ISSN 1000-0526
CN 11-2282/P

Volume 41,Issue 7,2015 Table of Contents

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  • 1  Characteristics of SpatialTemporal Distribution of Tornadoes in China
    FAN Wenjie YU Xiaoding
    2015, 41(7):793-805. DOI: 10.7519/j.issn.1000-0526.2015.07.001
    [Abstract](2284) [HTML](268) [PDF 1.62 M](2419)
    Based on “the Handbook of China Meteorological Disasters” published in 2008 and other relevant documents for period 1961-2010, spatialtemporal distribution characteristics of significant tornadoes (EF2 or greater) are analyzed according to the “Enhanced Fujita Scale”. And based on “the Annual Report of China Meteorological Disasters” which began to be published from the year 2005, spatialtemporal distribution characteristics of EF1 or greater tornadoes are investigated. The main results show there are total 165 significant tornadoes recorded in China during the 50 year period from 1961 to 2010, including 145 EF2, 16 EF3 and 4 EF4 tornadoes, with average 3.3 significant tornadoes each year. Most of the tornadoes occur in plain area, with higher frequency in Jianghuai Plain, South China, Northeast China Plain and the North China Plain. The highest frequency of tornadoes is during the period 1986-1990. Then, it starts to decline. Most of significant tornadoes occur in spring and summer (from April to August) which account for 87% of the total. The peak frequency of tornado genesis in the diurnal variation is from 12:00 to 20:00 local time. The 165 significant tornadoes killed at least 1772 people and wounded more than 31700.During the 10 year period from 2004-2013, according to “the Annual Report of China Meteorological Disasters” from 2005 to 2014, there are 121 EF1, 19 EF2 and 3 EF3 tornadoes recorded and their spatial distribution is similar to those of the significant tornadoes from 1961 to 2010. Furthermore, at least there are 570 EF0 tornadoes during the same period. With the data, we can infer roughly there is about at least 85 tornadoes and 21 EF1 or greater tornadoes seen in China on average each year, less than the tenth of the tornado occurring frequency in the United States.
    2  Intensity Evolution of Typhoon Megi (2010) Revealed from AnomalyBased Atmospheric Variables
    QIAN Weihong ZHANG Guangwen HUANG Jing
    2015, 41(7):806-815. DOI: 10.7519/j.issn.1000-0526.2015.07.002
    [Abstract](1555) [HTML](71) [PDF 3.61 M](1131)
    Analysis and reanalysis datasets derived from numerical models are commonly applied in diagnosing and forecasting weather extremes by using traditional synoptic charts. Recent studies have showed that any atmospheric variable from these datasets can be naturally decomposed into climatic and anomalybased components while the latter can be used to locate regional heavy rains, heat waves and low temperature, and also to indicate the intensity of these extreme weather events. This paper focuses on the analysis of anomalybased variables using different datasets during the lifetime of super Typhoon Megi (2010) because it has been studied recently by several researchers. The inconsistency of typhoon intensity estimated from four meteorological centers in China, Japan and the United States is first analyzed. A hydrostatic balance relationship from both height and temperature anomalies is described from the European Centre for MediumRange Weather Forecasts (ECMWF) reanalysis interim reanalysis. The results show that the anomalybased variables can be used in indicating the evolution of typhoon anomalous intensity. This work can provide an useful reference for applying the output products of mediumrange weather forecast models to the prediction and diagnosis of typhoon intensity.
    3  Analysis of Continuous Rainstorm Circulation Background and the Dynamic Process of SynopticScale in West of Southern Xinjiang
    ZHANG Yunhui LI Haiyan LIN Xilu Abulimiti YU Bixin
    2015, 41(7):816-824. DOI: 10.7519/j.issn.1000-0526.2015.07.003
    [Abstract](1506) [HTML](68) [PDF 2.96 M](4676)
    The continuous rainstorm appeared in West of Southern Xinjiang from 14 to 19 June 2013. The convention observation, T639, NCEP reanalysis data are used in the analysis in order to know why the rainfall could be so much. Based on the relation between environmental air humidity conditions and the rainstorm, this paper analyzed the weather scale dynamic process and its forming reasons why the water vapor was transmitted over a long distance to Xinjiang, getting accumulated over the West of Southern Xinjiang. The results showed that rainstorm develops in an abnormal environment. During heavy rainfalls the top value of specific humidity reaches to 16-18 g·kg-1 in the lower troposphere. The extreme humid situation maintains even though the heavy rain appears, which is favorable for the longlasting severe rainstorm. The abundant water vapor is transported from Arabian Sea and Bay of Bengal to West of Southern Xinjiang by a southern flow. The southern wind increased the water vapor transfer. At the same time, with the southern airflow’s approaching Xinjiang, strong water vapor flux convergence is generated by lowlevel troposphere eastern jet stream in West of Southern Xinjiang, making the strong couple between upperlevel divergence and lowlevel convergence of vapor lower, and also strengthening the ascending velocity and inducing more wet air to higher altitude and then thickening the moisture layer further. The diurnal variation of the heavy rain is related to the vertical discontinuity of mesoscale circulation circle in Aksu southern and the lowlevel easterly jet enhancements at night.
