Plateau Meteorology

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24 December 1988, Volume 7 Issue 4

INFLUENCE OF PHYSICAL PROCESSES AND RESOLUTION OF MM ₄ ON MESOSCALE SIMULATION OF THE EVOLUTION OF THE SW VORTEX
Cheng Linsheng;Kuo Y. H.
1988 Vol. 7 (4): 289-299.
Abstract ( ) PDF (797KB) ( )
A series of 96-and 72-h numerical experiments were carried out to simulate the evolution of the SW vortex during the period of 11-15 July 1981 through the use of the fourth generation version of PSU/NCAR mesoscale model(MM ⁴). Aim at investigating the influence of the physical Processes and spatial resolution of MM 4 along with PBL parameterization on mesoscale simulation of the formation and development of the SW vortex. The result of 96-h Control Experiment (Scheme I) showed that a version of MM 4 with 10-layer, a horizontal resolution of 160 km and bulk PBL, is capable of simulating better for the development of the SW vortex, however, this version has only the capability of preliminary simulating for the formation of the SW vortex. The physical processes effect mainly on the intensity and less on the location for the evolution of the SW vortex. The removal of latent heat release from Control has a substantial impact on the development of the SW vortex at the later stage. The intensity of the evolution of the SW vortex in the NO Flux Experiment is notable weaker than that in the Control.The Dry Experiment fails to develop the SW vortex during the period of heavy rainfall, and the vortex has slightly faster movement than that in the Control. The NO Friction Experiment showed that the surface friction is not important for the formation of the SW vortex. The enhancement of spatial resolution of MM ₄ and the adoption of high-resolution PBL model are able to improve substantially simulated location of the formation and development of the SW vortex, however, in which case the evolutive intensity of the SW vortex is more intensive than that realistic analysis. The fact showed that it is necessary to perfect further the physical processes of MM ₄, to improve PBL parameterization and to enhance spatial resolution of MM ₄.

NUMERICAL FORECASTING AND SEPARATION OF MESO-SCALE SYSTEM FOR EXTRAORDINARY HEAVY RAIN IN SICHUAN PROVINCE IN JULY 1981
Chen Yuchun;Li Suhua;Gu Hongdao;Qian Zhengan;Song Jie;Wang Tianwu
1988 Vol. 7 (4): 300-311.
Abstract ( ) PDF (848KB) ( )
In this paper, we use a nested grid model under complex topography and ECMWF global data with resolution of 2.5°×2.5° grid size to perform 48 hour forecasting experiment of coarsemesh and fine-mesh for the case of "81.7" heavy rain in Sichuan province. According to the principle of filtering we separate the fields of wind, geopotential height and temperature using optimum high-pass filter. The results show that the model can fairly predict the generation and development of meso-scale system causing this heavy rain. We have also roughly analyzed the dynamic and thermal effects. This model can fairly described the weather of heavy rain. In the other hand, it is also showed that the fine-mesh forecasting has been made further improvement in some aspect. The scale separative method can clearly separate the vortex in the southwest of China and other meso-scale system from large scale foundational field and make us further to recognize the effect of the meso-scale system during the early stage of disturbance on this heavy rain.

THE MEASUREMENTS OF AMPLITUDE SPECTRAL DISTRIBUTION OF LIGHTNING RADIATION FIELD AND THE ESTIMATION OF FIRST RETURN STROKE PARAMETERS
Qie Xiushu;Guo Changming;Zhang Guangshu
1988 Vol. 7 (4): 312-320.
Abstract ( ) PDF (628KB) ( )
Using a fast antenna and four narrow bandwidth receivers, we measured the electric field radiated by lightning, and calculated the spectra distribution from 2kHz to 80 MHz for both ground discharges and cloud discharges. We found the peak spectral amplitudes appear between 4 kHz and 10 kHz for ground discharges, and between 20 kHz to 80 kHz for cloud discharges. From 10 kHz to 2.8 MHz, the spectra amplitudes of ground discharges decrease as 1/f, from 2.8 MHz to 80 MHz decrease as 1/f ^1·4. Beyond 40 kHz, the spectra amplitudes of cloud discharges decrease as 1/f ^1·4. Below 40 kHz, the ground discharge is main lightning radiation source; above 40 kHz, both discharges behave similarly. The peak radiation field of first return stroke, normalized to 50 km, is(15.16±8.38 ) V/m. Below 1 MHz, the total energy radiated by first return stroke is(0.84± 1.57 ) × 10 ⁵J, peak power is(0.85±0.98 )×10 ¹⁰W, peak current is(27.80± 17.12 ) kA, peak current derivation is(109.3 ±91.53) kA/μs. A few unique phenomena were found and explained preliminarily.

