Plateau Meteorology

Current Issue

28 April 2007, Volume 26 Issue 2   
  • Numerical Simulation of East Asian Subtropical Westerly Jet Using Regional Climate Model with P-σ Mixed Coordinate
  • LU Yan-yan;ZHANG Yao-cun
  • 2007 Vol. 26 (2): 213-224. 
  • Abstract ( ) PDF (2136KB) ( )
  • The performance of a regional climate model with P-σ incorporated coordinate in simulating the seasonal variation of the East Asian subtropical westerly jet(EAWJ) in the upper troposphere has been evaluated by analyzing the differences between the model results and the NCEP/NCAR reanalysis data,and the relationship between the EAWJ seasonal variation and the meridional atmospheric temperature difference in the mid-upper troposphere has also been analyzed in this paper.The results show that the model can reproduce the major features of the EAWJ horizontal and vertical structures and seasonal evolution,in comparison with NCEP/NCAR reanalysis.The ability of model to simulate EAWJ is better over the ocean than over the continent,in lower latitude than in higher latitude.There also exist considerable biases in EAWJ intensity and location simulations.The model underestimates the EAWJ intensity throughout the year.Analyses of the EAWJ seasonal variation and the atmospheric meridional temperature gradient in the mid-upper troposphere indicate that the EAWJ center always corresponds to the largest meridional temperature gradient in the mid-upper troposphere,suggesting that the seasonal variation of EAWJ is a response to the meridional temperature difference.Comparing with the NCEP/NCAR reanalysis,the model reproduces weaker meridional temperature gradient with a value of about 2K/10-latitude,leading to the EAWJ intensity 10 m·s-1 weaker than the reanalysis.According to the thermodynamic equation,the atmospheric temperature change results from the diabatic or adiabatic heating.Comparison of the simulated surface sensible and latent heat flux with the NCEP/NCAR reanalysis data indicates that the discrepancies of surface heat flux are related to the location and intensity biases in the EAWJ simulation.
  • Nonlinear Singular Inertial Gravitational Wave Forced by Diabatic Heating and Its Association with the Tibetan Plateau Vortex
  • LIU Xiao-ran;LI Guo-ping
  • 2007 Vol. 26 (2): 225-232. 
  • Abstract ( ) PDF (404KB) ( )
  • In the recent 30 years,the investigation on the solitary and cnoidal wave of the nonlinear motion has attracted great interests in the atmosphere and ocean sciences.However,the most of former researches mainly emphasized on the aspects of the solving of solutions and the dynamic analyses of the wave,and rarely considered the relations between the diversified solitaries and the factual synoptic systems.The plateau vortex is one type of subsynoptic scale low-pressure vortex and a primary kind of synoptic systems over the Tibetan Plateau.It is the main rainfall system of the Tibetan Plateau in summer.Individual Plateau vortex can develop and move eastward out of the Tibetan Plateau coupled with the advantageous circulation pattern,which always gives rise to large-scale rainstorm or thunderstorm on the east side of the Tibetan Plateau(especially in Sichuan basin).Therefore,the study on Plateau vortex is not only an important problem of theoretical research on meteorology of the Tibetan Plateau,but also has practical meanings of improving the weather forecast accuracy in the area of the Tibetan Plateau and its east side.The KdV equation is derived from nonlinear inertial gravitational wave equation using the method of phase plane analysis and two types of solitary wave solutions with weather meanings are obtained by a direct integration method.We specially analyze the characteristics of singular solitary wave which has the association with the vortex over the Tibetan Plateau,and then discuss the effects of the plateau diabatic heating and the atmospheric stability on the origin,the movement,the vertical motion,the horizontal divergence,and the structure of warm core of the plateau vortex.It is proved in theory that the plateau vortex has the features of vortex eye and warm core similar to the tropical cyclone-like vortices(TCLV).
  • A Mechanism of Mesoscale Heavy Rain System Development in Moisture Baroclinic Atmosphere
  • CHEN Zhong-ming
  • 2007 Vol. 26 (2): 233-239. 
