ISSN 1000-0526
CN 11-2282/P
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    2020,46(9), DOI:
    Abstract:
    2020,46(9), DOI:
    Abstract:
    2020,46(9):1129-1142, DOI: 10.7519/j.issn.1000-0526.2020.09.001
    Abstract:
    Severe rainstorms struck South China on 7 May 2018, which were related to front-driven mesoscale convective system (MCS) and quasi-stationary MCS in warm zone. South-moving frontal MCS led to wide range of un-uniform precipitation, and warm-sector MCSs with short life time induced multiple mesoscale rainbands within the range of 30-200 km south to surface front. Quasi-stationary line-type MCS along the coast of South China grew up to 300 km in length, sustained more than 12 h and induced extremely severe rainfall beyond 300 mm. All types of MCS showed the low-echo-centroid structure on the vertical section of reflectivity, and the averaged 35 dBz echo-top was at the height of 5.5 km for frontal MCS cells, compared with 4.7 km for convective cells in warm sector. Analysis of raindrop size distribution revealed that MCS in coastal zone was with larger raindrop diameter and higher nuclei concentration compared with frontal MCS. Averaged large-scale precipitation efficiency of frontal convective system was at about 10%-15% according to ERA5 reanalysis, while the precipitation efficiency of MCS in warm zone could increase instantaneously more than 90%. Operational numerical models showed limited predictivity for convective precipitation in warm zone, while EC-Reforecasts showed improved performance on ensemble spread for the convective precipitation near South China coast. Mesoscale model’s forecast showed basic patterns of frontal MCS and warm-sector MCS, however obvious bias existed in the organization and intensity of MCS along coastal zone. Ensemble sensitivity analysis indicated that frontal MCS showed high sensitivity to synoptic forcing related to low pressure trough and low-level jet intensity, while convection in warm sector showed high sensitivity to CAPE in upstream environment.
    2020,46(9):1143-1152, DOI: 10.7519/j.issn.1000-0526.2020.09.002
    Abstract:
    Based on a flight case of the national MA60 seeding aircraft which took place on 21 October 2018, several flight parameters and meteorological elements observed from onboard various instruments are compared and analyzed to investigate their difference and verify the detection data quality. The results show that the deviations of the longitude, latitude and altitude location are relatively small showed on the GPS of aircraft platform, BeiDou Navigation Satellite System (BDS) and aircraft integrated meteorological measurement system (AIMMS-20). The observation of altitude on aircraft’s barometric altimeter is sharply lower than it showed on BDS and AIMMS-20. The changing trend of ambient pressure, true air speed (TAS), temperature, relative humidity and other elements are almost the same as shown on aircraft platform air data system (ADS), AIMMS-20 and cloud image probe (CIP). The observed values are also close to each other on ADS and AIMMS-20. The instantaneous changes of wind on AIMMS-20 are more accurate than on the ADS. The TAS on CIP is significantly slower than on AIMMS-20, 10 m·s-1 on average. The changing trend of environment pressure is the same on AIMMS-20 and CIP. There is 1.4℃ environment temperature lower on the average on ADS than on AIMMS-20, and there is obvious inversion when the lowest value happens. The ambient temperature on CIP probe is 0.6℃ lower than on AIMMS-20 and relative humidity is 8.6% lower than on AIMMS-20. The differences of aircraft location and those environment elements between different airborne observation sources are the result of different installation locations of those detection instruments or sensors, as well as the influence of inhomogeneous cloud structures. This comparison and analysis could not only provide some scientific bases for reasonable application of the airborne detection data, but also help to guide the design of airborne integrated mission systems for future national and local high-performance seeding and detecting aircraft constructions.
    2020,46(9):1153-1164, DOI: 10.7519/j.issn.1000-0526.2020.09.003
    Abstract:
    Using monthly wind speed data from 1979 to 2018 in Liaoning Province and reanalysis data, combined the UMR (urban minus rural) method and OMR (observation minus reanalysis) method combined with satellite remote sensing classification methods, this paper quantitatively analyzed the impact of urbanization of Liaoning Province on near-surface wind speed. The results show that in the past 40 years, the annual and four season wind speeds in Liaoning Province have shown a decreasing trend. The decreasing rate at urban stations is significantly faster than that at rural stations. The trend of UMR value (urban-rural anomaly) is -0.11 m·s-1(10 a)-1, and the contribution rate of urbanization impact is 73.3%. In spatial distribution, the decreasing trend of urban agglomerations in central and northern Liaoning is more obvious, and the wind speed decreases relatively slowly in the south and southeast. The urbanization impact calculated by UMR method shows increasing zonal distribution from west to east. The decreasing trend at the reanalysis data is closer to that of rural stations. The decreasing rate of wind speed in spring is the most obvious. The changing trend of OMR value is -0.10 m·s-1·(10 a)-1, and the corresponding urbanization impact contribution rate is 66.7 %. The urbanization impact and contribution rate calculated by the two methods are relatively consistent, and both can reflect the impact of urbanization on wind speed to a certain extent. Reanalysis data show that the wind speed in the Bohai Strait has a slight increasing trend, and the high-value areas with reduced wind speed are located in the northern Bohai Sea and the northern Yellow Sea. In a word, the spatial distribution of the urbanization impact calculated by the two methods is that the western and southern regions are less affected by urbanization while the central and eastern regions are more affected and their consistency is better.
    2020,46(9):1165-1177, DOI: 10.7519/j.issn.1000-0526.2020.09.004
    Abstract:
    A heavy rainfall process which occurred over the Taihang Mountains in central and northern Shanxi Province during 4-5 August 2019 was analyzed by using the GRAPES cloud analysis system, with which numerical experiments were also designed. The effects of the introduction of lightning mapping imager event (LMIE) data of FY-4A on the radar reflectivity, cloud microphysical variables, and rainfall prediction of the model calculation were mainly analyzed. The results indicate that the radar echo calculated by adding the LMIE data was closer to the measured radar echo, and the cloud microphysical elements such as cloud water, cloud ice and snow got adjusted, significantly increasing the content of cloud microphysical elements in the area where lightning occurs. The extreme centers of microphysical elements were generally consistent with the distribution of active areas of lightning. Thus, cloud information initialization could effectively improve the accuracy of precipitation forecast within 24 hours and reduce the spin-up phenomenon of numerical model. With the addition of LMIE data, the accuracy of 1-12 h precipitation forecast could be further improved.
