Plateau Meteorology

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24 December 1999, Volume 18 Issue 4   
  • INTERDECADAL VARIATIONS OF PRECIPITATIONS IN VARIOUSMONTHS OF SUMMER IN NORTH CHINA
  • LU Ri-yu
  • 1999 Vol. 18 (4): 510-519. 
  • Abstract ( ) PDF (597KB) ( )
  • The features of interdecadal variations of precipitations in various months of summer in North China are analyzed by using the observed data of summer monthly precipitations from 1951 to 1996 at 17 stations in North China.It is shown that the precipitations in each month have different features.In North China,the precipitation in June was the smallest and does not exhibit a decreasing trend in the interdecadal variations,but the precipitation in July was the largest with a large interdecadal variability and reached its minimum in the 1980's.There are a linear decreasing trend and a quasi-ten years oscillation in the interdecadal variations of precipitations in August.Both precipitations in July and August in North China remarkably decreased in the middle 1960's and at the end of 1970's.According to the different features of precipitations in July and August,the atmospheric circulation anomalies in the middle and high latitudes associated with the interdecadal variaitons of droughts and floods in North China are examined by using composite method.The analyzed results suggested that the interdecadal variations of precipitation in July not only were associated with the atmospheric circulation anomalies in July,but also had an important impact on the atmospheric circulation anomalies in August.In the relationship between the variations of summer precipitation in North China and the atmospheric circulation anomalies in the middle and high latitudes,the impact of the former on the latter may be more dominant.
  • CLIMATE CHARACTERISTICS OF WATER RESOURCES IN NORTH CHINA
  • MA Xiao-bo
  • 1999 Vol. 18 (4): 520-524. 
  • Abstract ( ) PDF (204KB) ( )
  • The climate characteristics of water resources in North China are analyzed by EOF method and Gaoqiao Equation using monthly precipitation and monthly mean air temperature data of 27 stations in North China from 1951~1995.We have obtained some preliminary results:(1) Under the background of climate warning,precipitation in North China had decreased tendency during the period of 1951~1995,especially since 1965,the precipitation decreased continuously.The maximum decreasing of precipication occurs in summer.(2) Land evaporation increases all over North China in above period,the maximum center is located at central part of it,Jinan and Liyi,Shandong province.(3) Water resources in North China were decreased from 1951 to 1998,but the decreases of water resources were very quickly after 1965.There are 3 distribution types:i.e.whole district is the same,north and south part difference,and east and west part difference.Water resources are mainly influenced by precipitation.The variations are simple in winter and spring,but complex,in summer.
  • THE ONSET OF THE SOUTH CHINA SEA SUMMER MONSOON AND LOW-FREQUENCY CHANGE OF SEA SURFACE TEMPERATURE AND CONVECTIVE ACTIVITIES IN THE ATMOSPHERE
  • PENG Chu-ming;HE You-hai;GUAN Cui-hua;LIN Xi-gui
  • 1999 Vol. 18 (4): 603-612. 
  • Abstract ( ) PDF (459KB) ( )
  • The onset time of South China Sea Summer Monsoon (SCSSM) is defined by the changes in phase of the filtered 30~60 day mode for anomaly of temperature of block body at cloud top (TBB) and sea surface temperature (SST) at Xisha meteorological station,and the process of change of TBB and SST associated with SCSSM onset time and strength is analysed.The main results are as follows.
    The mean onset time of SCSSM is the fourth pentad of May for the period 1980 to 1991.There exists a significant interannual variation in the onset time and strength of SCSSM and the states of ocean and atmosphere during the onset period of SCSSM are closely related to low-frequency oscillation of the atmosphere.In the years of early onset of SCSSM (the second pentad of May) the convective activities are deeper and SST decreases quickly after the onset,and vice versa in the years of late onset of SCSSM (the first pentad of June).The strength of SCSSM is also related to the phase of 30~60 day oscillation of TBB arrived over SCS during the onset period of SCSSM.High or low SST of SCS during the prior winter and early spring and the time of the deep convective occurred over the Indo-China from third ten days of April to May are indicators of later or early onset of SCSSM.Prediction of the onset of 1998'SCSSM based on SST during the prior period in SCS is consistent with the real fact.
