ISSN 1000-0526
CN 11-2282/P

Volume 43,Issue 4,2017 Table of Contents

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  • 1  Verification and Evaluation of the Southwest Vortex Forecast by GRAPESREPS
    WANG Jing CHEN Jing ZHONG Youliang ZHANG Jin LI Xiaoli
    2017, 43(4):385-401. DOI: 10.7519/j.issn.1000-0526.2017.04.001
    [Abstract](1299) [HTML](219) [PDF 18.14 M](1089)
    The data of Global/Regional Assimilation and Prediction SystemRegional Ensemble Prediction System (GRAPESREPS) from June to August 2015 are used and an objective method based on grid data is designed for locating the center position of the southwest vortex. Firstly, the accuracy of GRAPES to the southwest vortex is tested, then 4 longlife southwest vortexes are picked to evaluate the ensemble forecasting performance of GRAPESREPS in the generating, developing, moving and precipitation process of southwest vortex. The results show that: (1) accuracy of GRAPES to the southwest vortex keeps a high score, and the false rate is slightly larger than the missing rate. (2) GRAPESREPS performs well in forecasting generation and development of the southwest vortex. Most ensemble members can predict these processes, but the occurring time is earlier than observation. (3) The forecasted moving path for southwest vortex by GRAPESREPS in 24 h is reasonable, the ensemble forecast is averagely much better than control member, and the path goes to north after 24 h in the eastward moving cases. (4) The forecast of the intensity of the southwest vortex is too strong, with higher value of center positive vorticity and lower value of geopotential height. (5) In 24 h forecast, the rain score for light rain to heavy rain triggered by the southwest vortex performs well, and the rainfall area matches the observation very well, while area for torrential rain lies slightly north in some cases, but mostly is reasonable. After 24 h, since the pathway of the eastward moving southwest vortexes is by north, the prediction of strong rainfall area follows the same trend. It can be seen that the system has the ability to forecast precipitation caused by the southwest vortex. So, improving the capability of mesoscale ensemble forecast by GRAPESREPS would be helpful for the prediction of precipitation caused by the southwest vortex.
    2  A MultiTime Scales SVM Method for Local ShortTerm Rainfall Prediction
    HE Jiajia CHEN Kai CHEN Jinsong XU Wenwen TANG Li LIU Jun
    2017, 43(4):402-412. DOI: 10.7519/j.issn.1000-0526.2017.04.002
    [Abstract](1229) [HTML](337) [PDF 2.18 M](1417)
    In recent years, SVM (support vector machine) has been widely used in meteorological field. Single modeling is the most common approach for this type of application which just looks for a large, generic prediction mode to forecast surface rainfall. In this study, individual meteorological stations were modeled dynamically through multitime scale SVM. So we established a dynamic shortterm rainfall forecasting model and fully considered the difference of meteorological elements at different time stamps of different sites, solving the problem that the single fixed global model is concerned with the whole law too much and neglects the difficiency of local meteorological changes at different sites and different times. Therefore, our method has the ability of improving the accuracy of shortterm precipitation forecast. In our study, the prediction for higher density and finer rainfall in geographical space was basically achieved, the temporal resolution was 1 h, and the TS score was always kept at a high level. As a result, the average TS score of 1 h forecast is more than 40%, and for some sites, it is close to 50%. Thus, the prediction accuracy of the model has certain stability and reference value.
