ISSN 1000-0526
CN 11-2282/P

Volume 45,Issue 6,2019 Table of Contents

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  • 1  Impact of Two Different Deterministic Initial Condition Formation Schemes on Ensemble Forecast Skills
    CHEN Lianglü CHEN Jing HUO Zhenhua XIA Yu CHEN Fajing
    2019, 45(6):745-755. DOI: 10.7519/j.issn.1000-0526.2019.06.001
    [Abstract](1471) [HTML](249) [PDF 2.12 M](1064)
    In order to further improve the precipitation forecast skill of the GRAPES Regional Ensemble Prediction System (GRAPES-REPS), this paper uses the high resolution assimilation analysis field of GRAPES-Meso model to generate the deterministic initial condition of GRAPES-REPS by dynamic up-scaling scheme (hereinafter referred to as the GRAPES-M-US scheme). On this basis, a series of 10 d ensemble prediction experiments were carried out. Then the results were compared with the deterministic initial condition which was generated by dynamic down-scaling scheme from the T639 global model assimilation analysis initial filed (hereinafter referred to as T639-G-DS scheme) and the corresponding ensemble forecast results. The test results of the precipitation forecasts were more focused on. The results show that the deterministic initial condition based on the GRAPES-M-US scheme has more small- and mesoscale information at lower levels compared with deterministic initial condition based on the T639-G-DS scheme. Low-level continuous variable forecast skill is better, the root mean square error (RMSE) and continuous ranked probability score (CRPS) of 850 hPa geopotential height and temperature show some improvements, but the improvement of middle- and high-level elements is not significant. The RMSE and CRPS of 10 m wind speed have obvious improvement, and the RMSE and CRPS of 2 m temperature are basically equal. For the precipitation forecast, the TS score, Brier score and AROC of the 24 h forecast are improved to some extent for light rain, moderate rain and heavy rain, and the rest of the forecast lead time is generally equivalent or slightly negative. In the case of severe rainfall on 7 August 2017, the forecast of rainfall area and intensity of severe precipitation show a certain “refinement” and “corrective” effect. In general, the GRAPES-M-US scheme shows a certain advantage over the T639-G-DS scheme, especially in the short-range precipitation forecast.
    2  The Improvement of GRAPES Double Moment Cloud Scheme and Case Study of Cloud Precipitation: Modeling Study of Tropical Convective Cloud via GRAPES_SCM
    LI Zhe MA Zhanshan LIU Qijun YANG Junli
    2019, 45(6):756-765. DOI: 10.7519/j.issn.1000-0526.2019.06.002
    [Abstract](1077) [HTML](286) [PDF 2.18 M](861)
    In this study, the TWP-ICE case is simulated using GRAPES_SCM. By comparing with the observation data, we found that both the Liuma initial scheme and the WRF single moment scheme (WSM6) can well simulated the development of tropical cloud systems during the TWP-ICE. Besides, the active monsoon period and the monsoon suppression period are also reproduced. The results also show that the vertical distribution of ice-phase hydrometeors simulated by the Liuma initial scheme is very different from that simulated by the WSM6 scheme. Compared with the WSM6 scheme, the Liuma initial scheme produces much more graupel but less ice and snow. In the modified Liuma scheme, the order of calculation of the microphysical process is optimized. In the simulation with the modified Liuma scheme, the mixing ratio of graupel becomes smaller while the mixing ratio of ice and snow becomes larger, and surface the precipitation rate is closer to the observation.