    2020,46(9):1178-1188, DOI: 10.7519/j.issn.1000-0526.2020.09.005
    Abstract:
    From January to March 2017, we carried out an integrated field experiment in complex terrain of Winter Olympic Venue in Xiaohaituo Mountain of Beijing. The observation network consisted of 7 auto-matic weather stations (AWSs), 17 HOBO temperature and humidity data-loggers and 2 comprehensive super stations. During the 7 d intensive observing period (IOP), GPS radiosondes were launched every three hours. In this paper, the temperature profiles based on AWSs and HOBOs are compared with radio sounding temperature profiles. Based on the data of IOP, the characteristics of mid-mountain clouds (MMC) that have critical negative effects on alpine skiing are preliminarily analyzed. The results show that when MMC occurs, there are diurnal variations in surface wind direction. MMC tends to occur between 1 〖KG-*5〗100 m and 1 〖KG-*5〗700 m above ASL, shown up as a saturated moisture layer by radio soundings. In general, the top of MMC is at same height of the bottom of inversion layer, below which MMC exists. During nighttime, affected by downslope winds and down-valley winds, wind directions are more northwesterly or westerly below MMC. Inside MMC, winds blow more easterly or southeasterly at lower speeds through the day. Above MMC and inversions, westerly or northwesterly winds are obvious. Leeward subsidence-induced inversions and easterly moisture transportation in large scope could be the main causes for the MMC in Xiaohaituo Mountain.
    2020,46(9):1189-1198, DOI: 10.7519/j.issn.1000-0526.2020.09.006
    Abstract:
    In this paper, the dual-polarization weather radar data are used to improve the quality of the automatic rain gauge data. The quality of the rain gauge data is improved by using the inverse distance weighting method (IDW), and the rain guage data after quality control are used to correct the rainfall data derived from dual-polarization radar. The quality control method is determined by using the revised radar-gauge data, and the quality of gauge data is comprehensively controlled from the perspective of spatial consistency and observation consistency. The comprehensive quality control method is verified by using a typhoon precipitation process. The results show that there are some misjudgments in the spatial consistency of rain gauge observations by only using IDW method, mainly due to the abruptness of local precipitation, the inhomogeneity of rainfall structure and the sparse distribution of rain gauges. The misjudgments caused by the simple use of spatial consistent property control method can be effectively reduced by combining with polarization radar. The rainfall estimations of radar have been greatly improved after the rain gauge calibration and correction so that the effectiveness of the polarization radar used in the quality control of the rain gauge is improved. During typhoon rainfall, about 5% of the rain gauges per hour are considered as the error sites with wrong results. This comprehensive quality control method has some misjudgments when the distribution of the rain gauge is sparse or when the rain gauge lies in the edge of precipitation.
    2020,46(9):1199-1209, DOI: 10.7519/j.issn.1000-0526.2020.09.007
    Abstract:
    In order to study the vertical distribution of aerosol and cloud condensation nuclei (CCN) spectra, we combind the aerosol data with CCN data from aircraft and surface observations conducted in Shanxi on 30 July 2014 to analyze the vertical distribution of the parameters C and k of the CCN spectrum (N=C·Sk) and the activation characteristics of aerosols. The results show that the vertical stratification of aerosols in this process is obvious, and the vertical distribution of aerosols in different regions is different. According to the characteristics of potential temperature change, it can be divided into four layers from bottom to top. The vertical distribution characteristics such as aerosol concentration, effective diameter and particle spectrum are closely related to the stratification. The k is affected by the aerosol’s chemical composition and the particle spectrum, and the k of each layer is different. The k value of the first layer increases with height and the maximum value is 1. The k value of the second layer decreases first then goes up. It is the lowest between 1 〖KG-*5〗700 m and 2 〖KG-*5〗000 m, being 0.3. The third layer has little change in k, about 0.8, and the fourth layer stabilizes to 0.6. The aerosol sources are different in each layer by the backward trajectory modeling, and the properties of the aerosol are consistent with the ground aerosol properties of the corresponding source. The air masses at heights of 1 〖KG-*5〗000 m and 2 〖KG-*5〗000 m from the North China Plain in the southeast of Shanxi and the Loess Plateau to the west, respectively. The air mass above 3 〖KG-*5〗000 m is from Mongolia in the northwest. So, differences in vertical aerosol sources are responsible for the apparent stratification of the aerosol distribution and CCN spectrum.
    2020,46(9):1210-1221, DOI: 10.7519/j.issn.1000-0526.2020.09.008
    Abstract:
    The ECMWF (European Centre for Medium-Range Weather Forecasts) precipitation type forecast products (PTYPE) were verified using the weather observations of more than 2 〖KG-*5〗000 stations in China over the winter months (October to the next March) during 2016-2018. The products include the deterministic forecasts from high-resolution model (HRD) and the probability forecasts from ensemble prediction system (EPS) and the verified precipitation types include rain, sleet, snow and freezing rain. The results show that the accuracy of deterministic forecasts of ECMWF HRD is mostly higher than 90% and the TSs of rain and snow are the highest, followed by the TS of freezing rain, and the TS of sleet is lower, which indicates that the forecast skill of sleet is limited. The rain and snow dividing line of deterministic forecasts shows the errors of a little southward in short range forecast and more and more significant northward following elongating lead times in medium range forecast. The area of sleet forecast is smaller than observations and the area of freezing rain forecast is bigger for the HRD forecast. The EPS offsets these errors partly by probability forecast. The probability forecast of rain from the EPS is smaller than the observation frequency and the probability forecast of snow is larger in short range and smaller in medium range forecasts than the observation frequency. However, there are some forecast skills for all of these probability forecasts. There are advantages of EPS compared to the HRD. For rain and snow, for some special cost/loss ratio events the EPS is better than the HRD. For sleet and freezing rain, the EPS is better than the HRD significantly, especially for the freezing rain.
