ISSN 1000-0526
CN 11-2282/P
  • Current Issue
  • Online First
  • Archive
  • Most Downloaded
    Select AllDeselectExport
    Display Method:
    2021,47(12):1433-1443, DOI: 10.7519/j.issn.1000-0526.2021.12.001
    Abstract:
    Extreme precipitation struck Zhejiang Province induced by Typhoon Lekima in 2019. It was found that the spiral rainbelt staggering on the coast of Zhejiang Province during the daytime of 9 August, and rainfall was enhanced significantly due to inner-core convection during Lekima’s landing period over the night. Rainfall centers were significantly related to the near-shore of Tiantai Mountain, Kuocang Mountain and Yandang Mountain in Zhejiang Province. Based on analysis of GPM (Global Precipitation Measure) retrieval cloud parameters, Lekima’s spiral rainbands were dominant by mixed cumulus-stratus precipitation, while eyewall was dominated by tropical warm cloud precipitation. With larger effective diameter of raindrops and the higher density of raindrop particles, extreme rainfall intensity was formed in Lekima’s eyewall. Spiral rainbelt was enhanced due to the low-level frontogenesis and coast convergence during the landing of Lekima. Lekima’s inner-core convection was more intense on the left direction, leading to heavier rainfall on the left side of typhoon’s landing position. By comparing precipitation rate evolution between mountainous and plain areas via statistics with minute-interval automatic weather station observation, it was preliminarily proved that the topographic rainfall enhancing mechanism and the asymmetric inner-core convective structure have almost the same impact on precipitation intensity, both favoring the asymmetrical rainfall concentrating on the left side to Lekima’s forwarding direction.
    2021,47(12):1444-1456, DOI: 10.7519/j.issn.1000-0526.2021.12.002
    Abstract:
    The evaluation results of ECMWF and GFS on the track and strength forecasts of typhoons affecting Zhejiang from 2016 to 2019 show that ECMWF is better than GFS for track forecasting, and GFS has more advantages for strength forecasting. On this basis, the paper proposes a feasible typhoon initialization scheme to improve the performance of typhoon forecasting skill. Based on ECMWF and GFS analysis fields and oceanic typhoon observation data, as well as typhoon vortex separation, the vortex field is obtained by separating the GFS analysis field, and after vortex relocation and maximum wind speed adjustment procedure, it is superimposed with the large-scale environmental field separated from the ECMWF analysis field, realizing the reconstruction of typhoon initial field. For 14 typhoons affecting Zhejiang in recent years, the hindcasting results of the mesoscale numerical weather forecast model which uses the new reconstruction scheme demonstrate that the new scheme gives full play to the ECMWF’s advantages in track forecasting and GFS’s advantages in strength forecasting, improving the forecast accuracy of typhoon track and strength effectively. The absolute error of track forecast is reduced by 21 km and the standard deviation by 26.6 km compared with the prediction of the GFS-driven mesoscale model. Compared with the forecast result of the ECMWF driven mesoscale model, the absolute error of strength forecast is reduced by 1.7 m·s-1 and the standard deviation by 2.3 m·s-1. The analysis of the typical case of Super Typhoon Lekima (2019) further indicates that the initial field reconstruction technology has a better forecasting ability for atmospheric circulation characteristics and typhoon’s warm core structure.
    2021,47(12):1457-1468, DOI: 10.7519/j.issn.1000-0526.2021.12.003
    Abstract:
    In this study, the key area of upwind southwest wind speed is established, which is closely associated with spring persistent rains in Hunan (SPRH). The monitoring indicators of SPRH from 1980 to 2014 are defined. The temporal and spatial patterns of SPRH rainfall are analyzed. Besides, the anomaly of the atmospheric circulations during the strong/weak SPRH period and sea surface temperature (SST) during the early period are discussed. Results show that the climate average of SPRH occurs from the 13th pentad to the 27th pentad, whereas the starting date and ending date of SPRH vary in different years. The rainfall of SPRH exceeded normal conditions during the periods before the mid-1980s and after 2014, but it was lower than normal conditions during the periods of the mid-1980s to 2013. The rainfall of SPRH decreased from south to north and from east to west in spatial distribution. The spatial pattern of more (less) precipitation in the whole province can show the main spatial distribution of SPRH. In the strong SPRH years in whole province, the Western Pacific subtropical high (WPSH) remarkably becomes stronger and westward, the Indo-Burmese trough tends to become weaker, and an anomalous anticyclone exists in the southern Yangtze River regions in low-level wind field. Hunan is located in the center of anomalous anticyclone, causing heavy SPRH. However, in the weak SPRH years, WPSH evidently becomes weaker, the Indo-Burmese trough tends to become stronger, and an anomalous anticyclone is found in southern China. Additionally, Hunan is located in the center of anomalous water vapor divergence, resulting in weaker SPRH in whole province. In the following year of the occurrence of El Ni〖AKn~D〗o events, SPRH starts earlier, persists longer and has more intensive rainfall amount compared with the normal years. On the contrary, during the following year of the occurrence of La Ni〖AKn~D〗a, SPRH starts later, has short rainy periods, lower rainfall amount and weaker rainfall intensity compared with the normal years.
