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1988 Vol. 5, No. 2

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MAINTENANCE AND OSCILLATION MECHANISMS OF SUM-MER TROPICAL UPPER-TROPOSPHERIC EASTERLIES
Zhu Qiangen, Zhi Xiefei
1988, 5(2): 127-140. doi: 10.1007/BF02656775
Abstract:
The mechanisms of the maintenance and oscillation of 1982 summer tropical 200-hPa mean easterly flow and extra-long waves are investigated in terms of the energy equations in wavenumber-frequency space. Calculation results show that the difference in heating between land and sea and the boundary effect serve as the main source of energy; frictional dissipation as the sink; the conversion of available potential energy into kinetic takes place dominantly in the waves of number 1-2; such transformation is accomplished in just a small amount in zonal mean flow and therefore can be ignored because of the value.In the interaction between wave and zonal mean flow, the latter loses its available potential and gains kinetic energy. The tropical easterly belt over 20oN-5oS is found barotropically stable and that over 10oN-5oS, unstable. The waves of number 2 and 1 manifest themselves a primary source and sink of kinetic energy, respectively, in the interplay between waves and between zonal mean flow and wave.It is found that zonal mean flow and the waves of number 1-2 have a roughly 40-and 20-day oscillational period of kinetic energy, respectively, whose primary mechanism is the transfer of barotropic energy, the conversion of baroclinic energy, and the boundary effect.
MOUNTAIN TORQUE AND EXTERNAL FORCING
Wu Guoxiong
1988, 5(2): 141-148. doi: 10.1007/BF02656776
Abstract:
Theoretical research and numerical modelling show that, although mountain torque owes its existence to the unevenness of the ground surface, its sign and intensity depend strongly upon the relative disposition be-tween mechanical and thermal forcing. The strong annual variations of mountain torque in the northern subtropics revealed by Yeh and Zhu (1958) are attributed to the different thermal features of Tibetan Plateau between winter and summer.
LONG-TERM VARIATIONS OF CYCLONE ACTIVITIES IN EAST ASIA
Tomio Asai, Yasumasa Kodama, Ji-Cang Zhu
1988, 5(2): 149-158. doi: 10.1007/BF02656777
Abstract:
A statistical analysis is made of the temporal and spatial variability of cyclone activities in middle latitudes in East Asia for 52 years during the period from 1934 to 1985.Three principal tracks of cyclones are distinguished in East Asia almost all year around except for the disappearance of the south one in summer.A longer-term variation in frequency of cyclones passing over the Japanese Islands with a period of about 20 years is found, in addition to a shorter-term variation with a period of a few years. A significant decreasing trend in cyclone frequency is noted between the late 1960s to around 1980.
THE LOCAL SPLINE VERTICAL INTERPOLATION METHOD OF TEMPERATURE AND GEOPOTENTIAL HEIGHT FIELDS AND THE TIME-DEPENDENT DIFFERENCE FORM OF THE HYDROSTATIC EQUATION
Qian Yongfu
1988, 5(2): 159-170. doi: 10.1007/BF02656778
Abstract:
In numerical weather prediction (NWP), the accuracy of vertical interpolation of the initial data is a problem which is greatly concerned by people. In this paper, we specify vertical distributions of the temperature and the geopotential height fields and examine three interpolation methods, i.e. the Lagrangian polynomial inter-polation method (hereafter abbreviated to LP method), the linear interpolation method (LN method) and the local spline interpolation method (LS method) proposed by the author. The examination shows that when the vertical resolution of the initial data is high enough, for example, the number of the given data levels N is 10 or more, all the three methods get good accuracy of interpolation, especially, the LP and the LS methods have very little errors almost tending to zero, while the LN method has a little larger errors than the two formers and the errors at various levels have the same sign. When N is reduced to 5, the LP and the LS methods still have quite good accuracy and similar error distributions, while the LN method has less accuracy. If the geopo-tential height field needs to be adjusted in order to satisfy the hydrostatic equilibrium with the temperature field which is assumed fixed, then the LS method has minimum errors. The examination also indicates that the vertical resolution with at least 5 levels of initial data can keep the interpolation accuracy. Otherwise the accuracy will not be guaranteed no matter which method is used.It is also pointed out in this paper that the temperature and the geopotential height fields can be given inde-pendently in numerical prediction models in order to keep higher interpolation accuracy. However, the hydro-static equation should be finite differenced in other way which is somewhat different from the conventional one. In other words, the time dependent difference form of the equation should be used, so that the initial interpola-tion accuracy could have influence on the time integration.