  • Abstract ( ) PDF (504KB) ( )
  • Torrential rain and flood are the main disasters of meteorology in China in summer.So meteorology workers pay close attention to the cause of torrential rain and the forecast of it.Our level of understanding heavy rain process is low because of the complex nature of heavy rainfall formation.It is imperative to enhance research on the formational and development mechanism of the mesoscale vortex systems.According to divergence and vorticity fields evolution restricted by not only dynamic fields but also thermodynamic fields in adiabatic and non-frictional atmosphere,new typical divergence and vorticity equations are obtained by means of thermodynamic equation led into traditional divergence and vorticity equations.Dynamic property of low-level convergence and cyclone vorticity growth is analyzed on basis of new equations.Dynamic mechanism of mesoscale heavy rain system development in moisture baroclinic atmosphere is revealed.The results show that the reactions and overlap between low-level warm(moisture) disturbance from the south and high-level cold(dry) air mass from the north lead to quickly development of mesoscale heavy rain systems in instable stratified atmosphere. A typical case is that the low-level jet in combination with high-level trough often leads to the formation and development of meso-scale heavy rain systems in summer.
  • Effects of Surface Heat Flux on Surface Air Temperature Variation Trend in East Asia Region from Spring to Summer
  • YAO Su-xiang;ZHANG Yao-cun
  • 2007 Vol. 26 (2): 240-248. 
  • Abstract ( ) PDF (1556KB) ( )
  • The features of the Surface Air Temperature Variation trend(SATV) and the effect of surface heat flux on SATV in East Asia from spring to summer are analyzed in this paper,using the NCEP/NCAR reanalysis data from 1948 to 2003.The results indicate that there are notable differences of SATV from south to north because of the latitudinal difference of the solar radiation,and from west to east due to the land sea thermal contrast.The analysis of SATV index shows that from April to May,the intermonthly SATV is evident in the Indo-China Peninsula and the eastern part of the Tibetan Plateau,while from June to July,the SATV in the Indian Peninsula and the western part of the Tibetan Plateau becomes notable.This phenomenon means that the maximal SATV first appears to the east of 90°E,and then emerges in the west.Correlation analysis demonstrates that there exists a close relationship between SATV and surface heat flux variation in the areas where SATV is more visible,such as Indo-China Peninsula,Indian Peninsula.From April to June,the correlation coefficients between SATV and sensible and radiation heat flux variation are obviously positive in the Indo-China Peninsula,and negative between SATV and latent heat flux.From May to July,sensible and latent heat fluxes have significant effects on SATV in the Indian Peninsula,and the radiation flux plays an important role in the western part of the Tibetan Plateau.Over the ocean,the close relationship exists between SATV and sensible heat flux and latent heat flux variation in Kuroshio area.Further research on the correlation between surface heat flux and temperature in different altitudes over two peninsulas and the Tibetan Plateau shows that the surface diabatic heating has an evident effect on the air temperature variation in low levels,and it is different from the relationship between surface heating and air temperature variation in high level.
  • Change Characteristic and Correlation of OLR and Precipitation over East Qinghai-Xizang Plateau in Rainy Season
  • LIU Miao;LI Dong-liang
  • 2007 Vol. 26 (2): 249-256. 
