ISSN 1000-0526
CN 11-2282/P

Volume 40,Issue 9,2014 Table of Contents

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  • 1  A Case Study on the Effect of Southern Branch Trough in the Subtropical Westerlies Combined with Storm over the Bay of Bengal on Plateau Snowstorm
    SUO Miaoqing DING Yihui
    2014, 40(9):1033-1047. DOI: 10.7519/j.issn.1000-0526.2014.09.001
    [Abstract](3073) [HTML](148) [PDF 7.37 M](6682)
    Using NCEP (1°×1°) 6 h reanalysis data and the conventional and unconventional observational data, a case study on the plateau snowstorm that occurred in November 2007 was performed to explore the generation process of the severe weather over the southeast part of Tibetan Plateau due to combination of Southern Branch Trough (SBT) in the subtropical westerlies and storm of Bay of Bengal (BOB). The results show that: (1) The plateau snowstorm synoptic scale condition is formed by the combination of SBT and storm of BOB. The plateau shear line produced by low level jet is the direct influence system. (2) Because of the effect of the terrain and cold air, upward movement sloping to the north makes upward movement first appears in the mid upper troposphere over the plateau. Both the plateau shear and the ascending branch of secondary circulation of the upper jet stream enhance the upward motion. Due to the combination of SBT and storm of BOB, the northward moving of plateau shear line and the nearing storm causes the ascending motion of Deqin to strengthen three times. (3) The southern lower level jet occurs in front of the trough, which transports moisture to the north, and part of water vapor is lifted to the high level while other part of the water vapor passes by the southeast corner of plateau to the downstream. Meanwhile the high level water vapor travels over the plateau along the upper westerly jet downstream advection over a long distance. High and low water vapor channels do not overlap, often affecting the plateau and its downstream forecast in heavy rainfalls. Due to the high level water vapor transportion, the longitudinal range gorge region of southeast plateau has the characteristics of upper atmosphere being moistured first, and surface layer moisture flux strong convergence for a long time is conducive to the formation of the plateau snowstorm. (4) The cold air upstream along the southern branch of the westerly to the BOB, deepens and maintains SBT, which is beneficial to the northward moving of the storm BOB. The cold air from the plateau and the warm air from BOB meet over Deqin, forming strong front, which is the main synoptic system of snowstorm. (5) The frontal structure of plateau snowstorm has the mid latitude frontal synoptic characteristics. Snowstorm occurs near frontal zone, meeting the slantwise vorticity development and conditional symmetric instability.
    2  Diagnosis of the Frontogenesis and CSI Features During a Torrential Rainfall Event in Winter
    ZHANG Fanghua CHEN Tao YANG Shunan SUN Jun
    2014, 40(9):1048-1057. DOI: 10.7519/j.issn.1000-0526.2014.09.002
    [Abstract](2111) [HTML](87) [PDF 3.45 M](1262)
    Based on the observation, NCEP reanalysis data and the simulation of the mesoscale numerical model (WRF), the frontogenesis and conditional symmetric instability (CSI) during an extremely torrential rainfall event that occurred in southern China in 14-15 January 2012 is diagnosed. The results indicate that both the eastward propagation of the short wave trough along the southern branch trough and the cold air activity in the lower troposphere cause obvious frontogenesis in southern China, which is favorable for the torrential rainfall event in this region. The abnormal abundant water vapor transportation from the Bay of Bengal provides the moisture condition. The torrential rainfall is enhanced by the strong divergence at the right part of the exit of the abnormal strong higher level jet. The mesoscale rainbands form along the surface front. Analyses show the frontogenesis in Guangxi at the night of 14 January strengthens, thus the secondary frontogenesis circulation (SFC) develops. Affected by the latent heat releasing, the CSI is enhanced, leading to an intensifying upward movement in the warm side of the front. Under the circulation pattern, the strong mesoscale rainband occurs in the north part of Guangxi. Theoretic analyses reveal that both the SFC and the CSI are the solutions of the Sawyer Eliassen equation under different stable conditions, and the character of the SFC can be analyzed by the moist potential vorticity.
