Current Issue

• COMPARATIVE STUDY OF INFLUENCES OF THE TIBETAN PLATEAU AND THE ROCKY MOUNTAINS ON DIURNAL VARIATIONS OF THE METEOROLOGIC FIELDS IN SUMMER Part 1 Temperature and Geopotential Height Fields
• Qian Yongfu;Wang Qianqian
• 1983 Vol. 2 (1): 1-15. 
• Abstract ( ) PDF (1048KB) ( )
• The influences of the Tibetan Plateau and the Rocky Mountains on diurnal variations of the meteorological fields in July are investigated by the use of a five-layer global atmospheric general circulation model which includes various diabatic physical processes, especially, diurnal variation of solar radiation and topography. The integration started from the mean June zonally averaged geopotential height and sea level pressure as the basic initial data set is carried out to 6.5 days. The initial time is taken as 18:00 LST at 90E. The simulated results on day 6 are taken as daytime(nighttime) results for the Tibetan plateau(The Rocky Mountains) area, while the simulated results on day 6.5 taken as nighttime(daytime) results for the Tibetan Plateau(The Rocky Mountains) area, and the average from day 5.5 to day 6.5 as daily mean. The simulated results presented here are the first part. Besides a brief introduction of the method for polar region treatment, in this paper we emphatically discuss the results of contrast analysis of influences of the Tibetan Plateau and the Rocky Mountains on diurnal variations of temperature and geopotential height fields in Summer. It is found that in contrast with plain and oceanic regions there are prominent diurnal variations of temperature and geopotential height fields in mountainous regions.With increasing height the amplitudes of diurnal variations of temperature fields exponentially decrease while those of geopotential height fields increase. It is also found that the amplitudes of diurnal variations and the depth of their vertical penetration are proportional to the scale of topography. The maximum diurnal variation of temperature is +9℃ over the Tibetan Plateau and there is still the appearance of diurnal variation of temperature even at 500mb level. For the Rocky Mountains the maximum diurnal variation is +5℃ and it only appears in 700mb. The diurnal variations of geopotential height have similar properties. Further investigation of the nonlinear interaction between diurnal oscillations and synoptic systems is of importance for improvement of short-range forecasting in vicinity of the plateau and mountainous regions.

• COMPARATIVE STUDY OF INFLUENCES OF THE TIBETAN PLATEAU AND THE ROCKY MOUNTAINS ON DIURNAL VARIATIONS OF THE METEOROLOGIC FIELDS IN SUMMER Part 2 Horizontal and Vertical Flow Fields
• Wang Qianqian;Qian Yongfu
• 1983 Vol. 2 (1): 16-29. 
• Abstract ( ) PDF (1013KB) ( )
• This paper is a successive part following the first ^l). Some results of comparative study of influences of the Tibetan Plateau and Rocky Mountains on diurnal variations of the horizontal and vertical flow fields are emphatically investigated by using a five-layer global atmospheric general circulation model. The simulated results show that there are prominent diurnal variations of wind fields in mountainous regions. The amplitudes of diurnal variations in flow fields are proportional to the scales of topography. At daytime the air converges toward the Plateau in lower layer and diverges aloft. In the layers right above the terrains there are prominent mountain -valley winds with a thickness of about 1 km. Because of the presence of mountains the upward motion is more intense at daytime than at nighttime, but the case is reversed over oceans. The seasonal meridional cells which are located to the south of mountains also have prominent diurnal variations.

• NUMERICAL EXPERIMENTS OF THE EFFECTS OF HEAT SOURCES AND OROGRAPHY IN EAST ASIA ON THE SEASONAL CHANGES OF ATMOSPHERIC CIRCULATIONS
• Wang Anyu;Hu Qi;Qin Guangyan
• 1983 Vol. 2 (1): 30-38. 
• Abstract ( ) PDF (623KB) ( )
• As it is well known, the underlying surface conditions and the differential heating caused by those conditions have very important influences on the formations of the atmospheric activity centers, planetary average troughs and ridges and their seasonal changes. In order to investigate those influences weuse a 2-layer primitive equation numerical model with incorporated P-o coordinate system developed originally by Qian et al.(1978) to make a series of simulations with twelve monthly mean heat source distributions of 1979 computed by Yiao et al.(1982). There are two groups of simulations, the first group has no diabatic heating but orography and the second has both diabatic and orographric factors. Each group has twelve experiments for each month. The main conclusions of these experiments are as follows:1.The large-scale disturbances and their annual changes resulted from the effects of large-scale orography are similar to the observed ones. 2.Annual change of large orographic disturbance and westerly zone are related to each other, the strength of westerly is proportional to that of orographic disturbance. The seasonal change of disturbance, however, is mainly related to the position change of westerly jet. 3.The effect of heating over East Asia is mainly to deepen the so -called East Asia main trough and to weaken the orographic ridge north of the Plateau. 4,Heating always increases the maximum speed of westerlies and contributes to seasonal change of jet positions in the troposphere. 5.The heating over the East Asiatic area has an important contribution to the formation of the summer Tibetan anticyclone. It appears that the necessary condition for the Tibetan anticyclone to form is the location of the heating which should be at the interface of westerly and easterly both with very small mean speed in the troposphere.

• A STUDY ON THE PATTERNS OF THE CLOUD COVER BY TIROS-N TELEVISION PICTURES OVER QINGHAI-XIZANG( TIBET ) PLATEAU IN SUMMER 1979
• Zhou Yunhua;Ye Fangde;Zhou Shuxiu;Shan Fuzhi
• 1983 Vol. 2 (1): 39-51. 
• Abstract ( ) PDF (939KB) ( )
• Using TIROS-N infrared television pictures over Qinghai-Xizang plateau twice a day in the period of May-August 1979,we estimate the values of the cloud cover by 2° × 2° grids. Geographical positions were fixed by means of ground characters such as rivers, lakes and ridges of mountains etc.. The patterns of monthly average cloud cover are obtained for daytime and nigh t respectively. It is shown that there are strong ascending motions over the plateau during the daytime in summer. The convergence line is situated along the long axis of the plateau(near 35°N), and the sinking motions of the air are distributed mainly over the north and sputh side of the plateau.

• THE CONDITIONS FOR OCCURRENCE OF EXTENSIVE HAILSTORMS
• Lei Yushun
• 1983 Vol. 2 (1): 52-60. 
• Abstract ( ) PDF (645KB) ( )
• Based on the analyses of 145 cases of extensive hailfall in East-China, we found that extensive hailfall may be divided into cold hailfall and warm hailstorms according to temperature of lower and middle troposphere before occurrences of them.The latter are severe hailstorms.According to the temperature and humidity anomaly in lower or middle troposphere, the warm hailstorms may be divied into cooling-hailstorms and warming-hailstorms.The concept model showing the common conditions of severe extensive hailstorms is given in this paper.The seasonal and local variation of these conditions and its effect on the weather phenomena of hailstorms is also discussed.