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1992 Vol. 9, No. 4

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Study on Clouds and Marine Atmospheric Boundary Layer
Zhao Bolin, Zhen Jinming, Hu Chengda, Du Jinlin, Zhu Yuanjing, Zhang Chengxiang
1992, 9(4): 383-396. doi: 10.1007/BF02677072
A set of remote sensing instruments of Peking University, which includes mainly a dual~channel(22.235GHz and 35.5GHz) microwave radiometer, a 8mm microwave and a 5mm microwave radiometer, has been developed for the Western North-Pacific Cloud-Radiation Experiment (WENPEX). The instruments were used to observe the cloud and marine atmospheric boundary-layer in the southwest sea area of Japan in winter time from 1989 to 1991. In the weather change process, the characteristics of the marine atmospheric boundary-layer and liquid water content in cloud of this area in winter time are studied from observation data. A one-dimensional mixed layer model is presented for the growth and evolution of a cloud-topped marine boundary-layer. The model is used to study in the WENPEX. The simulation results are in agreement with observation data, especially the integral water in cloud.
Longitudinal Heating Gradient: Another Possible Factor Influencing the Intensity of the Asian Summer Monsoon Circulation
Song Yang, Peter J. Webster, Min Dong
1992, 9(4): 397-410. doi: 10.1007/BF02677073
The Largest longitudinal heating gradients in the tropics exist between the African desert and Asian convective regions during summer once the South Asian monsoon is established. The heating gradients are anchored by the la-tent heat release and net radiative flux convergence over the monsoon region, and by the dominant net radiative flux divergence over the desert.An apparent relationship is found between the intensity of the Asian summer monsoon circulation and the longitudinal healing gradients mentioned, in addition to the latitudinal heating gradients cross the monsoon region. The monsoon circulation measured in terms of the zonal wind component is stronger when the longitudinal heating gradients are large, and vice versa. Thus, we claim that the longitudinal heating gradient may be another important factor which influences the intensity of the Asian summer monsoon circulation. There is little evidence that the interannual variability of the longitudinal heating gradients between Africa and Asia and, thus, the intensity of the Asian summer monsoon circulation, is a strong function of the El Nino / Southern Oscillation cycle.
Spatial and Temporal Variations of Blocking and Cyclogenesis in the 1978 / 79 Winter
Hengyi Weng
1992, 9(4): 411-430. doi: 10.1007/BF02677074
Complex empirical orthogonal function (CEOF) and Fourier analyses are applied to 500 hPa geopotential height anomaly for two selected latitude belts in the Northern Hemisphere from Dec 1978 through Feb 1979 based on the ECMWF FGGE III-b data. The positive anomalies in the three leading CEOFs for the high-latitude belt mainly show the preferred locations for blocking activity in the North Atlantic, the North Pacific and to the west of the Ural Mountains. The negative anomalies in the three leading CEOFs for the mid-latitude belt mainly show the preferred locations for cyclogenesis in the east coasts of Asia and North America, and the Mediterranean; weak cyclogenesis is also seen in the western United States and off the coasts of Spain and Morocco. The travelling components of the pos-itive anomalies in the high-latitude belt mainly propagate westward, weakening as approaching the east side of some mountain chains while intensifying to the west side. On the contrary, the travelling components of the negative anom-alies in the mid-latitude belt mainly propagate eastward, intensifying over the lee side of mountain and / or ap-proaching the east coasts of the two continents. These preferred locations for blocking and cyclogenesis are basically consistent with the climacological results, and related to some teleconnection patterns found earlier.The temporal variation of blocking highs seems to relate with the vacillation of the potential vorticity (PV) index defined by Weng (1992). There are two build-up stages of the PV index during the winter. Each build-up stage corre?sponds to a westward propagation of a large-scale positive anomaly in the high-latitude belt, resulting in the occur?rence of a series of blocking highs over the western Eurasia, Scandinavia, Greenland and the Pacific. In general, the temporal variation of cyclogenesis is less reflected by the PV index than blocking highs. The duration of a PV index cycle of build-up and break-down is about 30-50 days. Within this low-frequency envelope, there is a global quasi-two-week vacillation of the PV index, reflecting one of the preferred time scales of mid-latitude cyclone and anticyclone activity in some preferred locations during the 1978 / 79 winter.