  • Abstract ( ) PDF (1183KB) ( )
  • Based on the NOAA monthly mean gridded OLR data with the grid size of 2.5°×2.5° Lat./Lon.over Qinghai-Xizang Plateau from June 1974 to December 2003(missed from March to December of 1978) and the observed monthly rainfall data at 84 stations over the Plateau at the same period,the change features of time and space of their anomaly have been analyzed by EOF method.It is found that:(1) In rainy season(May~September),the locations of both the low center of OLR and the rainy center are approximately superposition;OLR could be response to the situation of precipitation.(2) From June 1974 to December 2003,the precipitation over the Plateau in rainy season is gradually increasing,but OLR is gradually decreasing.There are close inverse correlation between the OLR and precipitation in the time variation.(3) In rainy season,OLR in southeast Plateau is lower;in northwest,hight.Then the precipitation distribution is just the opposite,precipitation in southeast Plateau is more than that in northwest.The location of the low center of OLR and the location the high center of precipitation are approximately corresponding.(4) The changing direction of characteristic vectors of OLR and precipitation is opposite too,and we unify the change of principal component(PC1~PC3),we could obtain that the precipitation in North Plateau reduce and increases in South.But OLR is opposite.It increases in North Plateau and reduce in South.The tendency of the changing direction of characteristic vectors of OLR and precipitation is opposite what is further revelation over Plateau OLR in rainy season and precipitation are inverse correlation.
  • Landuse Patterns of Heihe River Basin and Its Impact Modeling
  • LIU Wei;GAO Yan-hong;LI Hai-ying;RAN You-hua;CHENG Guo-dong;FEI Chen
  • 2007 Vol. 26 (2): 278-285. 
  • Abstract ( ) PDF (812KB) ( )
  • Based on the 1：100000 landcover map of the Heihe river basin in 2000 and the global 25-type classification systems,the 30 s landcover map of the Heihe river basin(Heihe data for short) was brought out combined with the 1：1000000 vegetation classification map,which is the same classification format with global 30 s landcover data(USGS data for short) brought forward by Loveland at the beginning of 1990's.By the comparison between these two datasets,it is found that the landcover type difference mainly locates at the middle reache of the baisn,where the landcover type is most grassland in the global data and irrigated cropland/pasture in the Heihe data.These two landcover data sets were implied into atmospheric model to investigate the influence of different landcover data on environmental element modeling.The following results were concluded.Except for wind field,shortwave radiation and ground heat flux,simulated environmental element distribution patterns are higher related to albedo,emmisivity pattern than the roughness and resistance.The different landcover types in the middle reache lead to the local air temperature increase.Urban effect is included maybe.Either from the spatial correlation coefficient between environmental element pattern itself and landcover pattern or from air temperature changes near surface because of land cover alteration at meteorology stations,simulated air temperature near surface was affected by emmisivity greatly than the other parameters.There are not much observation to estimate emmisivity,one could get more accurate air temperature simulation results by raise emmisivity.Absolutely,it needs more observation and simulation study to validate.
  • Characteristics of Radiation Budget in Intercropping Field in the Middle Reach of Heihe River Basin
  • WU Jin-kui;DING Yong-jian;WEI Zhi;WANG Gen-xu
  • 2007 Vol. 26 (2): 286-292. 
  • Abstract ( ) PDF (780KB) ( )
  • Based on the experiments conducting in an intercropping field in Zhangye Oasis in the middle reach of Heihe River basin in 2003-2004,the characteristics of radiation budget are analyzed.The results show that the annual mean solar radiation Rs is 192.9 W·m-2·d-1.It is lower in winter and spring, and higher in the other two seasons.Reflecting radiation Rr,which has an annual mean value of 37.8 W·m-2·d-1,varies with the vegetation of crops.When the soil is bare,it is higher.While the soil is covered with crops,it is getting lower.The surface albedo,with a mean value of 0.22,has a same trend with Rr.the annual mean values of upward longwave radiation and downward longwave radiation are 353.3 W·m-2·d-1and 278.0 W·m-2·d-1,respectively.They both have a minimum value in January,increase in February and reach the maximum value in July.The surface effective radiation(Rlu-Rld)is about 70 W·m-2·d-1 from May to September.It rapidly rises in the end of spring and the beginning of summer.The net radiation,with an annual mean 79.8 W·m-2,takes up 35% of Rs.In the main growing stages(from May to September),daily mean Rn is 141 W·m-2.In the months of no crops growing(i.e.,January,February,November and December),it is 8 W·m-2·d-1.The annual total of photosynthetically active radiation(PAR) is 2580.9 MJ·m-2 with a daily mean 82.7 W·m-2.It takes up 42.2% of Rs.PAR varies in the year.The daily mean varies between 40~50 W·m-2 without growing months.In March,it rapidly increases and reaches 78 W·m-2.In July,PAR gets the maximum value of 128 W·m-2
  • Analyses on Surface Sensible Heat Characteristics over Hexi Region
  • LI Zhen-chao;WEI Zhi-gang;Lü Shi-hua;FU Rui
  • 2007 Vol. 26 (2): 293-299. 
