Abstract:A rain storm associated with a flashflood event is simulated by the Advanced Weather Research and Forecasting(WRFARW) model of National Center for Atmospheric Research(NCAR) and Gridpoint Statistical Interpolation(GSI) data assimilation system of U.S.NOAA.The event is based on a flashflood that occurred in the central Guangdong Province of southeast China during 20—21 June 2005.Comparing to a mixed rain gauge and satellite retrieved precipitation data,the model shows a capability to reproduce the intensity and location of rainfall.However,the simulation depends to a large extent on three conditions:model resolution,physical processes schemes and initial condition.In this case,the Eta Ferrier microphysics scheme and the initialization with satellite radiance data assimilation with fine 4 km resolution nested grid and coarse 12 km resolution outer grid are the appropriate options.

Abstract:Based on the annual average NCEP/NCAR reanalysis data,the seasonal variation characteristics of the intensity and location of the Middle East jet stream(MEJS) and their relations with the SouthNorth temperature differences(SNTD) are discovered.Results show that there are obvious seasonal variation characteristics for the vertical structures of intensity and location of westerlies over the Middle East area.The intensity of westerly center is stronger in winter and spring,but weaker in summer and autumn.Above 600 hPa,the location of westerly center is southward in winter and spring,but northward in summer and autumn.In each season,the velocity of 200 hPa westerly center is maximum.The intensity and location of MEJS have obvious seasonal variation characteristics.MEJS is stronger and locates in 275°N from November to the next April.MEJS is weaker from May to October and moves northward after May with its center maintaining over about 40°N from June to September and 325°N in October.The seasonal variation characteristics of the intensity and location of MEJS are significant with good corresponding relations to the SNTD averaged from 500 to 200 hPa.It shows that the seasonal adjustment of SNTD has important effects on the seasonal variations of intensity and location of MEJS according to the principle of thermal wind.

Abstract:Based on the daily precipitation data from 740 stations in China and NCEP／NCAR daily reanalysis datasets,the interdecadal variability of largescale precipitation conditions over North China during rainy seasons is analyzed by means of composite analysis methods.The results show that:with a turning point from flood period to dry period in 1978,anomalous moisture budget over North China changed from south boundary and west boundary to north boundary and east boundary and thus made water vapor become divergent and absent from convergent and abundant.Warm and moisture air mass from ocean could reach the north area of North China or even its northern border before 1978,but it could only reach the south bank after 1978.The interaction between the cold and warm moisture air mass along the Taihang Mountain became weaker.In addition,anomalous upward motion became anomalous downward motion over the North China;areal average vorticity changed from two layers structure(positive vorticity in the low levels and negative vorticity in the high levels) to three layers structure(negative vorticity in the middle and lower troposphere,positive vorticity in the middle and negative vorticity in up troposphere) and the value of total vorticity became smaller.Vertical configurations of areal average divergence and vertical velocity presented no conspicuous interdecadal variability,but their values all became smaller.

Abstract:Based on the WRFVar assimilation system developed by the U.S.and the cloud drift wind information of China,the threedimensional and fourdimensional variational data assimilation is performed on a single case of heavy rain in the valley of Yangtze River on 10 June 2008.Results show that the two kinds of data assimilation of cloud drift wind can improve forecast accuracy in heavy rain and torrential rain.The fourdimensional experiment scheme works particularly well in improving the accuracy of torrential rain.This is considered the most important in precipitation forecast.The further analysis of initialization of two assimilation tests shows that the assimilation of cloud drift wind can well improve the initialization,and has positive impact on the prediction of the physical variables.Overall,the use of fourdimensional assimilative scheme can more effectively adjust the initial field,and reduce the forecasting errors of various elements.The causes of heavy rain are also discussed.Results show that this torrential rain process occurs under the combined effects of upper trough and lowlevel shear line as well as the highlow jet.The lowlevel jet provides not only water vapor needed by the rainstorm,but also energy for positional instability of stormforming convection.

Abstract:Quality test and reliability evaluation are prerequisites for reanalysis data to be used.To evaluate the reliability of NCEPII,ERA40 and JRA25 reanalysis data used in West China,the study analyzed the quality of the 2m temperature products.The three types of air temperature reanalysis data could well reflect the spatial distribution in West China.The difference in air temperature at stations of complex topography was relatively large while the three types of reanalysis data could provide highquality air temperature data in flat areas.Air temperature data from ERA40 and JRA25 are more reliable and can reflect more detailed air variability in large scale because they assimilate the groundbased data.Overall,the quality of ERA40 is better than the other two types of reanalysis data.

Abstract:Based on Chinese satellite in geosynchronous orbit (FY2C) information on cloud physical characteristics parameters of the retrieval,and observations by radar,microwave radiometer and precipitation on ground,the structural features of cloud merging of a strong precipitation process are analyzed in Anhui Province,China on 17 July 2008.Results show that the development of convective clouds merging is the main reason for the occurring of heavy precipitation.The cloud optical thickness retrieved by FY2C satellite is found to be well consistent with radar echo of the corresponding region and the evolution of surface precipitation distribution.The heavy rainfall areas are in good agreement with the those of big cloud optical thickness and strong radar echo.Cloud liquid water distribution is very uneven and mainly in group block structure.The top of clouds often merge in the initial stage of convective cloud merging.Once the uneven liquid water in clouds unites,the cloud optical thickness in the combined parts increases rapidly,the whole layer of liquid water content from the ground microwave radiometer changes dramatically,and the ground heavy precipitation occurs.The statistic result shows that the top of cloud rises,and its optical thickness often increases before the reinforcing of precipitation.If the top of cloud is high with small optical thickness value,precipitation on ground is usually not obvious.The optical thickness of cloud is more related to precipitation.In the initial period of convective clouds merging,the clouds base consists of small particles,showing a deep zone of diffusional growth on the map of 〖WTB1X〗Tr〖WTB1〗e relations.Then,the effective radius of cloud droplet of total layer significantly increases,and the mixed phase and glaciation temperature is warmer.

