliness precipitation forecasts of global models is smaller than that of regional models. That is, the fluctuation of model precipitation forecast is small. The volatility of each model for the western part of the southwest region, the eastern part of the northeast region and southern part of South China is smaller, while that for the western part of the northwest region is larger. In terms of the change trend of multiple timeliness precipitation forecast, the stability of CMA-MESO, NCEP-GFS and ECMWF is better in the two cases, and the index of FFnorm is smaller than that of HHUPS-ST and CMA-SH9. Among them CMA-MESO has a more prom-inent stability effect in the forecast for Southwest China and parts of South China. The index of CMA-SH9 is the largest and the model forecast is unstable. Each model has a relatively large index in the middle and lower reaches of the Yangtze River, and the stability of multiple timeliness forecast is poor. When there is precipitation, the frequency of stable (monotonically increasing or decreasing or constant) trend of precipitation forecast of CMA-MESO is the most, followed by NCEP-GFS. Under the two precipitation conditions, the precipitation forecast of the two models for each region is that the number of monotonically increasing times is greater than the number of decreasing times, and the monotonically increasing characteristics of the CMA-MESO model are particularly significant. The above characteristics could provide some references for model debugging and forecast decision-making.
    2024,50(4):434-448, DOI: 10.7519/j.issn.1000-0526.2023.061401
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    Abstract:
    The circulation classification of 850 hPa hourly wind field in the rainy season in Hunan Province from April to September in 2021 is carried out by using the T-mode oblique rotating principal component analysis method. On this basis, the evaluation is carried out for the hourly precipitation forecast of Rapid Updating Cycle Assimilation and Forecasting System in South China (CMA-GD-R3) in the same period. The results show that the main circulation types affecting the rainy season in Hunan in 2021 are the southwest vortex shear type, the shear type, the southerly type at the edge of the subtropical high and the easterly type at the periphery of the typhoon. The model shows good forecasting ability for the clear-rainy accuracy rate and graded precipitation. The daily variations of clear-rainy accuracy rate and TS of hourly precipitation forecast of CMA-GD-R3 are obvious. The clear-rainy accuracy rate is higher in the night time than that during the day, the peak value of TS score for graded precipitatin appears in the morning, and the effects of rainfall nowcasting of all circulation types are better. The southwest vortex shear type, which has the highest frequency of short-term heavy precipitation, has the lowest accuracy. The southerly type at the edge of the subtropical high has relatively poor performance in heavier precipitation. The SAL test shows that the rainfall location forecast of the model in the cases of the southwest vortex shear type and the shear type is closer to the observation. The intensity forecast is weak first but then strong. The precipitation location forecast in the cases of the southerly type at the edge of the subtropical high is scattered, and the location forecast is unstable. The overall intensity is obviously weaker than the observation. The location forecast in the cases of the easterly type at the periphery of the typhoon is close to the observation in the short-time forecast, and the intensity forecast is significantly weaker. The SAL method can more objectively reflect the structure, intensity, and location deviation in the hourly precipitation forecast.
    2024,50(4):449-460, DOI: 10.7519/j.issn.1000-0526.2023.082701
    Abstract:
    In order to improve the numerical modeling of vertical turbulent transport of water vapor and sensible heat in atmospheric boundary layer and also the simulation of fog, this paper adopts the three-dimensional non-hydrostatic WRF model, with the help of a scale-aware MYNN_SA scheme of both local and non-local turbulences, to simulate a dense foggy weather process that occurred in a broad region from North China to Jiang-Huai Region during 28-29 December 2017. Impacts of the scale-aware boundary-layer turbulent scheme on the development of stable boundary layer, the turbulent transport and the simulation of fog are focused in a model resolution from mesoscale to large eddy. Compared with the surface observations in China and the ERA5 data, the scale-aware MYNN_SA scheme can improve the results of sub-grid-scale turbulent mixing when model resolution approaches the gray-zone scale, which shows better fog density, spatial and temporal variation of the dense fog in comparison with the original MYNN scheme. Detailed vertical structures of the fog, liquid cloud water and temperature inversion are well simulated by the scale-aware MYNN_SA scheme.
    2024,50(4):461-474, DOI: 10.7519/j.issn.1000-0526.2023.053002
    Abstract:
    Taking the high temperature and summer drought areas of ratoon rice in the eastern part of Sichuan Basin as the study area, and based on the mechanism of the influence of meteorological conditions on the growth and development of ratoon rice during the axillary bud germination stage, this article explores the impact factors, pathways, and degrees of axillary bud germination with a structural equation model. Furthermore, combined with the membership function and analytic hierarchy process, a meteorological suitability model for axillary bud germination of ratoon rice is constructed, and the meteorological impact factors and changes in meteorological suitability of axillary bud germination stage of ratoon rice in the study area from 1981 to 2021 are analyzed. The results indicate that temperature, air humidity, and precipitation are key impact factors for axillary bud germination in the high temperature and summer drought areas of ratoon rice in eastern Sichuan Basin. The meteorological suitability model based on these factors can effectively evaluate the meteorological impact of axillary bud germination of ratoon rice. From 1981 〖JP2〗to 2021, the temperature suitability, air humidity suitability, and synthetical meteoro-〖JP〗logical suitability all showed a downward trend, while the precipitation suitability did not have a significant change trend. In general, the spatial distributions of temperature suitability, air humidity suitability, and synthetical meteorological suitability were characterized by “high in the west and low in the east”, while the precipitation suitability was distributed in the pattern of “high in the east and west, and low in the middle”. From 1981 to 2021, there was a significant upward trend in temperature 〖JP2〗and a downward trend in air humidity in the study area,〖JP〗 resulting in significant increases in the accumulated temperature causing harmful high temperatures (daily mean temperature ≥32℃) and the days of harmful low humidity (daily average relative humidity ≤65%). This is major cause for the overall downward trend in meteorological suitability of axillary bud germination stage of ratoon rice.
    2024,50(4):475-487, DOI: 10.7519/j.issn.1000-0526.2023.121201
    Abstract:
    Based on the basic method of consistency evaluation between 〖JP2〗radar base data, this article analyzes〖JP〗 the influence of radar altitude difference, terrain blockage, noise, congestion, temporal and spatial overlap rate, attenuation, etc. on consistency evaluation algorithm result quality, and takes corresponding improvement measures, that is, using radar beam blockage percentage data to correct or directly eliminate overlapping points with blockage, eliminating the overlapping points with low SNR, incomplete filling and abnormality, adding the factors of temporal spatial overlap rate, and analyzing the impact of different threshold temporal and spatial overlap rates on the evaluation results. The improvement measures have improved the quality of the deviation mean and standard deviation in the consistency evaluation results. The improved algorithm is used to evaluate the radar system deviation of Yueyang Station and the consistency of radar echoes in Jiangsu and Anhui regions. The results show that the deviation value between the Yueyang Radar and the surrounding radars has obviously decreased after being maintained, returning to the normal level, and the standard deviation value has also decreased slightly. The average value of deviations between radars in Jiangsu and Anhui is mostly within 2 dB. The vector triangle composed of the deviation mean has a good closure, with standard deviation between 2.9 dB and 3.3 dB and correlation coefficient between 0.40 and 0.55.
    2024,50(4):488-498, DOI: 10.7519/j.issn.1000-0526.2023.121801
    Abstract:
    With the increasing number of X-band dual-polarization radar networks, making network observation of X-band dual-polarization radars and S-band dual-polarization radars has become more necessary. Based on the observation data of the severe convective weather in Beijing on 27 July 2021, the consistency of polarization parameters between the X-band radar network and S-band dual-polarization radar is quantitatively analyzed. The results indicate that Beijing X-band radar networks and S-band dual-polarization radar have a favorable consistency on reflectivity factor (Z), and the differences of differential reflectivity (ZDR) are concentrated near 0 dB, specific differential phase (KDP) has significant difference in the area where Z≥30 dBz. Based on the characteristics of the observed polarization parameter differences, two fusion mosaic methods of parameters are compared: one is direct fusion mosaic and the other is distance-weighted with an exponent. By analyzing vertical cross-section (VCS) of polarization parameters, we see that the blind area of radars could be made up for each other, and KDP can have a more natural transition through the fusion mosaic method distance-weighted with an exponent. The fusion effect could provide some references for different band radars needing fusion mosaic.
    2024,50(4):499-513, DOI: 10.7519/j.issn.1000-0526.2024.022602
    Abstract:
    Based on the NCEP/NCAR reanalysis data and climate observations from 2400 stations of China, the characteristics of climatic anomalies over China in autumn 2023 and the possible causes are analyzed. The results denote that, in autumn 2023, the average temperature in China peaked the record in the same period since 1961, and the average precipitation was close to the climatic mean, but had uneven spatial distribution and significant intra-seasonal variability. The circulation in the mid-high latitudes of Eurasia showed a “negative-positive-negative” pattern on the seasonal mean scale, leading to the abnormal warming in China. In September, the circulation was in a “positive-negative-positive” pattern that caused the frequent activity of the trough near Balkhash Lake and the increase of precipitation in Northwest China; in October, the “negative-positive-negative” pattern of circulation caused further warming in northern China; and in November the circulation pattern of “positive in west and negative in east” formed, enhancing the cold air in the east and causing the temperature in Northeast 〖JP2〗China to drop to below normal and precipitation〖JP〗 to be more than normal. The Western Pacific subtropical high (WPSH) was stronger and more westward than usual overall, and its ridge line swung frequently in the meridional direction, that is, the ridge line was abnormally further north than usual in September, further south than usual in October and close to normal position in November. The India-Burma trough was significantly stronger in September and near normal during October-November. In September, the stronger Indo-Burma trough and the northerly WPSH jointly contributed to the heavy〖JP2〗 rainfall in the region between the middle and lower reaches of Yangtze〖JP〗 River and the lower reaches of Yellow River. The basic water vapor transport condition in eastern China became negative from October to November. In addition, typhoon activities in southern coastal area of China were frequent in September and October, resulting in more precipitation in South China. These results reveal that the climate anomaly in autumn 2023 was significantly affected by the intra-seasonal variation of the atmosphere, and it did not match the typical responses to the tropical SST anomaly.
    2024,50(4):514-520, DOI: 10.7519/j.issn.1000-0526.2024.032901
    Abstract:
    The main characteristics of the general atmospheric circulation in January 2024 are as follows. There were two polar vortex centers in the Northern Hemisphere. The Eurasian mid- and high-latitude circulation showed a two-trough-one-ridge pattern. The East Asian trough was more eastward. The monthly mean precipitation (16.3 mm) over China was 15.6% more than normal (14.1 mm). The monthly average temperature was -3.8℃, which was 1.0℃ higher than that in the same period of normal years. Cold and warm temperatures fluctuated greatly during the month. There was one nationwide cold wave process and two widespread persistent fog-haze weather processes, among which the cold wave weather process from 20 to 22 January presented the characteristics of a wide range of influence, and cooling, long duration of strong wind and heavy snowstorm.