    2020,46(9):1222-1234, DOI: 10.7519/j.issn.1000-0526.2020.09.009
    Abstract:
    In order to understand the circulation characteristics of air pollution events in autumn and winter in Chongqing, this paper uses NCEP reanalysis data to classify the surface sea level pressure fields of air pollution events by using the self-organizing map (SOM) algorithm. Then by means of subjective comparative analysis, three types of typical surface pressure fields are summarized: uniform pressure pattern, low pressure pattern and the bottom pattern of high pressure. Among them, the uniform pressure pattern is divided into two types: one is the uniform pressure pattern between two cold fronts and the other is in the weak high pressure. The bottom pattern of high pressure can be divided into three types according to the center position of cold high pressure, including north high pressure type, northwest high pressure type and northeast high pressure type. By comparative analysis, it is found that the concentration of air pollutants on the bottom pattern of high pressure is the highest, thus the air pollution is the most serious. The analysis by using conventional observation data and L-band radiosonde data shows that all kinds of pollution weather patterns are characterized by high static wind frequency on the surface, low horizontal wind speed near the surface, high probability of inversion, stable atmospheric stratification and low height of atmospheric boundary layer. Based on the large-scale synoptic circulation, dynamic and thermal conditions and backward trajectory simulation, the causes for the three types of typical pollution weather processes are investigated, and the results would provide a reference for air pollution potential forecast and concentration prediction in Chongqing.
    2020,46(9):1235-1244, DOI: 10.7519/j.issn.1000-0526.2020.09.010
    Abstract:
    This paper investigated the roughness, stability and temperature inversion (TI) properties of urban boundary layer based on the analysis of wind and temperature observations from Tianjin meteorological tower. The results indicated that there is significant roughness length and zero plane displacement in all directions of the meteorological tower under the influence of surrounding buildings. The impact of urbanization on wind field is more evident below 80 m. Affected by the diurnal variation of turbulence intensity, the diurnal variation characteristics of wind speed in the upper and lower levels of meteorological towers are obviously different in each season. Based on the temperature difference wind speed method, atmospheric stratification is found more stable in autumn and winter. The occurrence of TI is more frequent under stable conditions and both the intensity and height of TI are much larger than those under unstable and neutral conditions. Furthermore, the occurrence of TI near ground is more frequent under stable conditions, which is very favorable to severe air pollution episode. The intensity of urban heat island is correlated with the temporal distribution of atmospheric stability.
    2020,46(9):1245-1253, DOI: 10.7519/j.issn.1000-0526.2020.09.011
    Abstract:
    The summer maximum power load variation and its correlation with meteorological factors were analyzed by using the 15 min power load and the daily meteorological data in Wuhan from 2016 to 2018. Based on stepwise regression and double hidden layer BP neural network algorithm, the prediction model of summer maximum power load was established. The results show that there is a significant positive correlation between the mean temperature, average maximum temperature and average minimum temperature and the meteorological load. The correlation between the maximum load on the day and the load on the previous day is the best. The load on the day is most sensitive to the average temperature and comfort index in the previous two days. With historical load and meteorological data as joint forecasting factors, the stepwise regression and BP neural network algorithm have a good simulation effect on the maximum summer power load in Wuhan, especially on the maximum load of high-level operation caused by continuous high temperature in 2018. When the sensitivity is lower than 10%, the positive contribution of the meteoro-logical factor in the stepwise regression algorithm is less than the negative contribution, and the positive contribution in the BP neural network algorithm is higher than the negative contribution. But when the sensitivity is higher than 10%, the meteorological factors in both algorithms contribute positively.
    2020,46(9):1254-1260, DOI: 10.7519/j.issn.1000-0526.2020.09.012
    Abstract:
    The main characteristics of the general atmospheric circulation in June 2020 are as follows. There was one polar vortex center in the Eastern Hemisphere, stronger than usual. The circulation in Eurasian middle-high latitudes showed a multiwave pattern. The strength of Western Pacific subtropical high was stronger and the covered area was larger than in normal years. The monthly mean temperature was 20.7℃, 0.7℃ higher than normal. The monthly mean precipitation amount was 112.7 mm, which is 13.5% more than normal. Five regional heavy rainfall processes occurred in China this month and some places were hit by severe rainstorm and floods. Droughts were found in nothern part of North China, southern part of South China, northern Xinjiang and Yunnan etc. in June. Typhoon Nuri landed in Yangjiang, Guangdong Province, which is the second landing typhoon in China this year.
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    Available online:  October 20, 2020 , DOI:
    Abstract:
    On March 21 2019, convective weather disasters in large areas occurred in the southern part of the south of the Yangtze River with kinds of disasters, and it was also the first regional severe convection case encountered after the dual-polarization transformation of the Ji'an SC Doppler radar in southern Jiangxi. Using the detection data, the distribution and evolution characteristics of the dual-polarized radar parameters are analyzed, and compared with the observation data of cloud-to-ground flashes(CGs), the differences in performance characteristics between short-term heavy rain and windy-hail are explored. The results show that in this case the increase of the horizontal reflectivity Z_H and the differential reflectivity Z_DR at low elevation angle are significantly ahead of the change of ground rainfall, while the changes of CGs frequency are more advanced, over 6-min earlier than Z_H and about 5-10 min earlier than Z_DR. The peak time of KDP lags behind lightning On March 21 2019, convective weather disasters in large areas occurred in the southern part of the south of the Yangtze River with kinds of disasters, and it was also the first regional severe convection case encountered after the dual-polarization transformation of the Ji'an SC Doppler radar in southern Jiangxi. Using the detection data, the distribution and evolution characteristics of the dual-polarized radar parameters are analyzed, and compared with the observation data of cloud-to-ground flashes(CGs), the differences in performance characteristics between short-term heavy rain and windy-hail are explored. The results show that in this case the increase of the horizontal reflectivity Z_H and the differential reflectivity Z_DR at low elevation angle are significantly ahead of the change of ground rainfall, while the changes of CGs frequency are more advanced, over 6-min earlier than Z_H and about 5-10 min earlier than Z_DR. The peak time of KDP lags behind lightning for about 15 minutes, which can helps to predict the evolution trend of ground rain intensity about this process. During the windy-hail process, the moment when Z_H begins to increase is about 15 min before the ground sag, and the other polarizations advance earlier. At the same time, CGs increase rapidly when hail occur. These have a good indication for hail predictions about this process. This paper also explores the relationship between the precipitation value M of ice particles and hail. It is found that it surges 15 minutes ahead of falling to the ground, and the higher the altitude, the earlier the M peak appears, which could provide reference for predicting the possibility moment of hail.
