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1990 Vol. 7, No. 4

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The Dynamic Mechanism of the Formation of the Low Level Jet
Yang Dasheng, Jian Maoqiu
1990, 7(4): 383-394. doi: 10.1007/BF03008869
The ordinary multidimensional reductive perturbation method is generalized so as to apply to the general case including the dissipative factor. With this the corresponding Cubic-Schr?dinger equation is deduced, and by the pre-liminary study of its solution, it shows that it is more admissible to consider atmospheric meso-scalc systems as the nonlinear Cubic-Schr?dinger waves. With suitable boundary and initial conditions, the Cubic-Schr?dinger equation is numerically integrated so as to investigate the possible dynamic mechanism as well as the impacts of the nonlinear action, turbulent friction and topography to the formation of the LLJ. The results indicate that the downward transfer of the momentum and the effect of the surface friction are responsible for the concentration of the momentum in the layer between 850 and 700 hPa. The location of the horizontal concentration of momentum depends on the propaga-tion of momentum, in the process the inertia-gravity internal wave is very important, whereas turbulent friction is unfavourable for or delays the formation of the low level jet.
Generalized Available Potential Energy
Yong. L. McHall
1990, 7(4): 395-408. doi: 10.1007/BF03008870
The kinetic energy generation in either the dry or moist atmosphere may be estimated by the same relationships if we introduce the new concept of generalized available potential energy. The largest magnitude of generalized availa-ble potential energy and corresponding reference state of either dry or moist atmosphere are calculated in terms of the initial conditions and entropy variation of the atmosphere. The obtained relationships are applicable for the statically unstable atmosphere as well. The generalized available potential energy associated with reversible processes reaches the maximum with respect to same initial state. While the generation of kinetic energy in irreversible processes is characterized by sudden changes. When the reference state is assumed to be saturated, we may predict the final tem-perature and moisture fields corresponding to provided initial state and entropy variation.
The Phenomena of Bifurcation and Catastrophe of Large-Scale Horizontal Motion in the Atmosphere under the Effect of Rossby Parameter
Wan Jun, Yang Fanglin
1990, 7(4): 409-422. doi: 10.1007/BF03008871
The stability question of large-scale horizontal motion in the atmosphere under the effect of Rossby parameter is discussed in this paper by using the qualitative analysis theory of ordinary differential equations. The following as-pects are reviewed: The stability of large-scale horizontal motion in the atmosphere accords with the common inertial stability criterion when the effect of Rossby parameter is not considered (Yang, 1983), and that, on the other hand, the motion will bifurcate two times with the variation of absolute vorticity of basic Zephyr flow at the initial position under the effect of Rossby parameter. Furthermore, in the inertial stable region, if the effect of geostrophic deviation at the initial position is considered, the motion will not only bifurcate but also generate a catastrophe.
Delineation of Mesoscale Features of Ocean on Satellite IR Image
Li Jun, Zhou Fengxian, Gao Qinghuai
1990, 7(4): 423-432. doi: 10.1007/BF03008872
An ICSED (Improved Cluster Shade Edge-Detection) algorithm and a series of post-processing technique are discussed for automatic delineation of mesoscale structure of the ocean on digital IR images. The popular derivative-based edge operators are shown to be too sensitive to edge fine-structure and to weak gradients. The new edge-detection algorithm is ICSED (Improved Cluster Shade Edge-detection) method and it is found to he an excel-lent edge detector that exhibits the characteristic of fine-structure rejection while retaining edge sharpness. This characteristic is highly desirable for analyzing oceanographic satellite images. A sorting technique for separating clouds or land well from ocean at both day and night is described in order to obtain high quality mesoscale features on the IR image. This procedure is evaluated on an AVHRR (Advanced Very High Resolution Radiometer) image with Kuroshio. Results and analyses show that the mesoscale features can be well identified by using ICSED algorithm.
Topographically Forced Rossby Wave Instability and the Development of Blocking in the Atmosphere
Luo Dehai
1990, 7(4): 433-440. doi: 10.1007/BF03008873
In this paper, the linear stability of disturbance superimposed on basic state Rossby wave forced by topography is investigated, and pointed out that when a certain criterion is satisfied by the basic flow and the height of topogra-phy for the subresonance, the small disturbance may be unstable. Furthermore, we also compare the evolution of the instability disturbance with the development of blocking in the Pacific, and we suggested that the topographically forced Rossby wave instability may provide a possible mechanism for the development of blocking in the Pacific.
The Impact of Soil Moisture on Dispersion-Related Characteristics
Jia Xinyuan, Ye Zhuojia
1990, 7(4): 441-452. doi: 10.1007/BF03008874
This study investigates the impact of soil moisture availability on dispersion-related characteristics: surface fric-tion velocity (u*), characteristic scales of temperature and humidity (T* and q*), the planetary boundary layer height (h) and atmospheric stability classified by Monin-Obukhov length (L), Kazanski-Monin parameter (μ) and convective velocity scale (w*) during daytime convective condition using a one-dimensional primitive equation with a refined soil model.