    4  Diagnostic Analysis of One Heavy Rainfall Process Induced by Southwest Vortex in the MiddleLower Reaches of the Yangtze River
    LIU Xiaobo CHU Hai
    2015, 41(7):825-832. DOI: 10.7519/j.issn.1000-0526.2015.07.004
    [Abstract](1367) [HTML](54) [PDF 4.60 M](1299)
    A heavy rainfall event induced by the moving and developing southwest vortex occurred in the middlelower reaches of the Yangtze River from 6 to 7 June 2013. Using conventional observation and NCEP reanalysis data, diagnostic analysis was done on this event, especially on the physical mechanism of the vortex moving and developing and on the variability of the rainfall climax. The results show that the southwest vortex moving easterly along the 700 hPa shear line is the direct impact system to the heavy rainfall. Southwest vortex moves eastward and develops, and when reaching its deep phase, positive vorticity column stretches up to 400 hPa height with a nearly vertical structure in the relative vorticity chart. Largescale condition of lowerlevel convergence and upperlevel divergence in the vicinity of southwest vortex, dynamic structure of the coupling of southwest vortex and southwest lowlevel jet, positive vorticity advection in front of the highlevel trough and other favorable weather conditions are the main causes for the vortex reinforcement when it gets to the middlelower reaches of the Yangtze River. Heavy rainfall area that accompanies the southwest vortex is mainly located within 3 latitudes to the south and east side of the vortex. Convergence of two water vapor advection provides abundant humidity and latent unstable energy for the rainfall. One is the southwest monsoon flow, and the other is the southeast flow from the southwest side of the tropical high. Besides, cold air from the middlelower level of troposphere coming down to the rear side of the vortex reinforces the development of vortex, promoting an unstable stratification, which provides convective triggering mechanism to the heavy precipitation.
    5  Diagnostic Analysis of One Widespread Thunderstorm Coexisting with Snowstorm in North China in March 2013
    KONG Fanchao LI Jiangbo ZHANG Yingxin MAI Wenming
    2015, 41(7):833-841. DOI: 10.7519/j.issn.1000-0526.2015.07.005
    [Abstract](1463) [HTML](71) [PDF 5.41 M](949)
    A relatively rare process of widespread thunderstorm coexisting with snowstorm was analyzed by adopting conventional meteorological data, CINRAD radar data, and NCEP analysis data. The results are as follows. The widespread thunderstorm was an elevated thunderstorm over the lowlevel cold air mass. Although lowlevel convergence of moisture flux was weak over the thunderstorm area, the deep warm advection formed over Hebei, and decreased with height in the middleupper troposphere, leading to conditional instability. The 850 hPa shear line and convergence zone in the southwest airflow caused convective instability energy to release. Strong moisture flux convergence was suddenly thickened around the middle troposphere in the north of Hebei, and the strong convergence of southwest airflow and west airflow in the front of the 700 hPa trough formed, which led to heavy snowfall in central Hebei. In addition, at the middlelower level, positive differential vorticity advection was more distinct than divergence in expressing dynamic action.