    3  Comparison of Synoptic Circulations of Heavy Rain Associated with Typhoons Polly and Matmo over Liaodong Peninsula
    LIANG Jun ZHANG Shengjun FENG Chengcheng LI Tingting HUANG Ting
    2019, 45(6):766-776. DOI: 10.7519/j.issn.1000-0526.2019.06.003
    [Abstract](1240) [HTML](331) [PDF 9.85 M](1015)
    The tracks of tropical cyclones (TC) Matmo (1410) and Polly (9216) were very similar over Liao-dong Peninsula. However, the former caused only scattered rainstorms, but the latter produced large-scale rainstorms. Using CMA Tropical Cyclone Yearbook, FY-2D temperature of brightness blackbody (TBB) product (0.1°×0.1°), satellite observed TBB data issued by Japanese Meteorological Administration, hourly rainfall observations from Dalian’s automatic weather stations (AWSs), conventional observation and ERA-Interim reanalysis data (0.125°×0.125°), the two TC cases that affected Liaodong Peninsula were compared and diagnosed. The results showed that (1) Polly and Matmo experienced extratropical transition when approaching westerly troughs. Frontogenesis zones were found in the lower layers of them. The western frontal zone had the cold frontal feature and the northern frontal zone had the warm frontal feature. Both of the precipitation over Liaodong Peninsula appeared in the northern frontogenesis processes. Meanwhile, the vertical wind shears were enhanced. But the characteristics of large-scale circulation of the two TCs were quite different. The cold air in the lower and middle troposphere invaded into Polly’s northwest side, the frontal zone slanted towards northwest with height, Polly produced heavy precipitation with a much longer time period due to abundant moisture supply from the low-level southeast jet. However, the frontal zone slanted towards northeast with height under the interaction between Matmo and the low level cold air being from the northeast of the typhoon. It met with a weaker rain rate with poor dynamic lifting condition and being cut-off with the low-level moisture jet. (2) The distributions of rainfall of Polly and Matmo showed clear asymmetric structures when impacting Liaodong Peninsula. The locations of heavy rain mainly occurred in the left along with the direction of the vertical wind shear. However, when the upper-level trough was located over different quadrant of TC, it suffered from a very different formation and strengthening of mesoscale cloud cluster.The convection activity of Polly was located at the north quadrant of typhoon inclining to southwest afterwards, but for Matmo, the convection activity only occurred in the northeast quadrant of typhoon. (3) Severe rainfall was closely related to the cold and warm advections in the typhoon circulation. The cold advection on the northwest side of Polly was strengthened, and Liaodong Peninsula was just controlled by the north of typhoon, possessing the cold and warm advections intersection in low-level circulation, strong low-level convergence, and deep and persistent vertical motion. However, there existed strong cold advection on the northeast side of Matmo, and Liaodong Peninsula was gradually under the west of typhoon, where the cold advection produced downward motion, dynamic lifting was reduced and the atmospheric stratification tended to be stable.
    4  Analysis of Typhoon-Tornado Activity Characteristics and Environmental Condition in the Pearl River Delta
    HUANG Xianxiang YU Xiaoding YAN Lijun LI Cailing LI Zhaoming
    2019, 45(6):777-790. DOI: 10.7519/j.issn.1000-0526.2019.06.004
    [Abstract](948) [HTML](551) [PDF 7.91 M](2195)
    Based on the data of conventional observation, automatic weather station and Doppler weather radar, this paper analyzes the activity characteristics and environmental condition of the typhoon-tornadoes in the Pearl River Delta. The results show that tornadoes occur from June to October and the time is concentrated in the period from 10:00 BT to 20:00 BT. Tornadoes occur between 1.3 h and 21.3 h after typhoon landfall. A strong preference for tornado occurrence is in the northeast quadrant with respect to land-falling typhoon center. High risk periods of tornado genesis in the Pearl River Delta correspond to the typhoon center locating between Zhanjiang of Guangdong and southeast Guangxi or Beibu Gulf. The synoptic situation of upper-level divergence, low-level convergence, and superimposition of strong southeasterly jets at mid- and low-layer over the Pearl River Delta are conducive to the weather background of tornadoes. The common environmental conditions for strong or weak tornado genesis 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 weak and strong tornado cases is that the latter has stronger deep-layer and low-level VWS and greater SRH. The significant diversities are VWS at 0-1 km and SRH between tornadic and nontornadic environmental conditions under the similar typhoon tracks. With the higher values of VWS and SRH, the possibility of supercells and mesocyclones increases, thus tornadoes are most likely to be detected. Tornado storms are mini supercell storms with low centriod. Strong or moderate mesocyclones are likely to be detected through the radial velocity data of the CINRAD/SA radar at low level, and significant tornadic vortex signature (TVS) may be found in the center of mesocyclones. The tornadoes lie in the interior of the hook echo or near TVS. Compared with the supercell tornadoes in the westerlies, mesocyclones of typhoon tornadoes are smaller in scale and lower in stretching height.