  • A SIMPLIFIED MODEL FOR EVALUATION OF WATER RESOURCE
  • ZHOU Jia-bin;ZHANG Hai-fu
  • 1999 Vol. 18 (4): 618-624. 
  • Abstract ( ) PDF (256KB) ( )
  • The present situation of ground surface water of main river systems,in North China,such as Luanhe river,Haihe river,and middle and lower reaches of Yellow River,is simply described.The inter-decade statistical analysis of yearly averaged runoff in some important runoff control stations is made.The important result is,as rainfall rises and falls as decade passes,runoff undulates just as rainfall.The difference is that the runoff has an obvious decreasing tendency decade by decade since 1970's.Based on the observed runoff and precipitation and computed evaporation,a simplified model for evaluation of water resource is developed.The model is represented as follows
    P= R+ a E c+ U,
    where P is observed precipitation, R is runoff, E c is computed evaporation, U is water stored in soil, αis a correction factor for computed evaporatin.
    By using the model the water resource in North China is evaluated.It is indicated that the plenty and deficiency of runoff is basically determined by precipitation though runoff is influenced largely by anthropogenic activities.Since 1980s,the relationship among different components of water source has changed greatly because of increase of anthropogenic activities.
    Water resource for high flow years and low flow years is also discussed.
  • NUMERICAL SIMULATION STUDY FOR THE EFFECT OF GROUND VEGETATION TYPE ON NORTH CHINA SUMMER PRECIPITATION
  • FAN Guang-zhou;Lü Shi-hua
  • 1999 Vol. 18 (4): 649-658. 
  • Abstract ( ) PDF (404KB) ( )
  • We have five numerical experiments to study the effect of vegetation type on North China summer precipitation.The results show,when the deciduous forest over North China is replaced by grasslands or desert,the area mean summer precipitation will be reduced.But it will be increased when replacing the grasslands by desert over northwest part of North China and it is caused by the increasing of the precipitation over northern part of North China.To above-mentioned three experiments,the changing of precipitation is mainly caused by the changing of cumulus convective precipitation over southern part of North China,but mainly caused by large scale precipitation changing over northern part of North China.When the deciduous forest is replace by farmland,the summer precipitation over North China will be increased and it is mainly caused by the changing of large scale precipitation.The further analysis of the physical mechanism tells us that the effect of the ground vegetation type on North China summer precipitation like this:first changing the ground vegetation will change the surface roughness and surface albedo,then it will change the variation of the energy exchanging between ground and atmosphere,again then it changes the local circulation.
  • THE CHARACTERISTICS OF RAINFALL AND ITS TENDENCY ESTIMATE OVER NORTH CHINA
  • YANG Guang-ji
  • 1999 Vol. 18 (4): 668-676. 
  • Abstract ( ) PDF (359KB) ( )
  • North China is situated in arid and semiarid regions.Climate rainfall is not only one of main sources of water resources,but also one of major factors affecting periodic change of water resources over this region.Change trend of annual rainfall anomalies is similar in North China,and northern,southern and middle part of North China.Years of positive and negative anomalies occurr continualy that are not more than 4 years and 6 years respectively in four regions mentioned above.
    The positive correlation between summer rainfall anomalies over North China and most of India,and negative correlation between summer rainfall anomalies of two regions mentioned above and winter rainfall anomalies of most of Australia are observed.Occurring frequency of this teleconnection mentioned above is 63% over North China,most of India and Australia.The frequency of same sign of summer rainfall anomalies is 80% between North China and its adjacent regions and most of India.The frequency of opposite sign of rainfall anomalies is 73% between North China and its adjacent regions and most of Australia during June to August.
    Rainfall anomaly series with quasi -3,5,6,7 years oscillation period are composed over North China,percentage of same sign between composed and original rainfall anomaly series is 76%.Rainfall anomaly series with quasi -3,4,8 years oscillation period are also composed over northern part of North China,The percentage of same sign between composed and original rainfall anomaly series is 92%.
    Finally,the sign of annual rainfall anomalies is estimated by wave-composite method over North China during 1995 to 2004 years.The results indicate that annual rainfall anomalies of 1995 1996,1999,2002 and 2003 years are positive,annual rainfall anomalies of 1997,1998,2000,2001 and 2004 years are negative.

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