    Available online:  October 20, 2020 , DOI:
    Abstract:
    In this paper, the meteorological observation data, NCEP reanalysis data, Himawari-8 satellite data, etc. are used to analyze a rare thunderstorm in the northwest semi-arid region from October 8 to 9, 2017. Its causes and mechanisms were discussed. The results show that the rare thunderstorm process originated from the eastern part of the Qinghai-Tibet Plateau, which was developed in the background of a ground warm center in the in front of the trough, and had the characteristics of surface-based convection. The thunderstorms in Lanzhou, about 150 km away from the ground front, occurred with a deep and stable cold air cushion. There were obvious inversion layers in the middle and lower layer, and warm and humid air with conditional instability above the inversion layer, which has the structural characteristics of elevated thunderstorms. The process is different from the thunderstorm in the eastern humid region in the following aspects. In terms of its development and evolution, this elevated thunderstorm is actually the continuation and development of the surface-based thunderstorm in the Qinghai-Tibet Plateau, which moved to the cold air cushion in lower elevation. In terms of the structural characteristics, the heights corresponding to each feature level (cold air cushion, inversion layer, etc.) in this process were significantly higher than those in the low-altitude areas in the east, but there was no significant difference in the thickness of the corresponding layer. In terms of the formation mechanism of the cold air cushion, the land-atmosphere energy exchange in the semi-arid area of the northwest is dominated by the sensible heat. With the combined effect of the unique underlying surface and strong cold air, the loess plateau with complex topography can also form a relatively stable cold air cushion. From the perspective of instability mechanism, the surfaced-based thunderstorm in east of the Qinghai-Tibet Plateau and the elevated thunderstorm are both caused by conditional instability. The structure of “cold and dry in the upper level, warm and wet in the lower level” was observed in the east of the Qinghai-Tibet Plateau. The updraft was induced under the combined action of high-altitude jet and 500hPa high-altitude trough. In Lanzhou, the strong warm-wet advection in the middle troposphere enhanced the conditional instability above the inversion layer. The convergence effect of 700hPa shear line cooperating with the synoptic-scale forcing of 500hPa trough triggered the ascending motion and released the unstable energy, which provided favorable conditions for the maintenance and development of vertical convection that moved eastward from the plateau to the cold air cushion.
    Available online:  October 20, 2020 , DOI:
    Abstract:
    In order to evaluate the wind speed forecast ability of Shanghai Meteorological Service-WRF ADAS Rapid Refresh System (SMS-WARR), the 10-m wind has been divided into three levels to analyze the error characteristics and corresponding causes of formation,especially during the period of typhoon influence. The results show that the SMS-WARR model overestimates the wind weaker than 6 grade and underestimates the wind stronger than or equal to 6 grade in each lead time; the wind speed forecast score will decrease in the wind weaker than 6 grade and increase in the wind stronger than or equal to 6 grade with lead time;forecast and observational wind speed have similar distribution between 5%~90% quartiles. During the period of typhoon influence , the area of strong breeze(6 grade) is much larger than the area where the strong breeze was actually recorded. The area of large deviation is mainly distributed in the area of forecast strong breeze. These error characteristics is speculated to be related to the cold and hot starting of the system and the weak predictability of the wind field during the rapid intensification phase of typhoons.
    Available online:  October 20, 2020 , DOI:
    Abstract:
    Measurements within the atmospheric boundary layer (ABL) play a key role in understanding the exchanges of energy and mass between the land surface and the atmosphere. But the commonly used radiosonde and remote sensing observations have some limitations in capturing the details of the temperature and moisture variations in the lower ABL – surface layer. Small unmanned aircraft system (sUAS) is a good alternative because of its flexibility, low cost and capability to provide measurements of higher spatiotemporal resolution in the lower ABL. The goal of this study is to demonstrate whether the accurate and high spatiotemporal resolution thermodynamic profiles of the lower ABL over the urbanized areas could be obtained using sUAS. Twenty flights in total were conducted in Shanghai during winter (in December 2018) and spring (in March 2019) months, and 19 profiles (surface - 200 m) of temperature and moisture were collected. Measurements from automatic weather station (AWS) and radiosonde at the same site were used to evaluate these profiles. Results show that surface temperature and relative humidity derived by sUAS are close to those from AWS, with the mean differences of -0.5 ℃, 4.9% for winter flights and 0.9 ℃, -5.9% for spring flights. The general features of temperature and relative humidity profiles obtained from sUAS are consistent with those from radiosonde, such as temperature inversion near the ground and so on. These findings indicate that sUAS is capable of revealing detailed structures and variations of the lower ABL over the urbanized areas.
    Available online:  October 20, 2020 , DOI:
    Abstract:
    Based on the data of three traffic meteorological stations set on Nanjing-Suqian-Xuzhou expressway observed every ten minutes during 2015 to 2018, the Random Forests Regression was used to forecast the road surface temperature in the next hour in winter and the feasibility and applicability of the models were analyzed. The results were showed as follow: (1) The Random Forests Regression models could be used to predict the road surface temperature of the expressway in winter, and the feature input and parameter debugging are different in types of traffic meteorological stations. (2) Compared with the simple features, the complex features could replenish and explain the environment and meteorological elements of the traffic meteorological stations better, and they had a higher degree of differentiation between the ordinary road traffic meteorological stations and the traffic meteorological stations near the bridge and water. As a result, the model has a good forecast effect on the general road traffic meteorological stations and the traffic meteorological stations near the water and bridges, but a little poor forecast effect on the traffic meteorological stations in the service areas. (3) The reduction of the average error rate out of bag did not mean the improvement of the prediction accuracy. (4) The random forest regression models simulated from the complex features could be used to predict the road surface temperature of different types of traffic weather stations in winter no matter what weather conditions. Their forecast effect was the best in rainy and snowy days, followed by cloudy days and slightly worse in sunny days.
