Abstract:It is shown in this paper that North China winter air temperature bears a significant relation with Arctic Oscillation(AO),especially on a time scale of decades,by applying the methods such as wavelet analysis,EOF and correlation analysis and by using the AO index,the NCEP/NCAR reanalysis data and monthly mean air temperature at 160 stations in China.The North China winter air temperature was successively cold before 1970s but warm after 1980s,and the years between them were relatively normal.The winter AO index showed similar three-stage variations.When the winter AO index was high/low,North China winter was warm/cold.The reason may be that the AO can excite anomalies like the EU teleconnection pattern from low to high level in the troposphere which affect the Siberian High and East Asian Trough, thus influencing North China air temperature.High/low AO index years are characterized by weak/strong East Asian Winter Monsoon,weak/strong Siberian High and East Asian Trough and by weakened/strengthened northeast surface wind over Asian continent.

Abstract:In this paper,numerical simulations and diagnostic analyses of moist potential vorticity for a land explosive cyclone are performed.We find that the burst of the cyclone is close associated with the advection of moist potential vorticity.The development of cyclone doesn't begin at the time when a center of moist potential vorticity is above the cyclone, but at the time when the center is behind the cyclone. In addition,the existence of a distinct inverted conical subsidence zone below 200hPa is also favorable to the development.The large value zone of moist potential vorticity in lower layers has an obvious connection with activities of a lower front.The local change of moist potential vorticity connects with the magnitude of horizontal moist potential vorticity gradient.The variation of the negative/positive values of baroclinic moist potential vorticity below 850hPa is in good correspondence with the development of the cyclone.

Abstract:Using the forced dissipative nondivergent nonlinear barotropic vorticity equation and by means of various schemes,we get its numerical solution,which accords with the attribute of its analytical solution.The results show that diabtic heating strengthens Kelvin cat's eyes,and cooling weakens cat's eyes.The dissipative effect slows down the evolution of stream function field.The strength,movement,shape and vorticity field attribute of simulated cat's eyes possesses some similarity to the evolution of actual subtropical high.

Abstract:Multi-scale fluctuations in climatic temperature variations are analyzed in She and Leveque's framework of the Hierarchical Structure model of turbulences.Through analyzing Jones'northern hemispheric monthly mean temperature series,it is shown that the hierarchical symmetry exists in climatic temperature fluctuations. We obtain a hierarchical similarity parameter β≈0.7,which is notably smaller than that for turbulent flows(β=0.8-0.9),implying stronger intermittency associated with extreme fluctuations in climatic dynamics.

Abstract:Static chamber-gas chromatographic techniques are used for studying the emission of greenhouse gases CO₂,CH₄ andN₂O from a typical Nei Monggol semi-arid grassland.The pattern of diurnal variations of CO₂ emission in different seasons is almost the same,and the total effect of CO₂ exchange with the atmosphere is net release.The key factors that decide the patterns ofN₂O and CH₄ emissions are soil physical properties and soil water content,and temperature determines the intensity of diurnal variations.Because of the relatively fixed diurnal variation pattern of Greenhouse gases emissions from the Nei Monggol Grassland,weekly observed results in the same growth stage can be corrected to get more accurate and representative data.

Abstract:Based on the weekly snow cover data in the Northern Hemisphere from Jan.1,1973 to Dec.31,2000 provided by NOAA-NESDIS,the spatial/temporal characteristics of winter snow cover anomaly over Eurasia are studied.It is found that the perpetual snow of mid-high latitudes in Eurasia has obvious whole-distributing feature,while the winter perpetual snow south of 50°N varies with latitudes;the first EOF eigenvector of the inter-annual departure field of winter snow area over Eurasia indicates that the winter perpetual snow of mid-high latitudes exhibits an east-west opposite-phase distribution.Using wavelet analysis,time coefficients of the first and second spatial patterns of EOF analysis are analyzed,and it is found that the 3~4-year fluctuation period is the largest component in the temporal variation of Eurasian winter perpetual snow.Analysis indicates that the thermal anomaly of underlying surface brought about by Eurasian perpetual snow anomalies may possibly offer a triggering mechanism for the outbreak of El Nino in the next year.

