Plateau Meteorology

Current Issue

28 August 2012, Volume 31 Issue 4   

articel

  • Numerical Simulation of Precipitation Mechanisms for an Isolated Forest Mountain Area in Semi-Arid Region of Middle of Northwest China
  • CHEN Lei-;TIAN Wen-Shou-;HUANG Qian-;HUANG Jian-Ping-;WANG Chan-;SUN Lan-Dong-
  • 2012 Vol. 31 (4): 885-899. 
  • Abstract ( ) PDF (2181KB) ( )
  • Using a numerical model and the long term observation data, the precipitation differences between an isolated mountain forest (Xinglong, 103.84°E， 35.86°N) and its surrounding area over the arid/semi-arid region of Northwest China is studied in order to understand the mechanisms for the persistence of the isolated forest. The results indicate that the precipitation differences between Xinglong Mountain and its surrounding area are the largest in summer and autumn. The Xinglong Mountain area is dominated by the southeastern wet flow in summer and autumn and consequently a stable water vapor source. In addition, the meso-scale high mountainous terrain blocks the water vapor from the southeastern flow and enhances precipitation. The contribution of local evapotranspiration to the precipitation is less than that of advection effects of water vapor. On the other hand, the rock tectonics of Xinglong Mountain covered by soil and forest also help to hold and store water for the growth of plants. Therefore, the persistence of the forest island   of Xinglong Mountain in semi-arid regions is the consequence of the large-scale circulation, which transports more water vapor, the orography and the special geology which tend to help and store more water vapor for this area.
  • Characteristics of Winter Apparent Heat Source in the Key Area of Snow Cover on Qinghai-Xizang Plateau and Spring Drought in Southwest China
  • GUO Ji-Bing-;XU Xiang-De-;SHI Xiao-Hui-;XU Jie-
  • 2012 Vol. 31 (4): 900-909. 
  • Abstract ( ) PDF (1294KB) ( )
  • Using NCEP/NCAR reanalysis data, observational snow depth and precipitation data in China, adopting the statistical correlation model, including anomaly index and the correlation vector calculation method, the regional characteristics of spring drought in Southwest China and the ‘strong signal’ of snow cover and heat source in the Qinghai-Xizang Plateau were analyzed. The typical region of spring drought in Southwest China was studied and then  the key area of atmospheric apparent heat source  of snow cover on the Qinghai-Xizang Plateau was got which in its later stage  influenced the spring precipitation over the typical region of spring drought in Southwest China. Through the comprehensive analysis of the correlation between the snow depth and the atmospheric apparent heat source in all levels over the ‘strong signal’ Key area of snow cover on the Qinghai-Xizang Plateau, it is found that February is the precursor ‘strong signal’ typical month of  the snow cold source in the Key area of snow cover on the Qinghai-Xizang Plateau. Through the anomaly index and the correlation vector analysis, the correlation of the annual change of anomaly index between the apparent heat source (Q1) in  ‘strong signal’ typical month (February) in the Key area of snow cover on the Qinghai-Xizang Plateau and spring precipitation in the later period over the area of spring drought in Southwest China  were focused on. Then,  the relation between the two anomaly index above have a character of ‘anti-phase’ in annual change is found. The analyzed result showed that when the snow depth on the Qinghai-Xizang Plateau was shallow, the apparent heat source (Q1) in the Key area of  snow cover on the Qinghai-Xizang Plateau was high. And this was beneficial for relative dry northerly flow over Southwest China in spring. This also lead to a abnormal less precipitation in spring in Southwest China. The atmospheric apparent heat source in all levels  over the Key area of  snow cover on the Qinghai-Xizang Plateau has a obviously precursory effect to predict the spring drought in Southwest China.
  • Comparison Analysis of Meteorological Elements between Nagqu Meteorological Station and Field Meteorological Station
  • XU Li-Jiao--;HU Ze-Yong-;LI Jing-Hua-
  • 2012 Vol. 31 (4): 935-941. 