    3  Structure and Mechanism Analysis of One Jiangnan Cyclone with Northern Track
    GUO Dafeng XIONG Qiufen ZHANG Xin
    2017, 43(4):413-424. DOI: 10.7519/j.issn.1000-0526.2017.04.003
    [Abstract](1173) [HTML](242) [PDF 6.08 M](1105)
    The structure and mechanism of a Jiangnan cyclone with a northern track that occurred during 10-13 May 2014 was analyzed by using conventional observations, NCEP 1°×1° reanalysis data and water vapor images from FY2E. The results are as follows: (1) The distribution of pressure and rainfall areas is similar to the output of ShapiroKeyser conceptual model. (2) The Jiangnan cyclone occurred under the weather situation of the divergence at 250 hPa, and trough merger and ridge development downward at 500 hPa. (3) The weak warm core existed close to the low center under 850 hPa, but there was no backbent warm front as ShapiroKeyser conceptual model showed. (4) When the positive relativity vorticity tilted westward with height, the cold frontal zone intensified in the western side of surface cyclone and the positive relativity vorticities in the upper troposphere strengthened, the cyclone was rapidly deepening; when the positive relative vorticities at different levels were nearly vertically overlapped and the cold frontal zone in the low troposphere weakened, the cyclone developed slowly. (5) Heavy rain was caused by warm and moisture air, strong upward vertical volecity with two secondary circulation crossing the warm front. (6) It was also found by equation that surface cyclone hardly developed without upward vertical velocity at the initial stage, but it moved rapidly toward northeast as the result of warmer advection and larger differential vorticity advection between the upperlevel and lowlevel troposphere downstream during cyclogenesis. Then surface cyclone was intensified rapidly by srtong upward vertical velocity, but it moved slowly due to the less warm advection and differential vorticity advection. Surface cyclone was slowly deepening due to weakly upward vertical velocity, and it moved more slowly because of the weakly warm advection and differential vorticity advection.
    4  Investigation of Extreme FlashRain Events on the Impact of Taihang Mountain
    WANG Congmei YU Xiaoding LI Zhixia LI Jiangbo WANG Xiuming
    2017, 43(4):425-433. DOI: 10.7519/j.issn.1000-0526.2017.04.004
    [Abstract](1867) [HTML](162) [PDF 9.17 M](1653)
    In the midnight of 2 August 2015 and the early night of 9 August 2011, extreme flashrain events were observed in the Taihang Mountain area under the background of different weather systems. The thunderstorms strengthened in the Taihang Mountain area, and extremely heavy rainfall were observed in Pingshan Station and Shijiazhuang Station in 2 h. Based on routine upperlevel and surface observation, automatic weather station (AWS) data and Doppler weather radar data, the reasons of the extreme flashrain impacted by Taihang Mountain with different backgrounds are analyzed. The results show that easterly air flow is forced to uplift in the mountains, then encountered with thunderstorm outflow forming mesoscale convergence line to trigger new thunderstorms. Local heavy rainfall is affected by the backward propagation characteristics and train effect of radar echo. Convergence ascending motion and vertical wind shear are enhanced by the Taihang Mountain terrain strengthening thunderstorm in the process of going down the mountain. The Taihang Mountain terrain plays different roles in the development of thunderstorms under different weather systems. Under the guide of westerly flow, extreme heavy rainfall is triggered by a gust front in warm sector, charactered by abruptness, short time and strong winds. Thunderstorm outflow down mountain is accelerated and convergence with piedmont easterly wind is strengthed to trigger new thunderstorms, being combined with the downhill flows and forming extremely heavy rainfall in the hilly region. However, under the guide of northeast flow, extreme shorttime heavy rainfall triggered by reflux cold front and gust front features longer duration, heavier rainfall, and weaker wind. Northeast cold wet reflux is resisted by east slope of Taihang Mountain. The western end of the thunderstorm outflow boundary from NNEward is forced to uplift on windward slope to trigger and strengthen thunderstorms. Northeast airflow turns its direction in cyclonic deflection and the thunderstorms flow down to the southeast, so that convergence with the easterly wind in plains is strengthened, making the total time of rainfall longer and precipitation greater in hilly areas and piedmont.