Abstract:The temporal and spatial variation characters of local flow fields in Shanghai are simulated and investigated in this paper by using the 0800 BST observed meteorological element fields as the initial fields and by employing a 3-D terrain-following coordinate atmospheric meso-β scale hydrostatic model,in which some physical processes are considered in detail such as turbulent excharge,long-and short-wave radiation,condensation,evaporation and surface heat energy budget.Then the Eulerian advection-diffusion equation solved by the finite element method is used to simulate the distribution of sulphur dioxide concentration.The results show that the local flow fields exhibit a distinct diurnal variation,and are obviously affected by the sea-land temperature differences;the wind velocity in day time is greater than that at night and the wind rotates clockwisely from daytime to night;under the condition of unstable stratification the air pollutants from elevated point source can be transported to the ground leading to an increase in the surface SO₂ concentration.

Abstract:In terms of artificial neural network method,mean generation function and stepwise regression analysis,a prediction model for the annual number of tropical cyclones affecting Guangxi is developed in this paper.The model allows for not only the significant periods of the prediction but also the physical factors,such as the sea temperature fields and height fields of large scale environment.The test results indicate that the multivariate factors model is more effective than the single factor model.

Abstract:The community characteristics of evergreen broad-leaved forest are studied based on the investigation of the forest vegetation in Gutian Mountain Natural Reserve.The result shows that the forest vegetation in Gutian Mountain Natural Reserve has the typical characteristics of sub-tropical evergreen broad-leaved forest.

Abstract:The extremes characteristics of daily rainfall greater than or equal to 25mm are calculated and analyzed by cross theory and EOF method using the daily precipitation data of 22 stations in Huang-Huai area. The results show that the extreme precipitation in Huang-Huai area mainly belongs to three patterns:i.e.uniform pattern,south-north difference pattern,and east-west difference pattern.The frequency of extreme precipitation and its duration both show a decline tendency.The annual rainfall was decided by the times of rainstorm and its average duration.

Abstract:The Meiyu rainstorms in the Changjiang-Huaihe valley from 22 June to 1 July 1999 are simulated by the meso-scale model MM5 developed by PSU/NCAR.The purpose is to investigate the influence of various moist physical schemes on the forecasted precipitation of Meiyu front rainstorm.The experimental results reveal that the MM5 can reproduce some of the observed meso-scale featuers.The convection parameterization schemes are sensitive to horizontal resolution.Explicit cloud microphysical schemes including ice processes can improve the simulation skill of the model,and especially the double-moment microphysical parameterization including graupel(Reisner) performs best in simulating precipitation.

Abstract:The paper describes the definition of ElNino events and discusses the influence of ElNino events on the summer precipitation over East China under different climatic backgrounds.The analysis suggests that 14El Nino events have occurred since the 1950s and the SST in Equatorial Pacific exhibited a significant increasing trend from the late 1970s to early 1980s.Under different climatic backgrounds ElNino events have different influence on the summer precipitation over East China,but have the same influence-less summer rainfall over the middle and lower reaches of the Changjiang river and the Changjiang-Huaihe valley.

Abstract:This paper presents an automated and efficient cloud classification scheme based on radial base function neural network (RBF),which has an average classification accuracy of more than 86% for less than 5 cloud patterns and 67% for more than 10 cloud patterns.An additional self-organized competitive neural network is also suggested to find out the center of the hidden layer neurons of RBF network,which greatly ameliorates the efficiency of the RBF classifier.Features abstracted by using the two-dimensional wavelet packet 3-level decomposition provide essentials for the description of cloud patterns,thus improving the capability of pattern recognition of neural network classifier.The input dataset employed in the scheme are defined by 2912 samples of 8×8 pixels size taken in July-October 1999 over SE China maritime regions from the visible(0.55-0.9μm) and infrared(10.5-12.5μm) channels of Geostationary Meteorological Satellite 5(GMS-5).These images in Lambert Conformal Conic Projection and in a coarsened resolution of 13.03km×13.22km for both channels are downloaded from the meteorological operational networks.Each of the samples in the dataset is classified into one of the eleven predefined classes in accord with the SYNOP codes used in weather reports.

