Abstract:The method of direct solving equations is often applied in the retrieval of lower layer 2-D winds from the dual-Doppler radar data,but there are many limitations:singular points shall pollute their circumambient retrieval results and the observations’ errors would affect the accuracy of retrieval,etc.A variational method in combination with a regularization method is introduced in this paper,wherein a regularization term is added to the target functional and regularization parameters are reasonably selected.Numerical experiments show that the introduction of the regularization term can efficiently filter the errors of retrieval wind field,resulted from singular points and observations,improve the retrieval accuracy,and yield the optimal global retrieval wind field.

Abstract:Nonlinear characteristics of the precipitation anomaly over china during the last five decades were investigated by applying a back-propogation neural network-based nonlinear principal component analysis(NLPCA) method to the seasonal rainfall anomaly data.The results show that the NLPCA could describe more general characteristics of the low-dimension structure of precipitation.The precipitation anomaly of each season has a certain extent nonlinear space pattern,but the nonlinearity of autumn and winter precipitation is weaker than spring’s and summer’s.The spatial pattern based on the leading NLPCA mode approximation manifests obvious asymmetry when the nonlinear principal component takes the maximum and minimum value.The leading NLPCA made approximation is more realistic to the original precipitation anomaly data than the leading PCA mode approximation,and changes with season.

Abstract:Based on observed data,we compare the photosynthetic rate and stomatal conductance of sunlit and shaded cotton leaves respectively.Results show that the photosynthesis in big-leaf model is totally 13% higher than that in two-leaf model.Therefore,the contribution of cotton’s potosynthesis to carbon sink might be exaggerated in past estimating photosynthesis by using big-leaf model in carbon exchanges between the biosphere and the atmosphere.

Abstract:An algorithm of motion vectors,tracking and nowcasting of echoes based on Fast Fourier Transform(FFT) technique is developed for the radar volume-scan data.The basic principle is that firstly,the FFT is separately used to two successive volume-scan radar echo data whose time interval is small,yielding a phasic difference between the two radar echoes;secondly,using the phasic difference,the direction and speed of radar echo motion can be obtained.This algorithm is validated with the data of a Doppler polarimetric meteorological radar from the Institute of Atmospheric Physics,Chinese Academy of Sciences.The retrieved results show that using the new algorithm,a more precise structure of echo motion vectors is captured,and some typical dynamic characteristics of meso-and micro-scale weather systems are also depicted.The technique also has a good performance of tracking and nowcasting radar echo movement.It is also found that there was obvious non-uniformity in movements of strong echoes in a squall line on 12th July 2006.

Abstract:Stratiform cloud precipitation processes in Henan Province on October 16—20,2002,were mainly caused by trough-line,low-level shear and surface trough.The vortex and trough cloud systems produced light to moderate rains.The convectively unstable stratification and the easterly and southerly warm/moist flows in middle-and low-levels provided advantageous conditions for the rainfall.Deep clouds had a mixed-phase structure,and the radar echoes had distinct bright bands in most cases.The water content of ice particles was higher than that of supercooled droplets in supercooled cloud layers,and the water content of cloud droplets was relatively low in warm cloud layers.Raindrop number concentrations reduced exponentially with raindrop diameters,and large raindrops contributed more to the rainfall rate.It can be inferred that the cold-cloud process was stronger than the warm-cloud process,and the deposition of ice particles was its major growth mode,and the melting of ice-phase particles had the greatest contribution to the surface rainfall.Both the macro-and micro-physical structures of cloud systems and precipitation features indicate that heterogeneity existed in different parts of the stratiform cloud systems.