  • Abstract ( ) PDF (1055KB) ( )
  • Using the routine meteorological data of thirteen meteorological stations in Hexi region and Jinta experiment data in 2004,the change characteristics of surface sensible heat in Hexi region are statisticed and analyzed.The main results have been shown as follows: The maximum value of sensible heat transferring at the thirteen stations in Hexi generally appears in May and June,and the minimum value,in December.The sensible heat transferring at most of stations of Hexi in spring,appear an obvious rising tendency,while in summer,it is dropping.It is a common phenomenon that the data suddenly increases from March to April,moreover the sensible heat flux from majority stations have a process that suddenly decrease from October to November.The period oscillations of sensible flux in Hexi are main 3 years.The significances of these period oscillations are not the same in different regions and periods. In the center area of Hexi,sensible heat is in good correlativity with wind velocity and soil-air temperature difference in spring.In the west area of Hexi,correlativity of sensible heat with wind velocity in spring is well.While in the east area of Hexi,correlativity of sensible heat with soil-air temperature difference in spring is well.
  • Study on Model Terrain Parameter Modification Using Cloud-Derived Wind in the MM5 Adjoint-Model Assimilation System
  • HE Fen;SHEN Tong-Li;HE Zhe;LAI Shao-Jun;MA Jing-Xian
  • 2007 Vol. 26 (2): 300-308. 
  • Abstract ( ) PDF (1969KB) ( )
  • Model terrain adjustment is carried out by means of the Pennsylvania State University(PSU)/National Center for Atmospheric Research(NCAR) non-hydrostatic mesoscale model MM5 with its adjoint-model assimilation system(AMAS).Two different initially-estimated terrains are given and modified by use of the AMAS,which indicates much the same assimilation for the terrains differing from each other.For the terrain parameter of identical errors,the adjiont model with inclusion of non-conventional cloud-derived wind will even more effectively improve the AMAS modification to the terrain parameter.As shown in the subsequent sensitivity runs,500 and 200 hPa wind fields are of more importance to the adjustment of orographic terrains,respectively,to the east and west of 110°E.To verify the effects of modified terrain on NWP,experiment is conducted on a large-scale rainstorm over the Changjiang-Huai basins on 23~24 July 2002,indicating that the terrain modified especially the one adjusted by cloud-derived wind used as the MM5 surface feature will improve prediction precision.TS(threat score) of 50 mm rainfall(non-modification compared to modification by cloud-derived winds) is found to go from 0.074 to 0.077,increasing by 4%,with other meteorological element fields accordingly ameliorated.These results show that the adjusted terrain goes more satisfactorily with observations.It is worth noting that to obtain reliable topographic modification needs cloud-derived wind from multiple operations to get rid of errors in observations.We now come to the conclusion that the application of AMAS to the improvement of NWP model parameters is found to be a new feasible approach.
  • Causes and Comparison of the Droughts of North China in 1980's and 1990's
  • RONG Yan-shu;YU Jin-hua;DUAN Li-yao
  • 2007 Vol. 26 (2): 319-325. 