  • Abstract ( ) PDF (783KB) ( )
  • Using the meteorological data obtained at NQ stationin1955-2009 and BJ station in 2001-2009, thedifferences of temperature and wind speed at the two stations were analyzed. The results showed that both the annual average temperature and the minimumtemperature at BJ station were lower than that at NQ station while the annual average wind speed at BJ station was higher than that at NQ station from 2001 to 2009. The increasing rate of the temperature difference between NQ station and BJ station performed as the minimum temperature (0.117  ℃·a-1) > the annual average temperature (0.034  ℃·a-1) > the maximum temperature (-0.014  ℃·a-1) in order, and the rate of annual average wind speed was 0.076 m·s-1·a-1. According to the strength of anthrogenic activities and the Tibetan Plateau Railway was built in2006, the period of 2001-2009 weredivided into two periods, one was the period of 2001-2005 as the weak period, another wasin 2006-2009 as the strong period. Comparing with temperature in the weak period, the differences of the minimumtemperature between the two stations in the period of strong human activitie had the marked increase with 0.512 ℃. The temperature differences showed the minimum temperature (0.512 ℃) > the annual average temperature (0.152 ℃) > the maximum temperature (-0.025 ℃) in order, and the difference of annual average wind speed was -0.198 m·s-1.
  • Vorticity Diagnosis of Continuous Rainstorm under the Influence of Strong Developing Mesoscale Vortex
  • GE Jing-Jing-;LU Han-Cheng-;ZHANG Qun-;ZHONG Wei-;HE Xun-Shan-
  • 2012 Vol. 31 (4): 952-962. 
  • Abstract ( ) PDF (2049KB) ( )
  • The potential vorticity (PV) on isentropic surface and moist potential vorticity (MPV) diagnoses in the mid-Juneof 2008during Guangxi flashflood rainstorm process under the influence of mesoscale vortex (Guangxi vortex for short) are carried out using the high-resolution model data. The results show that the location and strength of positive PVon low-value isentropic surface reflect the area and intensity of heavy rain; dry and cold high-value isentropic potential vorticity (IPV) on high-latitude and warm and moist high-valueIPVon low-latitude are, respectively transported to vortex area in Guangxi by westerlieson isentropic surface, resulting in the maintenance of high-value IPVin Guangxi vortex. While on the high-value isentropic surface, there is transportation of southern IPV to its downstream, which is beneficial to the IPVgrowth of Guangxi vortex which is inits downstream, resulting in strong development of Guangxi vortex and  precipitation enhancement. The analysis onthe MPVconservation principle shows that continuous heavy precipitation appeared in the convectively unstable area in front of high-value isentropic moist potential vorticity. The convective stability decreases with the going down of cold airinmid- and upper-leveltroposphere on north and south sides of rain area, making the corresponding cyclonic vorticity increase; while the warm and moist air climbs along dry and cold air, and there is strong convergence between the warm air and the cold onegliding down the isentropic surface, making the vorticity sharply increase, and with the uplifting effect forced by terrain, strong vertical ascending motion is formed and the vortex strongly develops. The distributions of isobaric surface MPVand its components show that negative MPVin the lower-leveltroposphere can denote the heavy precipitation, and there is convective instability and conditional symmetric instability during heavy precipitation period.
  • Analyses on Water Vapor Characteristics in Three Heavy Rainstorm Processes of Xinjiang in July 2007
  • YANG Lian-Mei--;ZHANG Yun-Hui-;TANG Hao-
  • 2012 Vol. 31 (4): 963-973. 
  • Abstract ( ) PDF (1816KB) ( )
  • Using the daily precipitation data at 99 stations in Xinjiang and NECP/NCAR reanalysis  the atmospheric water vapor transports associated with three heavy rainstorm processes in Xinjiang in July 2007 are analyzed. The results show that pathways of water vapor transport related to heavy rainstorm patterns are very different. In Pattern I, with bigger rainbelt over Tianshan Mountains and its northern piedmont regions, follows from a convergence of the western， the southern with the eastern water vapor transport. The western water vapor transport comes from westerly and the eastern transport is associated with a strong low-level easterly jet (LLEJ) extending from Gansu to Xinjiang. The water vapor over Tibetan Plateau penetrates even more northward entering Xinjiang. The water vapor transport is resulted in collocation of the Lake Baikal high on 700  hPa， the southward of Center-Asia low and eastward shift of Xinjiang high on 500  hPa. In Pattern II, with a main rainbelt over eastern Xinjiang, is supported by the convergence of water vapor both in the east-west and in the south-north; the water vapor comes from the west along westerly, the south from Tibetan Plateau, the north by Boreas and the east by LLEJ from Lake Baikal. Abnormal water vapor transport corresponds to a southeastward extension of Ural high, development and southward moving of center-Asia vortex, Xinjiang high and developing of the Qaidam low on 700  hPa. In Pattern III, with the heavy rain to the north of Tianshan Mountains, results from the convergence of water vapor in the east-west; eastern water vapor transport comes directly from LLEJ but originally from the Lake Baikal, the Bay of Bengal, South China and the western Pacific Ocean. The anomalous water vapor transport is associated with a northward extension of the WPSH and a westward shift of Lake Baikal high, a part of tropical abundant water vapor is transported for Xinjiang, and as a result eastern water vapor import takes a dominant role. The eastern transport of anomalous water vapor occurs mainly in the lower troposphere, while the transport of southern water vapor occurs mostly in the upper troposphere.