    2021,47(12):1469-1483, DOI: 10.7519/j.issn.1000-0526.2021.12.004
    Abstract:
    146 short-time severe precipitation cases in summer (JJA) were selected to analyze the distribution characteristics of short-time severe precipitation in Chengde from 2008 to 2017 based on the multiple data of automatic weather station, meteorological satellite, Doppler radar and NCEP reanalysis. The results show that the synoptic circulation patterns controlling severe precipitation in the Chengde Montains can be divided into the cold vortex type (45%), westerly trough type (34%) and edge of the western Pacific subtropical high (WPSH) type (21%). The short-time severe rainfall in June mostly occurs under the background of cold vortex circulations, with scattered rain falling areas. The dominant circulation pattern in the early-mid July is the westerly trough type but turns to be the edge of WPSH type after the late July. The severe precipitation under both the westerly trough type and the edge of WPSH type are generally distributed on the windward slope of Yanshan Mountain in the southern edge of Chengde. Differing from the traditional rainy season in North China, which is influenced by the position of subtropical high, the concentrated period of the short-term severe precipitation in Chengde is from late June to late July, and the peak appears when the cold vortex and the westerly trough circulations take action together. Mesoscale convective systems which are responsible for short-time severe precipitation move in Chengde mainly through southwest (northeastern Beijing) and northwest (Inner Mongolia) channels. In addition, a considerable number of convective storms are born locally in Chengde. The short-time severe precipitation in Chengde are often along with less water vapor and poor transportation compared with that in conventional rainy season. The water vapor content of cold vortex type is only 8 g·kg-1 at 850 hPa. The median of the area averaged atmospheric precipitable water (PW) is 33 mm in the Chengde Mountains and is only 29 mm under the cold vortex circulation. Even if the median of PW under the edge of WPSH type gets to 38 mm, it is still 15 mm lower than that in the south plain areas. The short-time severe precipitation often occurrs in extremely unstable stratification. The medians of temperature difference between 850 hPa and 500 hPa of cold vortex type and the westerly trough type are 28.6℃ and 27.9℃ respectively, while the others are below 25℃ in most of areas (including mountainous areas) of China.
    2021,47(12):1484-1500, DOI: 10.7519/j.issn.1000-0526.2021.12.005
    Abstract:
    The urban hydrological model is introduced into the urban flash flood forecasts and warning operation. The data of land use and land cover types and gridded urban drainage network capacity are parameterized in the model. Forced by the radar rainfall estimates, the model simulates the urban surface hydrological response and hydraulic processes. The hydraulic model is based on the shallow water equation, and the alternating-direction-implicit is used to solve the differential equation by two steps in the x direction and y direction, respectively. This solution comprises the back water effects in simulation and indirectly emulates the multiple flow direction methods, recalling the surface water dispersion in turbulence or diffusional effects. The case study demonstrates the online and offline running of the urban hydrological model for the purpose of flash flood warning, partially for the model validation. The online hydrological model takes the case study on the 21 July 2012 thunderstorm in Beijing, in which the radar quantitative-rainfall estimates are forced on the model for reproducing the gridded inundation mappings. The model simulation results resemble the flash flood scenarios of the waterloggings and water inundations on the 21 July 2012 thunderstorm day. The offline model simulation addresses measuring the rainfall intensity threshold for the ranked risks of the storm producing flash floods, especially the rainfall intensity thresholds for floods-susceptible places (FSPs). Therefore, the hydrological model simulation deduces the 1 h, 3 h and 6 h cumulative rainfall thresholds inducing water inundation depths over 0.2 m, 0.5 m, 0.8 m and 1.2 m in more than 49 FSPs, which are the rainfall intensity thresholds of the flash flood warning in the blue, yellow, orange and red signals, respectively.
    2021,47(12):1501-1511, DOI: 10.7519/j.issn.1000-0526.2021.12.006
    Abstract:
    On the basis of a quality controlled hourly rainfall dataset from 901 automatic weather stations (AWS) in 2013-2019, the fine-scale characteristics of summer rainstorm in Xinjiang are analyzed. The results show that the rainstorm days in northern Xinjiang are more than in southern Xinjiang, and the rainstorm days in mountain areas are more than in plains. In addition to the middle section of the Tianshan Mountains, parts of the northern slope of Kunlun Mountains in the southeastern part of southern Xinjiang also have rains frequently. In July (August), rainstorm days in Xinjiang are the most (fewest), and the proportion of short-time severe precipitation is the highest (lowest). In July, local convective rainstorm is the major event while in August regional systematic rainstorm is dominant. In Xinjiang, 75.3% of the stations had short-time severe precipitation during the heavy rain periods. The short-time severe precipitation events occurred frequently in the regions where the annual average number of heavy rain days was less than one day, but the regions with more heavy rain days were not hit by short-time severe precipitation very often. The proportion of short-time severe precipitation events in heavy rainfall periods in Xinjiang increases with the decrease of altitude, exceeding 85% stations below 500 m. The “daytime rain” characteristics of heavy rain in Bortala, Karamay, northern Tacheng and western Altay of northern Xinjiang are noticeable. The average rainfall time of the above-mentioned regional rainstorm days is short, and the occurrence percentage of short-time heavy rainfall events is high. The peaks of the regional average accumulated precipitation, frequency and average intensity of convective rainstorm often appear from afternoon to early evening. The average rainfall hours of rainstorm days in the Ili River Valley and the northern slope of Tianshan are more, but the short-time severe precipitation is at a low proportion. The peaks of accumulated precipitation and frequency often occur from night to morning, while the peak value of the average precipitation intensity appears from evening to the first half of the night, dominated by the systematic rainstorm. The diurnal variation of rainstorm in southern Xinjiang is more complicated than that in northern Xinjiang.