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    Available online:  May 22, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.031403
    Abstract:
    Based on hourly precipitation data from the National Meteorological Information Center of the China Meteorological Administration, combined with the diversity of the terrain, the temporal and spatial characteristics of hourly precipitation, as well as characteristics of different types of Hourly Heavy Rainfall Event(HHRE) before(1992-2002)and after(2003-2021)the impoundment in Three Gorges Reservoir Area in the summer(from June to August)are analyzed. The results show that:(1)After impoundment, the precipitation and frequency decrease but intensity increases, while the change trends of the three are not significant. There is an obvious geographical distribution pattern for precipitation changes, with precipitation, frequency and intensity increasing in the central north of Three Gorges Reservoir Area, mostly located in the north of the Yangtze River, and the precipitation and frequency decreasing in the southwest while the intensity decreasing in the central south and northwest of Three Gorges Reservoir Area, mostly located south of 31°N.(2)There is a spatial distribution difference in the diurnal peak phases of precipitation, frequency, and intensity of hourly precipitation before and after impoundment, with the degree of difference being as follows: precipitation intensity>precipitation>precipitation frequency. After impoundment, the number of stations increases with increasing trend for precipitation, frequency and intensity, and the diurnal peak phases of precipitation and intensity have phase shift features in high altitude mountainous areas..(3)There is no significant change in the precipitation probability and proportion of hourly precipitation at various grades before and after impoundment. The precipitation probability shows the maximum(about 42%)at the grade of [0.1, 0.5)mm, and the minimum(about 1%)at the grade of ≥20 mm. The precipitation proportion shows the maximum(about 35%)at the grade of [1, 5)mm, the minimum(not more than 4%)at the grade of [0.1, 0.5)mm, and about 15% at the grade of ≥20 mm.(4)The daily variation characteristics of hourly precipitation after the impoundment are more obvious. The bimodal structures of precipitation and frequency of hourly precipitation at the grade of ≥20 mm are more prominent, while the peak time ranges of precipitation and frequency of hourly precipitation at other grades tend to expand, while the diurnal scale fluctuations of hourly precipitation intensity at each grade are more frequent.(5)Analysis of different duration types of HHREs shows that both before and after impoundment, the short-duration type of HHRE is the highest(more than 50%), followed by medium-duration type(less than 30%), and the long-duration type is the lowest(less than 20%). The short-duration type of HHREs mostly start in the afternoon, while the other two types of HHREs mostly start at night. After impoundment, it is beneficial for HHRE maintenance, with a decrease in the proportion of short-duration type of HHRE and an increase in the proportion of medium-duration and long-duration types of HHREs, and the probability of the former starting at noon and afternoon increases, while the probability of the latter two starting in the morning increases.
    Available online:  May 21, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.033001
    Abstract:
    Using the detection results of GPM dual frequency rain radar (DPR) and microwave imager (GMI) from 2014 to 2021, the differences in observing snowfall processes between different precipitation products of DPR were compared. The macro and micro characteristics of three types of snowfall systems (deep, shallow, and near surface) were clarified, and the structural characteristics of typical snowfall systems were analyzed. The results indicate that DPR_NS dataset has good sensitivity to identifying snowfall clouds; The probability of shallow snowfall clouds appearing exceeds 60%, while deep clouds contribute the most to snowfall. The LWP (liquid water path) and IWP (ice water path) of the three types of clouds are mostly distributed in 80-450 g/m2 and 100-380 g/m2, with a positive correlation between the echo top height, LWP, and IWP and the near surface snowfall rate as a whole; The four selected cases are located in the Ale Mount Taishan area (a), the Ili River Valley (b), the hinterland of the Gurban tunggut Desert (c), and the northern foot of the Kunlun Mountains in southern Xinjiang(d).The snow system observation results of GMI"s 166 GHz high-frequency channel are more detailed, and the brightness temperature is concentrated between 200-275 K. A and b cases are mainly ice clouds, and c and d are mostly ice water mixed clouds, and the snowfall intensity and area of the former are greater than the latter; The radar reflectivity factor of the cloud profile is concentrated at 16-25 dBz and 0.75-4.65 km. Cloud clusters in cases a, b, and d exhibit a "left leaning" structure, with the highest echo intensity in the upper and middle parts of the cloud, belonging to a typical development stage cloud cluster. The echo intensity of case c is mainly located in the lower part of the cloud vertical contour, and the cloud cluster is in the mature stage. Dm (mass weighted average diameter) and dBNw (particle number concentration) produce more snowfall between 1.0~1.22 mm and 33~35.The snowfall intensity is not only related to the particle size of ice crystals or supercooled water, but also affected by the particle number concentration. This study helps to scientifically evaluate the potential and effectiveness of artificial snow seeding and cloud seeding in different regions of northern and southern Xinjiang from the perspective of the structural characteristics of the snowfall system in Xinjiang.
    Available online:  May 21, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.033002
    Abstract:
    Based on the squall line recognition standards, 36 squall line processes were identified using the radar combination reflectance mosaic product from May to September 2015 to 2020 in Liaoning Province,and the squall line characteristics and several different formation environment characteristics were summarized. The results show that: (1) The area with the largest frequency of squall line formation in Liaoning Province is obviously from the northwest of Liaoning Province and Chifeng City to Aohan Banner, followed by the west of Bohai Sea to the sea surface of Bohai Strait, and the area with the lowest frequency of squall line formation is the mountain line of Tangshan and Qinhuangdao in the east of Hebei Province. (2)The vast majority of squall line processes occur in June and August, while the least squall line processes occur in May. Squall lines are mainly formed from 12:00 to 21:00, and from 14:00 to 17:00 is the concentration period of squall lines. The length of squall line is between 114 km and 273 km, the maximum reflectivity is 65 bz, the average life cycle is 3.2 hours, and the average moving speed is 59.4 km/h (16.5 m/s). (3) The squall line process in Liaoning Province is 33.3% of the fault line, 19.4% of the rear extension type, 36.1% of the fragment type, and 11.1% of the stratiform cloud embedding type. The main organizational form is stratiform cloud trailing type TS, parallel stratiform cloud type PS and stratiform cloud leading type LS have fewer occurrences. 55.6% of squall lines dissipated in the form of reverse broken lines, and 8.3% of squall lines dissipated in the form of contraction lines. 36.1% of squall lines dissipated in the form of reverse fault zone. (4) In the circulation situation of squall line formation in Liaoning, the cold vortex front type is the most common, followed by the low trough front type. The circulation situation of squall line formation in Liaoning is the cold vortex rear type, accounting for 16.7%. The convective effective potential energy and the sink convective effective potential energy of each circulation pattern show the characteristics of "double 1000". Different circulation patterns have different characteristics in water vapor supply, stratification instability, vertical wind shear and other physical quantities.
    Available online:  May 21, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.032601
    Abstract:
    Based on the FY-4A satellite water vapor images and GIIRS products combined with potential vorticity products, using interpretation principle of meteorological satellite images and basic theory of potential vorticity conservation, the cold wave in central and eastern China from 6 Jan to 8 Jan in 2021 are analyzed. It is found that this cold wave is affected by the high-altitude cold vortex and the surface cold high. The low-level cold air moved from the south of Baikal Lake to the southeast and strengthened at 0800 BT 5 Jan. At 2000 BT 8 Jan, it weakened. The comparison of 24-hour temperature change of FY-4A/GIIRS 850 hPa and ERA5 850 hPa shows that the characteristics of the low troposphere cold air moving to southeast and the cold and warm temperature change regional distribution monitoring with FY-4A/GIIRS products are basically consistent with the ERA5 data. The intensity of the 24-hour temperature change center of FY-4A/GIIRS 850 hPa is slightly higher than the intensity of the 24-hour temperature change center of ERA5 850 hPa. The increase of high level potential vorticity near the enhancement of the dark area of the water vapor image triggers the enhancement of the subsidence movement behind the high level cyclonic circulation, and the dry air subsidence causes the enhancement of the surface high pressure. The increase of absolute vorticity near the center of 500hPa cold vortex is one of the reasons for the enhancement of cold air. During the period of sharp increase of cold air, the increase of vortices in the middle and lower layers causes the accumulation of cold air on the ground and the enhancement of cold wave. The analysis characteristics of potential vorticity theory on the enhancement mechanism of cold wave cold air are consistent with the development of cold wave cold air movement monitored by FY-4A/GIIRS temperature data, which indicates that the application of FY-4A/GIIRS temperature data can effectively monitor and analyze the change characteristics of cold wave cold air.
    Available online:  May 21, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.051601
    Abstract:
    Based on the high spatial-temporal resolution data such as ERA5(0.25°×0.25°) reanalysis data, automatic weather stations data, doppler weather radar data and the retrieval data from Variational Doppler Radar Analysis System(VDRAS), we compared and analyzed the mesoscale characteristics and triggering mechanism of three local sudden rainstorms in the urban area of Tianjin on 22 July 2018, 18 July 2019 and 23 August 2021.The results show that there is no obvious synoptic scale system leading the three local sudden heavy rainstorms, but the ambient atmosphere has a high convective available potential energy (CAPE) and a low convective inhibition energy (CIN). The lifting condensation height (LCL) was 0.2~ 0.4 km, and there was a certain wet layer in the lower level. The occurrence of local sudden rainstorm was mainly related to the mesoscale system caused by urban heat island and different underlying surface characteristics. Before the local sudden rainstorm, the difference of temperature and pressure between the urban area and the coastal area increased, and the temperature and pressure near the urban area had obvious non-uniform distribution characteristics. The mesoscale thermal low pressure and the high temperature gradient provided favorable environmental conditions for the occurrence of local convection. In addition, before the occurrence of local sudden rainstorm, the sea breeze in the coastal area was obviously strengthened, resulting in the convergence of wind speed. The thermal low pressure of the urban heat island and the disturbance of sea breeze made the mesoscale convergence intensity significantly strengthened, which was the main reason for the occurrence of local sudden rainstorm. γ-mesoscale convective cells were triggered at the edge of the strong convergence center.
    Available online:  May 21, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.051701
    Abstract:
    Based on the outpatient and inpatient data of heatstroke in Tianjin from 2016 to 2020, a comparative analysis of the relationship between meteorological factors and the heatstroke visit rate was conducted using the Generalized Additive Model (GAM) and Distributed Lag Nonlinear Model (DLNM). By introducing the human heat balance model and predicted mean vote (PMV), a localized heatstroke meteorological risk warning index was established. The results show that the number of outpatient and inpatient cases of heatstroke in Tianjin is concentrated from late June to early August each year, with 84% of the peak heatstroke days occurring in 6 continuous weather process over the 5 years. The occurrence is most correlated with the meteorological conditions of the current day and the previous day, with a significant increase in heatstroke cases when the maximum temperature exceeds 35°C. Males are more susceptible to heatstroke than females, and the visit rate of the elderly is significantly higher than the general population. The heatstroke visit rate is positively correlated with average temperature, maximum temperature, relative humidity, and solar radiation intensity, with the strongest correlation with average temperature and a negative correlation with wind speed. Introducing the human heat balance model, PMV shows a higher correlation with the heatstroke visit rate than any single meteorological factor, indicating PMV has a clear advantage in evaluating heatstroke meteorological risk. A forecasting equation with PMV as the key indicator was developed, which demonstrated significant advantages in predicting heatstroke high-incidence events.