  • Daily Evapotranspiration Calculated with RIEMS Model Output and Its Effect
  • SHAO Yue-Hong-;ZHANG Wan-Chang-;LIU Yong-He-;LIN Bing-Zhang-
  • 2012 Vol. 31 (4): 983-992. 
  • Abstract ( ) PDF (1285KB) ( )
  • The output products of the RIEMS model  are used to calculate daily evapotranspiration (ET) usingfour different ET estimation methods, such asthe modified Penman-Monteith method (P-M), Priestley-Taylor method (P-T), Hargreaves-Samani method (Harg) and the bilinear surface regression empirical function method (BEF). ET estimated fromfour methods were examined and compared with those so called ground truth transferred from the observed 20 cm evaporation pan data with validated evaporation pan coefficient from sixweather stations in upper Yishuhe watershed of the study area. The results show that for the estimation accuracy of ET, BEF algorithns is in the first place; Harg, the secord; P-T, the third; and P-M, the fourth, based onfour evaluation criterions such as mean bias, mean absolute bias, root mean square error and correlation coefficient. In the dailytime series, ET estimationfrom four approaches varies with the same trend to the observed evaporation pan generally, but has considerable difference in the strongest and the weakest evaporation duration, and in the maximum air temperature and precipitationin July, August and September. As a whole, the ET estimated by BEF method performs best and has a good agreement with theobserved value, the other three approaches followed by Harg, P-T and P-M methods have an obvious overestimation. Because of the excellent performance of BEF method and less meteorological parametersneeded for ET estimation with RIEMS predicted meteorological variables, BEF method was recommended as the best ET estimation approach to provide accurate ET for driving Hydrological process model TOPX coupled with RIEMS for the hydrometerological predictions in upper Yishuhe watershed, Shandong Province,.
  • Response Characteristics and Mechanism Analyses on Monthly Circulation to SST Anomaly Force
  • WANG Qiu-Liang--;ZHANG Li-Feng-;GUAN Ji-Ping-
  • 2012 Vol. 31 (4): 993-1000. 
  • Abstract ( ) PDF (1216KB) ( )
  • Using the spectral forecast model with the global medium range, the response characteristics of monthly atmosphericcirculation to SSTA (sea surface temperature anomaly) and the mechanism are investigated. In order to detect the model response characteristic in different seasons, two sets of sensitivity numerical simulations are conducted. For each experiment, except for the control experiment that is performed with climatological SST (sea surface temperature) for ocean boundary conditions, the other two integrations forcedwith prescribed and random SSTA added to climatological SST. The simulated results show that atmospheric responses firstly generate in areas with high SST oceans and large disturbed SSTA oceans, and the development and evolution of atmospheric responses are related to the background of atmospheric circulation. Furthermore, when the atmospheric responses in model come to a steady state, the simulated atmospheric responses are in zonal wavydistribution along westerly jet. During the different seasons, the speeds of atmospheric circulation response have the dissimilarSST distribution. However, both in winter and in summer, the size of responses can reach maximum within monthly time scale. In general, atmospheric responses are likely to be zonal wavy distributed after the forthpentad. Maximum value of atmospheric responses in winter reach higher altitude comparing to that in summer, and this may be caused by the fact that deep westerliesin winter are more convenientfor the vertical spread of Rossby wave.Andthe atmospheric responses in model are more sensitive to distribution of perturbation in winter then in summer. In extended-range, atmospheric responses depend more on the background of atmospheric circulation namely atmospheric internal dynamic than boundary conditions.
  • Relationship between Stratospheric Polar Vortex Change and Temperature, Precipitation in Winter of China
  • XIONG Guang-Ming-;CHEN Quan-Liang--;ZHU Ke-Yun-;FAN Guang-Zhou-
  • 2012 Vol. 31 (4): 1001-1006. 