    5  Correlation Between PVT Distribution and Movement of Typhoon Megi (2010) and the Impact Factors
    WANG Tianju ZHONG Zhong WANG Ju SUN Yuan
    2019, 45(6):791-798. DOI: 10.7519/j.issn.1000-0526.2019.06.005
    [Abstract](1188) [HTML](280) [PDF 13.23 M](1058)
    Relationship between changes of (potential vorticity tendency, PVT) centroid positions in diffe-rent radii and the movement of Typhoon Megi was analyzed by numerical experiment, and the impact radius of PVT equation factors on PVT centroids positions was also discussed. The results show that within smaller radius, changes of the positive PVT centroid position are in accordance with Megi’s movement and are able to indicate the recurving of Megi. However, within larger radius, though the positive PVT centroid does not indicate the movement and turning of Megi directly, it reflects that the adjustment of atmospheric dynamical and thermal conditions in the corresponding area are favorable for Megi’s steering. PVT centroid movement is mainly affected by the horizontal advection, and is less affected by vertical advection and diabatic heating. The influences of vertical advection and diabatic heating related to thermal convection of Megi on PVT distribution are mainly concentrated near typhoon center. However, horizontal advection related to typhoon horizontal circulation can not only affect the PVT distribution within small radius, but also transport typhoon potential vorticity to farther area along northeast direction, which is the main reason for the difference of positive PVT centroid positions within different radii.
    6  Causes Analyses of Precipitation Anomaly in Chongqing in Autumn 2017
    TANG Hongyu WU Yao DONG Xinning BAI Yingying WEI Linxiao ZHANG Chi
    2019, 45(6):799-810. DOI: 10.7519/j.issn.1000-0526.2019.06.006
    [Abstract](1062) [HTML](242) [PDF 7.53 M](1194)
    This paper analyzes the precipitation in Chongqing that exhibits positive anomaly during the early autumn and negative anomaly during the late autumn in 2017. To diagnose the cause of this extreme anomaly in the precipitation season, this paper uses daily precipitation data observed by 34 meteorological stations in Chongqing since 1961 (from early September to late November), NCEP/NECA and NOAA daily height field, wind field, water vapor field, sea temperature field and other reanalysis data. Using correlation, composite and other statistical diagnostic methods, we analyze the abnormal changes in the autumn precipitation in Chongqing in 2017. The diagnosis of related circulations shows that in 2017, precipitation in Chongqing witnessed a sharp transition from droughts to floods. The cause of this situation is that the subtropical high maintained along the section of Yangtze River in Chongqing and the middle and lower reaches of the Yangtze River for a long time. At the same time the development of the double-resistance type (the high-ridge of the Ural Mountains), together with the establishment and maintenance of the Okhotsk Sea high, slowed the eastward movement of the low trough in the west, resulting in frequent heavy precipitation and abnormal precipitation amount from September to early and mid-October in Chongqing. In late October, the West Pacific subtropical high anomaly weakened southward. In November, when the closed monomer completely exited from the mainland, the high dam in the low latitude cut off the northward transport of water vapor. The mid-high latitude subtropical high showed a west-positive east-negative type anomalous distribution. The area from the east of Lake Baikal to the west of the Okhotsk Sea exhibited a negative anomaly. The south edge of negative anomaly was located in the northern part of Hetao Region. The cold air path was eastward and northward, not conducive to the continued precipitation. Thus, a transition from above normal to below normal precipitation occurred. The analysis of the SST anomaly field indicates that the double-restricted circulation anomaly in the early-autumn and high latitudes may be related to the leading and current warming of the SST and northwestern Pacific Ocean. The SST of tropical Indian Ocean Basin-Wide Mode of the whole region and SST in the equatorial eastern Pacific may be the main causes and external forcing factor of the anomalous atmospheric circulation (West Pacific subtropical high) in the subtropical region in the late autumn.
    7  Relationship Between Heavy Rainfall and Altitude in Mountainous Areas of Sichuan Basin
    ZHOU Qiuxue KANG Lan JIANG Xingwen LIU Ying
    2019, 45(6):811-819. DOI: 10.7519/j.issn.1000-0526.2019.06.007
    [Abstract](1004) [HTML](508) [PDF 16.93 M](1392)
    Based on the hourly precipitation data of 1666 stations during 2011-2015 and high-precision terrain grid data of Sichuan Basin, the relationship between the characteristics of precipitation and altitude is investigated by using statistical diagnostic methods. The main conclusions are as follows. (1) The total precipitation increases with the elevation of altitude. Total rainfall day, light and moderate rain days also show the same trend. However, the total precipitation is not the same as that of the rainy day. The preci-pitation growth area is mainly concentrated in the altitudes 200-1200 m. When the altitude exceeds 1200 m, precipitation decreases rapidly. Heavy rainy days and rainstorm days are also rapidly decreasing after an altitude of more than 1200 m. (2) The heavy rainfall along the mountains of the northwest and southwest of the basin mainly results from the strong hourly rainfall. But the heavy rainfall in the notheast of the basin is mainly caused by the persistent precipitation. (3) The complex topography of Sichuan Basin has a significant effect on the diurnal variation of precipitation. The appearance of peak frequency in one day is ahead of time with the elevation of altitude. And the first occurrence time of severe short-time heavy rainfall postpones with the elevation of altitude.