    2021,47(12):1512-1524, DOI: 10.7519/j.issn.1000-0526.2021.12.007
    Abstract:
    In order to further discuss the application effect of a new type of “up-drift-down” sounding data to data assimilation and numerical prediction, assimilation comparisons were carried out based on the WRF (Weather Research and Forecast) model and WRFDA (WRF data assimilation) system. In this paper, based on the quality evaluation and sparseness of the new radiosonde data, the descending data are combined and assimilated with the conventional observation data. The influence and causes of the simulated data on the rainstorm forecast quality in the middle and lower reaches of the Yangtze River are discussed. The main test results include that the accuracy of the latest test data is verified by cross-comparison of the test data with the FNL data and sounding data from the same station. The scheme of combining the characteristic layers with the specific layers can be used to sparse the ascending and descending segments of the new radiosonde, which can get better results. The rainstorm forecasting technique can be improved to some extent by assimilating the data in the descending section. The adjustment of wind field and humidity field is one of the important reasons for the improvement of rainstorm forecasting skills.
    2021,47(12):1525-1536, DOI: 10.7519/j.issn.1000-0526.2021.12.008
    Abstract:
    Based on the GF-1 satellite images effectively observed in 2018 and 2019 and the chlorophyll-a concentration data in-situ observed on the lake surface, a random forest machine learning algorithm is used to quantitatively evaluate the importance measures and contribution rate of the band reflectance and select effective feature band combinations. Then a remote sensing inversion model of chlorophyll-a concentration in Taihu Lake based on in-situ automatic monitoring data is established in this paper. The results show that the green light band (0.52-0.59 μm) and the red light band (0.63-0.69 μm) are the key bands, which can be combined with other bands to estimate chlorophyll-a concentration. It is better to construct the estimation model of chlorophyll-a concentration in Taihu Lake by seasons, and the determination coefficients R2 of the spring, summer, autumn, and winter models are 0.84, 0.85, 0.96, and 0.82, respectively. The concentration of chlorophyll-a in Taihu Lake is highest in summer, followed by autumn and spring, and lowest in winter. The spatial changes of chlorophyll-a concentration in spring, autumn and summer are more obvious, while that in winter is not obvious. The areas with high chlorophyll-a concentration are mainly concentrated in the western coastal area, Zhushan Lake, Meiliang Lake and some lake core areas. Studies have shown that the random forest model can objectively determine the effective bands for chlorophyll-a concentration inversion, and achieve high-precision estimation of chlorophyll-a concentration in large inland water bodies.
    2021,47(12):1537-1545, DOI: 10.7519/j.issn.1000-0526.2021.12.009
    Abstract:
    Based on land use/cover change dataset at a resolution of 30 m×30 m, the characteristics of chilling dew wind in 2020 are analyzed for double-season late rice by using the information of underlying surface, gridded monitoring degree and chilling dew wind index. It is shown that the chilling dew wind in 2020 is characterized by earlier start date, longer duration and general low-to-heavy degree occurrence across double-season rice area. There is 24.7% of late rice area exposed to chilling dew wind, which is the third largest since 2000. The area percentages of low, medium and heavy chilling dew winds are 9.7%, 12.8% and 4.9%, respectively. In terms of the statistic in provinces, it is obvious that the area percentage of late rice area affected by chilling dew wind is more than 90% in Hunan, Jiangxi and Zhejiang, but is less than 30% in other provinces. The area percentage subjected to chilling dew wind in Hunan, Hubei, Anhui and Jiangsu is the largest since 2020, and Jiangxi has the largest area percentage of heavy chilling dew wind since 2000. The light degree of chilling dew wind occurs in 〖JP2〗Zhejiang, Fujian and Guangxi, and the occurrence area of chilling dew wind in Guangdong is small. The integrated index for chilling dew wind in double-season late rice area is 4.21 in 2020, which is the second largest since 2000. Moreover, the indexes in Hunan, Jiangxi and Hubei reach 7.16, 7.16 and 12.59, which is the second largest, the largest and the largest since 2000, respectively.
    2021,47(12):1546-1554, DOI: 10.7519/j.issn.1000-0526.2021.12.010
    Abstract:
    The observed yields of winter wheat from 123 agrometeorological observation stations and the announced yield of winter wheat at county level, where the observation station is located, are used to integrate the observed yield and announced yield at provincial and national levels by the proportion of winter wheat planting area. And the observed yield and announced yield sequences of winter wheat are compared at provincial and national levels. The observed and announced yields of winter wheat at national level are predicted based on the climate suitability index forecast method. Also, the forecast accuracy of different yield sequences is analyzed. The results show that the observed yields are higher than the announced yields at provincial level in all provinces. The correlation coefficient between the observed and announced yields is good in each province and has passed the significant test except in Xinjiang. The correlation coefficient between the observed yield and announced yield at national level reaches 0.97, and the observed yield could reflect the characteristic of announced yield. Besides, the percent of consistency statistics of trend meteorological yield of observed and announced yields remains good at national level, so it is suitable to carry out yield prediction, but it is unsuitable to carry out yield prediction at province level due to the low percent. The accuracy of different yield sequences in forecasting their own sequences is high and the accuracy of announced yield is higher than the observed yield. However, the accuracy of the forecast conversion of the announced yield by using the observed yield would be reduced. Conclusively, it is feasible to carry out yield forecast at national level based on the observed yield series because of the real time, objectivity and representative of the observed yield. At the same time, the new yield series could provide new data support for yield prediction.