THE VARIATION OF THE HEAT SOURCES IN EAST CHINA IN THE EARLY SUMMER OF 1984 AND THEIR EFFECTS ON THE LARGE-SCALE CIRCULATION IN EAST ASIA
Ding Yihui, Hu Jian
1988, 5(2): 171-180. doi: 10.1007/BF02661291
Abstract:
The distributions and daily variations of the apparent heat source (Q1) and the apparent moisture sink (Q2) in East China in the early summer of 1984 have been estimated with the budget calculation method. It has been found that during this time period, there occurred three significant episodes of strong heating that corresponded to the three events of heavy rainfalls prior to, during and post to the onset of mei-yu (plum rains). The peaks of Q1 were generally found at 200 hPa, with the heating rate of 6°-10°C/day observed, while the peaks of Q2 were located at about 700 hPa, with their magnitudes being 12o-20°C/day. The vertical distribution of Q1 and Q2 indicates the importance of eddy vertical flux. In other words, the convective activity plays a very important role in the processes of precipitation in East Asia in the early summer. This result is different from the finding obtained by Luo and Yanai (1984) in their calculation of the case of 1979. They pointed out that in the early summer of 1979 the continuous precipitation dominated the region of East China.Among the three terms of Q1 and Q2, the maximum contribution was made from the adiabatic term, which was caused by strong ascending motion. The adiabatic cooling produced by this term may compensate for the heating created by the condensation process.In addition, it has been revealed that the three significant heating processes were closely related to the seasonal transition from spring to summer in East China. One major synoptic event associated with it showed up in the sudden jump of the upper tropospheric, subtropical jet-stream from 30°N to 40°N. So did the plane-tary frontal zone in East China.
THE EFFECTS OF TOPOGRAPHY ON THE SUMMER ATMOS-PHERIC ENERGETICS OF THE NORTHERN HEMISPHERE IN A LOW-RESOLUTION GLOBAL SPECTRAL MODEL
Ni Yunqi, Bette L. Otto-Bliesner, David D. Houghton
1988, 5(2): 181-194. doi: 10.1007/BF02656780
Abstract:
An analysis is made of the effects of topography on the summer atmospheric energetics of the Northern Hemisphere in a low-resolution global spectral model. The numerical model is a global, spectral, primitive equation model with five equally spaced sigma levels in the vertical and triangular truncation at wavenumber 10 in the horizontal. The model includes comparatively full physical processes.Each term of the energy budget equations is calculated in four specific latitudinal belts (81.11°S-11.53°S; 11.53°S-11.53°N; 11.53°N-46.24°N; 46.24°N-81.11°N) from a five-year simulation with mountains and a one-year simulation without mountains, respectively. Differences between them are compared and statistically tested. The results show that synoptical scale waves transport available potential energy and kinetic energy to long waves and increase conversion from available potential energy of the zonal flow to eddy’s and from the eddy kinetic energy to the zonal kinetic energy in region 3 (11.53°N-46.24°N) due to mountains; topography intensifies the atmospheric baroclinity in region 3, consequently the baroclinic conversion of atmosphere energy is increased. The seasonal characteristics associated with the summer atmospheric energy source in region 3 are caused by seasonal variation of the solar radiation and the land-ocean contrasts and independent of topographic effects. The mechanism of topographic effects on the increase of long wave kinetic energy is also discussed.
ON TEMPERATURE INITIALIZATION IN PRIMITIVE EQUA-TION FORECAST MODELS
Shen Rujin, Elmar R. Reiter, James F. Bresch, Zhang Shuhua
1988, 5(2): 195-208. doi: 10.1007/BF02656781
Abstract:
Four procedures of specifying model initial temperature were described and tested in the present study. It was found that the use of observed temperatures along with a proper vertical interpolation scheme was not only acceptable, but produced less error than the use of temperatures derived from geopotential height through the hydrostatic equation did. Use of the difference form of the hydrostatic equation would produce unacceptable errors in the initial temperatures, unrealistic horizontal and vertical distribution of temperature, and these errors would influence the calculation of the pressure gradient force, resulting in substantial, artificial disturbances within the model domain.In addition, an approach to check the initial data was described. Taking advantage of the fact that the geostrophic wind in sigma coordinates should be nondivergent, geopotential height and temperature were used to calculate the pressure gradient force terms and an initial divergence of the geostrophic wind. This approach can he used for comparing different initialization schemes for identical input data.
