Plateau Meteorology

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28 April 2003, Volume 22 Issue 2   
  • Relative Vertical Acceleration and the Mesoscale Atmospheric Motion Equations
  • CHENG Lin-sheng;FENG Wu-hu
  • 2003 Vol. 22 (2): 97-103. 
  • Abstract ( ) PDF (312KB) ( )
  • It is not precise and unreasonable to describe for the motion of the mesoscale systems with severe convective character adopting directly the motion equations in pressure( p) and sigma( σ) coordinates included assumption of quasi-hydrostatic approximation.Therefore the more precise no n-hydrostatic mesoscale atmospheric motion equations must be developed.In this paper,the non-hydrostatic atmospheric motion equations in( x, y, ζ , t)(abbreviation ζ) coordinates has been derived through inducting a relative vertical acceleration delta( δ) and a generalized ζ coordinates.In the equations,the vertical motion equation is the non-hydrostatic;the relative vertical acceleration delta( δ) is predictable;the vertical acceleration may get directly from δ;the δhas directly effect on the fields of the velocity,geopotential height and mass,while the δ also has indirectly effect on the temperature field.It is quite easy to get the non-hydrostat ic motion equations in the p-or the σ-as well as other vertical coordinates through the use of the non-hydrostatic motion equations in the ζ coordinates.The motion equations in p-and σ-coordinates included assumption of quasi-hydrostatic approximation are simplifying results of corresponding to the equations when the δ=0.Because this effect of the δ did not considered in the atmospheric motion equations in the coordinates included assumption of quasi-hy drostatic approximation,therefore,the error must be generated for predicting a few fields.This error accumulation must be increased with time increasing of numerical integration.Obviously,the contribution of the δ has been considered in the developed new non-hydrostatic atmospheric motion equations,the errors have been removed in the equations.Therefore the equations are more precise and also suitable to describe and predict the motion of the mesoscale systems.
  • Study on Interdecadal Change of Heihe Runoff and Qilian Mountain's Climate
  • LI Dong-liang;FENG Jian-ying;CHEN Lei;LIU Hong-lan;ZHANG Jie
  • 2003 Vol. 22 (2): 104-110. 
  • Abstract ( ) PDF (1674KB) ( )
  • The interdecadal variety have been analyzed by using Yingluoxia hydrology station runoff data(1944~2000) of Heihe upper stream with the average monthly standardized precipitation and air temperature data of 7 weather observation stations located on the Qilian mountain area from 2240 to 3361 m high place.The results show that the runoff in 1980's is the biggest 10 years in past 57 years,1990's tend to decrease,but primarily appearing from summer to autumn,and yet still keeping the high runoff from winter to spring.The Qilian Mountain's climate evolution significantly exists the season change,the interannual change and interdecadal variety.Since 1970's,besides the summer with precipitation increasing,all the three quarters of autumn,winter and spring have obviously change to drought,and particularly for autumn and winter;Since 1980's,the climate is warming obviously in Qilian mountain area,air temperature of each season remarkably go up,particularly for the autumn and winter,this may be the main reason for Heihe river's runoff increasing and Qilian mountain's snow line rising.The synthesized analysis shows that the increase of Heihe river's runoff is decided by two aspects:The first is summer precipitation increasing,second is the obviously climate warming in the winter.
  • Impact of Strong/Weak Plateau Summer Monsoon on South Asia High Activity
  • MA Zhen-feng
  • 2003 Vol. 22 (2): 143-146. 