    2021,47(12):1555-1560, DOI: 10.7519/j.issn.1000-0526.2021.12.010
    Abstract:
    The main characteristics of the general atmospheric circulation in September 2021 are as follows. The polar vortex showed a single pole pattern. The circulation presented a three wave pattern in middle high latitudes. The northwestern Pacific subtropical high extended remarkably more westward than normal. The monthly mean precipitation amount was 83.8 mm, which is 28.5% more than normal (65.2 mm). The monthly mean temperature was 18.2℃, 1.6℃ higher than normal. Four large range heavy precipitation processes occurred over China, of which Southwest China, North China and Northeast China were caught by severe precipitation, and some local areas suffered from serious disasters. Four typhoons were generated over northwestern Pacific Ocean and the South China Sea, but none landed on China. The east of Southwest China, the east of Northwest China to North China, the Huanghuai Region and other places suffered from torrential rain and flood disasters. Autumn rain in West China came earlier than normal and were stronger. The meteorological droughtin Northwest China eased but continued in South China.〖JP〗 Periodic high temperatures occurred in the south of China with some areas experiencing drought.
    Select AllDeselectExport
    Display Method:
    Available online:  January 17, 2022 , DOI: 10.7519/j.issn.1000-0526.2021.111201
    Abstract:
    Based on the hourly precipitation data of 2647 national and regional stations from China Meteorological Administration, the extreme characteristics of cumulative precipitation, precipitation intensity and time evolution during the "21.7" (17-22 July 2021) torrential rain in Henan Province are analyzed. The results show that this rainstorm process has the characteristics of long duration, large accumulated rainfall, strong abruptness and concentrated rainstorm area. The average accumulated precipitation within 6 days reaches 219.5 mm/station, and 179 stations exceed 600 mm. There are about 5.43×104 square kilometers in Henan Province where the cumulative process rainfall is more than 250 mm, larger than that (3.45×104 square kilometers) in the "75.8" process. Three periods of heavy precipitation are 15:00 BJ on July 18 - 04:00 on July 19, 09:00 on July 19 - 08:00 on July 21, and 09:00 on July 21 - 14:00 on July 22. The maximum precipitation period occurs from July 19 to 21, and the falling area is concentrated in the southeast of Taihang Mountain and northeast of Funiu Mountain. 1690 stations have at least one time of flash heavy rain (≥ 20mm / h), the large value centers are located in Zhengzhou, Xinxiang and Hebi respectively, and the contribution rate of flash heavy rain in some regions exceeds 70%. The time evolution of heavy precipitation center shows a north-south swing, but the east-west swing is not obvious. The extreme of the rainstorm process shows obvious local characteristics. The rainfall of Zhengzhou national station at 17:00 on July 20 is 201.9 mm, exceeding the hourly rainfall intensity of the "75.8" process, and breaking the historical record among the national stations. The maximum rainfall intensity within 3 h and 6 h both occur at Jiangang reservoir in Zhengzhou. The total precipitation of Zhengzhou station in July is 902.0 mm, which is nearly 6 times of the historical average in recent 70 years.
    Available online:  January 17, 2022 , DOI: 10.7519/j.issn.1000-0526.2021.122902
    Abstract:
    In late July 2021, an extreme heavy rainfall process with the characteristics of long duration, large accumulated rainfall amount, and concentrated precipitation area occurred in Henan Province, causing serious casualties. Based on automatic station rainfall data and ERA5 reanalysis data, the important roles and influence mechanisms of multiscale system, jet and topography on the transport and convergence of water vapor and the formation of precipitation were discussed in this paper. It was found that the rainstorm occurred in the favorable circulation conditions with long-distance typhoon (In-fa). A large amount of water vapor coming from the western Pacific penetrated the east border of Henan Province from lower layer, while and the water vapor from the South China Sea entered Henan Province from the east side mainly in the middle-low layers of troposphere, causing heavy precipitation under the joint influence of cyclonic vortex, shear line and convergence line. The centers of water vapor convergence and ascending motion in lower layers were caused by the coupling impact of low-level jet and boundary layer jet. The terrain here played the roles of dynamic obstruction and lifting and thermodynamics raising at the same time. Besides, combined with the jet, topography made the heavy precipitation presented with a band shape and appear in front of the mountain, and located in central Henan on 20 July while in northern Henan on 21 July 2021.