    8  Application of Generalized Extreme Value Distribution Model to Short-Duration Extreme Precipitation in Chongqing
    WANG Ying LIU Xiaoran CHENG Bingyan SUN Jia LIAO Daiqiang
    2019, 45(6):820-830. DOI: 10.7519/j.issn.1000-0526.2019.06.008
    [Abstract](881) [HTML](455) [PDF 12.57 M](1208)
    Generalized extreme value (GEV) distribution is used to fit the short duration (1, 3, 6 and 12 h) extreme precipitation sequence of 34 national weather stations in Chongqing from 1981 to 2016. The results are as follows: GEV distribution can well fit the short-duration extreme precipitation in Chongqing. As the precipitation lasts longer, the number of the national weather stations subject to Weibull (Frechet) distribution gradually decreases (increases). The spatial distributions of different return periods are basically similar under 10 a and over 20 a. The precipitation to the north of Yangtze River, which is located in the northwestern part of Chongqing, is obviously more than in the areas to the south. And in southeastern Chongqing, there is more precipitation in Pengshui. The precipitation centers are more concentrated with the increase of recurrence period, and the great value center in Northeast Chongqing moves northward as time goes on. When the absolute value of the shape parameter of GEV distribution function is close to or greater than 0.5, the extreme precipitation of the calculated high recurrence (longer than the sample length) is greatly deviated. If there exists prominent difference in the shape parameter of different-duration precipitation, the result appears to be contrary to objective reality.
    9  Bias Correction Method for the 2 m Temperature Forecast of ECMWF High Resolution Model
    XUE Chenbin CHEN Xian ZHANG Ying ZHENG Jing MA Xiaohua ZHANG Yabin PAN Liujie
    2019, 45(6):831-842. DOI: 10.7519/j.issn.1000-0526.2019.06.009
    [Abstract](1393) [HTML](355) [PDF 7.02 M](1245)
    In this paper, a comprehensive correction technique by combining moving-biweight correction method with successive correction method for spatial error is proposed to correct and analyze the bias of 2 m maximum and minimum temperature forecast of ECMWF (European Centre for Medium-Range Weather Forecasts) high resolution model within 24-168 h forecast time lengths during the period from 1 May 2016 to 1 May 2017. The main conclusions are as follows. (1) The 2 m maximum and minimum temperature forecasts of ECMWF model are obviously lower, on average, than the observation in Jiangxi Pro-vince. It is feasible to correct the bias of model temperature considering that the spatial distribution of ECMWF model temperature shows a significant systematic deviation which is stable at different forecast times. (2) The moving-biweight correction method having longer moving correction period has a better effect on the model temperature, which is ideal for the 20 d forecast. By combining the successive correction method for spatial error, the quality of temperature forecasting with the moving-biweight correction method could be further improved, even though the effect of moving-biweight correction method might not be satisfactory during the seasonal transition period. (3) The temperature accuracy shows that the quality of temperature forecasting has been significantly improved after bias correction conducted by the comprehensive correction technique by combining moving-biweight correction method with successive correction method for spatial error. After bias correction, the maximum temperature accuracies of forecast errors ≤2℃ in 24, 48, 72 h forecasts are greatly increased from 0.59, 0.55, 0.52 to 0.75, 0.68, 0.62, respectively, and the minimum temperature accuracies are increased from 0.84, 0.83, 0.82 to 0.89, 0.87, 0.85, respectively. After bias correction, the maximum and minimum temperature accuracies of the 72 h forecast are even greater than that of the 24 h forecast before correction. In general, the deviation of the temperature forecasting is effectively reduced by this proposed comprehensive correction technique, even with a more uniform spatial distribution. (4) For the alpine station, the maximum and minimum temperatures after correction are basically consistent with the observation. In addition, the successive correction method for spatial error has a positive correction effect on temperature correction for the reason that the deviation is within ±1℃, but shows a certain negative correlation with that of moving-biweight correction method. This comprehensive correction technique has been successfully applied to the objective forecasting operational system of fine meteorological elements in Jiangxi Province.