    6  Mesoscale Analysis on a ShortTime Severe Rainstorm in the North of Hangzhou Bay on 21 July 2013
    HE Bin FAN Xiaohong SHENG Wenbin PAN Shixiong FAN Yufen
    2015, 41(7):842-851. DOI: 10.7519/j.issn.1000-0526.2015.07.006
    [Abstract](1169) [HTML](64) [PDF 12.14 M](1030)
    By using TBB data retrieved from FY2E satellite, Doppler radar data, mesoscale automatic observation data and fully assimilated model data with 5 km resolution from WRF model, a shorttime severe rainstorm in the north of Hangzhou Bay on 21 July 2013 is analyzed. The results indicate that the occurrence of the convective storm is related to the convergence of westsouthwest and eastsoutheast flows near the surface. The westerly outflow caused by local thermal convection in the east of Huzhou enchances the original intensity of the westerly flow in the west of Jiaxing, which is a very important factor to trigger the convection. When the convection develops to some extent, the downward current emerges in the lower troposphere. Part of it flows into east current near the surface and induces enchanced convergence in the lower troposphere and new updraft in the midtroposphere. Because of the weak vertical shear of horizontal wind from surface to 3 km above ground surface prior to the convection, the lifetime of cell thunderstorm in this event is short. In the vicinity of rainstorm the state of atmosphere near surface is neural or stable and the equivalent potential temperature is decreasing significantly above the lower atmosphere.
    7  Analysis on Formation Mechanism of the Backflow Rainstorm Occurring in First Rainy Season of Guangxi Based on Numerical Simulation
    LIN Quelue SHOU Shaowen YANG Hua
    2015, 41(7):852-862. DOI: 10.7519/j.issn.1000-0526.2015.07.007
    [Abstract](1425) [HTML](60) [PDF 4.00 M](989)
    By using the model WRF, the Backflow rainstorm process that occurred in Guangxi during 28-29 April 2010 was simulated. The formation mechanism of the backflow rainstorm was studied by diagnostic analysis. The results showed that, blocked by Wuyi Mountain and Nanling Mountains, the cold air can not directly affect the west of South China. When the cold air moves eastward into East China Sea, the west of South China is at the rear of high pressure. The isobaric line shows the trend of “southeastnorthwest” and the wind direction in lower layers turns clockwisely to southeast. The southeast air of back flow, flowing through South China Sea, is dry and cold in comparison with the southwest airflow from Bengal Bay and the crossequatorial airflow, so the airflows of different nature converge, forming the frontal surface and convergence line and providing lifting condition. This is the formation process of backflow situation. By diagnosing θe and moist potential vorticity (MPV), we find that conditional symmetric instability (CSI) in boundary layers and convective instability in lowmiddle layers are the instability mechanisms of occurrence and development of this rainstorm MCS. Wind convergence and frontogenesis of energy front in boundary layers are the main triggering conditions of the convection. Before the increase of the torrential rain, there is a process of accumulation of convective instability energy. The frontogenesis of energy front and convergence lifting in boundary layers trigger the release of instability energy, leading to the increase of the rainstorm. The negative anomaly of MPV has indication for rainstorm forecasting, and the positive center of helicity has good relationships with the increase of the rainstorm. The rainstorm happens in both sides of the boundarylayer front. The existence of boundarylayer front means this backflow rainstorm belongs to frontal precipitation in nature.
    8  Application of Online Bias Correction of Polar Orbit Satellite Observations in GRAPES3Dvar
    WANG Xueman LI Gang ZHANG Hua
    2015, 41(7):863-871. DOI: 10.7519/j.issn.1000-0526.2015.07.008
    [Abstract](1081) [HTML](76) [PDF 8.82 M](768)
    Bias correction is the key technology of data assimilation for satellite radiance data. Currently, global GRAPES variational assimilation system adopts scan bias correction and airmass bias correction based on the consideration of Harris and Kelly (2001). But it did not cover the changes of deviation property (such as instruments or pollution problems). This paper proposed a scheme called online bias correction based on Harris and Kelly’s TOVS radiation error correction scheme and the concept of online bias correction which was put forward for NWP system to solve the problem of data drifting. The scheme considers the characteristics of GRAPES system and the statellite pretreatment system of National Satellite Meteorological Centre of CMA. The online bias correction is an adaptive bias correction system. It uses variational method to adjust the coefficients of predictors. To test the effect of the new scheme, twomonthlong assimilation experiments were carried out. The results show that the online bias correction scheme can optimize the degenerate bias equation automatically and quickly, and keep the effect of bias correction stable.