    Available online:  January 18, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.011501
    Abstract:
    Based on VLF / LF three-dimensional lightning monitoring data, combined with S-band dual- polarization radar and ground observation data, the lightning characteristics of 31 hail cells in Fujian from 2017 to 2020 were analyzed by using statistical analysis and comparative analysis methods. The results show that: before hailing, about two-thirds of the lightning frequency peaks are more than 50 times / 6 min, and 80% hail cloud surface hail falls behind 3-25 minutes after the occurrence of the lightning peak; the total lightning frequency increases sharply before hail, and 70% of the hail storm cell average increase rate is more than 4 times / min, and the time of lightning rapid jump ahead of hail is mostly 6-40 minutes; cloud flash is the most in the three stages in mature stage The results show that, before hail falling, the above melting layer of hail
    Available online:  January 17, 2022 , DOI: 10.7519/j.issn.1000-0526.2022.093002
    Abstract:
    This paper uses hourly precipitation, radar, FY-4A satellite and other observational data, and ERA5 hourly reanalyzes data , analyze the mesoscale characteristics and circulation anomalies of the large-scale regional heav yrain process in the Qinba Mountains on April 23, 2021. The results showed that the rainstorm occurred in a large area, and the precipitation at multiple stations broke through the historical extremes value. And abrupt heavy rainfall events occurred in Daba Mountains. At 500hPa, the abnormal "high in the east and low in the west" circulation situation in the Qinba mountainous area has increased the pressure gradient between Shaanxi and the western Qinghai-Tibet Plateau, and the mid-level westerly airflow has increased.. At the same time, the superimposition of the mid- and low-level multi-scale weather system is the background dynamic condition of the heavy rain. The southeast airflow in front of the southwest vortex and the easterly wind on the north side form a shear line that provides the convergence ascending movement of the environmental field, the other side transports the water vapor brought by the southwesterly airflow and the southerly airflow to the Qinba Mountains to converge; the circulation associated with the long-distance typhoon and the northeast cold vortex activity in the same period caused the abnormal water vapor transportation (30%) of the northeast path to be this heavy rian,it was the uniqueness of the source of process water vapor, and the contribution of this water vapor transmission channel over the same period in history is not important. Compared with the same period in history, the specific humidity on the water vapor path of the South Passage and the Northeast Passage is abnormally positive, indicating that there are abundant water vapor during the heavy rain period. The heavy rain process is mainly caused by the activity of a mesoscale convective system (MCS) in front of the southwest vortex. The topographical uplift of the windward slope of the Daba Mountains and the convergent ascending of the southerly airflow in the environmental field are superimposed. Sufficient water vapor at the lower level is transported vertically to the upper level by strong ascending movement, with strong convective activity, strong hourly rainfall, and strong suddenness; while the near-surface of the Qinling Mountains is where easterly winds converge and rise in the front of the mountain, and the middle level is an environment where airflow is guided by the southwest. In the Qinling Mountains, the easterly wind converges and rises in the front of the mountain, and the ascending movement of the environment field with southwestern airflow in the middle layer is weaker than that in the Daba mountainous area during the precipitation period, and is dominated by stratiform precipitation. But the precipitation lasts for a long time, so the accumulated precipitation is large. Multi-scale system interactions, abnormal water vapor transport combined with topographical influences under abnormal circulation conditions are the main reasons for the occurrence of heavy rains in the Qinba Mountains.
    Available online:  January 17, 2022 , DOI: 10.7519/j.issn.1000-0526.2021.093001
    Abstract:
    The Fengyun-2 H satellite was successfully launched on June 5, 2018 and the operation is stable. The scanning radiometer VISSR-2 (Stretched Visible and Infrared Spin Scan Radiometer) on-board can provide high temporal and spatial resolution atmospheric TPW (Total Precipitable Water) products. Based on the split window algorithm, FY-2H VISSR TPW performs inversion by adding a 6.9channel.This article uses the water vapor products generated by the radiosonde in 2019 to evaluate the quality of the FY-2H TPW product from the two aspects of product accuracy and stability. Compared with the global sounding data of the first seven days of each month in January, April, July, and October 2019, the root mean square error of FY-2H TPW is 4.92 mm, and the correlation coefficient reaches 0.96.The relative error is within 20%, and the data accuracy is high during the day and night.The standard deviation of the monthly root mean square error of FY-2H TPW products relative to sounding data from January to December 2019 is 0.68mm, indicating that FY-2H TPW products are relatively stable during the inspection period. Analyzing and synthesizing the monthly average TPW products, FY-2H TPW can correctly reflect the distribution of atmospheric precipitation in the One Belt And One Road region.According to the above results, the FY-2H VISSR TPW product has high precision and stable quality, and has the application ability to be invested in the ‘Belt and Road’ area.
    Available online:  January 17, 2022 , DOI: 10.7519/j.issn.1000-0526.2021.070501
    Abstract:
    In this study, we proposed a new way to obtain motion vectors for extrapolation nowcasting,namely the Adaptive-scale Tracking Radar Echoes by Correlation (ATREC), which can automatically adjust the size of tracking area according to the scale of convection systems. ATREC method tracks the large-scale motion of the radar echo which identified by the automatically determined convection edges, then the different subscale motions were deduced by tracing the self-split small parts of radar echoes. ATREC method can retrieve the motions of different scales of the convection system and get a smooth motion field for extrapolation. Thereafter, this method can resolve the problems caused by the fixed size of tracking area applied in the traditional TREC methods, especially the inapplicability of TREC methods in small-scale convective systems. Nowcasting experiments using the ATREC method and MTREC (Multi-scale Tracking Radar Echoes by Correlation) methods were carried out in this study to demonstrate the practical ability of the ATREC method. Comparison based on a series of weather cases showed that the ATREC method have the abilities of automatic analysis and flexibly adjust for different scale convective systems. The evaluation scores based on the experiments also indicate that ATREC gave better performance than the MTREC method did.