    5  Evaluation on East Asia Summer Monsoon System Prediction by JMA/MRI-CPS2 Model
    CHENG Zhi YANG Wei XU Min ZHOU Kun
    2017, 43(4):434-442. DOI: 10.7519/j.issn.1000-0526.2017.04.005
    [Abstract](1605) [HTML](98) [PDF 1.79 M](945)
    Based on hindcast data of the a new version of JMA/MRICPS2 climate prediction model supplied by Tokyo Climate Centre, the skill of predicting East Asian summer monsoon (EASM) is evaluated by use of several estimating methods. The results show that some features of EASM can be predicted, including the climatical distribution of the main precipitation centers and the main members of EASM system, but with some systematic biases. Taylor diagram analysis shows the JMA/MRICPS2 model has decent skills in predicting the monsoon indices, as well as the area, intensity and western ridge point of subtropical high. However, for the southnorth position index of the ridge line, its prediction result is poor. Reviewed monthly, the results issued in April and May are better. The spatial distribution of the main modes of MVEOF analyses on EASM are also presented. Similar to the observation, the first mode in hindcast shows the influence of attenuating El Ni〖AKn~D〗o and the second one shows the influence of developing El Ni〖AKn~D〗o. The composite analysis reflects the different responses of EASM circulation to the different phases of El Ni〖AKn~D〗o in developing and decaying years. All of the analyses indicate the model’s high predicting skills in EASM region, which could be used as a reference in climate prediction for the flood season every year.
    6  Seasonal Variation of Kuroshio Extension SST Front and Its Influence on the Pacific Storm Track
    LIU Mingyang LI Chongyin TAN Yanke YU Zhaowen
    2017, 43(4):443-449. DOI: 10.7519/j.issn.1000-0526.2017.04.006
    [Abstract](893) [HTML](472) [PDF 1.14 M](1103)
    By using NOAA daily optimum interpolation sea surface temperature (SST) data and NCEP/NCAR daily atmospheric reanalysis data, this paper analyzes the seasonal variation of Kuroshio Extension SST front and its influence on the Pacific storm track. The results show that the seasonal variation of the SST front position is weak, but its strength has significantly strong seasonal variation, and the strength of Pacific storm track has a coordinated change with the strength of SST front in Kuroshio Extension. The SST front is the strongest in winter, enhancing the baroclinicity of the atmosphere above it. The baroclinic energy conversions from mean available potential energy to eddy available potential energy and from eddy available potential energy to eddy kinetic energy are increased in the Kuroshio Extension region, where the baroclinic eddies are generated more frequently, absorbing energy from the background mean flow during the process of moving downward along with west wind, and, finally, strengthening the Pacific storm track and anchoring the central axis of the storm track above the Kuroshio Extension region. The SST front is very weak in summer, weakening the baroclinicity of the atmosphere above. The baroclinic energy conversions from mean available potential energy to eddy available potential energy and from eddy available potential energy to eddy kinetic energy are greatly reduced, and baroclinic eddies are generated less frequently, weakening the Pacific storm track, and making the strength center move to central Pacific, located northward.