Abstract:The climatic features of south Asian summer monsoon are studied based on NCEP reanalysis wind data at 850hPa and 200hPa from 1958 to 1997.The results show that there exit significant differences of latitude-longitude winds in region,seasonal variations and peak style of wind over south Asian.There are two significant south-west wind centres over Arabian sea and Bay of Bengal(BOB) and their actions are different significantly.In BOB, the time of its onset and extending northward to 20°N of south-west monsoon is earlier than that in Arabian Sea while its drawback is later than that in Arabian sea,which lasts the longest in Asian monsoon.By contrasting vertical differences of winds at 850hPa and 200hPa during strong and weak monsoon years,it is found that the patterns of the cross-equatorial flow in tropics and the flow in south-Asian monsoon region are different significantly.

Abstract:Using the wet Q-vector and combining with the intense data output of the modified MM4(MMM4) model simulation,a typical Meiyu front heavy rain process occurred during 5-6th July 1991 in the Changjiang-Huaihe Basin is diagnosed carefully in this paper. The results are as follows:the convergence field of wet Q-vector divergence tilts northwards with height; the divergence/convergence fields of wet Q-vector divergence show an alternate distribution in the vertical direction at the developing and decaying stages of Meiyu front heavy rain; based on the convergence field of wet Q-vector divergence,the intrinsic mechanism of Meiyu front heavy rain is discussed, and a new thinking for the forecast of Meiyu front heavy rain is given.

Abstract:The "potential vorticity thinking" is a very intelligent and useful way to explain and predict the synoptic variations. And understanding exactly and inherently the original scientific "thinking" of the classical authors is the key to apply this theorem properly and effectually. Some views on "thinking" are given in this paper.

Abstract:In this paper the research result of the long-range forecast for the Yellow river basin regional rainfall in summer is summarized.On the basis of analyzing the temporal and spatial variation characteristics of the summer rainfall of the Yellow river basin,the summer rainfall is classified by the K-mean cluster.The inter-annual and inter-decadal changes of the summer regional rainfall and their relationship are also calculated and analyzed with lots of associated factors,such as the general circulation at 500hPa,SSTA in the east Pacific,OLR over the tropics,the blocking high in mid-latitudes and the snow cover over Eurasia and the Tibetan Plateau,then an objective numerical forecast system is developed for the summer regional rainfall in the Yellow river basin.The ten years hind-cast of the system shows that the system have fairy good skills in regional rainfall forecast.

Abstract:Using the linear programming method of system engineering theory Minqin County's crops structure is adjusted in the desert east of the Hexi corridor,the summer/autumn crops'proportion is adjusted from 1:0.65 to 1:1.81,the net output value is increased by 6839.43 million yuans than 2000 year.According to different region's climatic feature and yield level,a suggestion about crops'distribution adjustment is put forward,providing a scientific basis for the construction of local optimal crops base.

Abstract:A method using bitmap as weather symbol to draw surface weather chart and using regular triangle net to draw the contours of meteorological elements are introduced in this paper.The operational results of the programme developed under the Visual C++6.0 software environment show that the surface charts drawed by the method are clear,and the contours are accurate and smooth.It can meet daily routine requirement of meteorological observatory.

Abstract:An algorithm for image coding method is introduced based on tree-structured wavelet decomposition.According to some special energy rules,it can decompose adaptively the images.It also can choose proper coding method in accordance with the characters and positions of subbands in wavelet-image.The experiment shows that the new method can obtain high compression ratio under the circumstances of high image quantization.

Abstract:The image files of regional flooded area obtained by NOAA/AVHRR are transformed into a desk geographical information system(ArcView3.1),so that the covering types and area of flooded surface can be estimated with the aid of the Geography Information System(GIS).The main techniques used are as follows:the method of border test is used to recognize the flooded area in the BMP images;the coordinates of longitude and latitude in marctor projection are transformed into the coordinates of kilometer grid in Gauss-Laguerre projection;the key writing techniques of Shapefile is described in an example of the flood in Liaoning Province in August 4,1995.