    10  Statistical Analysis of Jianghuai Cyclone Causing Jiangsu Regional Heavy Rain in Summer Nearly 40 Years
    HUANG Wenyan SUN Yan LU Chuhan YAO Lina DONG Qin
    2019, 45(6):843-853. DOI: 10.7519/j.issn.1000-0526.2019.06.010
    [Abstract](931) [HTML](386) [PDF 3.41 M](1060)
    Using Jianghuai cyclone data obtained from Lu (2017) improved method of identifying and tracking of extratropical cyclone, this paper statistically analyzed the overview, path, circulation characteristics and corresponding rainstorm distribution of Jianghuai cyclone which brought the regional heavy rain of Jiangsu in summer in recent 40 years. The results show that most heavy rains in Jiangsu Province located between Yangtze River and Huaihe River are caused by Jianghuai cyclone in summer. The heavy rain caused by the summer Jianghuai cyclone is the most in June, accounting for about 1/3 of total number of heavy rains in this month. The rainstorm areas caused by Jianghuai cyclone are related to the path of cyclone, especially in the areas of north of Yangtze River where the heavy rains are evenly distributed on both sides of the cyclone path. However, heavy rain is mainly concentrated in the western and central sections of the cyclone path in south of Yangtze River. The circulation conditions causing heavy rain by Jianghuai cyclone can be divided into two types, which are the westward flow and the low trough patterns. The number of low trough pattern appears to be about twice of westward flow pattern. The heavy rain area is located in the transitional zone between warm and humid southwest airflow and northwest airflow at 500 hPa in the westward flow pattern and the heavy rain area of low trough pattern is located in southwest flow ahead of the trough. The two types of 850 hPa circulation conditions are similar basically, both of which are closed vortices, and the vortex position is obviously southward compared with 700 hPa. Most of heavy rain areas are located in the south side of 700 hPa and 850 hPa vortex centers and the north of 700 hPa and 850 hPa jet in south of Huaihe River. The areas of heavy rain caused by westward flow and low trough pattern are same, but the rain caused by low trough pattern is heavier than that of westward flow pattern.
    11  Analysis of Urban Factors Impacting Human Comfort Degree in Hangzhou
    GAO Chao SHEN Shuanghe JIANG Yelin PENG Qing
    2019, 45(6):854-861. DOI: 10.7519/j.issn.1000-0526.2019.06.011
    [Abstract](994) [HTML](350) [PDF 658.87 K](1153)
    There is a certain necessary connection between urban thermal environment and urban factors. In order to study the connection, this paper analyzes the main urban factors impacting human comfort degree from the perspective of human comfort degree. We adopt the way of thermal climatic index to calculate the uncomfortable days with high temperatures in Hangzhou from 1980 to 2017, and sum the change trend. By means of gray relational analysis of entropy-based optimization, we determine the weights of different factors and analyze the connection between urban factors and uncomfortable days with high temperature. The results are as follows. First, over the past 38 years, the average uncomfortable days with high temperature in Hangzhou are 30.6 d, and the climate tendency rate is 6.87 d·(10 a)-1, showing a significant upward trend. The interdecadal variation changes dramatically. The uncomfortably days with high temperature mostly appear in July and August and notably the uncomfortable days with high temperature appear more frequently from 1992 to 1993. Second, according to the results of gray relational analysis of entropy-based optimization, among 12 index factors, the weight of the occupying areas of secondary industry is the biggest, with highway passenger volume standing the next. Population density accounts for the smallest proportion.Third, highway passenger volume and the weight of occupying areas of secondary areas strongly correlate with days with high temperature, while the other ten factors such as garden area, green coverage area of built-up area, and population density correlate with days with high temperature moderately. In conclusion, gray relational analysis has advantages in the prediction of multiple factor connection. It can effectively analyze the main urban factors impacting days with high temperatures and has some values in application.