    3  Analysis on Characteristics of Elevated Thunderstorms Behind Cold Fronts in China During Spring
    SHENG Jie MAO Dongyan SHEN Xinyong LAN Yu HE Lifu
    2014, 40(9):1058-1065. DOI: 10.7519/j.issn.1000-0526.2014.09.003
    [Abstract](2284) [HTML](327) [PDF 1.43 M](2125)
    To study the physical mechanisms of elevated thunderstorms, the conventional observations and comprehensive monitoring data of severe convective weather are used to analyze the spatial and temporal characteristics of elevated thunderstorms and the associated severe weather events in spring of China. The results show that spring elevated thunderstorms behind cold fronts often happen in Southern China. They have diurnal variations and often accompaning with hail and short duration severe precipitation. Low and high level jets, low level shear lines and west troughs at 500 hPa are the important impact weather systems. The following three parameters can be used to predict the development of elevated thunderstorms: relative humidity at 850 hPa and 700 hPa exceeds 70%, temperature difference between 700 hPa and 500 hPa is at least 16℃, and a southwesterly jet is at 700 hPa, a low level shear line and a trough at 500 hPa.
    4  Simulation of Brightness Temperature in Infrared Channel of FY 2F and Bias Analysis
    ZHANG Xinghai DUAN Yihong
    2014, 40(9):1066-1075. DOI: 10.7519/j.issn.1000-0526.2014.09.004
    [Abstract](1656) [HTML](113) [PDF 4.81 M](1189)
    To assimilate the radiance data of FY 2F imagery directly in West Pacific and East Asian, WRF for Hurricane (HWRF) and Community Radiative Transfer Model (CRTM) are used to simulate the brightness temperature (BT) of FY 2F. Under the cloudy condition, the frontal clouds are well simulated in the middle and high latitude while the substantial bias exists in tropical cloud cluster of low latitude. In the clear sky condition, the BT of infrared channel 1, 2, 4 (IR1, 2, 4) are strongly influenced by the surface emission with big biases above the land because of the inhomogeneity and the radiation transfer model under estimates the emissivity of land on average. Meanwhile it performs well above the ocean surface. The observation of IR4 channel are higher than simulated BT because of the influence of sun radiation. The cloudy contamination data are abandoned to keep the clear sky radiance in Community Gridpoint Statistical Interpolation (GSI). After quality control and bias correction of GSI, the bias of IR2 has a reduction of 50% on average and the average bias of IR3 is decreased from 3.7 K to 0.34 K. The quality of IR1 observation is better than other channels, and there is little change of the bias after correction.
    5  Study on the Application of GRAPES Regional Ensemble Prediction System
    ZHANG Hanbin CHEN Jing ZHI Xiefei LI Yinglin SUN Yun
    2014, 40(9):1076-1087. DOI: 10.7519/j.issn.1000-0526.2014.09.005
    [Abstract](1438) [HTML](102) [PDF 22.86 M](775)
    In order to develop GRAPES (Global and Regional Assimilation and Prediction System) regional ensemble prediction system (GRAPES REPS), using ensemble transform Kalman filter (ETKF) as initial perturbation scheme, coupled with multiple physical processes combination as model perturbation, an regional ensemble prediction system is constructed based on the GRAPES_MesoV3.3.2.4 model in this paper. Besides, 40 d consecutive ensemble forecast experiments are conducted, the structure and evolution characters of ETKF generated initial perturbation are emphatically investigated, various methods are utilized to evaluate GRAPES REPS performance and its precipitation forecast capabilities, and a severe rainfall case is also analyzed to further illustrate the precipitation forecast performance of the EPS. The experimental results indicate that GRAPES REPS can generate promising initial perturbations characterized by flow dependent structure and good correspondence to the distribution of observation sites, and meanwhile the perturbations are orthogonal. Total energy of perturbations can keep appropriate growth in all forecast lead times. Ensemble forecast verification shows that ensemble forecast outperforms control forecast, the ensemble spread can maintain reasonable growth in 72 h forecast lead time. Comparisons between operational WRF REPS and GRAPES REPS on precipitation forecast are carried out, and the results show that GRAPES REPS outperforms WRF REPS. Case study indicates that ensemble forecast can provide much better heavy rainfall forecast than control forecast.