    9  Causes of Temperature Anomaly and Analysis on Low Temperature Process in Qinghai Plateau in Spring
    SHEN Hongyan LI Lin LI Hongmei ZHANG Tiaofeng LI Wanzhi
    2015, 41(7):872-880. DOI: 10.7519/j.issn.1000-0526.2015.07.009
    [Abstract](2128) [HTML](61) [PDF 4.48 M](1256)
    Using the temperature observation data in Qinghai, NCEP monthly mean reanalysis data, 74 pieces of circulation characteristics materials provided by National Climate Centre of China Meteorological Administration (CMA) and 52 pieces of climate indices from U.S. National Oceanic and Atmospheric Administration (NOAA) from 1961 to 2012, temperature anomaly characteristic and its impact factor in spring Qinghai Plateau were studied. The results show that the spring temperature in Qinghai Plateau presents a remarkable increasing trend, having obvious interdecadal variation features. The winter Eurasian pattern (EU) teleconnection pattern in Northern Hemisphere has very good indicative meanings to the temperature amomaly in the next spring. When it is in the EU pattern, the sping temperature is prone to be lower. The Ural pressure ridge, East Asian trough, subtropical high and polar vortex indices in Northern Hemisphere and Plateau height field, all affect the spring temperature. At the same time, the spring temperature has good response to the SST in SomaliaArabian SeaBay of Bengal of North Indian Ocean, Northwest Pacific and Equatorial Pacific. When the SST is colder (warmer), spring is colder (warmer). The continuous low temperature process is the direct cause for low temperatures in Qinghai in spring. The main impact system of frequent low temperature process is the low pressure in area south to Lake Baikal. As it develops significantly, Qinghai Plateau lies in the northwest airflow in front of ridge and behind trough then the plateau height field is lower. Thus, frequent cold airs tend to cause the persistent low temperature process. Otherwise, the situation is opposite.
    10  Multivariable Lagged Regressive Model of Low Frequency Rains over the Lower Reaches of Yangtze River Valley for Extended Range Forecast in the Early Summer of 2013
    YANG Qiuming
    2015, 41(7):881-889. DOI: 10.7519/j.issn.1000-0526.2015.07.010
    [Abstract](1392) [HTML](64) [PDF 4.94 M](869)
    Lowfrequency rainfall over the lower reaches of Yangtze River Valley (LYRV) and the principal component of 850 hPa meridional wind anomalies over the extratropics of the Southern Hemisphere are employed to construct a multivariable lagged regressive (MLR) model, which is applied to the daily forecasting of low frequency rainfall over LYRV in June-July of 2013 for the extended range forecast. The result indicates that this method for the 20-30 d lowfrequency rainfalls over LYRV has good predictive skill up to 25-30 d. By many hindcast experiments during the period of 2001-2012, this MLR model for the 20-30 d rainfalls over LYRV has good predictive skill up to about 30 days for the years with the stronger or normal 20-30 d oscillations. Based on the development and evolution of the southern circumglobal teleconnection (SCGT) wave train, it will help us to forecast the process of lasting heavy rainfall in early July of 2013 over LYRV over 20 days in advance. Hence, the low frequency variability of extratropics over the Southern Hemisphere is one of the main factor of the changes of the heavy rainfall over LYRV in early summer for the extended range.
    11  Comparative Analysis of Pollution Diffusion Conditions Under the Control of Sustained Easterly System in Shanghai
    MAO Zhuocheng MA Jinghui XU Jianming GENG Fuhai ANG Dandan
    2015, 41(7):890-898. DOI: 10.7519/j.issn.1000-0526.2015.07.011
    [Abstract](1044) [HTML](62) [PDF 1.83 M](986)
    Based on the conventional meteorological data, physical quantity data, hourly PM2.5 concentration data and laser radar data, two distinct temporal and spatial distribution characteristics and diffusion condition of pollution under the control of sustained easterly system in Shanghai are comparatively analyzed. The results show that landsea temperature difference obviously affects the vertical transportation of pollutants. In the 26 January process, the sea surface temperature is higher and easterly flow is warm advection relative to the interior. Landsea thermal contrast makes the vertical temperature stratification in the surface layer tend to 〖JP2〗be unstable and speed up the vertical diffusion of pollutants in the boundary layer. On the contrary, In the 10 March process, the sea temperature is lower and easterly flow is cold advection relative to the interior. Landsea thermal contrast makes the vertical temperature stratification in the surface layer tend to be stable and inhibit the vertical diffusion of pollutants in the boundary layer. In addition, the laser radar data can intuitively reflect the vertical distribution of pollutants and have a certain guiding significance for our understanding of transmission characteristics and formation of pollution process.