    Available online:  January 10, 2022 , DOI: 10.7519/j.issn.1000-0526.2021.123001
    Abstract:
    A rare extreme rainfall occurred in Sichuan Basin on May 21, 2018. Both subjective and objective forecasts failed to capture this disastrous event. In this study, the large-scale circulation, the triggering and developing mechanisms of mesoscale systems and the possible causes of forecast biases are analyzed based on the observational and reanalysis data. During this extreme rainfall event, the northwestward extension of the western Pacific subtropical high moved and the abnormally strong Mongolia cold vortex jointly led to the southward invasion of the cold air. The water vapor and unstable energy in the southern Sichuan Basin were extremely stronger than normal, which favored the occurrence of convective heavy precipitation. The special topography near the Sichuan Basin was closely related to the triggering and maintaining of mesoscale convective systems. The northerly wind converged and was lifted up over the unique “bell mouth” terrain and formed a mesoscale convergence line and mesoscale low around the gorge. The temperature gradient on the west and south edges of the basin was increased due to the basin terrain and upstream heavy rainfall. Then, the ascending motion was induced in the large temperature-gradient area. The persistent convergence of the northerly wind and the topographic obstruction made the convective systems move slowly, resulting in the increase of accumulative precipitation. While the convections in the southern basin were mainly affected by the synoptic-scale systems. The underestimate of convective precipitation by the EC model was possibly caused by the deviation of wind in the lower troposphere in the basin and the undetailed description of the basin terrain. Keywords: Sichuan Basin, extreme rainfall, mesoscale convective system, cold air, terrain, forecast bias
    Available online:  January 07, 2022 , DOI: 10.7519/j.issn.1000-0526.2021.101801
    Abstract:
    Based on intensive observation of snow depth, Snow-to-liquid Ratio (SLR) of a snowfall event in central North China on 14 February 2020 is studied. The distributional characteristics of SLR and its reasons are discussed. Results show that the SLR increases from eastern Beijing to western Tianjin and then decreases to eastern Tianjin. The maximum of SLR locates in the western part of Tianjin and there is a big difference of the SLR between Beijing and Tianjin. The 3-hour average SLR shows that, in Beijing and in central and northern part of Tianjin, the changes of SLR with time are little. In the southern Tianjin and the coastal areas of Tianjin, by contrast, the SLR tends to increase with time. The same characteristic of the SLR in cloud based on Cobb snow-fall algorithm is also found in east-west direction. This indicates that the process in cloud is the main factor forming the above distribution of the SLR in central North China and the snowmelt in eastern Beijing intensifies this characteristic due to surface temperature above zero and the weak warm layer in surface layer. In addition, errors of the SLR in cloud are analyzed. It is found that errors occur mainly in central and western part of the research area, especially in the western and southern part. This is related to the snowmelt caused by higher surface temperature and the error in eastern Beijing comes from this. In western Tianjin, the error comes probably from riming growth induced by co-existing of ice and water in cloud and sublimation under cloud.
    Available online:  December 31, 2021 , DOI: 10.7519/j.issn.1000-0526.2021.092901
    Abstract:
    Winter sports are closely related to meteorological conditions, which is one of the most important factors for the success of Winter Olympics. According to the meteorological support requirements of Beijing Winter Olympic Games, the National Meteorological Center has developed the multi-scale blending (MSB) initial condition perturbation method and lateral boundary condition (LBC) perturbation method, initially established the high resolution regional ensemble prediction experimental system, and carried out continuous tests for the 2022 Beijing Winter Olympic Games. The statistical results of the preliminary test show that the root mean square error of the ensemble mean values of the high, medium and low pressure surface elements of the main forecast variables is basically less than or equal to the control forecast error, which reflects the advantage of the ensemble mean over the single deterministic forecast. The forecast effect of surface element wind and precipitation is good, but the deviation of 24-hour temperature forecast is higher than 2 ℃, which is far from the accurate Winter Olympic meteorological support. The high resolution regional ensemble forecast synoptic analysis of two cold wave and strong wind processes during the test period shows that the ensemble forecast products can accurately describe the main distribution characteristics of ground temperature, cold wave movement process and precipitation forecast, and provide valuable probabilistic forecast information for forecasters, such as cold wave standard 24-hour variable temperature forecast and gale forecast. Based on the diagnostic method, the weather elements ensemble forecast products of visibility, gale, precipitation phase and other Winter Olympic events are developed, which have an important impact on the performance of athletes. The preliminary test results show that the choice of different ensemble members is sensitive to the visibility forecast, and has a certain forecast ability, but the forecast range is too large, and the value is low, which needs to be further improved; the distribution of gust forecast is consistent with the actual large value area; the precipitation phase forecast is consistent with the observed distribution, especially the boundary of rain and snow, and the reasonable range of rainfall, sleet, snow and ice fall area, which further improves the meteorological support ability of Beijing Winter Olympics.
    Available online:  December 31, 2021 , DOI: 10.7519/j.issn.1000-0526.2021.092902
    Abstract:
    Almost all numerical prediction models have systematic errors. Although the statistical correction method has achieved some success in reducing the wind speed deviation in individual stations, it is still urgent to develop a high-resolution wind forecast bias correction method under complex terrain based on grid points. In this study, a fusion prediction and correction technique for high-resolution wind field at different altitudes in Winter Olympic Games area under complex terrain is proposed. Firstly, the statistical bias correction method is used to obtain the 1-12h average system deviation of each station by using the wind observation data of 133 automatic weather stations in the Winter Olympic mountain competition area and the high-resolution wind forecast data of RMAPS-RISE system. Then the wind of RMAPS-ST model was modified by downscaling and optimized by the grid deviation correction coefficient. Finally, the optimized high-resolution wind will be modified by incorporating the latest surface observational data. The results show that the method greatly reduces the systematic deviation of wind speed, greatly reduces the average absolute error of wind speed forecast. The reduction rate of the average absolute error and root mean square error of wind speed within 12 hours is more than 40%. With appropriate modification, this method can also be applied to the bias correction of other variables.
    Available online:  December 30, 2021 , DOI: 10.7519/j.issn.1000-0526.2021.120101
    Abstract:
    In order to compare the difference of mesocyclone identification between S-band dual polarization radar (SPOL) data and X-band phased array weather radar (XPAR) data, based on the SPOL and XPAR and ground observation data, a small and medium scale weather process occurred in Guangzhou on April 19, 2019 is compared and analyzed. The results show that: (1) the identification algorithm used can correctly identify the mesocyclone; (2) the high spatial-temporal resolution data of XPAR can make up for the lack of SPOL elevation layer, more complete vertical structure of mesocyclone was observed, and the parameters in the identification results were more detailed than those in SPOL, which revealed the short-term evolution of mesocyclone more accurately. The results show that compared with SPOL, XPAR has the advantages of longer duration, more fine vertical structure, larger difference between positive and negative velocity extremum, and more detailed evolution with the whole weather process, which is conducive to the detailed and in-depth study on the rapid development and evolution of mesoscale weather system.