    Available online:  October 14, 2020 , DOI:
    Abstract:
    Extreme Meiyu struck Yangtze River Basin (YRB) during June to July 2020 which was ranked first in history exceeding Meiyu season of 1998 since 1961. Meiyu rainfall events were characterized with long time duration, short intervals and spatial overlapping with nocturnal rainfall peak. Accumulated precipitation centers were obvious correlated with topographical features of Dabie Mountain, Wannan Mountain and mountainous territory in west of Hubei Province. It was revealed that main rainbelt swung over YRB in June compared with quasi-stationary rainbelt along Yangtze River in July. Staggering of Meiyu front over YRB was correlated with persistence of strong blocking high pressure systems in mid-high latitude zones of Asia and abnormal position of the Western Pacific subtropical high pressure staging at about 20°N during July with significant positive vapor flux anomaly beyond 3\sigma over YRB. Due to the interaction of low-level southwest jet, upper-level westerly jet and upper-level easterly jet, displacement of low-level convergence with upper-level divergence was conducive to intense precipitation along Meiyu front. Heavy rainfall events on Meiyu front could be identified into two synoptic types. One type was characterized with quasi-stationary Meiyu front, and the other type was characterized with mesoscale cyclogenesis on Meiyu frontal zone. The former type was dominated by steady quasi-zonal upper level flow, and staggered low-level wind shear zones with quasi-stationary rainbelts. The other type of rainstorm events developed with distinct cyclonegenesis along Meiyu front, and accompanied with long-life mesoscale convective systems organized with complicated β-mesoscale convective rainbelt adjoining to low-level vortexes. Forecast verifications indicated that high predictivity for the first type of heavy rain events, while the second type of Meiyu events were associated with low predictivity and more uncertainty. Obvious forecast deviations occurred due to unrealistic positive feedback between over-intensified low-level vortex, precipitation latent heat releasing and low-level jet enhancing in ECMWF-HR forecast.
    Available online:  October 12, 2020 , DOI:
    Abstract:
    The Meiyu in 2020 is a typical super Meiyu, with the characteristics of the earlier onset, later end, longer rainy season, wider rainfall range, abundant accumulated rainfall, and more heavy storm processes than normal. Through the analysis of simultaneous atmospheric circulation systems, it is found that the average positions of the key East Asian monsoon circulation systems are relatively stable, with significant quasi biweekly oscillation (QBWO) in the Meiyu period of 2020. The onset and end of Meiyu, the northward shift and stagnation of the rainfall belt, and the occurrence and persistence of heavy rainstorm processes have a good relationship with the QBWO. During the Meiyu period, the western Pacific subtropical high experienced six periodic oscillations of northward uplift and southward retreat. Meanwhile, the upper- and low- level monsoon circulation systems strengthened for five times corresponding with the QBWO in the Meiyu season, especially the strengthening of the southwesterly low-level jet, the repeated establishment of the large value centers of southerly with relatively consistent latitude, which made the water vapor transport from the tropics strengthened again and again, and the water vapor convergence and upward movement developed repeatedly, and led to the long-term persistence of Meiyu in the YHRV, with frequent occurrences of the rainstorm. On the other hand, two blocking highs are maintaining in the middle and high latitudes, which is characterized by the spatial pattern of "two ridges and one trough" over Eurasia, and the low trough along the East Asian coast is also active. The cold air falls continuously southward through the northwestern and/or northeastern paths, frequently merging with the repeatedly strengthened warm moisture from the low latitude over the YHRV, which is another important factor causing the super Meiyu in 2020. Moreover, we compared the temporal and spatial distribution of Meiyu, and the corresponding flood disaster in 2020 with other super Meiyu years since 1951. It is shown that the super Meiyu in 2020 is weaker than that of 1954, but stronger than that of 1998 and 1991. Benefits from the improvement of both the accuracy of climate prediction and the ability of disaster prevention and mitigation, the flood and disaster losses caused by this super Meiyu in the YHRV are significantly decreased than before.
    Available online:  September 29, 2020 , DOI:
    Abstract:
    The high-resolution water vapor density, integral water vapor content(V)and liquid water path(L)measured by ground-based microwave radiometer have important application potential and value in the prediction and research of strong convective precipitation. The paper uses these data to study the water vapor distribution, evolution and vapor-liquid conversion in different stages before and after the two thunderstorms that happened in Urumqi and Chengdu airports: during the 7.4 thunderstorm in Urumqi, under the action of water vapor transport and vertical motion, the low-level water vapor density significantly increased before precipitation and recovered rapidly after precipitation. Before the 7.15 thunderstorm precipitation in Chengdu, the whole layer of water vapor experienced the evolution process of increasing first and then decreasing. During the process of water vapor accumulation, the maximum increment was 4.99 g·m-3. During the process of water vapor conversion, the whole layer of water vapor decreased rapidly. The water vapor density decreases more at the height of the cloud. The cloud water vapor content (IWVc) inversion in the text is better than V and L in indicating the start and end of precipitation. Before Urumqi 7.4 precipitation, IWVc increased by 1.8 times and 2.2 times, respectively. After the precipitation ended, IWVc decreased rapidly. Before the precipitation in Chengdu 7.15, IWVc increased by 1.3 times and 1.5 times, respectively. During strong precipitation, the growth rate of water vapor in the cloud was lower than that of water vapor. In addition, the increase or decrease of IWVc can also be good indicators for the precipitation intensity of two thunderstorm processes. For the stable precipitation of Urumqi 7.4 thunderstorm, when the IWVc increases, the ground precipitation intensity also increases, and the greater increase of water vapor in the cloud, the greater ground precipitation intensity observed; when the IWVc decreases, the precipitation is less than 0.01 mm. For the convective precipitation of Chengdu 7.15 thunderstorm, the accumulation of IWVc is ahead of the occurrence of surface precipitation. The more IWVc accumulates, the stronger the ground precipitation happens. After turning into stable precipitation, the relationship between IWVc and ground precipitation returned to the same increase and decrease, and the decline of IWVc increment or decrement also predicted the decrease and end of the precipitation.