    Available online:  May 20, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.020701
    Abstract:
    Based on Guangdong meteorological disaster archives, ERA5 reanalysis data and Doppler radar data, the spatiotemporal distribution, weather background and parent storm patterns of Guangdong tornadoes during 1961-2022 are analyzed, results are as follows:In the past 62 years, Guangdong has recorded a total of 225 tornadoes. Among them, since 2006, when multiple sources of observation data are relatively complete, about 6 tornadoes have occurred annually, about 50% of tornadoes occur in the background of tropical cyclone weather, followed by 40% of tornadoes in the Westerlies weather system, but the number of tornadoes fluctuates greatly year by year, up to 17 (2008), and only one tornado or no tornado record in some years. Tornadoes mainly occur from April to September, with 54% occurring from April to June, mostly in the context of the westerly weather system, and 34% occurring from July to September, mainly in the context of tropical cyclones and disturbances. More than 85% of tornadoes occur between 0800-2000 BJT (Beijing Time, the same below), with the highest occurrence occurring between 1400-1800 BJT (accounting for about 40%). Tornadoes occur most frequently in the Pearl River Delta, Leizhou Peninsula and Chaoshan Plain. There are few tornadoes in the northern mountainous areas. Foshan, Zhanjiang and Guangzhou are the cities with the highest incidence of tornadoes. Among the convection patterns that generate tornadoes in Guangdong, more than 50% of tornadoes are generated from miniature supercells embedded in the zonal convective system, and about 30% of tornadoes are generated from supercell in the multicells storm system. Different from the situation that isolated convection cell in the United States are more likely to generate tornadoes, the relative frequency of isolated convection cell that generate tornadoes in Guangdong is very low, accounting for about 5%. More than 90% of tornado parent storms have low-level mesocyclone, but only about 44% of tornado parent storms are accompanied by low-level TVS. Strong tornadoes (EF2+) are typically characterized by low-level mesocyclones with rotational speeds exceeding 20 m·s-1 and TVS velocity differences exceeding 40 m·s-1 .
    Available online:  May 07, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.030801
    Abstract:
    Guangxi encountered a double convective bands process from 20:00 BT 25 March to 08:00 BT 26 March 2023, which are significantly different from that of the double traditional rain belts, resulting in a significant deviation in the subjective forecast. Based on multi-source observation data and ERA5 reanalysis data, the Rossby wave energy dispersion, moist potential vorticity and horizontal frontogenic forcing were diagnosis and analyzed in this process. The results show that the process occurred under the background of large-scale circulation adjustment. The two Rossby wave trains originated from the polar vortex and the Black Sea in the middle and high-latitude jointly promoted the gradual vertical rotation of the northeast transversal trough, and guided the mid and high latitude cold air further southward. During this period, the south branch trough in the low latitude gradually moved eastward, which provided the dynamic lifting above the cold cushion in Guangxi, and also promoted the convergence of cold and warm air in the low level in Guangxi. With the addition of cold air to the south and southerly winds advance northward under the inertial oscillation, the convergence of warm and cold air in Guangxi was enhanced, and the enhancement of atmospheric moist baroclinicity leads to the development of moist potential vorticity, resulting in conditional symmetric instability of stratification. Warm and moist air climbed from south to north to the conditional symmetric instability area near 700 hPa, and then combined with the positive vorticity advection in front of the upper level trough to trigger elevated convection, resulting in the development of the northern branch convective band. Influenced by the special topography of Guangxi, the favorable configuration of the θse isoline and the flow formed a tensile deformation effect, resulting in frontogenic forcing, which triggered the initial convection in the south branch of Northeast Vietnam. The large θse latitudinal gradient and strong vertical wind shear in the low level of the central Beibu Gulf resulted in strong moist baroclinicity, which promoted the organization development of the southern branch convective system when it passed through, and formed bow echo due to the mid-level dry air ensnagging.
    Available online:  April 26, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.041701
    Abstract:
    In order to analyze the distribution characteristics of ice crystals in cold clouds and reveal the evolution mechanism of growth, the ice crystals are labeled with 8 categories according to the shape and scale characteristics, and?a type of barsis labeled for data quality control. Integrate 9 types of label images and build an image dataset.Using the transfer learning VGGNet16 method for identification training, the classification accuracy of the trained model reaches 98%. The model is applied to the study of ice crystal characteristics of cold clouds in autumn, and 3-order convective-stratiform mixed cloud and the 3-order stratiform cloud precipitation process are selected to analyze the proportion of ice crystal shape in different temperature ranges and the change characteristics of ice crystal spectrum. The results show that the initial shape distribution of ice crystal is determined by the temperature by affecting the ratio of base surface to edge surface.In the same temperature range, the proportion of spherical ice crystals and linear ice crystals in convective-stratiform mixed cloud is higher than that in stratiform cloud, and the proportion of various ice crystals is relatively fixed when the temperature lower than -12℃.In convective-stratiform mixed cloud,the diameter of linear ice crystals is concentrated in 300-800μm, the ice crystal spectrum is multimodal distribution.The aggregate diameter is greater than 600μm, the concentrations at the beginning and the end of the ice crystal spectrum are equal.The diameter of spherical ice crystals is concentrated in 120-300μm, and the ice crystal spectrum shows a monotonically decreasing trend.
    Available online:  April 25, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.022401
    Abstract:
    Based on the Tianjin Doppler radar data, conventional observation, ground automatic station meteorological data, ERA5 reanalysis data and VDRAS data, a rare heavy precipitation(HP) supercell storm which was guided by a multi-cell strong storm occurred in the eastern Hebei on 19 June 2017 was analyzed, the evolution characteristics and maintenance mechanism of supercell storms are mainly discussed. The results indicate that the sea-breeze front and the gust front of the multi-cell strong storm provide better dynamic conditions, the high temperature and high humidity area of tongue shaped by sea-breeze front and the gust front in the lower layer surrounding provide better thermal conditions for the formation of the supercell, when the convection cell moves into the tongue area, then it rapidly develops into a supercell and moves southeastward along the outflow boundary of multi-cell strong storm. The relatively stable gust front provided by the slowly weakening severe thunderstorm not only provides long-term thermodynamic conditions for the development and maintenance of supercell, but also guides its movement, which is of great significance for the short-term and imminent warning of the convective weather. At the beginning of the formation of supercell, affected by the outflow of multi-cell strong storm cold pool, the southerly winds near the ground turn to stronger easterly winds, the configuration of mesoscale environment has changed significantly, the vertical wind shear of 0~6 km increases to 27 m.s-1 and the shear of 0~3 km increases to 17~19 m.s-1 is the main reason for the rapid formation of mesocyclone, Secondly, the strong vertical vorticity advection on the convergence line is also conducive to the formation and maintenance of mesocyclone. The reason why the cyclone in supercell started at the lower level is that the vertical wind shear of 0~3 km obtained from VDRAS data is always about 20 m.s-1, the oblique vortex effect is obvious which provides a large and long-term horizontal vorticity input for the development and maintenance of supercell. During the formation and development of supercell, the relative helicity (SRH) of the storm is between 140 and 171 m2.s-2, which is more than 150 m2.s-2 for most of the time, Before the formation of supercell and near the dissipation stage, the SRH is significantly smaller, which is less than 150 m2.s-2 for most of the time, that indicates the SRH has a clear indication for the occurrence and development of supercell. The outflow of the cold pool precedes the formation of the supercell, which strengthens the convergence and uplift of the inflow, and is conducive to the development and maintenance of the supercell, In addition, there are more cells splitting from parent storm, which to some extent weakens the strong development of the supercell, but it just makes the sinking outflow not too strong and causes the gust front to move away quickly, making the cold pool always maintain a certain intensity, at the same time, the front of multi-cell storm provides a stable vertical wind shear of 0~3 km (maintained at about 20 m.s-1) for the supercell, this results in a long-term balance between the wind shear and the strength of the cold pool, and finally the supercell maintains a stable state for a long time. In a word, the main reason why the supercell maintains self-organization for a long time is that the appropriate vertical wind shear provided by the mesoscale environment keeps balance with the development of the storm.
    Available online:  April 19, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.031402
    Abstract:
    This paper is the second part to introduce the physical understanding and fuzzy logic combined forecasting system for short-term multi-category convective phenomena that developed by the National Meteorological Center (NMC). A convective case occurred on 13 June 2022 is firstly studied. Then the deterministic and probabilistic properties of lightning, short-duration heavy rainfall, thunderstorm high wind, and hail provided by the objective forecasting system are evaluated. The forecasting data lasts from 1 April to 30 September that initiated at 08 Beijing Time with intervals of 12-hours within 96 hours are used. The operationally used spatial verification method and matrix indicating deterministic and probabilistic properties are adopted. The case studies show the focused area can be well predicted 24-hours in advanced. Verification results show that short-duration heavy rainfall has the best performance among the four different convective weather phenomena. Then is the lightning. The thunderstorm high wind has certain applicability. All the four convective weather phenomena are obvious over-forecasted. There are daytime and nighttime variations on evaluation results. The evaluation results provide an overall reference for the operational use of the physical understanding and fuzzy logic artificial intelligence combined forecasting system. Further development plans can be designed based on the evaluation.
    Available online:  April 12, 2024 , DOI: 10.7519/j.issn.1000-0526.2023.092802
    Abstract:
    In order to investigate microphysical characteristic in the hailstorm, the dual polarization radar and raindrop spectrum data, with the hydrometer classification algorithm were used to analyse a hail weather occurred in Mount Tai on 1 June 2020, the distribution of the radar variable, hydrometer and the raindrop in the region around the Mount Tai station were obtained when the hailstorm cloud passed through the Mount Tai, the studies showed: 1) when the edge of hailstorm began to effect the Mount Tai station, the large gradient area of reflectivity (ZH), which coinciding with differential reflectivity(ZDR) arc position, was next to the Mount Tai station, the particles identified in ZDR arc were mainly composed of abundant big drop, which was formed by melting graupel particles over Mount Tai station; the structure of the raindrop spectrum was double-peak, the greater contribution to precipitation is 2-3mm particles. 2) When the main part of the hailstorm cloud influenced the Mount Tai station, there occurred three-body scattering echo in radial front of the station and overhang echo over the station, the particles in the vicinity of the station were mainly identified as hail; on the south side of Mount Tai station there occurred the bounded weak echoSregion(BWER), the convergent ascending motion was enhanced in the BWER, which was semi-surrounded by the large value of ZDR(ZDR ring), the particles in ZDR ring were mainly identified as big drop and hail, with small amount of graupel and wet snow; the contoured frequency by altitude diagram(CFAD) showed the ice phase process was enhanced, the hail particles under the -10℃ were mainly formed by the graupel particles between 0℃ and -10℃ layer riming the big drop and light rain particles carried by updrafts, these particles could not fall and collide to form larger precipitation particles during this period, therefore the structure of the raindrop spectrum became single-peak, the greater contribution to precipitation was 14-16mm particles. 3) When the hailstorm cloud left the Mount Tai station, CFAD showed the ZHcorresponding toSthe high frequency region decrease, the ice phase process was weaken, the efficiency of the cold cloud droplets attached to the ice crystals to converted into graupel was reduced, a large number of ice crystals and dry snow particles were identified above Mount Tai station, where the feature of the stratiform cloud precipitation appeared; big drop particles were formed by the melting hail, the structure of the raindrop spectrum became double-peak again, the second peak value of particles was 2-3mm, which contributed more to the precipitation.