THE MICROSTRUCTURE FEATURES OF PRECIPITATION OVER MOUNTAIN AREA ALONG PLATEAU BORDER
Zhang Hongfa;Cai Qiming
1988 Vol. 7 (4): 321-329.
Abstract ( ) PDF (581KB) ( )
Based on the raindrop spectrum data of different type precipitation over plateau border, this paper analysed the frequency, the duration of rainfall and the structure of the precipitations cell. The mean spectra for this region are basically the exponential distribution, though there are some deviation with concave or convex shape for individual events.The raininess mainly depends on the concentration of raindrop, and bears no relation to the maximal diameter. The analysis of Joss spectrum parameter indicated that most of the instant raindrop spectra for this region were convex. This provids a base for determining the Z-R relation of radar precipitation detection.

THE RESULTS AND DISCUSSIONS OF QUANTITATIVELY MEASURING RAINFALL WITH A DIGITAL X-BAND WEATHER RADAR
Xue Zhengang;Cai Qiming;Xu Baoxiang;G. L. Austin
1988 Vol. 7 (4): 330-344.
Abstract ( ) PDF (962KB) ( )
The accuracy of quantitatively measuring rainfall in Lanzhou area with a X-band weather radar has been discussed. The influences on the measurements of microwave attenuation and different precipitation patterns have been analysed. Two methods of correcting radar measurements with raingage data have been discussed.

APPLY THE THERMAL WIND ADJUSTMENT THEOREM TO ANALYSE GENESIS MECHANISM OF THE WARM SOUTH-WEST VORTEX OF CHINA
Lu Jinghua
1988 Vol. 7 (4): 345-356.
Abstract ( ) PDF (680KB) ( )
According to the thermal wind adjustment theorem of non-adiabatic and topographic effect, using σ-p mixed coordinate system genesis mechanism of warm South-west Vortex of China is discussed in this paper. Analysis shows, positive non-thermal wind is an important symbol for the vortex growing up. Warm advection center of lower-middle troposphere, surface sensible heat and warm air of lower troposphere, correlative with negative change pressure of surface pressure p _* or with center of its negative advection, would cause the growing up of positive non-thermal wind vortex. Gradient ▽p _* of surface pressure, spatial distribution ▽ ²p _* of lower-high pressure center, change pressure ∂p _*/∂t and advection(-??? _h·▽p _*) of surface pressure et al. are all correlated with vortical motion directly. The topography effects the characteristic scale L ₀(or radius of change form) of adjustment process of warm wind. Under general condition, the effects of topography and latent heat make L ₀ smaller than L ₀ ^* without considering them, velocity field adjusting toward temperature field, therefore L>L ₀ is satisfied easily.

A NUMERICAL STUDY OF INTERNAL BOUNDARY LAYER CAUSED BY ABRUPT CHANGE OF THE UNDERLYING EARTH'S SURFACE CHARACTERISTICS
Zhou Dingwen;Hu Yinqiao
1988 Vol. 7 (4): 357-366.
Abstract ( ) PDF (654KB) ( )
A two dimensional internal boundary layer(IBL) numerical model in which stratification is considered is developed to study IBL caused by abrupt changes of surface roughness, temperature and humidity. The results show that significant differences exist between the velocity IBL caused by the abrupt change of surface roughness and temperature IBL caused by the abrupt change of surface temperature.

DEBATE AND CORRECTION OF ATMOSPHERIC POLLUTION COEFFICIENT CONCEPT AND ITS TENTATIVE APPLICATION IN SOME GANSU REGION
Shi Jiekuan;Huang Jianguo;Hong Guoping;Dong Anxiang
1988 Vol. 7 (4): 367-373.
Abstract ( ) PDF (434KB) ( )
In this paper, we have investigated the effects of the wind direction frequency and wind speed distribution on the long time air pollution level. We have given a new,more reasonable definition of pollution coefficient. Further, we have analysed the characteristics of pollution coefficient using the self-registering wind data in 12 cities in Gansu. It is shown that the pollution potential is heavy in the central and southern section and light in the western and eastern in Gansu. And there are evident different pollution coefficients in different directions in every region. So we can appropriately select the direction for setting pollutant sources in city programme to reduce the pollution.

THE RELATIONSHIP BETWEEN THE FLOW OF HEIHE (BLACK RIVER) AND THE METEOROLOGICAL ELEMENT DURING LATE SPRING AND EARLY SUMMER
Hu Tianqing
1988 Vol. 7 (4): 374-376.
Abstract ( ) PDF (220KB) ( )
In this paper, the relationship between the flow of Heihe and the meteorological element during late spring and early summer is analysed with the data of Yingluoxia hydrometric station and Qilian meteorological station. It is found that the flow in April depends first on snowfall which have snowed before, secondly on the temperature of April; and that the flow of May and June depends first on the rainfall, secondly on the prevenient srowfall and the temperature of may. This study provides the basis of forecasting the flow.