Vol.2, NO.1, 1987

Display Method:
The Effect of Diabatic Heating on the Formation of the South Asia High and Its Quasi-periodic Oscillation
1987, 2(1): 1-11.
By using a quasi-geostrophic, two-level baroclinic highly truncated spectral model on a β plane, computations have been made in the cases with diabatic heating differently in basic current. The results are as follow: ① When the values of the parameter relevant to the external thermal forcing are selected properly, the establishment and oscillation of South Asia High may occur. On the other hand, the “chaos” phenomenon may appear if the greater values of the parameter of thermal forcing are taken. ② When the land-sea thermal contrast is reduced to a certain extent, the South Asia High tends to be in equilibrium state. ③ South Asia High cannot occur if there is only medional inhomogeneous external thermal forcing
The Warm θse Lid in a Heavy Rain Case During Mei-yu Season
1987, 2(1): 12-23.
A 10 layer moist mesoscale model has been employed to simulate a heavy rain case over Yangtze Valley, China during Mei-Yu season. The rain-band and subsynoptic fields are simulated realistically. The results also show that: ① A θse warm lid existed over heavy rain region, which was maintained and enhanced during rainfall period. It is a moist lid, characterized by the inversion of θse and is different from the dry lid with the severe local storms over middle United States. ② The heavy rain region located at the northern or northeastern part of the lid, where the horizontal gradient of θse is considerable large; besides, the upward motion and the potential instability of the stratified atmosphere over there are significant. ③ The warm moist lid not only restrained the release of potential unstable energy from the under running flow, but also enhanced the potential instability of the layer above. Thus, the lid played a role in providing a favorable thermodynamic environment to the development of deep cumulus convection. ④ Based on the thermal wind vorticity eq and the modeling results, the phenomena of the location of heavy precipitation coincide with the strong ascending area and the maximum potential unstable region over 850—700 hPa can be explained by the coupling of vertical motion and the potential instability, ω▽2σs and σs▽2ω. They would induced the imbalance between the mass field and the thermal field so that the “pumping” secondary circulation would develop over the heavy rain region, and the inertial gravity instability would occur as well. Thus, the lid is also favorable to the development of atmospheric imbalance indirectly. ⑤ Based on the eq of stability and the modeling results, the formation of the moist lid is caused by moisture advection of geostrophic thermal wind and differential geostrophic advection ofθse . Therefore, the existence of moist low level jet in the south or south-west of the rainfall region is favorable to the development of the lid.
A Study of Forecast Errors in ECMWF Operational Model
1987, 2(1): 24-35.
In order to have a better uderstanding on ECMWF model and make proper use in operation, the distribution of monthly mean errors and its seasonal variation is studied with one year data of the predicted charts from May 1984 to April 1985. ECMWF numerical forecast is best in middle latitude. In the area north of 75oN, 500 hPa height is forecasted too high and 500—1000 hPa thickness is too warm in spring, summer and autumn, especially in summer, but the latter becomes colder than that observed in winter. In the area south of 30oN, 500 hPa height forecast is too low and 500—1000 hPa thickness is too cold in summer and autumn, with the coldest error center situated on the southeast slope of Xizang Plateau; but in winter and spring, value of error is not so large as in summer and autumn. This seasonal variation seems to correspond with the cloud and precipitation amount or the activities of tropical low over there. Over the Xizang Plateau, the 500 hPa high forecast error is almost negative in every month of the year, with the largest negative value appeared in summer, but it approaches to zero in winter. Comparing the values of systematic error with standard deviation, we may find that in low latitude area, especially in the vicinity of Xizang Plateau, EC forecast charts need modification with systematic errors.
Some Climatological Characteristics During 1982—1983 Winter in East Asia
1987, 2(1): 36-42.
The main feature of the climate in winter of 1982—1983 is characterized by two kinds of anomalous states (warm dry and cold wet) distributed in three zones. It is found that as El-Nino is prevailing, the subtropical high in west pacific is especially strong which is the direct cause of the warm and dry climate in south of 15oN in East Asia. The warmer climate in Xinjiang Uygur Autonomous Region and colder climate in the southwest and the south of China have teleconnections with El-Nino event. The extremely abundant precipitation and cold climate in zone 15o—30oN is closely connected with the intensification and south movement of southern jet stream in East Asia. This jet stream is intensified by intensification of subtropical high on its southern side, and strong negative anomalous of air temperature and the large snow cover on its northern side, i. e. on Xizang (Tibet) Plateau. The rainfall zone in essence is the intensified monsoon rain, similar to Meiyu of Yangtze River in June
Evidence of a 22-year Cycle of Drought in China Related to the Hale Solar Cycle
1987, 2(1): 43-50.