    Available online:  April 08, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.040101
    Abstract:
    The snowfall in Beijing on January 12, 2023 was the first snowfall appearing in early and mid-January in last 42 years, and the precipitation types underwent complex changes during this process. In this paper, we utilize various conventional and non-conventional observations such as cloud radar and micro rain radar (MMR) data as well as ERA5 reanalysis data to analyze this event, focusing on causes of complex phase distribution and variation. Our findings indicate the following: The low level warm and wet southerly jet stream provides abundant moisture for precipitation. However, a lack of uplifting of warm and wet air by cold east winds and weak upper trough results in relatively low precipitation amounts, meanwhile the northeast wind just above the surface did not play the role of cold cushion, which was not conducive to the maintenance of snow and snow in the whole city. The disparity in the height of the 0 ℃-layer between western and eastern Beijing, caused by low-level warm advection, explains the snowfall in the west and rain in the east. Additionally, the cooling effect caused by melting and evaporation process is the main reason for the rapid decrease of 0 ℃-layer height just lower than 500 m, which caused rain to snow in plain areas. Thickened > 0 ℃ warm layer and decreased snowflake size and density immediately above the melting layer caused snow to turn into rain reaching the ground. When it comes to forecasting precipitation types, deterministic models struggle to accurately depict the snow-melting process. However, short-range ensemble forecast results can compensate for the errors in deterministic models. Integrating cloud radar, micro rain radar, and microwave radiometer data ETC. enhances our ability to monitor and analyze snow formation within clouds and melting in the boundary layer, thus improving the accuracy of precipitation type now casting.
    Available online:  April 07, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.022002
    Abstract:
    Using the basic reflectivity factor PPI image data of 50 S-band Doppler weather radars for 47 severe convective cases in the central-eastern region of China from 2016 to 2020, the three-body scatter spike characteristics are analyzed based on the screening of 2626 the three-body scatter spike samples. The results show that: (1) TBSS is most frequently observed at altitudes of 1.5 km and 5 km and an elevation angle of 2.4°. (2) TBSS is mainly observed in the radar radial distance from the edge of the radar static cone area to the radar radial distance of 210 km. It reaches its peak nearly 115 km from the radar. In the radar polar coordinate system, TBSS appears more in the south than in the north, and more in the west than in the east. It is better to observe TBSS when the angle between the moving direction of the convective storm and the radial direction of the radar is larger than 30 degrees. (3) The TBSS echo strength decreases rapidly to 5 dBZ within 0-15 km radially outward from the beginning, and fluctuates between -5 and 10 dBZ after 15 km, with more than 70% of the TBSS region being weak echoes below 25 dBZ. The length of 99% of TBSSs is under 40 km, and the patterns of TBSSs with varying lengths follow a normal distribution. (4) There is no significant correlation between the frequency and length of TBSS occurrences and the highest value of the high echo core as well as the area of the high echo.
    Available online:  April 07, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.032801
    Abstract:
    Based on the precipitable water vapor (PWV) data from GNSS Meteorological Network and the time series of hourly precipitation, temperature, pressure and relative humidity from the adjacent meteorological station in Hubei between June and July from 2019 to 2020, a new model including three predictors (PWV, 6-houly PWV tendency (PWV_6) and pseudo-equivalent temperature anomalies (Δθse) ) for short-term heavy precipitation is proposed. The critical success index (CSI) and probability of detection (POD) are used to determine and validate the threshold for the three predictors. This new model is tested using the data between June and July in 2021, and proved to be more effective than the traditional methods. The analysis found that 78.6% of the heavy precipitation samples occurred under the condition of the 15 hours cumulative value of PWV_6 (ΣPWV_6) exceeded 75 mm and the 24 hours cumulative value of Δθse (ΣΔθse) exceeded 30 K. It could be indicative of heavy precipitation in Meiyu period very well while comprehensively considering the high-value zones of ΣPWV_6 and ΣΔθse. An analysis of "21?7" southern extreme rainstorm showed that the threshold method could provide scientific data support for the objective forecast of heavy precipitation.
    Available online:  April 02, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.021701
    Abstract:
    Lightning and conventional ground observations provide complementary atmospheric background information, and the combined assimilation of these two types of data has the potential to further improve the accuracy of forecasting severe convective weather compared to assimilating only one type of data. In this study, a mesoscale convective system occurred in Guangdong Province on June 16, 2017 as an example to analyze the effect of the combined assimilation of the above two kinds of data on the simulation and prediction of mesoscale convective system compared with the single assimilation of one of the two kinds of data. The lightning data is continuously assimilated into the model through the WRF-FDDA system with a lightning accumulation window of 15 minutes, the conventional observations data is assimilated into the model by the WRFDA-3DVAR system at one hour interval. The results show that the introduction of lightning data in the joint assimilation experiment improves the accuracy of updrafts, cold pools, and gust fronts in the background fields, which in turn improves the simulation and forecast accuracy of the convective system, compared with the assimilation of conventional ground observations only. The introduction of conventional ground observations in the joint assimilation experiment reduces the background field errors in temperature, water vapor, and wind fields over a larger area, suppresses the spurious convection in some areas, and overall improves the simulation and forecast accuracy of the convective system. The results of prediction skill score show that the combined assimilation of the two kinds of data also improved the prediction skill score of the analysis period and the forecast period to some extent.
    Available online:  April 02, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.031404
    Abstract:
    Operational positioning and intensity estimation errors, as well as track and intensity forecast errors of typhoons over the western North Pacific and the South China Sea in 2022 were evaluated according to the “Regulations on Typhoon Operations and Services”. The results show that in 2022, the positioning errors made by the official typhoon forecast agencies displayed negative correlation with the typhoon intensity grades. The mean positioning errors made by the National Meteorological Centre (NMC), CMA, were the smallest at each typhoon intensity grade. In 2022, the mean positioning errors made by NMC (15.4 km) was 21.8 % smaller than that of 2021 (19.7 km), and the mean absolute error of intensity estimation made by NMC (1.3 m·s-1) was slightly smaller than that of 2021 (1.4 m·s-1). The mean track forecast errors by subjective and objective forecasts were generally reduced compared with 2021, while the mean absolute errors of intensity forecasts were generally increased compared with 2021. Track forecast skill scores by SSTC, CMA-TRAMS, and ECMWF-IFS were relatively high. Intensity forecast systematic biases by NCEP-GFS, JMA-GSM, CMA-TRAMS, and CMA-TYM were insignificant, and intensity forecast skill scores by NCEP-GFS, HWRF, and CMA-TRAMS were relatively high.
    Available online:  April 01, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.031401
    Abstract:
    Accurate and objective short-term thunderstorms, short-duration heavy rainfall, thunderstorm high winds, and hail forecasting are meaningful for extending the validation of warnings and taking targeted preventive measures. In this paper, the framework and implementation details of the physical understanding and fuzzy logic artificial intelligence combined objective forecasting system that provides short-term forecasts for lightning, short-duration heavy rainfall, thunderstorm winds, and hails developed by the National Meteorological Center (NMC) are introduced. The key predictors used for the four different convective weather phenomena, the methods for obtaining the membership functions, and the weighting sets of predictors are discussed. The property for the wide applicability of the physical understanding and fuzzy logic artificial intelligence combined method is further explored by that the combination of the two can cover and reveal the key characteristics of the ever-changing environmental features favorable for a specific convective weather phenomenon.
    Available online:  April 01, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.020401
    Abstract:
    This study employs observational data from stations in the eastern part of the southwestern region and ERA5 reanalysis data to examine the characteristics and causes of the inverse phase shift anomalies in winter temperatures (hereafter referred to as anomalous shifts) in this area. The findings indicate that post-2000, this region tends to experience a pattern of colder temperatures earlier in the winter followed by warmer temperatures later (referred to as P1 type), whereas a pattern of warmer temperatures followed by colder ones (P2 type) was more prevalent in the 1970s. During the occurrence of these anomalous shifts in winter temperatures, the 500 hPa geopotential height field reveals that the Tibetan Plateau plays a crucial role in the circulation system, even surpassing the influence of the Ural blocking high. At the 200 hPa wind field level, systems such as the westerly jet stream affect the East Asian winter monsoon, thereby influencing the intra-seasonal variations in winter temperatures. In terms of sea-level pressure fields, when the Mongolian high exhibits significant weakening after an initial strengthening in winter, P1 type temperature shifts are more likely to occur, and vice versa for P2 type shifts. Additionally, during these anomalous temperature shifts within the winter season, significant anomaly signals are observed in the North Atlantic, the equatorial central and eastern Pacific, and the equatorial Indian Ocean. High sea surface temperature anomalies in these three areas during the preceding summer and autumn seasons tend to lead to P1 type shifts in winter temperatures, whereas the opposite conditions tend to result in P2 type shifts, serving as potential precursors for prediction.
    Available online:  March 29, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.031901
    Abstract:
    To address the limitations of traditional models in capturing long-term dependencies and generalization ability in meteorological sequences, a novel Air Temperature Forecasting Model based on Sparse Attention and Adaptive STL (ATFSAS) is proposed. ATFSAS employs an encoder-decoder architecture, integrating a sparse attention mechanism to effectively capture long-term dependencies in meteorological observation data. An information distillation method is introduced to reduce redundancy during the encoding process. The model refines the seasonal and trend components in the forecast signal by combining a multi-layer decoder with an adaptive Seasonal and Trend decomposition using Loess, achieving precise air temperature prediction. In a 24-hour air temperature forecasting task on the Jena climate dataset, ATFSAS achieved a mean absolute error of 1.7108°C. Compared to the LSTM model, ATFSAS demonstrated superior performance in medium-short term daily average air temperature and multi-region single-day average air temperature forecasting on the China Ground Climate Daily Dataset, enhancing prediction accuracy by 35.56% and 23.66%, respectively.
    Available online:  March 20, 2024 , DOI: 10.7519/j.issn.1000-0526.2023.121101
    Abstract:
    In order to reveal the weather causes of the rainstorm process that caused the flood in the Mintuo River and Jialing River basins, the rainfall and flood law of Yichang Control Station, and deepen the research on the occurrence and development mechanism of the flood in Yichang Station, based on the NCEP/NCAR(National Centers for Environmental Prediction/National Center for Atmospheric Research,NCEP/NCAR)reanalysis data and the conventional meteorological and hydrological observation data, the flood characteristics of 19 flood causing rainstorm processes that occurred in the Mintuo River and Jialing River basins from 1980 to 2020 were analyzed and studied using statistical and synoptic methods Flood causing rainstorm source, rain belt characteristics, topography and weather system configuration, etc. The results show that: (1) Before the continuous rainstorm process starts, the initial inflow flow of Yichang, the main control station in the Yangtze River basin, needs to reach about 19000m3 · s-1, and the average time from the beginning of the continuous rainstorm process of Mintuo River or Jialing River to the peak flood is about 6 days. The duration of rainstorm and cumulative area rainfall have a good correspondence with the flood peak. Each flood generating process requires at least one rainstorm of more than 3 days, most of which are 4-6 days. (2) The entire flood process occurred from July to September. Mid July to mid August is the main month in Yichang where peak type floods occur most frequently, with 62% of the daily average flow of over 50000 cubic meters per second occurring during this period. (3) The process of flood causing rainstorm is dominated by quasi-static rain belt, followed by easterly type and turning type. 85% of the process rain bands are distributed in a northeast southwest direction. The central source of heavy precipitation is closely related to special terrain, mainly distributed in three places: the intersection of the lower reaches of the Minjiang River and the Qingyi River, where turning precipitation mostly occurs; The middle and lower reaches of the Jialing River, the Fujiang River basin, and the Qujiang River basin are mostly of quasi static type; In the middle reaches of the Fujiang River and the northern part of the Qujiang River basin, the eastward moving rainstorm process often occurs here. (4) The precipitation process is divided into two categories: quasi stationary persistent precipitation and mobile persistent precipitation. There are three types of weather conceptual models that are prone to major floods: Type I is the edge of the subtropical high in the Western Pacific. The westerly short wave moves eastward to trigger the rainstorm type. The subtropical high generally presents a north-south meridional type, often blocking in eastern Sichuan, forming a situation of "low in the west and high in the east". The short-wave low value system moving southward and eastward is blocked in the Mintuo River basin by the subtropical high, which is stable and less dynamic, and produces more quasi-static rain belts; Type II is the rainstorm type triggered by the eastward movement of the low value system of the Qinghai Tibet Plateau. The subtropical high is mostly distributed in the latitudinal direction. The multi low value system of the plateau is active, and the shear line is mostly transverse. The vortex is often formed in the west of the shear line, moving eastward along the shear line, which is easy to form mobile precipitation; Type III is a low-level easterly flow rainstorm type, with few precipitation processes, mostly occurring in August. In the north, the continental high pressure or the Western Pacific subtropical high cooperate. The Mintuo River and Jialing River are affected by the northeast flow at the bottom of the low pressure, with weak cold air infiltration. The tropical low-pressure system in the south is blocked for a long time and moves steadily westward. A strong easterly flow is easy to form between the two. Combined with special terrain areas, continuous heavy precipitation is very easy to produce and strengthen. (5) Nearly 70% of the processes involve tropical low value systems or typhoons, among which the existence of the Bay of Bengal tropical depression system is crucial to the continuous rainstorm in the upstream. Not only does it bring enough energy and water vapor to the Mintuo River and Jialing River basins, but the involvement of water vapor on its eastern side can easily trigger low eddies in the Mintuo River and Jialing River basins, combined with special terrain, resulting in strong upward motion.