Abstract:By utilizing a high resolution f-plane barotropic pseudo-spectral model,the physical process of the influences of a meso-β vortex on the binary interaction of typhoons is analyzed.The results show that the meso-β vortex may alter the process of binary interaction and trigger a merging process.The physical mechanism by which the meso-β vortex can alter the final state of binary interaction is:when the meso-β vortex locates in the positive influencing area of one typhoon at the initial period time,an antisymmetric vorticity field comes into being and inspire airflows pointing to the other typhoon;and if those airflows are sufficient strong,they will make the two typhoons moving to each other and entering into the merging critical distance in a shorter time,which finally causes the mergence of the two typhoons.

Abstract:The land surface temperature(LST) of the study area of the Yellow River Delta are retrieved from Landsat7 ETM+ images using three different methods(thermal radiance transfer equation,the mono-window algorithm by Qin et al in 2001,and the generalized single-channel method by Jimёnez-Muoz & Sobrino in 2003),and the mean accuracy of retrieval results also disscussed.The retrieval results show that the mono-window algorithm and the single-channel method both have a higher accuracy within 1 K deviation when the integrated water vapor in the atmosphere is low;While the water vapor of air is high and the LST is retrieved with the water vapor estimated by the ground-base weather data,the error is about 0.95 K for the mono-window algorithm in contrast to 1.94 K for the single-channel method.Meanwhile,the Normalized Difference Vegetation Index(I_NDV) is corrected by 6S mode,and then,differences in LST and I_NDV for different land use types and their quantitative relations are analyzed.The result of regressive analysis shows a significant negative correlation relationship between LST and I_NDV for all land use types,and the negative correlation holds for each land type,but with different correlation coefficients.

Abstract:Based on the routine observational data as well as automatic weather stations data,FY-2C satellite cloud pictures,the NCEP/NCAR reanalysis data and Doppler radar data in Guizhou,a torrential rain on June 13,2006 in Wangmo,Guizhou Province is analyzed.The direct impact system of the torrential rain,the evolution of mesoscale convective cloud clusters,the characteristics of Doppler radar echoes and physical characters are researched.The diagnostic results show that the heavy rain in a short time in Wangmo was caused by the vigorous development of meso-β cloud clusters,induced by the frontogenesis on a convergence line in the southwest of Guizhou under the impact of the rapidly southward moving of the cold air from Hetao.The region of heavy rainfall was directly linked to the convergence zone,where an energy front existed in low levels.Moist available potential energy was accumulated ahead of the front.The baroclinic disturbance induced the development of vorticity,leading to the intensive development of convective unstability.Radar echoes revealed typical mesco-scale characteristics of the torrential rain.

Abstract:A comprehensive observation of boundary layer structure was carried out at Pancheng town in the north suburb of Nanjing during fog days between 24th and 27th December,2006,using a DigiCORA Ⅲ system for boundary layer elements sounding and an Envirostation TM for surface element observation.The physical mechanism and boundary layer structures of the advection fog are studied thoroughly,and the results are as follows.The formation and maintenance of the relatively typical advection fog was mainly determined by the warm/wet airflow and the systematical sinking motion,and the invasion of dry/cold air resulted in the dissipation of the fog principally.Besides,the fog two-layer structure appeared during the descending period of fog top.The middle temperature inversion,belonging to the subsidence inversion and advection inversion,was a primary inversion,and its intensity center was near or under the fog top.There were several speed maximum values of wind in the vertical.The jets in the middle layer and in the lower layer exhibited strong and weak alternation after the coalescence of the middle layer jet and the weaker ones in the middle-upper and upper layers.While the speed was low,the wind field approached homogenous,and during the period of dissipation,the wind field of the lower layer showed a linear distribution of wind speed with height.The moisture source of the fog was mainly from the warm/wet air flow.There was a good spatial-temporal distribution correspondence between moisture and wind fields,and the intensity center of the main temperature inversion was also the intensity center of the moisture inversion,so that the spatial-temporal distribution of the moisture was mainly determined by both the wind and temperature fields.