    7  Variation Characteristics of Hail Days in Gansu Province During 1974-2013
    HUANG Yuxia WANG Baojian WANG Yanfeng HUANG Wubin KONG Xiangwei TAN Dan LI Wenli
    2017, 43(4):450-459. DOI: 10.7519/j.issn.1000-0526.2017.04.007
    [Abstract](1438) [HTML](97) [PDF 14.25 M](1360)
    According to hail observation data based on 80 weather stations in Gansu Province and the NCEP/NCAR data with resolution of 1°×1°, spatiotemporal characteristics of hail events during 1974-2013 in Gansu are analyzed by the methods of statistical analysis and physical diagnosis. The results show that hail occurs frequently in plateau and mountain regions but rarely in valley, basin, and Gobi desert. Annual mean of hail days is 0.05-9 days with three largest values in plateau and mountains, which indicates that the altitude plays an important role in the formation of hail in Gansu. The seasonal cycle shows that hail falls earliest in March, latest in November, and mainly from May to August. The hail days present an evident decreasing trend during the recent 40 years. Hail days decrease rapidly by 0.5 d/10 yr on average in the whole province since 21st century after a high incidence during the seventh-eighth decades of last century. The decreasing trend can also be found in hail days from May to August. However, its interannual and interdecadal variations are greatly different. Except in Hexi area, the annual means of hail days in the other four regions undergoes an abrupt change of decline. Comparison analysis of years with more and less hail days in May over Gansu reveals that: As hail is a product of severe convection, the most significant character in more hail years is the positive abnormal convective energy, which can be more than two times of the normal value. After that, environmental temperature and humidity level in the more hail years develop into favorable conditions for a series of physical processes of hail formation in cumulonimbus, growing and melting before the hail falls to the ground. For example, there is an evident temperature trough at 500 hPa with temperature of 2℃ below normal value, and meanwhile, humidity increases in low level and decreases in middle level. Such condition is beneficial to form the unstable “upper dry and lower wet layer”. The 0℃ layer (3900-4500 km) is favorable for hail increase and the -20℃ layer (6400-7000 km) is helpful for hail’s falling. In addition, the vortex at 200 hPa guarantees a strong upward stream to support the increase of hail.
    8  Study on Immigration Path of Rice Leaf Roller Based on FLEXPART and Atmospheric Background
    LIU Wei CAI Xuewei LIU Yao GUO Anhong WANG Chunzhi LU Minghong BAO Yunxuan
    2017, 43(4):460-467. DOI: 10.7519/j.issn.1000-0526.2017.04.008
    [Abstract](957) [HTML](274) [PDF 11.34 M](805)
    The spatiotemporal distribution pattern of the rice leaf rollers was analyzed and the atmospheric circulation background in which the typical immigration process happened were studied. The model of FLEXPARTWRF was used to speculate the immigration path in order to illustrate the influence of atmospheric background on the path. The research results showed that (1) the bimodal type was the major type of the rice leaf rollers in 2008 and the most extensive serious immigration process was during the period from 15 to 18 July. (2) The representative station Huaiyin in Jiangsu Province was chosen to simulate the source by FLEXPART, and the immigration of the rice leaf rollers was from the middle of Jiangsu and the midwest of Anhui Province. (3) The synoptic situation including the distribution, movement and strength changes of weather system at 850 hPa isobaric surface played important transferring and controlling roles on the migration and landing of the rice leaf roller. The prevailing deflectednorthward wind at 850 hPa isobaric surface was favorable for the northward migration of rice leaf roller. However, the prevailing deflectedsouthward wind at this height had no obvious influence on the southward migration. The zones with anticyclonic circulation in the wind field at 850 hPa isobaric surface were beneficial to the immigration and landing of the pest, and the cyclonic shear was beneficial to the emigrating of the pest. (4) The rainfall in the migrating paths of the rice leaf rollers played a critical role in the intensive landings of the pest.
    9  Climatic Characteristics and Major Meteorological Events over China in 2016
    MEI Mei JIANG Yundi WANG Zunya LIU Lüliu YE Dianxiu WANG Youmin ZHU Xiaojin CAI Wenyue HOU Wei HUANG Dapeng YIN Yizhou XIAO Fengjin ZHONG Hailing LI Ying ZENG Hongling ZHAO Shanshan SHAO Xie WANG Dongqian
    2017, 43(4):468-476. DOI: 10.7519/j.issn.1000-0526.2017.04.009
    [Abstract](1526) [HTML](350) [PDF 5.59 M](1550)
    The climate in China was very abnormal in 2016 when there were more extreme climate events, such as severe disasters and damages caused by the heavy rainfalls, floods and intensive typhoons. The annual mean air temperature over China was 0.8℃ higher than normal, which is the third warmest since 1951. The averaged air temperatures in every season are above normal, especially the summer is the warmest since 1961. Precipitation was more than normal in all the four seasons, and the winter and autumn precipitations have broken the historical records since 1961. The annual mean precipitation in China was 730.0 mm with 16% more than normal, breaking the historical record since 1951. The first rainy season in South China and rainy season in Southwest China started earlier than normal. The Meiyu event started earlier but ended later with more rainfall than normal. The rainy season in North China was not so long but rainfall amount was more. The autumn rainy period in Western China was shorter than usual, so the rainfall amount was less. In 2016, torrential rains and floods occurred more in southern and northern China. There were more landing typhoons this year and the intensity of the typhoons was stronger when landing. Severe convection weather, like hail, occurred frequently and caused heavy economic losses, especially in northern China. The temperature presented a large fluctuation during this year and the heat wave affected a wide scope over China in summer. The haze events occurred frequently in JingJinJi (Beijing, Tianjin and Hebei Province) and the neighboring regions during this autumnwinter period. Positively, the disasters caused by drought, low temperature freezing, heavy snow and sandstorm in spring were lighter in this year.