    Available online:  March 20, 2024 , DOI: 10.7519/j.issn.1000-0526.2023.092001
    Abstract:
    In order to improve the service capability of gust forecast in offshore, this paper uses the observation data from January to December 2021 and the wind and temperature from the ECMWF deterministic model 24-hour forecast data, and uses the support vector machine regression method to build the offshore gust forecast model of China. Using the data from January to September 2022 for independent sample test, through the comparison test with the gust factor method, the following conclusions are drawn: the wind speed and temperature values at different altitudes or the vertical wind speed and temperature changes will have an impact on the surface gust, thus causing the gust factor method to overestimate or underestimate the surface gust in some cases. The prediction effect of China"s offshore gust forecast model constructed by incorporating high-altitude meteorological element information on the basis of gust coefficient method is generally better than that of gust factor method. For 9 magnitude gust wind speed, the accuracy of support vector machine regression method is 50%, significantly higher than 30% of gust factor method. It also has a good effect on the large scale gust forecast in different sea areas. Although the 10m wind speed forecast of the ECMWF deterministic model has some deviation from the observation, the support vector machine regression model taking into account the high altitude factor information can obtain the gust forecast results closer to the observation than the gust factor method.
    Available online:  March 19, 2024 , DOI: 10.7519/j.issn.1000-0526.2023.072101
    Abstract:
    The paper discusses the coordinate effects of CODAS-SST and the assimilating FY-4A temperature?profiles on sea fog simulation with WRF model around the Yellow-Bohai Sea. The analysises show that the CODAS-SST significantly improves the results of sea fog simulation with WRF model around the Yellow-Bohai Sea, which makes the area and intensity of simulated fog more reasonable. By analyzing the sensitivity of various elements in the foggy area to changes in SST, it is clarified that the 2-meter temperature and specific humidity, as well as the sensible heat, latent heat, and water vapor fluxes at the sea-air interface, exhibit varying degrees of positive correlation with SST, while the liquid water content shows a significant negative correlation with SST. The assimilation of FY-4A vertical sounding data can further optimize the vertical distribution of specific humidity and wind speed in the boundary layer of WRF model, so as to improve the vapor transport and liquid water content. The coordinate assimilation of FY-4A vertical sounding data and CODAS-SST can better simulate the meso-scale characteristics of fog area, which indicates the high-precision and high resolution observation data is beneficial for improving the simulation capability of sea fog.
    Available online:  March 19, 2024 , DOI: 10.7519/j.issn.1000-0526.2023.082101
    Abstract:
    Based on CMA best-track and ECMWF fine grid data, 16 variables during TC genesis were calculated. The stepwise regression algorithm of double test was used to select seven prediction factors with significance, and the TC genesis forecasting equation was established. The independent sample test results show that the hit rate of the wind speed predicted by the regression method is higher than that of the wind speed and pressure predicted by the numerical model. In 2022, the stepwise regression algorithm based on double testing was trialed in the TC genesis forecasting operation. The test results of generating forecast for typhoon 2203 " Chaba " show that the regression method has a good performance, which can provide a reference for forecasters to judge whether and when the typhoon is generated.
    Available online:  March 15, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.012201
    Abstract:
    From July 29 to August 2, 2023, Beijing experienced an extreme precipitation event known as "23?7". In this paper, we analyzed the spatiotemporal characteristics and extremity as well as causes of this extreme precipitation event by using weather stations from meteorological departments in Beijing with complementary rain gauge stations from Beijing Municipal Commission of Planning and Natural Resources, multi-band dual-polarization radar, wind profiler, GPS data and ERA5 reanalysis data. The results indicate the following: The accumulated precipitation and intensity of this event were significant, with an average accumulated precipitation of 331 mm, maximum precipitation at a single point of 1025 mm, both of which broke historical records, and maximum hourly rainfall of 126.6 mm?h-1 ranking second in history. This rainfall process can be divided into 5 stages, the II and IV stages of the rainfall accounted for 37.1% and 39.7% of the total process being the primary phases. During stage IV, the corresponding jet stream intensity got stronger, the characteristics of high temperature and high humidity were more obvious. Terrain had a significant impact on the increase in rainfall. The rainfall accelerated most rapidly in the area between 100~300 m above sea level,the maximum value appeared near areas approximately an altitude of 400 m, with the average accumulated rainfall and maximum hourly rainfall in mountainous areas being 2.1 (3.0) times and 2.0 (2.7) times that of the plains during stage II (stage IV), respectively. Stage II is primarily influenced by direct terrain lifting of low level jet, while stage IV is characterized by the combined effect of terrain lifting and blocking convergence. On the morning of the 31 (stage IV), the coupling of the boundary layer convergence at the terminus and the low-level divergence at its entrance led strong ascending motions, which promoted the massive β-MCS to develop into a linear shape accompanied by a γ mesoscale vortex, the β-MCS propagated northward along the western mountainous regions, forming a short train effect and triggering extreme short-term heavy rainfall of over 100 mm?h-1 at 8 stations.
    Available online:  March 11, 2024 , DOI: 10.7519/j.issn.1000-0526.2023.110101
    Abstract:
    Using observation data from Yantai S-band dual polarization doppler weather radar, Rongcheng CINRAD/SA(China New Generation Radar, S-band) radar, sounding, surface meteorological stations,ERA5(ECMWF Reanalysis V5) and hail, tornado information obtained from field surveys, a severe hailstorm and tornado occurred on 1 Oct 2021 in eastern of Shandong peninsula is analyzed. The results are shown below.1) Compared to the climate mean-field, the northeast cold vortex of 500 hPa is strong, and the 850 hPa has continuous southward water vapor transport from south China to the west of northeast China on 1 Oct 2021,under the influence of a high altitude clod vortex and low altitude wind shear, the atmospheric thermal and dynamic conditions such as dry and cold in the upper troposphere, but wet and warm in the low troposphere, with strong vertical wind shear and convective available potential energy(CAPE), et al on the eastern Shandong Peninsula before the storm occurred, it’s very favorable for the occurrence of strong hail and tornadoes. The features of pre-storm low pressure, thunderstorm high pressure, and cold pool are obvious near the surface. (2)In the hail-fall period, the supercell features were very typical, with distinct hook-shaped echo and inverted "V" anterior inflow gaps in the lower layers, and vertical profiles showing distinct Bounded Weak Echo Region(BWER) and differential reflectivity(ZDR) column characteristics. According to the large hail information, statistics the median value of reflectivity factor(ZH),ZDR and cross-correlation coefficient(CC) was 48.7 dBZ,0.89 dB and 0.90 respectively. When tornado and large hail appeared on the ground, the maximum storm-top divergent outflow(STD) reached 71.5 m·s-1. (3)The cold pool airflow at the northern end of the Rear Flank Gusts Front (RFGF) and the south inflow on the pre-storm side form a strong vortex upward motion, resulting in an EF1-level tornado. The tornado occur at the tip of the hook-like echo, and large hailstones appeared on the north side of the inflow gap. (4)About 5 minutes before the tornado was found on the ground, the radar detected the Tornadic Debris Signature(TDS) features, the ZDR was as low as -0.1 dB, CC was as low as 0.81, and about at 11 minutes before the tornado genesis, the ZDR arc in the lower layer and the descending reflectivity core(DRC) in the rear flank side of the supercell was detected. Rongcheng and Yantai radars identified mesoscale cyclones and Tornadic Vortex Signature(TVS) about 22 min and 5 min in advance, respectively, which can provide an important reference for a tornado warning. (5)Based on the observational analysis, the schematic diagram of the low-layer air flow field and the tornado and large hail-falling area of the super monolithic storm is summarized.
    Available online:  March 05, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.030401
    Abstract:
    In view of the difficulties in monitoring summer rainy season in North China, the concept of the summer potential rainy season in North China was proposed, and a new monitoring method, the specific humidity subtropical high method (QH), was established. The main monitoring results are as follows: 1) The average start date of the summer rainy season in North China from 1961 to 2022 was July 10, the end date was August 8, and the length of the rainy season was 28 days. The start and end time of the rainy season in North China has no obvious long-term change trend, but the interdecadal change is significant. After 2005, the rainy season has become significantly longer. 2) The summer rainy season precipitation and the comprehensive intensity index of rainy season monitored by this method in North China are very consistent with the changes in summer precipitation, with a high positive correlation, indicating that the monitored rainy season parameters have a good indication of the changes in summer precipitation in North China. 3) The beginning and end of the summer rainy season in North China are accompanied by significant changes in atmospheric circulation. The East Asian subtropical summer monsoon at 850 hPa level strengthens and weakens, and the atmospheric specific humidity in North China north of 30°N rapidly increases and decreases; The 500 hPa height field presents positive and negative anomaly centers in North China, and the Northwest Pacific subtropical high begins to significantly lift northward or retreat eastward along the coast of East Asia; The upper westerly jet axis at 200 hPa moves from 30°N north to 45°N or from 45°N south to 30°N. These can be used as auxiliary conditions for circulation monitoring at the beginning and end of the summer rainy season in North China.
    Available online:  March 05, 2024 , DOI: 10.7519/j.issn.1000-0526.2023.063001
    Abstract:
    In order to evaluate the performance of millimeter-wave radar in the case of typhoon, the millimeter-wave cloud radar data of Shanghai during the four typhoons in 2018 and 2019, combined with the data of disdrometer, satellite and S-band weather radar are studied to explore the feasibility of using the millimeter-wave radar to study the outer rainbands of typhoon. It is shown that the millimeter-wave radar has a good detection performance, and has certain application potential for detection of vertical structure of cloud and precipitation. Determination of cloud top height is more accurate when the rainfall rate is lower than 5mm/h. A method for bright band determination is proposed, and the results of application are found to be in good agreement with the sounding. Comparison of the retrieval of rainfall rates by millimeter-wave radar and S-band radar shows feasibility of retrieving rainfall rate profile by taking advantage of the millimeter-wave radar attenuation. In the situation of significant growth of raindrops, it is necessary to revise the retrieval algorithm.This research provides a reference for millimeter-wave radar detection of typhoon outer rainbands.