    Available online:  September 28, 2020 , DOI:
    Abstract:
    Based on the operational TRAMS (Tropical Region Assimilation Model for South China Sea) 2.0 version model, a series of technical updates were conducted, including model resolution, dynamical frame, physical process, and TRAMS 3.0 version model is formed. Verifications for the typhoons in 2017 showed that track errors and intensity errors were reduced significantly, the 72h mean track error was 7% decreased (about 13.6km), and the intensity was 10.5% decreased (about 1.2 hPa). The meteorological elements were also improved by the newly upgraded TRAMS model. Increasement of model resolution and revised cumulus scheme provided major contribution to forecast improvement in TRAMS 3.0 version.
    Available online:  September 27, 2020 , DOI:
    Abstract:
    The impact of the Madden-Julian Oscillation (MJO) on the high-latitude wintertime surface air temperature (SAT) is examined based on NCEP-NCAR reanalysis daily data during 1979-2016. The real-time multivariate MJO (RMM) index, which divides the MJO into eight phases, where phase 2 (phase 6) corresponds to the enhanced (reduced) convection over the Indian Ocean and Maritime Continent, is used. A significant positive SAT anomaly over northern high-latitude region of (180, 60) is found 5-15 days following MJO phase 2, while a negative SAT anomaly appears over the same region about 5-15 days after the MJO is detected in phase 6, as the tropical forcing changes sign. An analysis of the lagging composite of the geopotential height at 500 hPa indicates that the Arctic SAT anomaly is a result of a north-eastward propagating Rossby wave train associated with the tropical convection anomaly of the MJO. An analysis of the wave activity flux indicates that the north-eastward propagating wave train is likely a result of Rossby energy propagation. A composite analysis of the specific humidity at 700 hPa shows that cool (warm) surface temperatures occur under dry (moist) air, due to the positive relationship between mid-troposphere specific humidity and downward longwave radiation. These composite fields suggest SAT signals due to the MJO result from both advective and radiative process. Hence, the MJO phases provide useful information for the extended-range forecast of high-latitude surface air temperature during boreal winter.
    Available online:  September 27, 2020 , DOI:
    Abstract:
    Severe flood occurred in the middle and lower reaches of the Yangtze River Basin (MLYRB) in June-July 2020 (JJ2020). In this paper, the extreme features of the flood are analyzed based on daily precipitation observation at national stations from 1951 and hourly observation at national & regional stations in JJ2020. Both the flood range (anomaly percentage more than 50% or 100%) and the total amount are significantly greater than those in 1998 and 2016, and ranked the second in recent 70 years followed 1954. There are three rainfall centers with maximal accumulated precipitation greater than 1500 mm, including Dabie Mountain area, Southern Anhui Province and southwestern Hubei Province. The flood is closely related to the extreme long-term persistence of Meiyu in MLYRB. The Meiyu period in 2020 lasts for 53 days, 23 days more than the climatology. In JJ2020, positive precipitation anomaly existed in each dekad, which was never occurred before since 1961 and also indicates the extreme features of the flood. Total station numbers in JJ2020 are all the maxima since 1961 at four different rainfall grades (i.e., 10-24.9 mm/day, 25-49.9 mm/day, 50-99.9 mm/day and ≥ 100 mm/day), especially in the latter three grades. Extremity of the flood can also be found in the short-duration heavy rain processes. In JJ2020, the accumulated station number is 1612 and 100 with hourly precipitation over 20 mm and 50 mm, respectively. Both of the numbers are the highest since 1981. At four stations with total precipitation exceeding 1500 mm, frequencies of hourly precipitation greater than 20 mm are 2~4 times to their climatologies. Accumulation of the first 43, 21, 19 and 27 strongest hourly precipitation exceeds their seasonal average, respectively. Above results indicate the significant extremity of the flood in MLYRB existed in the total rainfall, the duration and the short-term intensity.
    Available online:  September 25, 2020 , DOI:
    Abstract:
    Abstract: By using the NCEP/ NCAR reanalysis data, satellite, radar and aircraft observation data, the artificial precipitation enhancement conditions of a precipitation process on 5 November 2018 in Hennan Province were analyzed. The results show that the precipitation process is mainly affected by the low-altitude shear line and the ground cold front. The operational area has good water vapor and a thick ice surface supersaturated layer, and the dynamic conditions are conducive to promoting the development of precipitation. The aircraft operating area is mainly a stratified hybrid cloud, and the cloud system is in the development stage.The relationship between the supercooled water area of satellite inversion and the concentration of DMT detection particles is analyzed importantly. By using the FY-4A satellite visible light channel, 3.7 μm channel and infrared channel data for three-color fusion analysis, it is found that when there is supercooled water in the cloud, and the concentration of particles detected by the CAS probe is also greater than 20个?cm-3.They have a good correspondence, indicating that the method analysised supercooled water in the cloud by the three-color synthesis can be applied to be one of the conditions for selecting the artificial precipitation enhancement area.