NUMERICAL EXPERIMENTS ON NH SUBTROPICAL UPPER TROPOSPHERIC QUASI-STATIONARY VORTICES IN SUMMER
Zhu Zhengxin, Cheng Shaopeng
1988, 5(2): 209-216. doi: 10.1007/BF02656782
Abstract:
To reveal the possible factors affecting the maintenance and interannual variations of the subtropical planetary-scale vortices such as the south Asian anticyclone and the mid-oceanic troughs, a series of nu-merical experiments are conducted with a quasi -geostrophic low-resolution spectral model. Firstly a simu-lation experiment is performed in which the realistic thermal and topographic forcing are incorporated. The results of simulation show a certain similarity to the actual subtropical flow field in July. On the basis of simulation experiment a series of contrast experiments are performed. It is found that the topog-raphic boundary forcing is less important than the thermal forcing in the dynamics of these systems, and that the anomaly of heating field may cause significant change in position and intensity of the south Asian high and the other systems. It is speculated that the response of the subtropical large-scale systems to heat-ing anomaly is an important cause for the interannual variations of circulation, especially the monsoon circulation.
POSSIBLE SOLAR INFLUENCE ON ATMOSPHERIC ELECTRIC FIELD
Poonam Sikka, A. Mary Selvam, A.S. Ramachandra Murty
1988, 5(2): 217-228. doi: 10.1007/BF02656783
Abstract:
A physical hypothesis for the electrical coupling of the troposphere, ionosphere and magnetosphere has been proposed. It is shown that the vertical mass exchange takes place in the troposphere, ionosphere and magnetosphere by the gravity wave feedback mechanism through a chain of eddy systems. The vertical mass exchange gives rise to a vertical aerosol current which is responsible for the generation and mainte-nance of atmospheric electric field and also the variations in the H-component of the geomagnetic field. Any per-turbation in the troposphere would be transmitted to ionosphere and vice versa. A global perturbation in ionosphere, as the one caused by solar variability, is transmitted to troposphere influencing weather systems/geomagnetic/atmospheric electrification processes.The theory relating to the above physical mechanism is discussed. Also, results of analysis of at-mospheric electrical field data for Colaba, Bombay (8°53’ 56”N, 72° 48’ 54”E, 9.8 m ASL) and solar activity indices (Ap index, DST index and MSB crossing dates) for the 31 year period from 1936-1966 which provide statistical evidence for solar influence on atmospheric electrification processes are presented.
SENSITIVITY OF LIDAR EQUATION SOLUTION TO BOUNDA-RY VALUES AND DETERMINATION OF THE VALUES
Qiu Jinhuan
1988, 5(2): 229-241. doi: 10.1007/BF02656784
Abstract:
An analytical dependence of the optical depth solution to lidar equation on boundary values was con-firmed. According to the dependence this paper analyzed the sensitivity of lidar equation solutions obtained by forward and backward integration algorithms to the boundary values and quantitatively expounded an error limit to the boundary values under a given inversion accuracy. Furthermore, this paper presented a method for determination of the far-end boundary value in the case of inhomogeneous atmosphere, improving the accuracy of lidar equation solution.
MONSOON RAINFALL AND SOUTHERN OSCILLATION RESPONSES IN THE PRESSURES OVER THE NORTHERN INDIAN OCEAN
K.D. Prasad, S.V. Singh
1988, 5(2): 243-251. doi: 10.1007/BF02656785
Abstract:
The pressure variations over the North Indian Ocean during the summer monsoon season have been exam-ined using the monthly data from June to September for the period 1961 to 1968. It is found that these varia-tions can be described by two significant eigenvectors (EV1 and EV2) which together account for 53% of the total variance.The first eigenvector (EV1) represents in phase variation over both, the Arabian Sea and the Bay of Bengal with higher variations over the northern side of the area. The second eigenvector (EV2) depicts the out-of-phase variation between the pressure anomalies over the north and the south of 15°N latitude with two areas of pronounced variation, viz., the head Bay of Bengal and the equatorial region near 65°E longitude.The coefficients of EV1 show significant association with rainfall of West Coast and Central India for the concurrent months. These coefficients also show significant association with the pressure and temperature indices of the Southern Oscillation. The coefficients of EV2 show significant association with the monsoon rainfall of south peninsular India.