Abstract:Numerical simulation is made on typhoon Bilis and Kaemi(2006),the simulated vapor,dynamic and energy fields are analyzed,and two forecast models for preciptation of landfalling typhoons are summed up.The analysis results show that Bilis was affected by the southwest monsoon and got a lot of vapor and energy supplies,while Kaemi did not have such supplies,so precipitation in the south of Kaemi is smaller than that of Bilis.However,Kaemi caused flood calamity in the middle and lower reaches of Yellow River area when its circulation interacted with the cold air from the north.

Abstract:By use of the empirical orthogonal function(EOF) method,we can get the Northern Hemisphere annular mode(NAM) of summer sea level pressure(SLP) fields during 1948—2005 from NCEP/NCAR reanalysis data.As one of main modes of SLP fields,summer NAM,exhibiting an annular structure in the Northern Hemisphere,involves a seesaw between the Arctic basin and parts of the surrounding zonal ring,which displays the zonal symmetry of high degree.Using the empirical mode decomposition(EMD) and Hilbert-Huang transform(HHT) methods,we conclude that the summer NAM index has the interannual periods of quasi-2 yr and 6 yr,and the interdecadal periods of quasi-11 yr and 21 yr,in which the interannual signal is the primary part.

Abstract:A heavy rainfall during 5—7th June 2006 in Fujian province was simulated by the WRF mesoscale numerical model.Diagnoses were made based on the output data,to get the structure of the rainstorm and the influence of complex topography.Results show that,the WRF model successfully revealed the circulation’s evolution and the distribution of rainfall belt.It was a typical South China quasi-stationary precipitation which was associated with the stationary front,low-level wind shear and low-level jet.The convergence of the low-level flows intensified the ascending motion which triggered the release of potential instable energy,resulting in the genesis and maintenance of the rainstorm.The vertical configuration of potential temperature was found favorable to the development of vorticity at low level.With the help of Bell-mouthed terrain and the windward slope of the Wuyi mountains,southwest airflow veered and converged at low level,resulting in the form of mesoscale shear and vortex.Warm and wet air was raised by the mountain,thus enhancing severe convection at the middle-level.All of the above factors reinforced the rainfall at Jianou,Shaowu and Pucheng on the windward slope.

Abstract:In order to study the atmospheric stratification characteristics and the thermal structure of sandstorms,we performed an intensive observation during the passage of strong sandstorms process in Minqin,Gansu province from 23rd to 24th May 2004,by using the L-band radar sounding.The vertical profiles of meteorological elements and energy synoptic meteorology are used to analyze the characteristics of the atmospheric stratification and the evolutional characteristies of the atmosphere during the development process of the sandstrom.The results are as follows:Before the sandstrom arrived at Minqin,the wind speed below 500 hPa was small,there was the easterly flow below the 800 hPa level and the westerly flow at the middle-upper level.When the sandstrom passed through Minqin,the wind speed increased apparently in the surface layer,below the 700 hPa level was the northwesterly flow and the southwesterly flow in the upper atmosphere.The high-layer relative humidity was higher than that of the low-layer atmosphere before the passage of the strom,however after the passage,the relative humidity increased obviously,and there was a humidity inversion phenomenon near 800 hPa.Around the passage the entire atmosphere had a vertically consistent trend of humidity.The surface temperature was higher before the passage,there was a super low temperature phenomenon near 200 hPa,and a thicker subsidence inversion layer near 250 hPa,along with the passage of the sandstorm,the temperature in the lower level dropped markedly,the temperature inversion layer near 250 hPa gradually weakened and another temperature inversion layer occurred near 800 hPa.Before the passage,there were low pressure,high temperature and weak wind near the ground surface,when the storm arrived at Minqin,the pressure surged up,the wind speed rapidly increased,and the temperature dropped.The atmosphere was convectively below 500 hPa before the passage,during the saturation energy deficit reduced gradually,the unstable energy was transferred from upper layers to low layers,the development of vertical motion was intensified.After the passage,the whole atmosphere was stable,the unstable energy was used up,and the whole atmospheric humidity increased greatly.