    10  Global Major Weather and Climate Events in 2016 and the Possible Causes
    SUN Shao LI Duo LIU Lüliu WANG Zunya YIN Yizhou
    2017, 43(4):477-485. DOI: 10.7519/j.issn.1000-0526.2017.04.010
    [Abstract](1278) [HTML](286) [PDF 4.34 M](1184)
    The year 2016 is the hottest year on the world record. The surface temperature is 1.1℃ above those of the preindustrial with the major greenhouse gas concentrations continuing to rise. Under the impact of global warming, Arctic sea ice remained at very low levels and there was significant melting of continental ice on Greenland and Antarctic. Warming also affected the oceans, resulting in global sea level rising and the changes of marine environment. Droughts continued into early 2016, causing food and water crisis in numerous parts of the world. Various kinds of extreme climate events occurred frequently and caused serious social and economic losses worldwide. This paper summarizes the major events and the impact in 2016, and analyses the main causes of typical events including the flood disasters in the Yangtze River Basin in China and the heat wave during summer in the United States. Analysis shows that the westward extension and enhancement of West Pacific subtropical high led to the transport of warm and moist air flows from low latitude to the Yangtze River Basin, while the upper trough in Northeastern Asia brought the cold air southward. The interaction of the warm and cold air masses led to the extremely heavy rainfalls and severe floods in China. The stagnation and stability of North America subtropical high and the weakening condition of water vapor transport are the main cause for the summer heat wave in the United States.
    11  Overview of Climate Prediction of the Summer 2016 and the Precursory Signals
    GAO Hui YUAN Yuan HONG Jieli WANG Dongqian
    2017, 43(4):486-494. DOI: 10.7519/j.issn.1000-0526.2017.04.011
    [Abstract](1284) [HTML](107) [PDF 7.81 M](1390)
    In summer 2016, climatic condition in China was worse than normal. The average precipitation all over China was more than normal and floods were more severe than droughts. The disasters caused by floods in 2016 were much heavier than the flood disasters in 1983, but weaker than those in 1998. Extreme heavy rainfall occurred along the Yangtze River valley, leading to severe flood disasters. The preflood season in South China began earlier. The South China Sea summer monsoon started in the 5th pentad of May. Both the beginning and the ending dates of the Chinese Meiyu in the Yangtze River were later than normal, but its intensity was much stronger than normal. The rainy season in North China ended also later and the rainfall during the period was slightly more than normal with a positive percentage of 20%. All these features were forecasted well in the climate prediction issued in March 2016. The forecasts captured the facts that the mean intensity of all the typhoons during the year was stronger and they became more active after July. The forecasts also provided a correct prediction that it was warmer in most regions of China in summer 2016, especially in the northwestern China. The heat waves that occurred in late July in southern China were also predicted well. However, obvious errors appeared in the precipitation forecasts for northern China, especially the extreme flood in North China in July and the droughts in Northeast China in July and August. In making the forecasts, the potential influences of the super El Ni〖AKn~D〗o event and the possible roles of the tropical Indian Ocean were considered in great detail. Influenced by the tropical sea surface temperature anomaly, the western Pacific subtropical high was thought to be stronger than normal and extend more westward, and the East Asian summer monsoon would be weaker than normal. These prediction results were consistent with the observations, revealing the main causes for the floods along the Yangtze River.