    Available online:  February 27, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.020201
    Abstract:
    Abstract: In order to improve the understanding of precipitation characteristics about hailstorm on the Qinghai-Tibet Plateau, using the raindrop size distribution data observed by DSG5 disdrometer, radar reflectivity, FY-4A satellite and minute precipitation data and so on, the precipitation microphysical characteristics of the hailstorm occurred in Lhasa on July 23, 2020 is analysed. Results show that there were some slightly difference at the time of beginning and end, precipitation peak and total precipitation between rain gauge and DSG5 disdrometer. The average spectrum distribution of raindrops and hailstones were monotonous decreasing. The raindrop size spectrum fitted Γ distribution and the hail size spectrum accorded with M-P distribution. In the early stage of hail occurrence, the precipitation particles were mostly small, this was mainly caused by the evaporation of the raindrop. In the later stage, the collision & fragmentation of the particles and the melting of graupel particles produced a large number of small raindrops, leading to a sharp increase in the number of particle concentration. The significant increase of number concentration and the widening of the droplet spectrum about this stage were the reason of the increased rainfall. The concentration of hailstones only accounted for 1.6% , while the hailstones were the major contributors of the total precipitation. The empirical formula for the average terminal falling velocity and the diameter of the hails was V=5.135×D0.5092.
    Available online:  February 19, 2024 , DOI: 10.7519/j.issn.1000-0526.2023.071002
    Abstract:
    The severe convective rainstorm occurred at west side of Liupan Mountains on 15 July 2022 were analyzed based on the data from X-band dual polarization weather radar, C-band Doppler weather radar, wind profiler radar, ERA5 hourly reanalysis, automatic weather station and conventional observation data. The results showed that the rainstorm occurred in the northwest of the Western Pacific subtropical high. The main area of heavy rainfall is the south side of the low-level shear line and the left front side of the low-level jet. Affected by the Liupan mountain terrain, the mesoscale ground convergence line, mesoscale low-level southwest jet and mesoscale eddy might be important systems of triggering, maintaining and enhancing of the process. The rainstorm was caused by two mesoscale echo bands, the convective cells on them propagated backward, and the train effect was obvious. The strengthening of low-level jet, the increasing of vertical wind shear, the downward disturbance of wind speed, and the dry intrusion appeared 1~2 hours ahead of the increase of precipitation in five minutes, which had a certain reference value for rainstorm forecast and early warning. The center of heavy rainfall had a better corresponding relationship with the echo area with intensity ≥50 dBz and the large value area of vertical integrated liquid water, echo tops, the large range of differential phase shift (KDP) and differential reflectivity (ZDR). KDP was a good indicator for intensity of heavy rainfall. The maximum value of KDP and ZDR appeared 10 minutes earlier than the maximum rainfall in five minutes. The ZDR arc and ZDR column also appeared 10~20 minutes earlier than the maximum rainfall. During the strongest rainfall period, the KDP was 3.0~4.0 °·km-1, the ZDR was 3.0~3.3 dB, and the correlation coefficient was 0.90~0.95. This suggested that the spectrum of rain particulates contained a large amount of relatively large-sized raindrops, increasing the extremes of precipitation.
    Available online:  February 19, 2024 , DOI: 10.7519/j.issn.1000-0526.2023.061601
    Abstract:
    The rapid intensification (RI) of tropical cyclones (TCs) has been an unresolved problem in operational forecasting. At present, it remains unclear the capability of operational numerical models to forecast TC rapid intensification (TCRI) and the sensitive factors which affect the forecasting capabilities of numerical models. In this paper, the operational forecast for rapid intensification of ekima (1909) by the CMA-TRAMS and HRES models is analyzed. Numerical sensitivity tests were designed and carried out from the perspectives of horizontal resolution, initial and boundary conditions, physical parameterization schemes. The CMA-TRAMS and HRES models can predict the enhancement of "Lekima" to some extent, but the enhancement speed predicted is obviously lower than that of observation. Both models neither can meet the 24-hour and 12-hour RI standards, but can reach the 6-hour RI standard. The experiment using higher horizontal resolution (e.g., 3 km) has produced better forecasts of track and intensity than which used lower resolution (e.g., 9 km) based on CMA-TRAMS, however does not improve forecast for TCRI. Nevertheless, the prediction of TCRI has been significantly improved if adopting 3 km resolution nested to 9 km resolution. The experiments using the MRF boundary layer parameterization scheme generally performs better in forecasting TC track, intensity and RI than that using the YSU scheme. When the initial and boundary conditions with higher vertical resolution are used, accompanied with the SST parameterization scheme, the forecast for TCRI has been obviously improved on the frequency and maximum speed of TCRI. The main reason for improvements is that the SST parameterization scheme increases the differences between sea and air temperature, which has a significant impact on heat transfer and exchange between the atmosphere and the ocean in a short period of time.
    Available online:  January 26, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.011801
    Abstract:
    A large-scale convective gale event was studied based on conventional observation data, automatic weather station data, GFS analysis data at spatial resolution of 0.25°and temporal of 6h, observations of Doppler radar , and Fengyun-4 satellite data in East China on 12 April 2020 under the background of consistent northwesterly air flow from the lower to the middle layer behind the North China Cold Vortex. The results demonstrate that after the strong cold air gales moved southward on the morning of the 12th, a convective storm was triggered near the drylines at the junction of Shandong and Jiangsu province on the afternoon in the favorable thermal background of cold advection at the middle level and warm advection at the lower level, the convective storm occurred in the area with a large temperature difference between 500hPa and 850hPa and the initial shape of the convective cloud matches the dryline well;The convective system was strengthened under favorable conditions such as better water vapor condition, stronger wind speed in the middle layer, merged of gust front and the influence of the special land and sea distribution in Hangzhou Bay, which caused the large-scale convective gale weather in Jiangsu, southeast Anhui and north Zhejiang again, and 13 extreme gales occured near the Zhoushan Islands ; The 13 extreme gales occurred at the fracture area of echo and theγ scale mesoscale vortices, which caused by the radiation of rear inflow jet and the strong downdraft, smooth underlying surface, fast-moving convection system and small-scale downburst currents within the system.
    Available online:  January 26, 2024 , DOI: 10.7519/j.issn.1000-0526.2024.012301
    Abstract:
    Based on the hourly rainfall data of 2066 automatic weather stations and rainstorm disaster information in Chongqing from 2011 to 2021, the slide sampling of rainstorm process and the percentile method are used to determine the rainstorm warning signal standards for counties and the disaster risk warning grades for the whole city, which can provide reference for Chongqing local departments to initiate rainstorm emergency response. The main conclusions are as follows: (1) a total of 5363 rainstorm processes occurred in 34 counties with meteorological authorities in Chongqing, with an average of 14.3 times per year in each county and 1h, 3h and 12h are selected as the reference duration for issuing rainstorm process warning signals. (2) Rainstorm warning signal (blue, yellow, orange, and red) standard thresholds of different durations are obtained by taking 30~50%, 70~80%, 90~95%, and 99~99.9% precipitation levels and adjusting according to the actual application, which are as follows: 1h-30-50-70-100 mm, 3h-50-70-100-150 mm, 12h-70-100-150-250 mm. The issuance of warning signals for counties adopts the highest level of different durations. (3) The probability of disaster caused by different warning signals increases both with signal strength and duration, warning signals of blue, yellow, orange, red for each county have an average of 5.4, 4.0, 1.3, 0.18 times per year according to the highest warning level of different durations and each signal takes from maximum disaster probability of different durations as 30%, 60%, 85%, and 95% respectively. (4) A total of 114 regional rainstorm processes occurred in the city, and rainstorm disaster risk warning levels determined by the number of possible disaster counties issue an average of 5.3 (IV), 3.1 (III), 1.6 (II), 0.1 (I) times per year, which is basically consistent with the frequency of counties and conforms to the regularity of warning releases. Key words: rainstorm warning signals; slide sampling during rainstorm process; percentile method; probability of disaster; rainstorm disaster warning.
    Available online:  January 26, 2024 , DOI: 10.7519/j.issn.1000-0526.2023.061001
    Abstract:
    Using the Doppler weather radar and ground-to-ground lightning observation data from March to September in Jiangxi Province from 2013 to 2020, a statistical analysis was carried out on the distribution characteristics of lightning and its relationship with the main characteristics of the radar. The results show that the CG lightning frequency in Jiangxi Province gradually decreases from the northeast to the southwest, and the Poyang Lake Plain in the north is the area with high CG lightning frequency. The CG lightning frequency has obvious seasonal and diurnal variation characteristics, and the total CG lightning frequency reaches the peak of one day at 16:00. The relationship between CG lightning frequency and the low-level (3km) radar echo intensity can be described by a logarithmic fitting equation. The number of CG lightning frequency is positively correlated with the variation trend of the low-level (3km) radar echo area, and the stronger the echo, the stronger the correlation. However, there is a phase difference between the two, and the increase of the CG lightning frequency precedes the increase of the echo area in about 57-60%. In most cases, an increase of both can be found within 18 minutes. The boxplot features show that with the increase of the echo intensity, the extension height of the echo decreases correspondingly, while the echo thickness increases slightly. When the CG lighting occurs decreases correspondingly, so that the radar echo characteristics of the 10km radius around the ground flash occurrence grid point with different intensity echoes are obtained.
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      2012,38(12):1482-1491, DOI: 10.7519/j.issn.1000-0526.2012.12.005
      Abstract:
      By using the conventional meteorological data, Doppler radar data and NCEP/NCAR reanalysis data, the characteristics of Doppler radar’s reflectivity, environmental condition and trigger mechanism of the heavy rain are analyzed and compared between two abrupt heavy rain processes occurring in Sichuan Basin on 3 July (7.3) and 23 July (7.23) 2011. The results show that: the “7.3” heavy rain happened under a typical circulation background, and moisture transporting to the heavy rain area from the South China Sea was smoothly, thus the heavy rainfall maintained so long, but the “7.23” heavy rain occurred behind the upper cold vortex, and convective unstable energy was abundant and vertical wind shear was strong, thus this heavy rain process happened with hail and thunderstorm weather accompanied, its radar reflectivity was 5 dBz stronger than “7.3” case and had the characteristics of severe storms such as the low level weak reflectivity and the upper echo overhang. As a whole, the non equilibrium force is contributed to the occurrence of heavy rain and it is the excited mechanism of the two heavy rainfalls, and the change of the divergence evolvement is consistent with the strength and the position of the heavy rain which would happen 6 hours later.
      2006,32(10):64-69, DOI: 10.7519/j.issn.1000-0526.2006.10.010
      Abstract:
      Based on the data of CINRAD Doppler Radar which located at Xinle of Hebei Province,the hail,strong wind and heavy rainfall weather events in mid-south Hebei in 2004 are statistically analyzed.The routine radar products,such as echo reflectivity,radial velocity,Vertically Integrated Liquid(VIL)Water,hail index,mesocyclone,velocity azimuth display wind profile,etc.are used in this statistics.The results show that hail's VIL value is larger than generic thunder storm's.At the same time,greater VIL value and longer sustaining will bring about greater diameter hail and larger effect area.It is the very useful index to indicate strong wind in mesocyclone products and the wind direction sudden change in radial velocity products.A reference based on analyzing this type synoptic forecast with radar system in future is proposed.