    Available online:  December 27, 2021 , DOI: 10.7519/j.issn.1000-0526.2021.112201
    Abstract:
    By conventional observation , automatic station, Doppler radar and reanalysis data(1°×1°) from FNL,this paper analyzed the spatial and temporal distribution Characteristic, environmental conditions and radar key features of the typhoon-tornadoes in Jiangsu during the 2007-2018, and compare with the corresponding characteristics of typhoon-tornadoes in Guangdong. The analyses indicate that the frequency of typhoon-tornado in Jiangsu has increased compared with the past, occurrence time of the tornadoes is concentrated in July and August from 16:00 BT to 20:00 BT. Jiangsu typhoon-tornadoes occur after typhoon landfall 24 hours later, different from Guangdong typhoon-tornadoes occur within 24 hours. A strong preference for tornado occurrence is in the northeast quadrant with respect to land-falling typhoon center. High risk areas of tornado occurrence in Jiangsu concentrated in the central of Jianghuai and Xuzhou. The low-level jet transports abundant water vapor and unstable energy, which provides favorable environment for tornado, ground convergence line is an important system for tornado development.The synoptic situation of upper-level divergence, low-level convergence, and superimposition of strong southeasterly jet and low-layer are conducive to the weather background of tornadoes. The common environmental conditions for Jiangsu and Guangdong tornado appear to be low LCL, strong deep-layer and low-level vertical wind shear (VWS) and high storm relative helicity(SRH). The major difference between Jiangsu and Guangdong tornado cases is that the GuangdongJiangsu tornado has strongerweaker CAPE and CIN, lower LCL,but weaker stronger deep-layer and low-level VWS. About 2/3 of typhoon tornadoes in Jiangsu accompanies with TVS,The thunderstorm cells that produce strong tornado is associated with mesocyclone and TVS。Strong tornado is more likely to occur when the LLDV of TVS exceeds 23 m·s-1 。The LLDV of tornado TVS in Jiangsu is weaker, and the maximum shear is smaller (1/3 of that in Guangdong).
    Available online:  December 16, 2021 , DOI:
    Abstract:
    In this paper, a hybrid variational data assimilation scheme by extended control variable, which introduces flow-dependent background error covariance (statistically described with ensemble forecast perturbations), has been developed based on the GRAPES_TYM 3DVar system. Tests have shown that the assimilation of single-point typhoon central sea level pressure will cause the formation of asymmetric wind increments, and lead to the appearance of humidity increments that are considered irrelevant with pressure in the traditional 3DVar scheme. Experiments of a typhoon case show that the hybrid En3DVar scheme can effectively extract scattered observation data, and propagate it around according to the actual typhoon dynamic characteristics and distribution area, thereby it will change the structure and intensity of typhoon in the analysis field. At the same time, compared with the traditional 3DVar scheme, the hybrid En3DVar scheme has significant effect on improving the typhoon track and intensity forecast.
    Available online:  November 30, 2021 , DOI:
    Abstract:
    Based on conventional observation data, Doppler weather radar data and wind profile radar data, a rare strong hailstorm event(1-3 cm in diameter) in southwest Hubei at the end of winter is analyzed in detail. The results show that: Strong hailstorm produced under the circulation background of upper cold-dry and warm-wet lower and low-altitude convergence and high-altitude divergence. Convective weather is triggered by mesoscale convergence on the ground with favourable terrain at the trumpet and intensified by cold front. Strong vertical wind shear in the lower for the formation of a strong storm and maintain the extremely favorable conditions. The Strong hails are produced by isolated supercell and a supercell in a multicell. In comparison , the isolated supercell will be higher and continue longer. The structure of the supercell reflects typical features such as mesocyclone, high mass center, low-level inflow, weak echo zone and echo drape, middle-level radial convergence and storm-top divergence et al. The vertically integrated liquid (VIL) and the VIL density maintained high above 35 kg·m-2 and 4 g ·m-3 for a long time in the winter. The hail index(HI)of Radar Software predicts the strong hail with high probability. The strong inversion in the middle layer and the parameters values such the CAPE,three-body scattering and bouded weak echo zone and other parameters of hail,that often used to determine if there is large hail are not typical, which increases the difficulty of hail forecast and early warning.