  • Abstract ( ) PDF (745KB) ( )
  • Using the monthly circulation index data of National Climate Center from 1951 to 2010, the relationship among the intensity,area and central intensity indexes  of the Northern Hemisphere polar vortex are analyzed. And the temporal variation features of the polar vortex intensity in winter werediscussed through the intensity index. The results show that the polar vortex intensity index has a good correction with the area index and the central intensity index, which can representthe change of the stratospheric polar vortex well in winter.The polar vortex mainly has a decadal oscillation period  of 13 years and an interannual oscillation period of5 years after the 1990s. The  changes of temperature, precipitation and the generalcirculation in winter are discussed by the observation data and monthly meanreanalysis data fromNCEP/NCAR. In relative strong years of polar vortex, the temperatures in North China and East China, especially in Northeast China are higher than thatof  relative weak years of polar vortex. At the same time the temperature in most of Southwest China is lower, but ithas little change in the Yangtze River region and South China. And the precipitation is above normal in Southern China region especially in mid- and lower-reaches of the Yangtze River and South China, but belownormal in the North China.Besides, it can be found that the  500 hPa potential height is higher in the mid- and high-latitudes and lower in the high latitude, whilethe polar vortex is relative strong. The circulation implies that the East Asian winter monsoon and East Asian trough is weaker correspondingly. Under this situation, the cold air gathered around the polar and warm air flows to inland region, which causes the higher temperature in East China and Northeast China, and more precipitation in the southern China  and the Yangtze River regions.
  • Main Modes in East Asian Monsoon Circulation Evolution and Its Relationship with Precipitation Anomaly in Eastern China
  • HAO Li-Sheng--;DING Yi-Hui-;MIN Jin-Zhong-
  • 2012 Vol. 31 (4): 1007-1018. 
  • Abstract ( ) PDF (2162KB) ( )
  • Based on the reanalysis circulation data from American National Centers for Environment Prediction/National Center for Atmospheric Research (NCEP/NCAR), the surface sea temperature (SST) data reconstructed by American National Oceanic and Atmospheric Administration (NOAA) and precipitation data at 752 stations from Chian National Meteorogical Information Center (NMIC), the seasonal evolution of main modes in East Asian monsoon and their relationship with the precipitation anomaly in eastern China are analyzed. The results show that there are two main modes in the East Asia monsoon seasonal evolution on 850 hPa. The first mode is mainly affected by Indian Ocean Dipole (IOD) evolution control under the low SST in tropical Indian Ocean and the equatorial eastern Pacific; the second mode is mainly affected by the equatorial eastern Pacific El Nio/Southern Oscillation (ENSO) cycle and IOD evolution control. Corresponding to the first mode, there is rainy in North China in summer, dry in the Yangtze River. Corresponding to the second mode, there is more rain in North China and the Yangtze River in summer, drier than usual in the Huaihe River and South China. The two modes have taken place significant change in recent 50 years, being a good relationship with the precipitation anomaly.
  • Analysis on Environment Field Characteristic of Influencing Convection System during a Severe Convective Process in Southern China in Spring
  • CHEN Tao;ZHANG Fang-Hua;ZONG Zhi-Ping
  • 2012 Vol. 31 (4): 1019-1031. 
  • Abstract ( ) PDF (2211KB) ( )
  • Using the surface observation data, Dopple radar data and FY-2E satellite cloud image, a severe convective event in spring of Southern China on 5-7 May 2010 is studied. The initialization and developing of the MCS occurred in this event are analyzed, and the influence of variant environmental conditions on the MCS is discussed in detail. The resoult shows that the convective systems are caused to develop into various forms due to the difference of allocation in the dynamical structure, water vapour, and convective instability conditions. The relative storm helicity is used specially to analyze the dynamical characteristics of environmental flow and its impact on the MCS organization and structure. The resoult shows that there is drier air in the mid-upper level of local region of Chongqing, the vertical shear is strong, and the cyclonic rotating motion of environmental field is relative deeper, an isolate and similar supercell's server convective storm is developped under the forced lifting mechanism of front surface, which cause the local hail, thunderstorm and gale weathers. The moist layer near Guizhou Province is deeper, and the coupling effect between upper and lower level jets is more clearly, so the organized multi-cell convective storm in larger space scale developed in north Guizhou Province, and the local short-time heavy rainstorm formed. There is the strongest vertical shear and deep moist layer in Guangdong Province, under the trigger mechanism of shallow cold air, the severe MCS with deep and moist convection form appears high organizing linear convection belt, and the MCS with large space scale and a long lifetime cause the severe precipitation.
  • Characteristics of Sub-Synoptic Scale Circulation of Strong Gale in Yellow Sea and Bohai Sea
  • LIANG Jun-;ZHANG Sheng-Jun-;ZHU Jing-;ZHAO Ya-Xuan-
  • 2012 Vol. 31 (4): 1032-1041. 