Some Experiments with Multivariate Objective Analysis Scheme of Heights and Winds Using Optimum Interpolation
S. K. Sinha, S. G. Narkhedkar, D. R. Talwalkar, S. Rajamani
1992, 9(4): 431-440. doi: 10.1007/BF02677075
A two-dimensional, multitvariate objective analysis scheme for simultaneous analysis of geopotential height and wind fields has been developed over Indian and adjoining region for use in numerical weather prediction. The height-height correlations calculated using daily data of four July months (1976-1979), are used to derive the other autocorrelations and cross-correlations assuming geostropic relationship. A Gaussian function is used to model the autocorrelation function. Since the scheme is multivariate the regression coefficients (weights) are matrix.Near the equator, the geostrophic approximation relating mass and wind is decoupled in a way similar to Bergman (1979). The objective analyses were made over Indian and adjoining region for 850, 700, 500, 300 and 200 hPa levels for the period from 4 July to 8 July 1979, 12 GMT. The analyses obtained using multivariate optimum in-terpolation scheme depict the synoptic situations satisfactorily. The analyses were also compared with the FGGE ana-lyses (from ECMWF) and also with the station observations by computing the root mean square (RMS) errors and the RMS errors are comparable with those obtained in other similar studies.
Simulation of Desert-Scrub Growth: A Forcing to Warmer and More Pluvial Climate
Joseph Otterman, Ming-Dah Chou
1992, 9(4): 441-450. doi: 10.1007/BF02677076
Desert-fringe vegetation growing over bright, sandy soils reduces the surface albedo from above 0.4 to well be-low 0.3. Called desert-scrub, these shrubs form a predominantly vertical clumps protruding from the soil-level, thereby significantly increasing the coefficient of turbulent heat transfer from the surface. The impact on global and desert-belt climate of changes in these two surface characteristics was simulated by a multi-layer energy balance model. Evaluated only as a forcing to a further climatic change (that is, without accounting for any possible feedbacks) the results are: if vegetation (such as apparently existed under the warmer climate of 6,000 BP) grows over large areas in the arid, currently bare-soil regions, the annual Northern Hemisphere surface temperature increases by 0.7oC (by 0.6oC in July ), the surface temperature over land in the 20-30oN zone increases by 0.9oC in both the annual and the July means, and the land-ocean annual temperature contrast in this zone increases by 0.25oC (0.2oC in July). These results represent the combined influence of the reduction in the surface albedo and of the increase in the coefficient of turbulent heat transfer. In the desert-belt zones, the increase in the transfer coefficient sharply reduces the land temperature and the land-ocean temperature contrast from the values produced by the albedo change alone. This reduction must be attributed to the increased land-to-ocean circulation (which our model does not evaluate ex-plicitly). Considering that a stronger circulation (resulting from land-ocean temperature contrast) generally forces a higher rainfall, the vegetation which emerged in the arid regions during the post-glacial optimum should be consid-ered a. significant positive feedback towards a still warmer, and also a more pluvial, climate. Our study may have im-plications for the 21st century, if the global warming expected from the enhanced greenhouse effects is accompanied by increased precipitation over the continents.
The Seasonal Climatic Simulation of 9000 Years before Present by Using the IAP Atmospheric General Circulation Model
Wang Huijun
1992, 9(4): 451-457. doi: 10.1007/BF02677077
The seasonal cycle of the climate of 9000 years before present was simulated with the IAP two-level atmospheric general circulation model. The incoming solar radiation was specified from the orbital parameters for 9000 years Ago. The boundary conditions of that time were prescribed to the present value because of the small differences between the two. The change in radiation makes temperature to be higher in summer and lower in winter over large areas of the land; and the increased temperature contrast between the land and the ocean strengthens the summer monsoon circulation and increases the precipitation over there. The asymmetry of temperature change between the Northern Hemisphere and the Southern Hemisphere and between summer and winter still exists, which agrees with that get from the previous perpetual experiments.