    Available online:  August 31, 2020 , DOI:
    Abstract:
    Researching the evolution of the polarimetric signatures, dynamical and microphysical characteristics in the heavy hail supercell can be beneficial in understanding the physical processes that lead to heavy hail formation and decay, determining possible precursive signatures associated with heavy hail formation and growth, and improving warnings for heavy hail supercell. A supercell accompanied by heavy hail in southern Fujian on 22 April 2019 was detected by the Xiamen S-band dual polarization radar is analyzed using the dual-Doppler radars wind field retrieval and hydrometeor classification algorithm. The study reveals:(1) The differential reflectivity (Zdr) at the beginning portion of the Three-Body Scatter Signature (TBSS) was very high located radially behind the horizontal reflectivity (Zh) core. It was also found that the cross-correlation coefficient (CC) was very low in the TBSS. Polarimetric signatures associated with TBSS are good indicators of heavy hail aloft. (2) The polarimetric signatures of the heavy hail region manifested as high values of Zh collocated with near-zero value of Zdr. However, during the heavy hail descent, Zdr increased and CC decreased on the periphery of the hail core. The increased Zdr and decreased CC due to the increasing presence of water coating on the melting hailstones. (3) At low level, an area of enhanced specific differential phase (Kdp) was observed within the Zh core of supercell, which called the Kdp foot. Kdp is less sensitive to heavy hail and thus is a better indicator of melting hail. Therefore, the Kdp foot may be a favorable index of the downdraft regions which driven by melting of hail. (4) The horizontal wind field showed a distinct double vortex developing in the supercell. The double vortex structure contributed to the development of supercell and the circulation growth of heavy hail. (5) On the northeast of the mesocyclone, a region of modest Zh, low Zdr, and high CC was observed, called the graupel belt. The hydrometeor classification algorithm (HCA) suggest that graupel is the dominant hydrometeor type. Because of the proximity to the mesocyclone, some of the graupel was entrained into the updraft serves as hail embryos. The schematic diagrams of polarimetric signatures and three-dimensional wind field structure of the heavy hail supercell are shown based on these analyses.
    Available online:  August 31, 2020 , DOI:
    Abstract:
    Aim to solve flood warning of the ungauged and small to middle-sized basin, the topography-based dynamic critical arearainfall threshold model is developed for solving flood warning of the ungauged and small to middle-sized basin in this paper. The exponential equation model between dynamic critical arearainfall threshold and four main characteristic factors is established. Four main characteristic factors include basin area, channel slope, land use and soil type, which taking main effect on flood generation process in small to middle-sized basin. Dynamic critical arearainfall threshold in the ungauged basin is calculated with the developed exponential equation model of the gauged basins and four main characteristic factors of the ungauged basin. Five small to medium-sized basins in the subtropical monsoon climate region of eastern China are selected as the test basins, including Huangchuan basin of Huaihe River, Tunxi and Yuliang basins of Qiantang River, Xitiaoxi and nantiaoxi basins of Taihu Lake. Taking the warning flood as an example, dynamic critical arearainfall thresholds of Huangchuan, Yuliang, Xitiaoxi and nantiaoxi basins are inversed with the long-term hydrological and meteorological data by the GMKHM hydrological distributed model. According to the developed critical threshold model, dynamic critical arearainfall threshold of Tunxi basin is calculated basing on basin area, channel slope, land use and soil type. The topography-based dynamic critical arearainfall threshold is applied to flood warning verification of 35 representative flood events in Tunxi basin. Results show that flood warning hit rate basing on the topography-based dynamic critical arearainfall threshold is 91.4%,Which is close to that taking the basis on dynamic critical arearainfall threshold calculating with long-term hydrological and meteorological data in Tunxi basin. The developed topography-based dynamic critical arearainfall threshold model has certain reference significance for similar flood warning of ungauged basins and flash flood warning.
    Available online:  August 27, 2020 , DOI:
    Abstract:
    The most common tropical cyclone (TC) center identification method is searching for minimum sea level pressure (MSLP), which still has some shortcoming. In this paper, TC center identification method and intensity estimation method based on GFDL Vortex Tracker Technique (GVT) has been studied in regional numerical weather prediction model application. Detailed comparisons between GVT and three traditional TC center location and intensity estimation techniques, including MSLP, using maximum vorticity value at 500hPa (VT500), and using minimum geopotential height at 500hPa (H500) was made. Using H500, VT500 and MSLP methods to determined TC center location, there will be some degree of zigzag-shaped irregular swing path, especially using VT500 method. The VT500 method has largest irregular swing amplitude and the positioning effect is the worst. GVT method can better correct the zigzag-shaped swing path and makes the model prediction path closer to the observed one, and the positioning effect is the best. However, the H500, MSLP and GVT are relatively closely when the typhoon location is away from the coastline. The errors of the minimum pressure of TC center by these four methods show that the VT500 method has the largest error, the GVT method has the smallest error, and the MSLP and H500 methods’ error are between VT500 and GVT. The errors of maximum wind speed near the TC center by four methods show the error of the four methods is not much different. The operational application in 2016-2018 show that the Zhejiang Typhoon Vortex Tracker System (ZJTVTS) based on GVT technology can improve the prediction quality of Zhejiang WRF-ADAS Regional Model System (ZJWARMS) and Zhe-Jiang WRF-ADAS Rapid Refresh System (ZJWARRS).
    Available online:  August 06, 2020 , DOI:
    Abstract:
    The GRAPES_Meso model was used to simulate the rainfall process of the westerly trough on May 5, 2018.The relevant cloud variables of model calculation and satellite observation were compared and analyzed. The results show that in the current cloud computing scheme of GRAPES_Meso model, there are excessive high cloud cover in some places and deficit cloud cover in the medium and low level dense closed cloud region. The cloud top temperature simulated by GRAPES_Meso model is obviously lower and the cloud top height is obviously higher. To address these issues, the principles and formulas of the cloud computing scheme are interpreted, and the calculation formula is optimized. After adopting the improved cloud computing scheme, the excessive high cloud cover has been greatly alleviated. Low cloud top temperature and high cloud top height has been greatly optimized.Based on satellite observation data, the preliminary exploration and test on the optimization of cloud computing scheme provides a new means and method for researching and optimizing cloud computing scheme.