    12  Analysis of Three Snowstorms in Southern Tibetan Plateau Affected by Southern Branch Trough
    LUOBU Jiancan JIA La DE Qing BAI Zhen CIDAN Basang
    2019, 45(6):862-870. DOI: 10.7519/j.issn.1000-0526.2019.06.012
    [Abstract](926) [HTML](381) [PDF 3.54 M](1107)
    Using the NCEP/NCAR reanalysis data and conventional observation data, this paper analyzes the circulation situation, dynamic and thermodynamic conditions of the three snowstorms in southwest of the Tibetan Plateau in 2013. The results show that, over the middle and high latitudes, there existed radial circulation situation. According to the ridge and trough positions, they can be divided into the long-wave trough and the horizontal trough. The Western Pacific subtropical high is by west and stronger, and Iran high developing to the northeast slowly plays a key role for the southern branch trough to deepen and move eastward. When the 560 dagpm line of southern branch trough area is south to 30°N, and moves eastward to 70°E near or to the east at the southern part of the Tibet Plateau, snowstorm begins to appear. The vorticity change in the vicinity of snowstorm area reflects the strength characteristics of the south branch trough. The vertical evolution of divergence field in mid-high levels plays an important role in the south branch trough development. Water vapor mainly comes from the Arabia Sea, and the water vapor in the Bay of Bengal plays a complementary role in the eastern snowfall. The southwest upper-level jet plays a key role in water vapor transport. At the same time, the Himalaya Mountain terrain uplift is conducive to the ascending motion and water vapor condensation. Water vapor flux, vapor flux divergence value changes and the center moving direction have better forecasting significances to the forecasting of snowfall intensity, falling area and time.
    13  Research on Weather Radar Environment Detection Based on SRTM Elevation Data
    JING Haoran XIE Xiaolin ZHENG Wei PENG Tao LIU Juan LIU Zongqing
    2019, 45(6):871-876. DOI: 10.7519/j.issn.1000-0526.2019.06.013
    [Abstract](917) [HTML](276) [PDF 6.97 M](1101)
    The sites were selected based on SRTM elevation data to effectively extract the locations where the electromagnetic wave was obstructed by surface features when the weather radar was placed at 0.5°, 1.0° and 2.4° in line with the working mode and detection principle of the weather radar. The obstructing conditions of surface features under the 3 elevations were obtained by means of elevation lattice data, so as to make SRTM data more precision and increase its arithmetic speed. The blind angle diagram of the sites, diagram of iso-beam heights and data at the elevations of 1 km, 3 km and 6 km at the site were finally obtained. This method fully reflects the high resolution characteristics of SRTM data. Finally, by combining with GIS map, the analysis on environment detection by using weather radar network in Sichuan which was taken as an example was finished. The analysis results at each site were provided.
    14  Research and Application of Key Technologies of Special Equipment IoT for Weather Modification
    LUO Junjie HE Wenbin LI Hongyu
    2019, 45(6):877-885. DOI: 10.7519/j.issn.1000-0526.2019.06.014
    [Abstract](790) [HTML](245) [PDF 1.71 M](1050)
    This paper introduces the architecture of the internet of things technology applied to weather modification field and the major operations of ammunition and equipment safety management. And the application of bar code, two-dimensional code and RFID tag technology in the internet of things of weather modification are also discussed. The analysis points out the key technologies such as marking and recognition, acquisition and transmission, and information fusion process of weather modification equipment. These key technologies can meet the informatization demand of weather modification operation, reduce the workload of grass-root operational staff, can improve the ability of safety supervision of weather modification operation efficiently.
    15  Analysis of the March 2019 Atmospheric Circulation and Weather
    HAN Xuqing ZHANG Tao
    2019, 45(6):886-892. DOI: 10.7519/j.issn.1000-0526.2019.06.015
    [Abstract](993) [HTML](417) [PDF 4.63 M](1103)
    The main characteristics of the general atmospheric circulation in March 2019 are as follows. There was one polar vortex center in the Northern Hemisphere, stronger than usual. The circulation in Eurasian middle-high latitudes showed a three-wave pattern. The East Asia trough was to the east of its normal, with a slightly weaker intensity, which made the weak cold air frequently affect China along an eastward path. The strength of Western Pacific subtropical high was stronger than in normal years. And the south branch trough was a little weaker than normal. The short-wave was active, and interacted with the cold air from east, leading to more rain in South China and south of the Yangtze River than normal years. The monthly mean temperature was 5.6℃, 1.5℃ higher than normal. The monthly mean precipitation amount was 30.0 mm, almost equal to normal. One wave of strong cold air process and seven rainfall processes occurred during this month. One dust weather event happened in the northern part of China. The severe convection weather happened frequently, and Jiangxi, Guangdong, Hunan, and Guangxi were hit by severe thunderstorms and hails.

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