Automatic Classification and Compression of GMS Cloud Imagery in Heavy Rainfall Monitoring Application
Li Jun, Zhou Fengxian, Wang Luyi
1992, 9(4): 458-464. doi: 10.1007/BF02677078
The Bayes Decision method (BD) has been implemented on GMS Stretched VISSR (S.VISSR) images. Several objects are identified. These are earth’s surface, stratiform, convective and cirrus clouds. Overlaid 6-hour surface rainfall observations show that the rain area on the ground matches with precipitable cloud area identified by BD method. Finally the data of classified image are compressed to about one-eighth amount by use of Line-Run-Cod-ing technique. It is helpful for data archive and remote transmission.
A Fine-Mesh Numerical Model with Detailed Boundary Layer Parameterization
Fei Jianfang, Zhang Ming, Lu Hancheng, Yang Guoxiang
1992, 9(4): 465-476. doi: 10.1007/BF02677079
A fine-mesh numerical model with thirteen-layer, three-dimensional primitive equation is designed, which has a relatively high vertical resolution in the boundary layer and detailed boundary parameterization. A strong cold frontal process is simulated by the model. Comparison of the simulated results of this process with different models shows that the result of this model is prior to that of others, and that it is necessary to increase the vertical resolution and to take account of the physical processes in the boundary layer.
Analysis-Prediction Experiments over Indian Region Using Primitive Equation Barotropic Model
M. Y. Totagi, D. R. Talwalkar, S. Rajamani, S. S. Singh
1992, 9(4): 477-482. doi: 10.1007/BF02677080
The impact of initial guess and grid resolutions on the analysis and prediction has been investigated over the In-dian region. For this purpose, an univariate objective analysis scheme and a primitive equation barotropic model have been used. The impact of initial guess and the resolutions on analysis and prediction is discussed.
An Easy Algorithm for Solving Radiative Transfer Equation in Clear Atmosphere
Yang Jingmei, Qiu Jinhuan
1992, 9(4): 483-490. doi: 10.1007/BF02677081
An accurate and rapid method for solving radiative transfer equation is presented in this paper. According to the fact that the multiple scattering component of radiance is less sensitive to the error of phase function than the single scattering component is, we calculate the multiple scattering component by using delta-Eddington approximation and the single scattering component by solving radiative transfer equation. On the ground, when multiple mattering com-ponent is small, for example, when the total optical depth τ is small, the accurate radiance can be obtained with this method. For the need of the space remote sensing, the upward radiance at the top of the atmosphere is mainly studied, and an approximate depression is presented to correct the multiple scattering component. Compared with the more precise Gauss-Seidel method, the results from this method show an accuracy of better than 10% when zenith angle θ < 50o and τ ≤ 1. The computational speed of this method is, however, much faster than that of Gauss-Seidel method.
Numerical Study on Dry Deposition Processes in Canopy Layer
Lei Xiaoen, Julius S. Chang
1992, 9(4): 491-500. doi: 10.1007/BF02677082
A coupling model between the canopy layer (CL) and atmospheric boundary layer (ABL) for the study of dry deposition velocity is developed. The model consists of six parts: chemical species conservation equation including absorptive factor; the species uptake action including detailed vertical variation of absorptive element in CL; momen-tum exchange in CL which is represented by a first-order closure momentum equation with an additional larger-scale diffusive term; momentum exchange in ABL which is described by a complete set of the ABL turbulent statistic parameters; absorptivity (or solubility or reflection) at the surface including effects of the physical and chemi-cal characters of the species, land type, seasonal and diurnal variations of the meteorological variables; and deposition velocity derived by distributions of the species with height in CL. Variational rules of the concentration and deposi-tion velocity with both height and time are simulated with the model for both corn and forest canopies. Results pre-dicted with the bulk deposition velocity derived in the paper consist well with experimental data.
The Buffer Capability of the Ocean to Increasing Atmospheric CO2
Xu Yongfu
1992, 9(4): 501-510. doi: 10.1007/BF02677083
The CO2-seawaler system and the method for calculating the partial pressure of CO2 (pCO3) in seawater are stu-died. The buffer capability of the ocean to increasing atmospheric CO2, is expressed in terms of the differential buffer factor and buffer index. Dissolutions of aragonite and calcite have a significant influence on the differential buffer factor. The trend of change in the buffer factor is obtained by a box model.