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24 March 1983, Volume 2 Issue 1   
  • 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.
  • 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.