  • Abstract ( ) PDF (198KB) ( )
  • Influence of the strong/weak summer monsoon over Qinghai-Xizang on the activity of 100 hPa South Asia high and drough/flood Three Gorge Reservior District were analyzed.It is found that there are good relationships between the intensity of 100 hPa South Asia high over Qinghai-Xizang Plateau and to its eastern area and the intensity of Plateau monsoon,its center is far northward and eastward(southward and westward) when the Plateau summer monsoon year is the strong(weak) year.In strong Plateau monsoon year,ridge axis of South Asia high jump to the north in June which is earlier 1 pentad than normal year,and withdraw to south in August which is later 1 or 2 pentads and nearly vice versa.Meanwhile,it is obtained that precipitition in Three Gorge Reservior District is increased from May to June,and one is decreased from July to August with ridge axis of South Asia high moving to the north when intensity of Plateau summer monsoon is strong.Otherwise,preceding precipitation in Three Gorge Reservior District is decreased,and following precipitation is more increased when intensity of summer monsoon over Qinghai-Xizang Plateau is weak.In addition,there are opposite correlation between the winter Plateau monsoon index and summer South Asia high and precipitation in Three Gorge Reservior District.
  • Variation of the Snow and Frozen Soil over Qinghai-Xizang Plateau in the Late Twentieth Century and Their Relations to Climatic Change
  • GAO Rong;WEI Zhi-gang;DONG Wen-jie;WANG Cheng-hai;ZHONG Hai-ling
  • 2003 Vol. 22 (2): 191-196. 
  • Abstract ( ) PDF (1104KB) ( )
  • By using the observation data of 72 weather stations from 1981 to 1999 in Qinghai and Xizang,the variation of winter-spring(from last October to this May) snow and frozen soil day and their relations to climatic change over Qinghai-Xizang Plateau are analyzed.The results show that the the day number of winter-spring snow is increasing in 1980's,but it is decreasing in 1990's.The day number of frozen soil is decreasing(from 1981 to 1999).The distribution of the mean number of winter-spring snow day and frozen soil day are different.The mean number of winter-spring snow day from 1981 to 1999 is decreasing from south to north;The mean number of frozen soil days from 1981 to 1999 is decreasing from center to around.The winter-spring snow and frozen soil days show the significant variations in 2~6-yr period,the temperature has the oscillation periods of quasi 3-yr,the precipitation of Xizang has the oscillations periods of quasi 8-yr and quasi 3-yr,the precipitation of Qinghai has the oscillation periods of 3~5-yr,the oscillation periods of the winter-spring snow day,frozen soil day and winter-spring temperature of Plateau have the quickening trend.The winter-spring snow day is negative correlation to the temperature and positive correlation to the precipitation.The correlations between the frozen soil day and the winter-spring temperature and the correlations between the frozen soil day and the precipitation are both negetive.
  • Diagnostic Analysis of the Helicity and Kinetic Energy for a Low Vortex of "98.7" Extraordinary Heavy Rainfall
  • HOU Run-qin;CHENG Lin-sheng;FENG Wu-hu
  • 2003 Vol. 22 (2): 202-208. 
  • Abstract ( ) PDF (1783KB) ( )
  • The "98.7" extraordinary heavy rainfall event was in close relationship with the intensive development of a low vortex with shear line on 700 hPa and the abundant moisture as well as strong vertical motion.The diagnostic results of the helicity revealed that there was a pair of close neighboring helicity bands with opposite sigh,which corresponding to both the heavy rainfall area and the low vortex with shear line,their vertical structure was a pair of intercompanying columns of helicity with opposite sigh.The order of magnitudeof the helicity and its each component were the same,which showed the horizontal shear of vertical velocity and the vertical shear of horizontal velocity as well as the horizontal shear of horizontal velocity were possessed of the same contribution to the helicity,which also mean that both intensive vertical motion and the lower level jet were very important to the genesis and development of the heavy rainfall.The diagnostic results of the kinetic energy showed that the area of the kinetic energy with high value was well correspondingto that of both the rainfall band and the low vortex with shear line,the centers of the high energy on the middle-and lower-level were also the center of heavy precipitation;the 700 hPa with the strongest kinetic energy was also the level of the intensive development of the low vortex with shear line.The area of the high value kinetic energy with strong gradient and the area of the strong helicity was basically consistent,which showed that the high value kinetic energy with strong gradient was possessed of important contribution to the rate of change of helicity and its fluxes.

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