  • Abstract ( ) PDF (1643KB) ( )
  • Using the conventional observation data and NCEP/NCAR global reanalysis data with 1°×1° resolution, a strong gale processes occurred in Yellow Sea, Bohai Sea and their coastal areas in December 2008 are analyzed. The sub-synoptic scale features of strong gale are analyzed and the conversion of kinetic energy and vorticity in the strong gale and sub-synoptic scale systems during  strong gale are calculated. The results indicate that the sub-synoptic scale stream  fields exhibit a kind of wave structure during strong gale. Whether the wave structure  maintained during the strong gale is closely related to the synoptic background. The circulations of Yellow Sea and Bohai Sea locate in front of a westerly trough, the wave structure is maintained. The transportations of the kinetic energy and positive vorticity from sub-synoptic scale systems are favorable to the formation of the strong gale and the development of the low. The circulations of Yellow Sea and Bohai Sea locate in the west of westerly trough, the wave structure is destroyed. The positive vorticity of sub-synoptic scale system is consumed and the kinetic energy is provided from synoptic scale system, which leads to the decrease of the low and the substation of the strong gale. More kinetic energy obtained from the sub-synoptic scale system in lower atmospheric layer is the dominant factor to identify whether wind will intensify or weaken rapidly. The maximum kinetic energy of sub-synoptic scale system is located in the layer below 850 hPa.
  • Analysis on Water Vapor Condition of a Short-Time Heavy Rainstorm Process in Guanzhong, Shaanxi in August 2007
  • MU Jian-Li-;LI Ze-Chun-;ZHAO Lin-Na-;CHEN Xue-Zhen-
  • 2012 Vol. 31 (4): 1042-1052. 
  • Abstract ( ) PDF (1556KB) ( )
  • The water vapor condition of a stort-time heavy rainstorm in the Guanzhong, Shaanxi  on 8-9 August 2007 was carefully analyzed using the T213 data and automatic meteorological observing data. The results indicate that the water vapor of heavy rainstorm is from a high humidity around the Guanzhong Shaanxi. Water vapor over the rainstorm area is shallow during the heavy rainstorm. Humidity change in rainstorm area has the process of  ‘reduced-increases suddenly-reduces fast’, because of wind direction fast change at the low level, and the vapor accumulation is obtained through the easterly current. The  moisture convergence in the east-west direction is main contribution of convergence of vapor in the heavy rainstorm area. Occurring, intensification and weaken of heavy rainstorm had a close relationship with inflow and outflow of moisture flux on the north boundary and sudden increase and decrease of vapor flux inflow on the east boundary. The heavy rainstorm center locates in region between the maximum of water vapor flux and convergence center of vapor flux. The precipitable water in heavy rainstorm area   primarily depends on the vapor flux convergence in horizontal direction, and vapor flux convergence largely is decided in convergence of horizontal wind. The occurrence and weakening of severe precipitation have more closer relationship with the local change of water vapor and water vapor advection change. Anti-circulation circle owing to the sufficient vapor supply at the surface layer and the water vapor vertical transportation causes rapid enhancement and lifting in the water vapor and energy, establishing the atmosphere of instability and triggering the energy release, which lead to formation of heavy rainstorm. On the contrary, vapor condition of formation rainstorm disappeared,  severe precipitation end.
  • Study of the Hydrothermal Condition and Aboveground Biomass in Typical Alpine Grassland in Tibetan Plateau
  • LI Xiao-Dong-;LI Feng-Xia-;ZHOU Bing-Rong-;XIAO Hong-Bin-
  • 2012 Vol. 31 (4): 1053-1058. 
  • Abstract ( ) PDF (671KB) ( )
  • The climate change present situation, climatic factors and  aboveground biomass change are calculated, and the relationship among the rainfall, air temperature and aboveground biomass was analyzed, using the surface meteorological data and aboveground biomass data in Haiyan county, Haibei district of Qinghai Province from 1979 to 2009. The results show that the annual mean temperature and rainfall present the increase trend, the increase rate of annual mean air temperature is 0.33 ℃·（10 a）-1 and that of annual rainfall is 33.1 mm·（10 a）-1. The accumulated temperature >0 ℃， biological temperature and actual evapotranspiration show the increase trend, but the moisture index appears obvious decreasing tend. The total aboveground biomass from 1997 to 2009 appears the increasing trend in Haiyan county grassland, there is highly significant positive correlation between the rainfall in winter and the total aboveground biomass and there is highly correlation between the air temperature in summer and annual aboveground biomass. The increasing trends of air temperature, rainfall and  the accumulated temperature ＞0 ℃ are obvious. It is found that the grassland aboveground biomass in alpine, winter rainfall and summer air temperature have significant correlation.