    Available online:  October 12, 2021 , DOI:
    Abstract:
    The mesoscale characteristics of a local short-time severe convective rainstorm that occurred at the eastern foot of Helan Mountains in August Ningxia in 2019 were analyzed based on the data from H8 satellite, Doppler radar, ERA5 hourly reanalysis, automatic weather station and conventional observation data. The results showed that: (1) The southerly jet of 700 hPa that established 6 hours before the rainstorm and strengthened at night not only contributed to high temperature, high humidity, and the enhancement of atmospheric instability and dynamic and thermal uplift mechanisms in the lower layers of the rainstorm area, but also helped mesoscale ground convergence line to trigger the meso-β scale convective system in the eastern slope of Helan Mountains and strengthen it to meso-α scale convective system, leading to the generation and development of the severe convective rainstorm eventually. (2) The rainstorm occurred in the front-left of jet axis of 700 hPa, the high humidity area with water vapor flux ≥6 g?cm-1?s-1?hPa-1 of 700 hPa and specific humidity ≥12 g?kg-1 of 850 hPa, the high energy area with convective available potential energy ≥1500 J?kg-1, the high temperature area with θse ≥346 K of 850 hPa, the vertical upwarding area with centric intensity ≤-1.2 Pa?s-1 of 800 hPa, and the front of cold cloud where the large gradient (G) of cloud top brightness temperature (TBB) occurred. (3) During the strongest rainfall period, the jet axis was closest to the rainstorm area, the TBB ≤-66 ℃, the G ≥27 ℃?km-1, the radar composite reflectivity (Z) ≥65 dBZ, the echo tops (H ) ≥10 km, the vertical integrated liquid water (VIL) ≥11 kg?m-2, and the area of the cold cloud below -52 ℃ was about 1/5 of mesoscale convective complex. (4) The lower TBB was and the higher G and cooling rate (CR) were, the greater intensity of precipitation would be. The minimum TBB, the maximum G, the leap of Z and VIL, and the increase of echo height appeared 10~20 minutes earlier than the maximum rainfall, and the mesoscale ground convergence line appeared 30 minutes earlier than the rainfall.
    Available online:  September 26, 2021 , DOI:
    Abstract:
    This paper used controlling data, National Centers for Environmental Prediction(0.5°×0.5°) reanalysis data by 6 hours and X-band dual-polarization radar observing data to diagnose and analyze the hailstorm triggered by small trough. According to the features of occurrence and development and these predictive indexes with good indicative significance to the hailstorm triggered by small trough, a diagnosis method was constructed. By the method, three hailstorms with different intensity triggered by small trough were diagnosed and analyzed, and the prediction effects were verified. The results indicate that:The hailstone potential of individual cases can be diagnosed effectively by the corresponding relationship between the central region with a large value of the vertical helicity of humid heat force greater than 0.8×10-1?m3?K?kg-1?s-2 and the center region with a large value of the vertical helicity of water vapor greater than 0.8×10-5m?s-1 and the hailstone land.During strong wind shear and monomer amalgamation promote its occurrence and development. In view of this feature, the probability of hailstorm monomer developing into strong hailstorm can be diagnosed by using the correspondence between the center region of large value with the absolute value of thermo shear advection parameter greater than 3×10-8K?Pa-1?s-1 and the threshold value of the relation between 45dBz echo top height and 0℃ height. The difference in squall line strong hailstorm and hailstorm were diagnosed by using the dignosis of hailstorm triggered by small trough formed by the above prediction indexes combined with echo features.
    Available online:  September 14, 2021 , DOI:
    Abstract:
    Based on the best-track data from Joint Typhoon Warning Center and ERA-interim 1°×1° reanalysis data from 1979-2018,a study is conducted to investigate the activity characteristics of super cyclonic storms formed in autumn over the North Indian Ocean. The results show that the number of super cyclonic storms formed in autumn over the North Indian Ocean increased significantly after 1998. The average maximum potential intensity (MPI) index of the North Indian Ocean in 1999-2018 is higher than that in 1979-1998. Compared with 1979-1998, the higher average sea surface temperature and ocean heat content in 1999-2018 provide favorable conditions for the formation and development of super cyclonic storms. Weaker vertical wind shear, stronger water vapor flux and lower level cyclonic vorticity transport promote the sustained growth of cyclonic storm intensity
    Available online:  May 10, 2021 , DOI:
    Abstract:
    Based on hourly and 5-minute observation data of automatic weather station, swan mosaic product of radar combined reflectivity factor in the middle reaches of the Yangtze River and NCEP FNL reanalysis data, the characteristics of four convective storms with low-echo-centroid type of short-term heavy precipitation in Wuhan were analyzed. The results showed that: (1) the characteristics of convective system induced by different weather background were different. Under the background of warm forcing, the environmental conditions were high energy and high humidity, and the accumulation of thunderstorm cold pool was conducted to triggering linear convection in the stable precipitation front; under the baroclinic frontogenesis background, the convergence of cold and warm was intense, and the baroclinic was strengthened; there were more mesoscale cyclone waves on the ground, and the stable precipitation in the front area was often accompanied by a short-term strong drop Under the quasi barotropic background, the baroclinic atmosphere was weak, but the high-energy and high humidity environment as well as the near surface layer flow field forcing and local thermal difference were easy to trigger severe thermal convection activities. (2) According to the radar echo characteristics and precipitation characteristics of convective storms, TS type moved faster, resulting in a small range of short-term heavy rainfall; quasi-stationary type showed that the echo of large-scale stratiform cloud with zonal trend was stable, and there were multiple cumulus convective echoes in the middle. The precipitation enhancement in each stage corresponds to the new convective cell passing through Wuhan station; the consolidation type was in the circulation When the wave merges, it was often accompanied by the occurrence of heavy rainfall, and the echo shape and direction after merging affect the intensity and duration of precipitation. (3) Under different environmental background, trigger inducement and organizational form, the surface meteorological elements before and after the occurrence of short-term heavy rainfall showed different change characteristics; the different front characteristics and convection trigger positions leaded to different temperature changes. (4) Ground mesoscale system played an important role in triggering and organizing the development of MCS. Its generation, elimination and transformation usually heaved a certain advance in time for MCS. Paying attention to the development and evolution of ground mesoscale systems such as ground convergence line and temperature front area was of great significance for predicting the triggering and organizational evolution of MCS.
      Select AllDeselectExport
      Display Method:
      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.
      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.
      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.
      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.
      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.
      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.
      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.

    WeChat

    Mobile website