    12  Features of Climatic Anomalies in China During the Fall of 2016 and the Possible Causes
    ZHU Xiaying SONG Wenling
    2017, 43(4):495-500. DOI: 10.7519/j.issn.1000-0526.2017.04.012
    [Abstract](1320) [HTML](94) [PDF 2.77 M](1073)
    During the autumn of 2016, accompanied by higher surface air temperature, the national average of precipitation for China was much more than normal, ranked as the first since 1961. Particularly in the region to east of 110°E, the rainfall was 50% more for near half of the weather stations. These anomalies were closely associated with the airsea background in this season. When cold tongue developed in the equatorial middle and eastern Pacific in autumn, the western Pacific subtropical high would be stronger, stretching more westward and northward. Thus, more water vapor was transported to the north of China, coupled with the cold air activities carried by the northeast cold vortexes in early autumn and persistent trough near Baikal Lake later, giving rise to excessive rainfall. In addition, higher sea surface temperature in the equatorial western Pacific and warm pool intensified convections and increased typhoon activities, leading to more precipitation in east areas from South China to YangtzeHuaihe River Valley.
    13  Verification on Forecasts of Tropical Cyclones over Western North Pacific in 2015
    CHEN Guomin BAI Lina WAN Rijin
    2017, 43(4):501-507. DOI: 10.7519/j.issn.1000-0526.2017.04.013
    [Abstract](1363) [HTML](112) [PDF 698.88 K](1007)
    Operational positioning, track, landfall point and intensity forecast error of tropical cyclones (TCs) over Western North Pacific in 2015 were evaluated on the basis of CMA/STI’s “Besttrack” dataset. The results showed that the average TC location errors of CMA is 14.1 km in 2015, better than in 2014. The average track forecast errors by CMA subjective method are 66.2 km (24 h), 119.5 km (48 h), 176.3 km (72 h), 244.3 km (96 h) and 328.5 km (120 h). Meanwhile, the global models’ average track forecast errors are 86.5 km (24 h), 146.5 km (48 h), 215.8 km (72 h), 321.6 km (96 h) and 475.8 km (120 h). Additionally, the average errors of regional models are 84.1 km (24 h), 147.1 km (48 h), and 230.8 km (72 h). In general, the ability of track forecasting by subjective methods, global models and regional models have got a major improvement compared to 2014. However, no marked improvement was found in the intensity forecasting. At present, the overall performance of statistical forecast methods is still better than numerical prediction method in the intensity forecasting.
    14  Analysis of the January 2017 Atmospheric Circulation and Weather
    ZHANG Nan MA Xuekuan
    2017, 43(4):508-512. DOI: 10.7519/j.issn.1000-0526.2017.04.014
    [Abstract](3692) [HTML](186) [PDF 7.47 M](2981)
    The main characteristics of the general atmospheric circulation in January 2017 are as follows. There was one polar vortex center in the Northern Hemisphere with the stronger strength than normal year. The circulation presented the troughridgetrough pattern in middlehigh latitudes. The south branch was as strong as normal, located near the west of 90°E averagely. The subtropical high also had the same strength as usual. In addition, the monthly mean precipitation is 12.4 mm, 6% less than normal and mean temperature is -3.4℃, 1.6℃ higher than normal (-5.0℃), which is the third high value for the corresponding period since 1961. There were two cold air processes, two major rainfall processes and two largescale foghaze weather processes during this month. Among them the foghaze event from 30 December 2016 to 6 January 2017 was characterized by the most extensive, the longest and the most intensive foghaze weather in January.

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