  • Influence of South Branch Trough of Westerlies on Weather of Yunnan Province
  • DUAN Xu-;TAO Yun-;XU Mei-Ling-;LU Ya-Bin-;LIANG Hong-Li-
  • 2012 Vol. 31 (4): 1059-1065. 
  • Abstract ( ) PDF (977KB) ( )
  • Using the daily surface observationand radiosonde data from 1980 to 2008, the cases of the south branch  trough  of westerlies influencing on the weather of Yunnan Province are investigated. The spatial and temporal distributionsof the south branch trough  of westerlies and   characteristic of influencing on the precipitation of Yunnan are analyzed. The results indicate thattheyearly averaged number occurred south branch trough  of westerlies influencing on the weather of Yunnan is 18.76. The monthly mean numbers from November to May in next year are almost the same. About 5.88% of processes of the  south branch trough will produce the weather from heavy rain  to rainstorm in Yunnan, about 54.83% of  processes will produce the weather from light rain to moderate rain in Yunnan. Other 17.28% of processes will produce the hail weather. The result shows that the advance and retreat of south branch trough are closely related to the  westerly belt circulation, position of subtropical high, the large-orography of plateau, and so on. The intensity of precipitation and occurring of  severe convective weather in Yunnan are determined by the position of the  south branch trough, water vapour transporting, moisture front zone and low-level jet and strong and weak cold air,  and so on.
  • Statistical Characteristic of Southwest Vortex Influencing Yunnan Region
  • LIANG Hong-Li-;DUAN Xu-;FU Rui-;GUO Rong-Fen-
  • 2012 Vol. 31 (4): 1066-1073. 
  • Abstract ( ) PDF (839KB) ( )
  • Based on the data of the  700 hPa synoptic map at 08:00 and 20:00 from 1980 to 2008, the characteristics of moving track, annual, monthly and daily variations, maintenance time, corresponding precipitationcaused by southwest vortex were statistically analyzed. The results show that nearly one eighth or one seventh of southwest vortexes can move out of Sichuan Province affect Yunnan, and its linear trend in past 30 years is decreased. Their vortex source regions are mainly near Jiulong and Sichuan Basin. The occurrence frequency of southeast ward path is the highest, then the southwest- and south-ward paths. Generally,under the topographical influence, southwest vortexes could not influence on the edge of western  and southwest Yunnan. In the late spring and summer, the movement of southwest vortex affects Yunnan with the highest frequency, while the frequency is the least in thelate autumn and winter. The probabilityof southwest vortex influencing Yunnan is about 61.54% at 08:00. Their life periods are exponential decay, mostly no more than one day.Nearly 13.5% of southwest vortex cause heavy precipitation process in Yunnan. The heavy  precipitation  caused in south path occurs mainly in western Ailao Mountains.  the heavy precipitation caused southeast path mostly occurs in the central and southeastern Yunnan, and one  caused southwest path mostly occurs in the east of Yunnan. Among of them, the frequency and intensity of occurringheavy  precipitation are the highest in southwest path, and which should be paid  more attention. Although the most of southwest vortexes can move out to influence Yunnan along the side   of southeast path, the frequency and intensity of occurringheavy    precipitation   were below the mean.
  • Characteristic Analysis on Temperature Change in Snow Layer in Western Tianshan Mountain in China
  • GAO Pei-;WEI Wen-Shou-;LIU Ming-Zhe-
  • 2012 Vol. 31 (4): 1074-1080. 
  • Abstract ( ) PDF (951KB) ( )
  • The temperature featuresof dry snow and moist snow after snowfall were discussed based on the temperature data in 10 snow layers every 5 min at a time at Tianshan Avalanche station. The results show that: (1) The temperature inevery snow layer is below zero in winter, the amplitudes of snow temperature at the top of the snow cover layer is largerthan that of the bottom. The occurrence of the temperature extremum at the top snow layer isearlier one or two days than that of the bottom. (2) The occurrence of  cold center of moist snow isearlier than that of dry snow, however, the occurrence of the warm center of  moist snow is later than that of the dry snow. And the solar radiation can penetrate the moist snow deeper than that of dry snow. (3) The distribution of solar radiation in the snow layer and the amplitudes of snow temperature are both depended on Lambert′s Law.Depth of penetration  increases with the increasing of the snow density. (4) The sensible heat  and latent heat fluxes in dry snow areboth beneath zero, so snow is accumulated; the sensible heat flux and latent heat flux exchanges in moist snow arecounteract, therefore, the net radiation is main factors  leading to melt the snow.