      2008,34(12):27-35, DOI: 10.7519/j.issn.1000-0526.2008.12.004
      Abstract:
      Cloud macro and micro physical characteristic parameters play an important role not only in the field of the analysis and forecast of the weather and climate, but also in the field of weather modification to identify the seeding c ondition. Based on the data from FY-2C/D stationary satellite and SBDART radiati on transfer model, associated with the sounding data and surface information, a method retrieving cloud macro and micro physical parameters is established in th is research. These parameters include cloud top height, cloud top temperature, d epth of super-cooled layer, depth of warm layer, cloud bottom height, depth of c loud, cloud optical thickness, cloud effective particle radius and cloud liquid water content. It has been run operationally. In this paper, the correlated info rmation such as physical meaning, retrieving method and technology, retrieving p rocess and data format are simply introduced. Furthermore, comparing with the ob servation of Cloudsat up to the minute, the retrieving results of main cloud par ameters are proved to be reasonable and usable. By contrast with same kind produ cts of MODIS, it also shows good corresponding relationship.
      2017,43(7):769-780, DOI: 10.7519/j.issn.1000-0526.2017.07.001
      Abstract:
      The spatial distributions of severe convective wind (SCW) and nonsevere thunderstorms (NT) over South China, occurring between 08:00 BT and 20:00 BT during spring and summer in 2010-2014, were analyzed by using the observational data from China Meteorological Administration. And then, their environmental characteristics were compared between SCW and NT in spring and summer. It was found that SCW in summer is more frequently than that in spring and that NT in summer is about 3.6 times the counts of NT in spring. SCW events mainly concentrate in the western Guangdong to the Pearl River Delta Region. Compared to NT, SCW is generally associated with stronger baroclinity, instability and stronger dynamic forcing. The precipitable water and averaged relative humidity between 700-500 hPa of SCW tend to be higher than those of NT in spring, while the opposite is the case for the pattern in summer. In conclusion, it is obvious that the dynamic forcing for SCW in spring is much better than these in summer, while the thermal condition is more significant in summer.
      2017,43(5):528-539, DOI: 10.7519/j.issn.1000-0526.2017.05.002
      Abstract:
      An extremely severe precipitation event took place in North China in 19-20 July 2016. It was characterized by large rainfall, persistent rainfall, warm cloud rainfall, strong local rainfall intensity and orographic precipitation. Its rainfall was larger than that of the extreme rainfall in 3-5 August 1996, and only next to the amount of the 2-7 August 1963 extreme rainfall event. It occurred under the circulation background of the South Asia high moving eastward, the West Pacific subtropical high moving northwestward and the low vortex in the westerlies developing in mid high latitude. The abnormal development of Huanghuai cyclone, southwest and southeast low level jets, and the abnormally abundant moisture indicates that the dynamic lifting and moisture conditions favored this severe rainfall process significantly. The whole rainfall event presented clearly the phase characteristics, and could be divided into two stages. The first stage was the orographic rainfall caused by the easterly winds ahead of the trough from the early morning to the daytime of 19 July, while the second part was produced by spiral rain bands in the north side of Huanghuai cyclone from the night of 19 to the daytime of 20 July. In the first stage, the easterly low level jet was lifted by the Taihang Mountains, which continuously triggered the convective cells along the east edge of the mountains. The weak dry and cold advection at mid level and the strong warm and wet advection at low level jointly maintained the convective instability. The cold pool generated by heavy rainfall and the mesoscale frontogenesis process created by local orographic effect provided favorable conditions for severe convections to occur continuously. The second stage rainfall was mainly related to the development of cut off vortex and Huanghuai cyclone. The blocking of the high pressure system slowed the steps of Huanghuai cyclone in North China, thus leading to the long lasting rainfall process.
      2013,39(10):1284-1292, DOI: 10.7519/j.issn.1000-0526.2013.10.006
      Abstract:
      Based on the fog observation data during 24-27 December 2006 (advection radiation fog), NCEP NC reanalysis data (2.5°×2.5°) and GDAS global meteorological data (1°×1°), detailed trajectory analysis of the boundary layer characteristics and water vapor transport of the fog is investigated, combined with the weather condition, meteorological elements and physical quantity field. The results show that: (1) there is thick inversion layer, even multi layer inversion throughout the dense fog event. Temperatures of different inversion tops in the middle and high levels are 2-5℃ higher than the surface temperature. The thickness of inversion layer is more than 200 m, and it gets to 500 m at 08:00 BT 26 December, indicating the atmosphere is very stable and conducive to the convergence of water vapor before the fog forms. However, it is not favorable for the divergence of water vapor after the formation of fog, which helps the development and maintenance of the fog, causing the fog to last about 64 hours with dense fog (visibility <50 m) about 37 hours; (2) The divergence of water vapor flux in low level is negative in the advection fog event. The upper air has persistent moisture convergence and the strongest moisture convergence appears at 02:00 BT 25 December, being -30×10-7 g·s-1·cm-2·hPa-1. The accumulation of low level water vapor makes fog form and develop while the divergence of water vapor flux speeds up its dissipation. 〖JP2〗The long lasting advection radiation fog is mainly caused by the continuous water vapor convergence; (3) The water vapor path is from the coastal area in easten China to Nanjing. The water vapor is continuously supplied from sea during the fog event, with the water vapor flux maximum getting to 2 g·s-1·hPa-1·cm-1. The sufficient supply and supplementary of water vapor determines the duration of the fog.
      2010,36(3):9-18, DOI: 10.7519/j.issn.1000-0526.2010.3.002
      Abstract:
      Potential vorticity (PV) is one of the important concepts in advanced synoptic and dynamic meteorology. This paper is a brief introduction to the theory of potential vorticity, including the concept of PV, the conservation and invertibility of PV, PV thinking, moist PV (MPV), and the application of PV theory.
      2009,35(1):55-64, DOI: 10.7519/j.issn.1000-0526.2009.1.007
      Abstract:
      A strong rainstorm is analysis which occurred in Xinghua located the north of Ji angsu province on 25 July 2007. Results show that wind disaster originated from two kinds of rainstorm. One kind was the gust front which occurred at the front of the storm. Strong wind of grade 7-9 was attained when it happened. Another ki nd was the downburst arose in the multi cell storm. The original height of refl ectivity core was higher than -20℃ isotherm. It had the characteristics of conv ergence on the mid level and descending of reflectivity core. The strong wind ab ove grade 10 was attained, when the descending airflow diverged strongly on the ground. A new cell was combined with the former storm above the gust front, thus the storm enhanced. When the downburst happened, the storm weakened, and another new cell was combin ed with the former storm. The downburst happened continuously, and the impact of gust front persisted.
      2014,40(2):133-145, DOI: 10.7519/j.issn.1000-0526.2014.02.001
      Abstract:
      By using the NCEP reanalysis data, the vapor budget of the area covered by the severe torrential rain over the northeast of North China on 21 July, 2012 is calculated according to the vapor budget equation. The results show that meridional water vapor transportation is dominant while the extremely heavy rain hits Beijing Region, where most moist vapor comes from the southern boundary below 500 hPa. The low level regional moisture convergence is consistent with the time and space when the torrential rain breaks out and develops. Above the middle level the vertical vapor transport is more prominent. Then the variation features of the vapor transport corridors and their moisture contributions are got through the HYSPLIT mode. The backward trajectory analyses illustrate two major vapor transport corridors. The moistest vapor derived from Yellow Sea and East China Sea along the low level make the main moisture contribution during the heavy precipitation. Moisture from the South China Sea and the Bay of Bengal strengthens the water vapor in the region when the heavy rain starts and develops. Also the drier vapor corridor along the high level from the northwest of China plays an important role in this case.
      2012,38(1):1-16, DOI: 10.7519/j.issn.1000-0526.2012.01.001
      Abstract:
      In this paper, the modulation of atmospheric MJO on typhoon generation over the northwestern Pacific and its mechanism are first studied by using the MJO index. The results show that the MJO plays an important modulation role in typhoon generation over the northwestern Pacific: The proportion of typhoon number is 21 between active period and inactive period; During the MJO active period, the proportion of typhoon number is also 2:1 between phases 5-6 and phases 2-3 of MJO. The composite analyses of atmospheric circulation show that there are different circulation patterns over the northwestern Pacific in different phases of the MJO, which will affect the typhoon generation. In phases 5-6 (2-3), the dynamic factor and convective heating patterns over western Pacific are favorable (unfavorable) for typhoon generation. Then, the comparing analyses of the 30-60 day low frequency kinetic energy in lower and higher levels of the troposphere show that the atmospheric intraseasonal oscillation over the northwestern Pacific has a clear impact on the typhoon generation. There is an evident positive (negative) anomaly area of 30-60 day low frequency kinetic energy in the more (less) typhoon years over the northwestern Pacific east of the Philippines, which means that strong (weak) atmospheric intraseasonal oscillation (ISO) over the northwestern Pacific is favorable (unfavorable) for typhoon generation. The analyses of 200 hPa velocity potential show that there is a clear divergence (convergence) pattern over the northwestern Pacific in the more (less) typhoon years, which is favorable (unfavorable) for typhoon generation. The modulation of the intraseasonal oscillation on the typhoon tracks over the northwestern Pacific is studied by observational data analyses. We classified the main classes of typhoon tracks into 5 types as straight west moving typhoons (I), northwest moving typhoons (II), recurving to Korea/west of Japan typhoons (III), landing on Japan typhoons (IV) and recurving to the east of Japan typhoons (V). Then the composite analyses of atmospheric low-frequency wind fields at 850, 500 and 200 hPa, corresponding to the typhoon forming date, for every typhoon track are completed. The analysis results of relationships between the low-frequency (ISO) wind fields and typhoon tracks have indicated that the typhoon tracks will be affected by wind pattern of the ISO. The low frequency positive vorticity belt (the maximum value line of cyclonic vorticity) associated with low-frequency cyclone (LFC) at 850 hPa is so closely related to the typhoon track, that the maximum value line (belt) of low frequency cyclonic vorticity can be an important factor to predicate the typhoon tracks over the northwestern Pacific. And the typhoon tracks will be also affected by the ISO circulation pattern at 200 hPa, particularly the strong low frequency wind associated with low frequency anticyclone (LFAC).
      2011,37(10):1262-1269, DOI: 10.7519/j.issn.1000-0526.2011.10.009
      Abstract:
      Based on the daily precipitation data at 110 observational stations during 1961-2008 in South China, the climatic characteristics and variation of torrential rain days, rainstorm intensity and contribution which is in annual, the first and second flood seasons in South China were studied by using statistical and diagnostic methods, such as linear regression analysis, Mann Kendall test, wavelet analysis and the computation of trend coefficients. The results have shown that the annual mean torrential rain days have a decreasing trend from coastal regions to inland in South China in recent 48 years, the highest center is in Dongxing of Guangxi (14.9 d), and the lowest center is in Longlin of Guangxi (3.2 d). About 72% of the total torrential rain days occurred in the flood seasons with about 45% in the first season and 27% in the second season. The mean torrential rain days have increased faintly in annual, the first and second flood seasons in South China, but it is not obvious. There are the characteristics of interannual and interdecadal changes. The mean rainstorm intensity has increased faintly in annual and in the first flood season in South China. However, since 2005 it has become obviously. The mean rainstorm intensity has declined in the second flood season, but it is not obvious. The annual mean rainstorm contribution to the total rainfall has increased obviously, but the mean contribution is not obvious in the first and second flood seasons. The wavelet analysis has shown that the changes of torrential rain days, intensity and contribution which is in annual, the first and second flood seasons in South China have two significant periods of 2-3 a and 3-4 a.