    12  Water Budget Characteristics of Winter Wheat and Its Impact on the Yield in Anhui Province
    ZHANG Hao MA Xiaoqun WANG Xiaodong
    2015, 41(7):899-906. DOI: 10.7519/j.issn.1000-0526.2015.07.012
    [Abstract](1227) [HTML](75) [PDF 2.32 M](843)
    Based on the meteorological data and the winter wheat yield data of 78 weather stations in Anhui Province from 1971 to 2010, the spatiotemporal variation of the water budget during the whole growth period and critical period of winter wheat (from booting to milk ripening stages) in Anhui Province was analyzed using the water budget index. The occurrence of droughts and floods and its impact on the winter wheat yield was also analyzed using the water budget index as the droughtflood indicator. The results showed that the water budget index during the whole growth period and critical period of the winter wheat presents zonal distribution and decreases from south to north. The water deficit occurs significantly in the area north to Hefei and the water supply is adequate in the southern part of the YangtzeHuaihe Area and the region south to this area, with large water surplus in south and small in north. On the whole, the water shortage degree is greater in the critical period than in the whole growth period. The change trend of the water budget index is not significant during the past 40 years. However, the interannual variation of the water budget index is obvious due to the large variation coefficient of the precipitation, increasing the risk of droughts and floods. The drought occurs mainly in the area along Huaihe River and the part north to the river. The frequency of waterlogging is higher in the YangtzeHuaihe Area and the region south. The average yield reduction rates of the winter wheat due to the drought and the flood are 4.2% and 12.4%, respectively. There is a significantly positive (negative) correlation between water budget index and relative meteorological yield in typical drought (flood) year of winter wheat. The medium drought risk of winter wheat is greater in north area than in south area, and the medium waterlogging risk is greater in south area. It is necessary to minimize the planting of the winter wheat in the south area where water is more because the yield loss caused by the waterlogging is greater than the drought.
    13  Features and Possible Causes for East Asian Winter Monsoon in 2014/2015
    WANG Dongqian CUI Tong SI Dong SHAO Xie LI Qingquan SUN Chenghu
    2015, 41(7):907-914. DOI: 10.7519/j.issn.1000-0526.2015.07.013
    [Abstract](1391) [HTML](91) [PDF 3.73 M](1023)
    The East Asian Winter Monsoon (EAWM) was weaker than normal during the 2014/2015 winter with a phase transition from strong to weak at the end of December 2014. A warmer winter was experienced in most areas of China due to the effect of weaker EAWM. In association with the phase transition of EAWM, a reverse of temperature anomalies over China occurred simultaneously with negative temperature anomalies in December 2014 and positive temperature anomalies in January and February 2015. Further study indicates that the weakening of EAWM is related to the extension of Arctic sea ice cover (without linear trend) in September 2014. The expanded sea ice coverage before winter restrains the development of Siberian high, leading to a weaker EAWM and a warmer winter over China. Besides, the combination of central Pacific El Ni〖AKn~D〗o and positive phase of PDO is also important in reducing the intensity of EAWM. The phase of PDO has an influence on the effect of El Ni〖AKn~D〗o on EAWM. Positive anomalies of SST over central Pacific is favorable for the negative anomalies of meridional wind over the east and eastern coast of China and a weak EAWM. El Ni〖AKn~D〗o event tends to exert stronger influence on the circulation over East Asia when the event is accompanied with a positive phase of PDO. The intraseasonal variation of EAWM is related to the response of atmosphere to El Ni〖AKn~D〗o event.
    14  Analysis of the April 2015 Atmosphere Circulation and Weather
    ZHOU Kanghui FANG Chong
    2015, 41(7):915-920. DOI: 10.7519/j.issn.1000-0526.2015.07.014
    [Abstract](1462) [HTML](130) [PDF 4.03 M](1226)
    The main characteristics of the general atmospheric circulation in April 2015 were as follows. The circulation of polar vortex in the Northern Hemisphere was in a dipole type, with one center located between the west of Greenland and Canada, and the other in the northeast of Asian. The strength of both centers was 4-8 dagpm lower than normal years, but the Ural Mountain ridge was 8-12 dagpm higher than normal. The Northwest Pacific subtropical high extended to west more than usual with larger area. The location and strength of south branch trough was close to normal annual means. The monthly mean temperature was 11.6℃, being 0.6℃ higher than normal. The monthly mean precipitation was 43 mm, which is close to the annual average (44.7 mm). While the precipitation in the region to the north of Yangtze River was more than average, the situation in South China was opposite. Severe convective weather events occurred frequently in April, with large scope of hail, thunderstorm and gust seen in 1-4, 19-20, and 28-29. Two sandstorms happened in the northern part of China.

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