  • Distribution of Precipitation Particle and Electrical Characteristic of a Thunderstorm in Pingliang Region
  • ZHANG Ting-Long-;YANG Jing-;CHU Rong-Zhong-;ZHAO Guo-;ZHANG Tong-
  • 2012 Vol. 31 (4): 1091-1099. 
  • Abstract ( ) PDF (1110KB) ( )
  • The fuzzy logic hydrometeor classification (FHC) was applied to analyze the distribution of precipitation particles in a thunderstorm which was observed by a X-band dual polarimetric radar in Pingliang region, Gansu Province. Combining the electrical characteristics of thunderstorms in the study region, the relationship between charge structure and precipitation particles of thunderstorm are discussed in details. The results show that each type of precipitation particles take different magnituds at different stages of thunderstorm, and only the magnitudes of graupels and dry snow are consistent with the evolution of thunderstorm. According to the surface electrical field and radar results, it is concluded that the solid-state particles in particular graupels and ice are related to the charging of thunderstorm. The intensity of lower positive charge center of thunderstorm in the Chinese inland plateau is likely to determined by the quantity of graupels based on the vertical distribution of each type of precipitaiton particles. In addition, the graupel-ice charging mechanism can well be used to interpret the origin of the tripole charge structure of thunderstorm.
  • Analysis on Lightning Activity Characteristic of a Squall Line System in Low-Latitude Plateau
  • YIN Li-Yun-;ZHANG Jie-;ZHANG Teng-Fei-;XU Ying-Jie-
  • 2012 Vol. 31 (4): 1100-1109. 
  • Abstract ( ) PDF (1608KB) ( )
  • The activity characteristics of cloud-to-ground (CG) lightning during a typical squall line system process in southwest Yunnan was analyzed based on the data from lightning detection system, Dopplar radar and satellite. The result showed that the typical squall line system process was caused by combination of convective clouds within the cloud band of shear line and the ones outside of typhoon. The negative CG flashes were in the leading position at the first developing stage of squall line system and the CG flash rates increased slowly with the fluctuation. The CG flash rate was higher at the mature stage of squall line system, and the peak time of positive CG was earlier 10～15 min than that of negative CG. The frequency of CG flashes rapidly declined with the increase of positive CG flash ratio at dissipating stage of squall line system．The CG flash activities started to diminish when the frequency of positive CG  flashes was more than 8%.The negative CG flashes clustered in the intense echo region (> 40 dBz), which  corresponded to the convergence area in radial velocity field from Doppler rader. The positive CG flashes clustered at the time of mature stage closely, which corresponded to the area of intense echo (> 40 dBz) beside convergence region, and sparse positive CG flashes were observed in the cloud anvil outside of the intense echo area, or in stable precipitation region．Every jumping change of the radar echo intensity at the heights with -10 ℃ and -20 ℃ corresponded to the jumping development of the frequency of CG flashes, and the jumping times of CG flash rate were always behind that of the radar echo intensity. To the TBB, the negative CG flashes clustered in the in -92～-90  ℃ and -76～-74 ℃ cloudy areas, while the positive CG flashes clustered in the  -90～-60 ℃ cloudy areas.
  • Analysis on Doppler Radar Feature of Snowstorm in Hebei in Late Autumn of 2009
  • PEI Yu-Jie-;WANG Fu-Xia-;ZHANG Ying-Xin-;WANG Li-Rong-
  • 2012 Vol. 31 (4): 1110-1118. 
  • Abstract ( ) PDF (1865KB) ( )
  • Using the Xinle CINRAD radar data in Shijiazhuang, dense-automatic station data, and four-dimensional variation data assimilation of wind retrieval, the strongest snowstorm occurred in Hebei Province from 10 to 12 November 2009, which is a new record in its meteorological history, are analyzed. The result shows that the snowstorm is divided into two phases: Shear line with return flow and westerly trough snow.  It is found that shear line with return flow snowfall echo is convective  mixed  cumulostratus. The westerly trough echo are stratiform clouds without bright bands. The vertical structure of convective snowfall echo is similar to that of summer rainfall echo, which is the most important reason for this extreme event. The radial velocity field exists ‘bovine-eye’ feature, zero velocity line appears ‘S’-, anti ‘S’-shaped and discontinuous zero line. When the  the warm advection with wind-direction and wind-speed convergence appear, the snowfall starts to enhance, while the warm advection with wind-direction and wind-speed divergence appear, the snowfall starts to abate. Boundary layer convergence line exists from the ground to 1.2 km boundary layer. The convergent uplifting of  vertical wind shear  enhances  the vertical motion and snowfall strengthing.