    6  Moist Helicity Application Test for Severe Precipitation Forecast in Sichuan Basin Based on the Fine Mesh Grid Model of ECMWF
    HUANG Chuhui HAO Liping NIU Jinlong ZHANG Ping
    2014, 40(9):1088-1096. DOI: 10.7519/j.issn.1000-0526.2014.09.006
    [Abstract](1349) [HTML](66) [PDF 9.66 M](964)
    Using high resolution prediction field (0.25°×0.25°) data of European Centre for Medium Range Weather Forecasts (ECMWF) and the data of encrypted automatic stations of Sichuan Province, 20 cases of heavy rainfall indexes for moist helicity in flood season from July to September 2011 and May to July 2012 were analyzed by the statistical method, including the moist helicity indexes of the occurrence, development and falling area distribution of 6 h, 24 h severe precipitation. Two cases of severe precipitation process and all heavy rainfalls in Sichuan Basin during the 2013 flood season were checked out by using these criteria and put into the forecasting operation in the flood season. The results show that the distribution of 700 or 850 hPa moisture helicity can give good indicator to the distribution of rainfalls. When extremely heavy rainfall occurs, moist helicity values exceed the index values two times or more in the 24 h forecast, with 3 h interval forecasting field, meeting the requirments of severe precipitation occurrence. In zero field prediction of the 24 h forecast with 3 h interval forecasting field. The moist helicity number at any time reaches the 6 h criterion value, which has instructive effect on subsequent 6 h rainfall area and can be used as a short time nowcasting reference. TS score for corrected moist helicity is higher than ECMWF model and has a good forecast effect.
    7  Study on Characteristics of Regional Drought Events over North China During the Past 50 Years
    AN Lijuan REN Fumin LI Yunjie LI Yiping
    2014, 40(9):1097-1105. DOI: 10.7519/j.issn.1000-0526.2014.09.007
    [Abstract](1807) [HTML](75) [PDF 2.43 M](1097)
    The objective identification technique for regional extreme events (OITREE) is applied to detect the North China regional meteorological drought events during 1961-2010. The parameter values of the OITREE method are determined, and the results show that the OITREE method has a good capability in identifying the regional droughts in North China. In the study, 100 events are identified, including 10 extreme events, 20 severe events, 40 moderate events and 30 slight events, in which the September 1998-May 1999 extreme drought in North China is the most serious meteorological drought event for the past 50 years. Further analysis reveals that the durations are generally between 17-120 d and the maximum impacted areas vary from 70×104 km2 to 105×104 km2. Meanwhile, the drought events have obvious seasonal features with two peaks of March to July and October to November in frequency. In regional distribution, the southern part of North China has the highest drought frequency and intensity, and strong (extreme and severe) North China regional meteorological drought events can be divided into six types, of which the whole North China type occurs more frequently. During the past 50 years, the North China regional drought events show an increase trend in both frequency and intensity, for which the main cause may be the obvious decrease of annual precipitation in this region, with the contribution of significant increase trend in temperature.
    8  The Low Frequency Characteristics of Precipitation and Its Circulation over North China in Summer 2012
    ZHOU Ningfang KANG Zhiming LAI Fenfen
    2014, 40(9):1106-1113. DOI: 10.7519/j.issn.1000-0526.2014.09.008
    [Abstract](942) [HTML](48) [PDF 7.34 M](856)
    The low frequency characteristics of summer rainfall over North China in 2012 and its associated low frequency circulations are studied. The results show that the summer rainfall over North China has a significant 10-13 d period. The evolution of the low frequency oscillation is well correlated to that of the severe rainfall, and such severe rain events usually take place on the peaks of the oscillation. At the same time, general circulation and impacting systems also have the low frequency characteristics. In the weak phase of the low frequency period, a low frequency anticyclone over the Bay of Bengal comes to intensify, and low frequency circulation systems over the Philippines and the South China Sea (SCS) propagate toward northwest gradually. Low frequency geopotential height anomalies over 500 hPa level propagate eastward, followed by a westerly trough at the high mid latitude. In the upper atmosphere, a low frequency cyclone over Iranian Plateau is weak, while a low frequency anticyclone over the eastern Tibetan Plateau strengthens and propagates eastward. In the strong phase of the low frequency period, low frequency south wind from the western North Pacific and the westerly trough with low frequency supply abundant water vapor to the North China. In the upper atmosphere, the low frequency anticyclone controls the east central part of China, favorable for the area from North China to the Northeast to become a divergence center. The upward motion strengthens, providing dynamic condition for precipitation. On the whole, the lower and upper low frequency circulations coordinating with each other result in severe rainfalls over North China.