      2014,40(7):816-826, DOI: 10.7519/j.issn.1000-0526.2014.07.005
      Abstract:
      In term of precipitation data of 2400 stations from 1981 to 2010, annual, seasonal and monthly distribution and evolution characteristics of rainstorm were analyzed. The results show that the processes of rainstorm have been increased evidently since 21 century especially in the south of China, but the duration is relatively short. Rainstorm days have been increased, but the amount of precipitation is not as much as in 1990s. Variation trend of the annual (monthly) precipitation amount is in accordance with that of rainstorm days, but rainfall is averagely more while the rainstorm days are less during spring rainfall phase over the south of Yangtze River. Distribution of the maximum annual rainstorm days is very similar with that of the annual mean rainstorm days, revealing the feature of more in south and east but less in north and west. Maximum annual rainstorm days are more than double of annual average rainstorm days with multi centers due to the effect of topography. The months of maximum monthly rainstorm days over different regions of the same province are incompletely same as the result of the impact of different weather systems. Generally, rainstorm days have been increased since 2000, rainstorm begins earlier, ends latter and lasts longer than before. Nowadays, as the extreme rainfall events and secondary disasters happen frequently, it is conducive for the forecast of quantitative precipitation forecast (QPF) to learn the spatio temporal distribution and evolution features of rainstorm.
      2011,37(5):599-606, DOI: 10.7519/j.issn.1000-0526.2011.5.012
      Abstract:
      Using the diurnal snow data of 120 meteorological stations in Yunnan Province during 1961-2008, the temporal and spatial distribution characteristics and the trend of climatic change of the annual and monthly snow fall are analyzed. It is pointed out that the total trend of snow frequency and covering stations has been decreasing in Yunnan in the recent 50 years. And the annual snow frequency has declined at a mean rate of 4.5 times per year. The temporal trends of monthly snow frequency and covering stations are all negative. Moreover the reduction of snow frequency in December is the largest in magnitude, therefore, it is the most remarkable. And the reduction of snow stations in April is the largest. As far as the spatial change of the secular trend variation of annual snow frequency is concerned, the reduction of annual snow frequency is larger in Northwest Yunnan than in its northeast and east, where the reduction rate is 0.44 times per year. And the temporal changes of annual snowfall and depth of snow cover are studied, the results show that the secular trends of annual snowfall and the maximum depth of snow cover are all positive. This means that in the nearly 50 years the heavy snow frequency has increased over Yunnan Province.
      2012,38(10):1255-1266, DOI: 10.7519/j.issn.1000-0526.2012.10.012
      Abstract:
      Precipitation characteristics, environment conditions, generation and development of the mesoscale convective system that brought about the extreme torrential rain in Beijing on 21 July 2012 were analyzed comprehensively in this paper by using various conventional and unconventional data. The results showed that the extreme torrential rain had the characteristics of long duration, great rainfall and wide coverage area and its process consisted of warm area precipitation and frontal precipitation. The warm area rainfall started earlier, the severe precipitation center was scattered and lasted long while the frontal rainfallprocess contained several severe rainfall centers with high precipitation efficiency, lasting a short time.Environment conditions of the mesoscale convective system that triggered this extreme severe rainfall were analyzed. The results showed that interactions of high level divergence, the wind shear and convergence with the vortex in the lower troposphere and the surface wind convergence line provided favorable environment to the severe extreme rain. The warm humid airs from the tropical and sub tropical zones converged over the torrential rain region, continuous and sufficient water vapor manifested as high atmospheric column of precipitable water and strong low level water vapor convergence and other extreme vapor conditions for the torrential rain. In addition, the intense precipitation was triggered by the vortex wind shear, wind disturbance on low level jet, surface wind convergence line and the effect of terrain under the condition of the plentiful water vapour and maintained. With the cold front moved eastward, heavy frontal rainfall was brought by the development and evolution of convective system made by the cold air and the suitable vertical wind shear.Generation and development processes of the mesoscale convective system were also studied. The findings suggested that stratiform cloud precipitation and dispersed convective precipitation occurred firstly in the precipitation process. The warm and steady stratiform cloud precipitation changed to be highly organized convectional precipitation as the cold dry air invaded. Many small scale and mesoscale convective clusters developed into mesoscale convective complex (MCC), leading to the extreme severe precipitation. Since all the directions of the echo long axis, terrain and echo movement were parallel, train effect was obviously seen in the radar echo imegery during this precipitation process. Meanwhile, the radar echo had the characteristics of backward propagation and low centroid which was similar to tropical heavy rainfalls. Finally, a series of scientific problems were proposed according to the integrated analysis on the observation data of this rare torrential rain event, such as the causes for the extreme torrential rain and the extreme rich water vapor, mechanisms for the warm area torrential rain in the north of China, the mechanism for the train effect and backward propagation, mechanisms for the organization and maintenance of the convective cells, the simulation and analysis ability of the numerical models to extreme torrential rains and so on.
      2007,33(12):116-120, DOI: 10.7519/j.issn.1000-0526.2007.12.018
      Abstract:
      A comprehensive analysis and process system based on ArcGIS, and its chief targ et, its software frame, standardized data, database system, basic functions and its key technique, etc. are are described. The system is professional especially to weather modification, and it mainly applies to comprehensive analysis and pr ocess for weather modification, decision-making of operation schemes, appraisal of operation effectiveness, and services for enhancement precipitation or suppre ssion hail by ways of cannons or rocks, etc. In this system, information collect ion, analysis, management and comprehensive application of the weather modificat ion are realized. It also can be used in other fields in meteorology.
      2011,37(1):122-128, DOI: 10.7519/j.issn.1000-0526.2011.1.017
      Abstract:
      The following are the main characteristics of the general atmospheric circulation in October 2010. There were two polar vortex centers in the Northern Hemisphere. The circulation presents a four wave pattern in middle high latitudes, in which the strong Ural ridge corresponds to a large 40 gpm positive anomaly area. Strength of the Western Pacific subtropical high is weaker than normal years. The monthly mean temperature (10.1 ℃) is 0.5 ℃ higher than the same period of normal years, and the mean precipitation (42.6 mm) is 15.1% above normal. The major weather events include: 8 precipitation processes occuring, in which a rare heavy rain has struck on Hainan in the first and middle dekad of October; two tropical cyclones generated, with one super typhoon (Chaba, numbered 1013) landed in Fujian; in the last dekad of October, strong cold air outbreak across most areas of China; heavy fog aroused in the central and eastern China.
      2013,39(9):1163-1170, DOI: 10.7519/j.issn.1000-0526.2013.09.011
      Abstract:
      Drought and flood have significant impacts on catchment water use and ecological balance. To develop practical drought/flood monitoring indicators that only need a few climate variables, it is fundamentally necessary to explore the relationship between hydrology variables and climate variables for the specific catchment. This study investigates the correlations between lake water level and various time scale climatological indices according to the standardized precipitation index (SPI) and the standardized precipitation evapotranspiration index (SPEI), based on the monthly water level records from Honghu Lake representative gauging stations and the monthly observations of 8 meteorological stations in the Four Lake Basin. The results showed that extreme droughts and floods are primarily controlled by precipitation variability over the Four Lake Basin, and both SPEI and SPI are well related with lake water level of Honghu Lake while the degree of the correlation varies between different seasons and SPEI/SPI time scales, with the highest correlations for rainy summer and autumn months. Generally, the 4-6 month scale SPEI/SPI drought index is most closely correlated with lake water level of Honghu Lake, showing an apparent response of lake water level to the current and former months’ water surplus and deficiency. When compared with the historical time series of monthly average lake water level of Honghu Lake, the 5 month scale SPEI/SPI agrees well with the variability of the lake water level. The response relationship found during the study can not only aid the monitoring and forecasting of flood and drought conditions in the Four Lake Basin based on conventional weather data, but also provides some references for other places of China.
      2013,39(3):281-290, DOI: 10.7519/j.issn.1000-0526.2013.03.002
      Abstract:
      By using conventional observation data and NCEP reanalysis data, diagnostic analysis is performed on a rainstorm process, which occurred on 22-25 July 2010 in the western part of Sichuan Basin. The result shows that the rainstorm was generated under the circulation background that low level southerly airflows had remained over the region from the South China Sea to Sichuan Basin, so this rainstorm was closely related to the evolution of the southerly wind speeds. The rainfall intensity increased as the south winds grew stronger. Speed convergence formed by the enhanced south winds and positive vorticity advections became main dynamic trigger factors for the rainstorm. Therefore, the rainstorm is pretty consistent with the low level convergence and the positive vorticity advection. In addition, the result of WRF numerical simulation further indicates that: the evolution of 3 h wind speed at 850 hPa has good indication for the development of mesoscale convective systems. On the leeward side of the 3 h wind speed increasing area, convective cloud clusters are to develop rapidly in the next 3 hours. Moreover, the topographic influence simulation tests suggest that the airflow convergence generated in the west of the Basin is closely related to the topography of plateau.
      2011,37(2):142-155, DOI: 10.7519/j.issn.1000-0526.2011.2.003
      Abstract:
      Using the Variational Doppler Radar Analysis System (VDRAS) combined with local unconventional observation data, a more in depth contrastive analysis is carried on the initiation mechanism of two storm cases in Beijing, one is 814 (August 14, 2008) case with strong rainfall that we call it as moist storm and the other is 824 (August 24, 2008) case with little rainfall that we call it as dry storm. The results show: (1) The synoptic scale systems of 814 storm were stable Northeast cold vortex low trough at 500 hPa and shear line at 850 hPa, the specific humidity that more than 12 g·kg-1 below 850 hPa and the relative humidity that more than 90% in the surface indicated that the atmosphere was very moist. It had convective instability caused by humidity advection in lower levels. The 824 storm had a prevailing straight west wind in high levels, an anticyclone in lower levels, and a surface cold front moving fast.The specific humidity that less than 6 g·kg-1, and the relative humidity that less than 30% below 850 hPa indicated that the atmosphere was very dry. It had convective instability caused by temperature advection. (2) There was much strong vertical wind shear in the whole vertical layer for 814 storm case, the clockwise wind direction with height within 500-1500 m intensified the warm and humidity inflow of lower layer advantageous to storm initiation and development. While there was weak vertical wind shear and unobvious warm and humidity inflow of lower layer for 824 case, which was not conducive to storm initiation and development. In addition, composited wind of the whole troposphere and storm movement speed were very low for 814 case, but they were very high for 824 case. (3) The 814 storm was formed by the collision and mergence of multi cell storms, a convergence line was formed by the cold pool outflow produced by the precipitation of the upstream of thunderstorm cell and the east wind in low levels which forced the low level warm and moist air to uplift, additionally the strong convective instability and vertical wind shear supported the formation and development of new storm. The interactions (collisions) of gust fronts in the leading edge of cold pool of multi cell thunderstorm group, further exacerbating the low level instability, leading to the regeneration and mergence of new convective thunderstorms. The 824 storm was a line convective system accompanied with cold front that rapid moved eastward and lasted for short time, there was no east wind with warm and moisture air accompanying the cold pool outflow produced by the downdrafts of thunderstorm. The absence of mesoscale lifting mechanism and moisture inflow couldn’t support the formation and development of new storm.

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