  • Study of an Automated Doppler Radar Velocity Dealiasing Algorithm
  • XIAO Yan-Jiao-;WAN Yu-Fa-;WANG Jue-;WANG Bin-;WANG Zhi-Bin-
  • 2012 Vol. 31 (4): 1119-1128. 
  • Abstract ( ) PDF (1463KB) ( )
  • Based on the horizontal continuity of velocity field， an automated Doppler radar velocity dealiasing algorithm which can solve velocity aliasing problem in isolated severe windstorm events, high shear environment and severe typhoon events are proposed. Most two sets of initial reference radials and gates by finding the weakest wind region is firstly determined in the algorithm, using the adjacent elevation initial reference radials in the azimuth continuity constraint condition and initial reserve radials of eliminating  inappropriate induced by false zero isodops. Then from these initial reference radials and gates, continuity checks adjacent gates and corrects for the differences between radial velocity values and reference velocity the larger than the given threshold. After twice round of radial-by-radial dealiasing, the algorithm will perform high gate-to-gate wind shear checking in the radial and azimuth directions, if the high wind shear still exists, it will second determine a set of initial reference radial and gate by finding the weak wind shear radial with the most valid velocity gates, then the preceding dealiasing procedures are repeated one time, which is needed for dealiasing velocities in isolated storm region away from the radar. Multiple passes of dealiasing are performed in the algorithm that use very strict criteria and little shear threshold in earlier passes and relaxed criteria and large shear threshold in the later passes to ensure a good reference for dealiasing in the later passes. The dealiasing algorithm is tested and evaluated across more than 1 000 volume scans of S-band Doppler weather radar from China encompassing events of tornadoes, squall lines, isolated strong storms and severe typhoons. The results show that the algorithm is very robust. It can correct for aliased Doppler velocity data properly in more than 99.5% of the cases tested and examined. In cases with isolated windstorm, high shears and severe typhoons, the new algorithm shows the improvement in the current China New Generation Weather Radar operational velocity dealiasing scheme.
  • Analysis on Cold Front Cloud Structure from  95 GHz Cloud Radar Data
  • HUANG Yi-Mei--;ZHOU Yu-Quan-
  • 2012 Vol. 31 (4): 1129-1138. 
  • Abstract ( ) PDF (1245KB) ( )
  • The cloud structure of a cold front on November 5-7, 2008 is analyzed using the comprehensive observed data from ARM project in Shouxian, Anhui Province, including cloud radar, ground microwave radiometer, sounding and ground observation data. The results show that the particle′s morphology and size can be preliminarily determined through the Doppler radar speed of cloud and whether or not it presence snow crystals or rain. Near 0 ℃ level there is a dark band, which is caused by the 3 mm wavelength radar to strong attenuation of the snow crystals and the Rayleigh scattering; cloud radar observation can identify clearly melt layer. It is found that the cloud structure is very uneven, there is a hydrometeor content big value area between 5～7 km. In this area, grown snow and ice crystal fall continuously to lead to the cloud base gradually stretched downward and produce an intermittent precipitation. Below 2 km above the warm area there is dry and cold northeast airflow, which limit the raindrop growth through the warm rain process,  the  precipitation intensity of front surface is caused to be small. The posterior between 4～7 km heights, because the snow and ice crystal settlement, the relative humidity is small, the clouds  are split into two-layer-clouds. There is severe precipitation after the cold front, which is caused mainly by the warm rain process.
  • Preliminary Estimates of Wind Energy Resources Deficit in Large Wind Farm
  • LIU Lei--;GAO Xiao-Qing-;CHEN Bo-Long-;;WANG Ning-Bo-
  • 2012 Vol. 31 (4): 1139-1144. 
  • Abstract ( ) PDF (600KB) ( )
  • The assessment of wind energy resource plays a fundamental role in itsexploitation. The assessment should take into account the influence of wind turbines on the current within the wind farm in the surface layer. An area of approximately 2 000 km2with a roughness length of 0.03 m in large wind farm is idealized. 6 667 typical wind turbines  about one million kilowatts are distributed uniformly over thearea. The  Frandsen method is used to analyze the influenceof wind farm on the wind energy resources within theareawhere the internal boundary layer has filled the whole boundary layer in the wind farm. The results show that the wind speed at the height of 65 m will decrease when the situation with the presence of the wind farms is taken. This reduction becomes less when the wind speed at the height of 65 m increases, due to the property of drag coefficient in wind turbine. Within the wind speed range of 3~20 m·s-1at the height of 65 m, the average wind power density considering the situation without and with wind farms are calculated, respectively. And the value decreases 58.45% when the wind farm is installed.coefficient

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