    9  Large Scale Circulation Factors of Early Summer Precipitation in Liaoning Province and Causes Analysis of Heavy Precipitation in 2012
    LI Ji FANG Yihe LI Fei HU Chunli
    2014, 40(9):1114-1122. DOI: 10.7519/j.issn.1000-0526.2014.09.009
    [Abstract](1137) [HTML](56) [PDF 2.86 M](819)
    Based on the daily rainfall data of 50 observational stations in Liaoning Province during 1961-2012, and NCEP/NCAR daily reanalysis data, the large scale circulation characteristics of Liaoning rainfall and the causes of heavy precipitation during early summer in 2012 were analyzed. The results show that the cooperation of large scale circulation system in different heights of troposphere in East Asia is the main cause for precipitation anomaly in Liaoning in early summer. The circulation features of the four main precipitation processes in Liaoning in early summer are almost the same. Upper level jet stream shows the phenomenon of branch at 200 hPa over the west of Northeast. Two ridges and two troughs control Asia mid latitude regions at 500 hPa, and one trough controls the Northeast, corresponding to negative geopotential height anomaly. 850 hPa wind field and the 1000-300 hPa moisture field show the cyclonic circulation feature over the Northeast. In rainy years, upper level jet stream presents the phenomenon of branch at 200 hPa, and the strength of subtropical westerly jet is stronger than normal years. Two ridges and one trough control Asian mid latitude regions at 500 hPa, and the Northeast is controlled by trough, corresponding to negative geopotential height anomaly. 850 hPa wind field has the cyclonic circulation feature over the Northeast, which indicates that a deep low pressure system controls the Northeast, from low to high levels in troposphere. Circulation features of every layer show that the deep Northeast cold vortex is the leading impact factor of anomalous rainfall over Liaoning Province in early summer in 2012.
    10  Comparisons of Atmospheric Specific Humidity in Reanalysis Datasets and Homogenized Radiosonde Dataset in China
    JIA Beixi XU Haiming AN Yuegai
    2014, 40(9):1123-1131. DOI: 10.7519/j.issn.1000-0526.2014.09.010
    [Abstract](1407) [HTML](68) [PDF 1.64 M](1147)
    Based on monthly mean homogenized radiosonde temperature and dewpoint depression dataset from 98 stations in China during the period 1980-2010, NCEP/NCAR reanalysis dataset, ERA Interim reanalysis dataset and JRA 25 reanalysis dataset, a comparative analysis of specific humidity from these four datasets over China is performed by means of analogical analysis and tendency analysis. The results suggest that: (1) In terms of spatial distributions, the spatial correlation coefficients between JRA and OBS datasets are the highest. (2) The values of three reanalysis datasets are generally higher than that of radiosonde dataset, JRA dataset is much closer to observed dataset except for several stations and levels. Relative tolerance between reanalysis and radiosonde datasets increases with height and it is higher in winter and spring than in summer. (3) When it comes to the long term trend, JRA is closer to OBS in lower troposphere, and in middle and upper troposphere, ERA is much closer to OBS.