  • Abstract ( ) PDF (925KB) ( )
  • The drought year frequency is more and more in North China, under the global warming,there are almost half of years in the 1980's and 1990's to drought. From drought conditions,the spatial patterns and intensities of drought,the droughts in North China between 1980's and 1990's are compared.Some possible causes linked to the global climatic warming and to atmospheric general circulation over the Northern Hemisphere were discussed.The results indicated that not only the characteristics of drought and spatial patterns of precipitation anomaly in the 1990's and in the 1980's were different,but the intensity of the 1990's were higher than the 1980's,that the responses of droughts of the 1990's coincidence with the global climatic warming were higher than the 1980's,and that atmospheric general circulation of 500 hPa for the drought years in the 1980's and 1990's existed differently,in which Arctic Oscillation(AO) produced many of the droughts in the 1980's,but in the 1990's,the droughts might have been linked to EU and PNA teleconnection.The Siberian High Index(Ih) was defined,the Ih of the 1990's were higher than the 1980's,and related significantly with the precipitation,so that spring and summer Ih can be as a forecasting index for precipitation in North China.
  • Simulation of Local Urban Planning to the Structure of Urban Boundary Layer
  • HE Xiao-feng;JIANG Wei-mei;GUO Wen-li;WANG Xiao-yun
  • 2007 Vol. 26 (2): 363-372. 
  • Abstract ( ) PDF (1372KB) ( )
  • We simulate meteorological environment of a little town(20 km×18.6 km) using the Urban Boundary Layer Model developed by Nanjing University.The model s horizontal grid space is very fine(100 m×100 m).The simulated results show that the most distinction about PBL structure between big city and little town is that the difference of temperature between city and rural is very small about 0.1~0.2℃,in another word,there is no heat island in little town.There are greater differences between The TKE profiles and potential temperature profiles of urban area and crop area and residence area in daytime while in nighttime there is about no difference.We design four sensible tests changing surface type of certain area in little town,such as building airport or residence area or artificial lake or high buildings in tested area.Results show that: The local urban planning affects urban meteorological environment in daytime while slightly in nighttime.When tested area is changed high buildings or residence zone,there are phenomena of temperature arising and wind speed decreasing in the city sitting in tested area s downstream,When tested area is built artificial lake or airport,there are contrary phenomena in the city sitting in tested area s downstream.In these four sensitive tests,man-made lake has great effects on downstream city while others have small effects.Through these analysis,we offer the department of urban planning some advantageous advise:(1)It's not well-chosen to develop high buildings or residence area in the city's upstream.(2)In order to enhance city airing,building artificial lake at the city's upstream is a very good idea.But these conclusions are not general,and it's very necessary to further research relationship between tract of teated area and affected degree in downstream.
  • Characteristic and Formation Cause of Drought and Flood in Yunnan Province Rainy Season
  • DUAN Chang-chun;ZHU Yong;YOU Wei-hong
  • 2007 Vol. 26 (2): 402-408. 
  • Abstract ( ) PDF (1047KB) ( )
  • The grades of drought and flood,the distribution characteristics of precipitation and the temporal and spatial distribution characteristics of drought and flood in the rainy seasons(from May to October) of Yunnan Province were studied with the methods of Z index and empirical orthogonal function(EOF and REOF).The results indicate that the precipitation of rainy season in Yunnan Province is consistent,and after 1980's,the drought and flood frequently take place in some regions of the west-and east-parts of Yunnan Province.And the utilizing composition analysis,the charactistics of 500 hPa heights and 850 hPa wind anomalies in the Northern Hemisphere,convergence and divergence on the levels of 200 hPa and 925 hPa were studied.The results show that stronger Iran-Qingzang highs and northward location of subtropical high and Indian low,and stronger upward stream over tropical areas,weaker Yunnan and northward location of Yunnan height,are likely to lead to more rain in Yunnan Province in the rainy seasons.There is a teleconnection relation between Yunnan summer rainfall and convective activities happening in tropical areas in spring and summer accomplished by the teleconnection wavetrain.During the flood years in Yunnan,the convective activities happening in the Bay of Bengal and tropical west Pacific and Walker circulation are much stronger than that during the drought years,but the convective activities happening in tropical east Pacific are weaker than those during the drought years.

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