    Available online:  June 28, 2020 , DOI:
    Abstract:
    Using the observation data from Zhejiang coastal stations, the ECMWF 10 m wind forecast from 2015 to 2018 was verified and evaluated. The result shows: The prediction error is closely related to the offshore distance, the farther the station is from the coastline, the higher the consistency is. For far-shore stations, the predicted wind speeds are lower than the observed values and the wind directions have counterclockwise deviations. While for near-shore stations, it shows higher and clockwise. With forecast lead time extending, the correlation coefficient of wind speed gradually decreases, while the root-mean-square error of wind speed and wind direction gradually increases, and this change is more pronounced for far offshore stations. Further analysis on buoy stations indicates that the forecasts of NW, N and NE winds prevailing in winter have significant systematic deviations. Wind speeds were predicted lower for strong winds, and wind directions had clockwise deviations for light winds. The forecast dispersions of wind speed and wind direction are NW>N>NE. The prediction errors of S and SW winds prevailing in summer are relatively smaller than that of NW and N wind directions. Regarding the three typical gale systems, the cold air gales obtain the best forecast outcome, with the accuracy reaching 97% and over 70% for 12 h and 96 h lead time. The accuracy of tropical cyclone wind forecast declined most significantly over the lead time. It remains 85% for 36 h lead time but decreases sharply to less than 50% beyond 96 h. For low pressures or reverse trough systems, the forecast accuracy remains less than 60% within 144 h. In specific, the maximum wind predictions and observations at buoy stations during cold air and tropical cyclone systems are basically in line with the linear distribution. The correlation coefficient for the cold air system can pass the 0.05 significance test within 144 h, while for tropical cyclones it passes only within 48 h. The linear regression method was used to correct the maximum wind speed forecast at buoy stations for cold air systems, and the independent sample tests prove that this method is effective in reducing prediction errors.
    Available online:  June 04, 2020 , DOI:
    Abstract:
    Severe downslope windstorm triggered by the interaction between the gap jet and the asymmetrical topography in the Tianshan canyon which caused severe disasters of trains rolloverin the Turpan Depression in Xinjiang on February 28, 2007. To understand the mechanism of downslopewindstorm between the interaction of large-scale circulation background,mesoscale system and complex topography in this extreme windstorm.We use a WRF model to simulated it.Base on the mesoscale diagnostic analysis to simulative results,We propose a mechanism for the windstorm : Under the pressure gradient between north-south sides of the Tianshan Mountain, the air parcel climbs windward slope and flows into the Tianshan Gorge and then forms gap jet due to effect of narrow,the jet generated gravity waves forced by the asymmetric terrain of the Tianshan Canyon, and produces a lee waves in the leeward, which transmits the energy of the gap jet to the ground,andSevere downslope windstorm formed finally. In this process, the turbulence formed by the wave breaking and the critical layer absorb the upper layer energy downward, which strengthens the energy of the gap jet,and the atmospheric stability stratification exacerbates the sinking movement, which sinks energy to the ground.
    Available online:  June 04, 2020 , DOI:
    Abstract:
    In order to quantitatively analyze and study the influence of lake on the intensity and properties of precipitation, this paper designed the control (HL) experiment and the sensitivity (NL) experiment of lake land-surface, it based on the mesoscale numerical model of WRF3.8 version and the FNL analysis data of with the 1°×1°, time interval is 6 h provided by NCEP/NCAR. The high value center of heavy precipitation near Poyang Lake on 14 to 15, June, 2011 was analyzed. The results show that: (1) The surface of Poyang Lake is a "cold source", which has obvious "cooling" regulation effect on the horizontal range of 100 km and the vertical range of 500 m. This weakening of thermal conditions affects the intensity and durability of the vertical upward motion in the troposphere, resulting in reduced precipitation intensity and shorter precipitation duration, which ultimately reduces the about 10% of accumulated rainfall near the lake. (2) The lower cushion surface of Poyang Lake can only improve the saturation degree (relative humidity) of atmospheric water vapor in the boundary layer, but "reduce" the absolute content of water vapor (compared with wet), which is one of the reasons why the NL than HL experiment precipitation center has greater strength and a wider range of heavy precipitation after lake land surface. (3) The lower surface of the lake water body by reducing the atmospheric temperature and absolute humidity of the boundary layer, so that the atmosphere has a weaker convection effective potential energy than NL, the lower atmosphere (1000~850 hPa) has a weaker convection instability, sounding reflects the HL test near the formation has a shallow inverse temperature structure, It has a lower CAPE than the lake terrestrial NL experiment, and finally weakens the convection properties of the HL test precipitation. Generally speaking, the lower surface of Poyang Lake changes the temperature and absolute humidity of the boundary layer, thus changing the environmental conditions of the lower atmosphere, and affecting the temperature and humidity conditions of the initial uplift gas block, which ultimately affects the precipitation properties and strength.
    Available online:  April 17, 2020 , DOI:
    Abstract:
    Based on circulation and precipitation hindcast and real-time forecast data of BCC Second-Generation Climate System Model developed by National Climate Centre, evaluation works of East Asian summer climate prediction are carried by synchronized and lag correlation, partial correlation and combined EOF decomposition analysis. Results show the main spatial distribution of high and low level circulation and precipitation climatical fields can be well predicted, particularly the location of the heavy rainfall center and members of the monsoon system, but with some systematic biases. The model predict precipitation interannual variability in East Asia especially in China with poor skill, but has decent prediction ability on 500hPa geopotential height interannual variability, and its skill improves as the approaching of starting month. The model can predict the temporal and spatial distribution of the main modes of interannual variations of the East Asian climate with high skill. It can also catch the main characteristics of the response of East Asian climate variability in developing El Ni?o and decaying El Ni?o period,which mainly come from east patern El Ni?o events. Overall, BCC_Second-Generation Climate System Model model can predict the East Asian summer climate with decent skill, which can benefit the short-term climate prediction.
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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.
      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.
      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.
      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.1000-0526.2012.1.001
      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.
      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.
      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.
      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.
      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(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.
      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.
      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.
      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.
      2008,34(4):124-126, DOI: 10.7519/j.issn.1000-0526.2008.04.017
      Abstract:
      随着青岛地区经济社会的高速发展,各个高炮作业点所在地的周边环境已经发生了很大变化 ,为确保高炮人工增雨防雹作业的安全,利用最新的高分辨率的卫星影像,结合高炮作业点 周边的实际情况,按照有关规定的要求,制作了高炮安全射界图。
      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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