    11  Characteristics Analysis of Doppler Radar Echoes and Lightning of Hailstorms in Central Yunnan Province
    ZHOU Hong DUAN Wei ZHAO Shuang WANG Bao
    2014, 40(9):1132-1144. DOI: 10.7519/j.issn.1000-0526.2014.09.011
    [Abstract](1444) [HTML](72) [PDF 5.45 M](1166)
    Using the data collected from Doppler radar and lightning detection network in Yunnan Province, the characteristics of radar echo and cloud to ground (CG) lightning in six typical hail processes are analyzed comprehensively in Central Yunnan Province from 2006 to 2011. The results show that there are typical characteristics of hailstone echoes in basic reflectivity radar images, such as bow echo, TBSS, side lobe echo, WBER (BER), V shaped notch, hook echo, etc. Hail area always appears in the places where basic reflectivity gradients are high, and the negative CG lightnings are dense and active as well. The movement of the concentrated CG lightning area can be the index indicating the moving of hailstone echoes. The hailing periods are the active phase of negative CG lightning, during which the appearance of positive CG lightning is seldom seen. This is significantly different from the hailing with the high positive CG lightning frequency feature in northern area of China. The peaks of 5 min negative CG lightning occur 5-12 min earlier than hailstone falling, which can be regarded as a reference index of predicting hailing in central Yunnan Province. The spatio temporal distribution and changing of negative CG lightning frequency could play some reference roles in monitoring and warning hails and commanding hail operations in Central Yunnan Province.
    12  Preliminary Comparison Research of the Wind Profile Radar Network Data
    DONG Liping WU Lei WANG Ling ZHAO Chengcheng LIU Yunlei
    2014, 40(9):1145-1151. DOI: 10.7519/j.issn.1000-0526.2014.09.012
    [Abstract](1418) [HTML](93) [PDF 753.06 K](1200)
    This paper firstly uses the horizontal wind data detected by radiosonde as a standard to assess the credibility of the horizontal wind observed by wind profiler (WPR), finding that the horizontal wind observed by the national wind profiler under 700 hPa height has a good consistency with that of radiosonde. Secondly, the correlation analysis on the vertical speed got by the wind profile and the one hour rainfall observed by the same address ground automatic meteorological station (AMS) reveals that the vertical velocity magnitude can clearly reflect the onset, end and precipitation intensity of a rainfall event. Finally, comparative analysis on horizontal wind data from the national wind profiler network is carried out, and the results show that horizontal wind observed by wind profiler at 700 hPa height is credible, the credibility of the wind direction increases with the increase of probe height, and the wind speed credibility decreases with the increase of probe height.
    13  The Design and Development of Grid Edit Platform Based on MICAPS 3.2 System
    GAO Song DAI Kan XUE Feng
    2014, 40(9):1152-1158. DOI: 10.7519/j.issn.1000-0526.2014.09.013
    [Abstract](1819) [HTML](72) [PDF 1.51 M](1298)
    This paper describes the design and development of grid edit platform based on MICAPS 3.2 system. First, the paper introduces the basic functions of Graphical Forecast Editor (GFE) being used in AWIPS system of NWS. Then it explains the secondary development ideas of MICAPS 3.2 system on the basis of the “addin tree” module and resource management design pattern. In addition, it provides the realization of interactive grid edit platform based on this framework. Finally, the paper presents the application of this platform in forecasting operations as well as the target of development in the future.
    14  Analysis of the June 2014 Atmosphere Circulation and Weather
    GUAN Yue HE Lifu
    2014, 40(9):1159-1164. DOI: 10.7519/j.issn.1000-0526.2014.09.014
    [Abstract](1090) [HTML](139) [PDF 5.17 M](1035)
    The following are the main characteristics of the general circulation of atmosphere in June 2014: There are two polar vortex centers in the Northern Hemisphere with more stronger strength than normal years. The intensity of the West Pacific subtropical high is stronger than climatological normals. The monsoon of the South Sea of China occurs 15 days later than usual. The monthly mean temperature over China is 20.5℃, 0.5℃ higher than the corresponding period of normal years. Meiyu begins late in the south this year, causing the precipitation amount there to be 20% less than normal. However, the mean precipitation (100.7 mm) of the whole country is 1.4% more than normal (99.3 mm). There are 4 main precipitation processes during the month. Severe precipitation occurs more in the South of China while showery rains occurs more in the northeast. And the drought in Yunnan is mitigated somewhat. High temperature event occurs at 101 stations. Strong wind and hail disasters hit 22 provinces. Typhoon Hagibis lands Guangdong Province, which is the first landing typhoon in China this year.

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