Off-Shore Sea Surface Electric Field Investigations around the Indian Sub-Continent during 9-20 May 1983
G. K. Manohar, S. M. Sholapurkar, S. S. Kandalgaonkar
1990, 7(4): 453-462. doi: 10.1007/BF03342564
Sea surface electric field observations off the coast from Goa (15o25N, 73o47E) to Madras (13o04N, 80o15E) around Sri Lanka, in a distance range 25-135 km from coast, during 9-20 May 1983 were taken. In this paper we have examined the diurnal variation of electric field in the Arabian Sea, Indian Ocean and Bay of Bengal regions cov-ered during the cruise of the research ship ORV Gaveshani. An aspect of electric field dependence on coastal distance and Aitken Nuclei concentration has also been studied. An attempt to examine the latitude dependence of field was also made. Results obtained in the above studies are presented and compared with those obtained elsewhere.
Diagnosis of the Medium-Range Variation of the Subtropical High over the Western Pacific during a Meiyu Process by Three-Dimensional E-P Flux
Zhang Qihe, Yu Shihua
1990, 7(4): 463-474. doi: 10.1007/BF03342565
In this paper, using the daily grid data (2.5 x 2.5) of the ECMWF / WMO, we have computed respectively the three-dimensional wave activity flux in the stages of pre-onset, prevailing and post ending of Meiyu from 1 to 31 July 1982. The potential vorticity field is taken as the physical quantity relating the wave activity flux to the variation of the subtropical high over the Western Pacific. It is found that the three-dimensional wave activity flux is a power-ful means for diagnosis of the variation of the subtropical high over the Western Pacific: The region of the subtropical high is just the confluence area of wave energy, whose changes in intensity and range decide the variation of the subtropical high. The confluence of wave energy comes from the monsoon flow in low latitudes, the Meiyu rain belts in middle latitudes and the heating fields on the eastern side of the Qinghai-Xizang Plateau. The relation between these sources and the subtropical high displays the self-adjusting mechanism among members of East-Asia summer monsoon.
Study on Microwave Remote Sensing of Atmosphere, Cloud and Rain
Zhao Bolin
1990, 7(4): 475-490. doi: 10.1007/BF03342566
In this paper, recent research of microwave remote sensing of atmosphere, cloud and rain in China is presented. It includes the following aspects:(1) Progress in the development of multifrequency radiometer and its characteristics and parameters;(2) Application of microwave remote sensing in prediction of atmospheric boundary layer. The atmospheric temperature profiles are derived with 5 mm (54.5 GHz) radiometer angle-scanning observations. Due to the fact that microwave radiometer could monitor the atmospheric temperature profile continuously and make the initialization of numerical model any time, it is helpful for improving the accuracy in prediction of the evolution of atmospheric boundary layer;(3) Theory and application of microwave radiometers in monitoring atmospheric temperature, humidity and water content in cloud. The field experiment of International Satellite Cloud Climatology Project (ISCCP) at Shionomisaki and Amami Oshima of Japan for studies of cloud and weather has been described;(4) Satellite remote sensing of atmosphere and cloud. The TIROS-N TOVS satellite data are used to obtain at-mospheric temperature profile. The results are compared with those of radiosonde, with rms deviation smaller than that of the current operational TOVS processing;(5) Microwave remote sensing and communication. The atmospheric attenuations are derived with microwave remote sensing methods such as solar radiation method etc., in order to obtain the local value instantaneously. The characteristics of Beijings rainfall have been analysed and the probability of microwave attenuation of rain is predicted;(6) For improvement of the accuracy of rainfall measurement, a radiometer-radar system (= 3.2 cm) has been developed. The variation of rainfull distribution and area-rainfall may be obtained by its measurements, which may be helpful for hydrological prediction.The prospect of microwave remote sensing in meteorology is also discussed.
Use of Surface Observations to Estimate Upper Air Humidity for the Objective Analysis of Relative Humidity over Indian Region
S. K. Sinha, D, R. Talwalkar, S. G. Narkhedkar, P. L. Kulkarni, S. Nair, S. Rajamani
1990, 7(4): 491-501. doi: 10.1007/BF03342567
In the present study objective analyses of relative humidity (RH) at surface and at the levels of 850,700 and 500 hPa have been made using Gandins (1963) optimum interpolation scheme. As the horizontal resolution of the radiosonde stations is rather inadequate for upper air humidity analysis, a scheme has been developed, following Rasmussen (1982) to estimate the upper air RH from the surface observations like surface RH, present weather and cloud cover. The relative humidities at the levels 850, 700 and 500 hPa were related to the surface observations through three separate regression relations. The RH values at 850, 700 and 500 hPa levels were estimated from the surface RH, cloud coverage and present weather using the above regression relations and subsequently the objective analyses at 00 GMT for the period from 4 July to 8 July 1979, were made using these estimated data along with the observed radiosonde data. Objective analyses were also made for the same period using only the radiosonde data for comparison to study the impact of those estimated data. Root mean square errors were computed for all the five days by interpolating RH at the observing stations from the objectively analysed field and comparing them with the actually observed RH to examine how best the analyses (with and without estimated data) fitted the observations. Lastly they were compared with satellite cloud pictures. This study shows that the estimated upper air RH values have positive impact on the analysis of upper air RH and could be used over radiosonde date sparse region and even over oceanic regions.