Plateau Meteorology

24 December 1987, Volume 6 Issue 4

NUMERICAL SIMULATION OF OROGRAPHIC EFFECT OF TIBETAN PLATEAU ON THE MEAN CIRCULATION IN SOUTHEAST ASIA IN OCTOBER
Luo Siwei;Li Weijing;Jiang Shizhong
1987 Vol. 6 (4): 289-296.
Abstract ( ) PDF (544KB) ( )
In this paper we use a five-layer preliminary equation model with P-δ combined coordinate system to study the effect of Tibetan Plateau on the formation of monthly mean circulation in October through simulations. It point out that the high pressure center at sea level over Republic of Mongolia in October is not true and may be resulted from the reduction of surface pressure to sea level. The anticyclone in lower layer over China plain near Tibetan Plateau is merely caused by the dynamic effect of the plateau. The large rainfall belt from Assam to Southwest China depends fully on the effect of the Plateau.

RELATIONS BETWEEN ACOUSTIC RADAR ECHOS AND SYNOPTIC SYSTEMS AT LANZHOU IN WINTER
Hou Yiru;Chen Changhe;Hong Bo
1987 Vol. 6 (4): 297-305.
Abstract ( ) PDF (2017KB) ( )
In this paper, some morphology features of the acoustic radar echos at Lanzhou during the period 15-24 November of 1984 and relations between the echos and the synoptic systems have been analysed. The main results indicate that in boundary layer the stable layers observed by acoustic radar echos correspond fairly to synoptic systems. Lower level inversion echos are prevailing when there is no invasion of cold air. Due to the influence of Tibet Plateau orography, there are remarkable diurnal variations of both flow and divergence in boundary layer on North-east side of the Plateau. During the night time there is a quasi-stationary divergent layer at the heights of from 300 to 600m above the ground. Therefore the subsidence warming caused by it is an important reason of formation of the lower level inversion. The lover level inversion echos are always dissipated after cold front passes through the area. In the rear of cold front, namely in front of cold high, it is also found that there exist some echos analogous to convective cell or fiber-like caused by strong shear of wind.

SEPARATE WAVE STRUCTURE OF STEADY CIRCULATION IN UPPER HALF OF TROPOSPHERE AND LOWER HALF OF STRATOSPHERE OF NORTHER HEMISPHERE AND SOME ASPECTS OF ITS SEASON VARIATION
Ge Ling;Pan Deyu;Guo Hua;Zhao Hongxu
1987 Vol. 6 (4): 306-316.
Abstract ( ) PDF (665KB) ( )
In this paper using about 25 year data of geopotential height fields in upper half of troposphere and lower half of stratosphere of Norther Hemisphere, the spacial structures of separate wave of mean steady circulation from middle troposphere to middle stratosphere were studied and some aspects of their season variations were also discussed.

A PRELIMINARY ANALYSIS OF INTRACLOUD LIGHTNING FLASHES AND LOWER POSITIVE CHARGE OF THUNDERCLOUDS
Shao Xuanmin;Liu Xinsheng
1987 Vol. 6 (4): 317-325.
Abstract ( ) PDF (666KB) ( )
In the summer of 1986,we observed simutaneously at three stations the electric field, thunder and field-change produced by lightning flashes nearby Zhongchuan Airport, Lanzhou. In this paper seven intra-cloud flashes of two storms on August 3 and 4 are analysed quantita-tivey. The results show that only one flash was a discharge between the main negative and the upper positive charge region. The other flashes were all discharges between the main negative charge region and the extensive lower positive charge region. The centers and the dipole moments destroyed by these flashes were at the altitude 3.8-6km(7.6-13.5℃) and 18-48 Ckm respectively.These phenomena of intracloud discharges in the lower part of thunderclouds have rarely been reported in the literature.

THE GEOGRAPHIC DISTRIBUTION OF THE GLOBAL RADIATION AND THE CHARACTERISTICS OF ITS SEASONAL VARIATION OVER THE QINGHAI-XIZANG PLATEAU
Shen Zhibao
1987 Vol. 6 (4): 326-334.
Abstract ( ) PDF (632KB) ( )
Based on the relationships between the global radiation and the percentage of sunshine or the cloud cover estimated from satellite cloud pictures, the empirical formulas for calculating global radiation are established, the monthly and decade mean charts of the global radiation over the Qinghai-Xizang Plateau are drawn for the year from August 1982 to July 1983. As a result of the influence of the sea level elevation, the plateau has its inherent high value system of the global radiation. It can be divided two basic patterns in the year, i. e. the rainy season pattern from July-September and the dry season pattern from October-June. The transition between the two basic patterns is similar to that of the natural synoptic seasons over the plateau.

ESTIMATION OF THE MEAN CLOUD-AMOUNT AND THE CHARACTERISTICS OF ITS DISTRIBUTION OVER QINGHAI-XIZANG PLATEAU
Shen Zhibao;Chen Youyu
1987 Vol. 6 (4): 335-344.
Abstract ( ) PDF (702KB) ( )
It the paper, using the cloudiness data for total clouds ten times a day from 4 stations of surface heat source experiment over Qinghai-Xizang Plateau during the period of the whole year from August 1982 through July 1983,the diurnal variations of the cloudiness for total clouds are analysed, the relationships between the total cloudiness averaged over whole day, daytime, and four weather observation times are discussed,and the methods estimated the formers from the latter are presented. Based on above results the mean cloud cover at 2°×2° grid points Lat./long. estimated from NOAA-7 satellite image in the same period are corrected to obtain the decade and monthly mean charts of distribution for total cloud over the plateau. The spatial distributions of the monthly mean total clouds over the plateau can be divided into two basic patterns in the year-winter and summer pattern, which are caused by the dynamic and thermal effects of the plateau under the different atmospheric circulation in the different seasons. The spatial distribution patterns of the mothly mean total cloudiness in different year may be approximately same, but the inter-annual variation of the cloud-amount can be found.

THE RELATIONSHIP BETWEEN THE ORIENTATION OF AN ICE CRYSTAL AND ITS INTERFERENCE COLOURS BETWEEN TWO POLARIZERS
Ma Wei;Yang Songxi
1987 Vol. 6 (4): 345-353.
Abstract ( ) PDF (605KB) ( )
The interference colours of an ice crystal within a slice of hailstone placed between two crossed polarizers depending on the orientation of the Caxis of the ice crystal have been inverstigated from the view of crystal optics. A simple method is recommended, with which we can judge the angle between the C-axis of the ice crystal and the normal of the hailstone slice from the photograph of the interference colours.It is convenient to the analysis of the ice crystal growth within hailstone.