In this paper, by using spectral analysis and superposed-epoch analysis based on the data of “Yearly Charts of Dryness/Wetness in China for the Last 500 Years Period”, the evidence of 22-year cycle of drought in China related to the Hale solar cycle is studied and some facts are found as follows: ① The 22-year cycle of drought generally exists in the region to the east of 105oE in China, particularly in the regions between the Yangtze River and the Yellow River. ② The 22-year cycle of drought is closely related to the sunspot magnetic cycle and their phase angle varies from place to place. Drought usually reaches a maximum about 6—10 years after the peak year of the even numbered sunspot cycle. ③ The most severe drought in a 50-year cycle occurs about 3—4 years before or after the peak year of the even numbered sunspot cycle
An Attempt of Representing the Features of Height Field in Polar Area by Using Experimental Orthogonal Function
1987, 2(1): 51-59.
By using monthly mean values of geopotential height field in 12 months in the polar region and the empirical orthogonal function we obtained a set of eigenvectors having a clear synoptic significance, every eigenvector represents a typical distribution of height field. We define the projections of monthly mean height fields for individual years on these eigenvectors as polar vortex coefficients. The polar vortex coefficients represent the degree of resemblance of real height fields to the corresponding tropical fields. It is found that the polar vortex coefficients have a close relation to the weather of out country.
The Measurements and Analysis of pH Value and Chemical Composition of Snow and Cloudwater During Winter in Wulumuqi
1987, 2(1): 60-66.
The measurements and analysis of pH value and chemical composition of snow and cloudwater were carried out during winters from 1982 to 1984 in Wulumuqi region of China. It shows that the mean pH value of snow is about 5.7, the pH value of cloudwater is about 4.0, with that simultaneously the observed pH value of surface snow is about 6.0. The ion concentration of liquid water in lowercloud generated within air mass is larger than that of cloud with precipitation made by synoptic systems about two orders of magnitude. A possible influence of microphysical processes of snow growth and the characteristics of aerosol particles scavenged by snow crystals on the acidity of snow is noticed
A Study of Atmospheric Diffusion Experiment in City Street Canyons
1987, 2(1): 67-73.
A series of tracer experiments in city street canyons under light wind was conducted to investigate the atmospheric diffusion of vehicle-generated pollutants. When the roof-level wind speed u was near or larger than 1 m/s, standing primary vortex formed in the street canyon, and as u was less than 0.6 m/s, the primary vortex vanished. The ratio of mean tracer concentrations on leeward side to that on windward side was about 8 for street canyons where the space between buildings was small. The tracer concentrations were near constant along vertical direction of buildings faced to the canyon, but it seems higher in the middle of the building heights than otherwheres, because the tracer plume may be resisted and raised by pine trees beside the lane. It was also found that the tracer concentration decayed with distance in a larger negative exponential order for the upwind direction than that for the downwind direction. According to the experiments mentioned above a practical diffusion model was developed for predicting concentration of inert and vehicle-generated pollutants in the city street canyon. In the model the turbulent diffusion was divided into two kinds of motion: the primary vortex and the microscale turbulence
The Multiplication Generated by Dendritic Snow Crystals Collision and Aggregation
1987, 2(1): 74-80.
The measurement during a case of snow precipitation on 11. Nov. 1982 in Xinjiang Uygur Autonomous Region in China was made on an aircraft equipped with PMS. It showed that the collision and aggregation of dendritic snow crystals led to the formation of snowflakes and the multiplication of ice crystals. As the results of the formation of snowflakes, the concentration of snow crystals (d>3000μm) markedly increased while the concentration of snow crystals (400<7<3000μm) decreased in like manner. At the same time, in the region where the multiplication of ice crystals generated, the concentration of ice crystals (18≤d<340μm) increased by about 35%, and the concentration of snow crystals (340≤d<6100μm) increased by about 10%
An Ecological Analysis on Soil Moisture Indices of Winter Wheat in Its Main Stages
1987, 2(1): 81-87.
In this paper, by using the experimental data obtained from Gong County Meteorological Station in Henan Province, the relation between the physiological function of winter wheat in its main stages and soil moisture is simulated, and the optimum index for soil moisture and the drought index for moisture are given. On the basis of these indices, the water consumption of winter wheat in its main stages is obtained from modified Penman equation by consideration of the relative evapotranspiration related to the coefficient of crop leaf area and the index of soil moisture.
A Study on Prediction Models for Immigrating Period of Moths of First-generation in the Outbreaking Region of Second-generation Army Worm by Using Sea Surface Temperature Data
1987, 2(1): 88-96.
In this paper, by using the stepwise regression technique, a correlation analysis is made on the relation between the immigrating period of moths of first-generation in the out-breaking region of second-generation army worm and the monthly mean values of sea-surface temperature in North Pacific Ocean from January of the previous year to May of this year. Some prediction models for the immigrating period are given. The results of experimental predictions in use of these models are consistent with the observation data.