Abstract:Matlab was used to simulate the typical radar’s radial velocity field when a cold front passes an observing radar.Doppler radar base velocity data were processed using the combined shear estimation algorithm to identify the characteristic structures of the cold front wind field,and the thresholds for automatic identification of cold front were investigated.A module for cold front identification was designed.The radar observations of the large scale heavy rain on 13th May 2002 in Hunan Province were processed,and the result suggests that the module had a fairy good ability to identify the cold front system.

Abstract:Based on the meteorological record of selected 616 weather stations in China during 1975—2004,reference evapotranspiration(E_T0) was calculated by using the Penman-Monteith equation recommended by FAO,and the wetness index was also estimated from precipitation and E_T0.According to wetness index values:0.03,0.2,0.5,1.0,China was classified into five climate zones:extreme arid,arid,semi-arid,semi-humid and humid zones respectively.The geographical distribution as well as time trend and variation of wetness indices in China are given and its inter-annual and decadal variations are discussed in this paper.Results show that significant wetting trend occurred in northwest Xinjiang District and southwest China,the significant drying trend was found in east Qinghai Province,south Gansu Province and north Sichuan Province.The variations in wet/dry conditions gradually became greater from eastern China to western China,with the smallest change in southwest China.1980 was a transitional year from when the climate turned from a drying trend to a wetting one.From the beginning of 1975,decadal changes were evident in that semi-humid and humid regions,semi-arid and humid regions expanded,and semi-humid ones shrank.

Abstract:In this paper,a global solution to the coupled elliptic-parabolic system modeling a class of engineering problem with thermal effect is studied.Under the assumptions that ^σ(s),^κ(s)∈W^1,∞(R),b∈[L^∞(Ω)]²,c∈L^∞(Ω)and (κ₁-α)λ₁(λ₁ denotes the first eigenvalue of-Δ in Ω,α>0),we apply Faedo-Galerkin method to construct an approximate solution to the problem that exists in a local time,then prove some a priori estimates to show that the approximate solution can be extended to the interval .By using the compact theorem,we get the global solution as n^→∞.If the coupled functions ^σ(s),^κ(s) are degenerate,we can also get the existence of solution to the considered problem by constructing their truncation functions.

Abstract:By analyzing daily observed routine meteorological variables such as sunshine-hours,maximum temperature,minimum temperature and solar radiation from 23 stations in China,models were established for assessment of daily solar radiation.The models include two independent variables i.e.percentage of sunshine and diurnal temperature range.Except for Lhasa weather station with a high elevation located in plateau,multiple correlation coefficients of all models range from 0.80 to 0.93.Through analysis on the modeled results,we found that it is necessary to use seasonal models to estimate daily solar radiation,especially for spring and summer.It could come to a conclusion that the models developed in this paper are effective and feasible in the assessment of daily solar radiation in whole China.

Abstract:Based on the analysis of sampled fog water in the north suburb of Nanjing city during December 2006,study is conducted of heavy metals of fog water and air pollution in foggy weather.Results show that foggy weather condition prevented the diffusion of pollutants,which led to the heavier air pollution and changes in pollutant concentrations were approximately in step with fog formation/dissipation;the heaviest concentration of PM₁₀ on fog days was 2.5 to 10 times that in the pre-fog stage.The heavy metal concentrations of fog-water ranged from 0.020 5 to 1.824 8 mg/L,with a mean of 1.32 mg/L;one-to-one correlation analysis between concentrations of heavy metals(Cd,Cr,Cu,Mn and Fe except As)and those of gaseous pollutants shows that their correlation coefficients were all greater than 0.91,thereby indicating that heavy metal and gaseous pollutants were emitted by the same pollution source.

Abstract:By using the fixed point theorem,we show the existence of positive solutions of a singular second-order three-point system,where 0<η<1,and a(t),b(t) are singular at t=0,1.