Abstract:Based on the meteorological data of 84 stations in the Yangtze River delta from 1961 to 2006,the basic features of temporal and spatial changes of temperature and precipitation are investigated.Results show that the annual mean temperature increased significantly during the past 46 years.Winter,spring and autumn mean temperature all increased significantly,and the temperature increasing rate in winter is the biggest.The areas with significant temperature increase coincide with the main urban areas.The annual minimum temperature shows an evident increasing trend while the frequency of extreme low temperature events decreased.In most regions,the maximum temperature increased significantly,especially in the megacity regions.The annual precipitation did not show any significant trend,but the seasonal distribution of the precipitation exhibits significant changes.The precipitation increased in both winter and summer while decreased in autumn.However,no significant trend was detected in spring.

Abstract:Starting from nonlinear equations on the 〖WTB1X〗f〖WTB1〗plane containing frictional dissipation and condensation heating under the Boussinesq approximation,the equation of generalized energy in moist air is presented,and the necessary condition of subcritical moist symmetric instability is derived.The influence of condensation heating on the subcritical symmetric instability is derived analytically at first.Then the critical values of the initial disturbance amplitude are calculated in the cases of unstable and stable mesoscale atmosphere stratification.It is found that subcritical symmetric instability is easier to happen in moist saturated air with either the unstable or stable stratification than in the dry air,and easier with the unstable than stable stratification.The results improve the theory of nonlinear subcritical symmetric instability in the dry air.

Abstract:The response characters of sea surface flow to external forcing (wind stress and sea surface heat flux) and the more sensitive areas are analyzed by some numerical simulations.It is found that the more sensitive response area of sea surface circulation to wind stress is located near the equator and the west boundary of ocean according to the simulation results in the control run and sensitivity experiments.Corresponding to that over the extratropical region,the wind stress anomaly over the tropics (20°S—20°N) is greater and more significant impact on the sea surface circulation over tropic sea and also east boundary flow in the mid and highaltitude.The response of sea surface circulanton to sea surface heat flux anomaly is significant over tropic sea and also east boundary flow in the mid and highaltitude.The east boundary flow in Atlantic is more sensitive to sea surface heat flux than wind stress by the same external forcing(20％).The sea surface heat flux anomaly could have some influence on east boundary flow in the southern Pacific Ocean and the circumpolar flow around Antarctic continent.

Abstract:Based on the NCEP/NCAR reanalysis datasets and the precipitation data from 160 stations in China during 1951—2010,the relationship between the flood/drought in the middle and lower reaches of the Yangtze River and the anomalous atmospheric circulation over Philippine Sea was investigated.Results indicate that the area around the Philippine Sea is the key region to significantly affect the precipitation over the middle and lower reaches of the Yangtze River.The intensity of the anomalous anticyclone(cyclone) located over the Philippine Sea is strongest at 850 hPa and decreases as altitude increases as well as its relationship with the above mentioned precipitation.When the anomalous anticyclone appears around the Philippine Sea,the distributions of the vertical velocity and water vapor flux,among others,are all favorable to bring more precipitation around the Yangtze River basin,and vise versa.

Abstract:Based on the temperature data of 74 conventional meteorological stations in Zhejiang province and the surrounding from 1961 to 2000,using the physicalexperience model of monthly air temperature,we generated spatial distribution maps at a resolution of 100 m×100 m for the monthly mean,the monthly mean maximum and minimum air temperatures of Zhejiang province.The local distribution characteristics of fitting temperature are analyzed,and the simulated results are validated from several angles.Results show that the mean absolute error are 009—059 ℃ for monthly mean air temperature,009—080 ℃ for monthly mean maximum temperature,and 010—058 ℃ for monthly mean minimum temperature,respectively.The simulation can reflect to a considerable extent for the macro and local distribution characteristics of air temperature,which makes a good foundation for the reasonable development and utilization of climate resource over the rugged terrain of Zhejiang province.

Abstract:Based on the meteorological data from 2008 to 2009,which were collected from an automatic observation system over water surface in Erhai and an automatic weather station in Dali National Climate Observatory,the diurnal and seasonal variations of wind speed,wind direction,air temperature,relative humidity,air pressure and precipitation were analyzed and compared.Results show that there is a local circulation in surface layer over the Erhai lake basin,which is caused by the lakeland breeze,the mountainvalley wind and the gorge wind affected by the local complex terrain and the Erhai lake.The prevailing winds are southeast in the day,and southeast and west southwest at night over the water surface.The prevailing winds are east southeast in the day,and static wind and west northwest at night over the land surface.The annual mean wind speed is 29 m／s over the water surface and 24 m／s over the land surface.The annual mean air temperature is 168 ℃ over the water surface and 160 ℃ over the land surface.Air temperature,relative humidity and air pressure show significant diurnal variations over the water and land surfaces.The occurrence time of maximum and minimum of air temperature and relative humidity over the water surface is later than that over the land surface.The annual rainfall mainly takes place from May to October.

Abstract:〖WT5HZ〗Abstract:〖WT〗Based on the NCEP final analysis data,a mesoscale modelWRF was used to simulate a heavy rain process,which occurred in Jiangsu Province during 22—23 July 2008.The results show that the WRF has a strong simulating ability for precipitation as well as has a good capacity to predict the mesoscale weather systems.In this rainfall event,the rational allocation of lowerlevel wind shear,cold air and upper air jet stream strengthened the development of vertical circulations,which inspired the convection development in the rainfall region.Also,the upper air convergence and lowerlevel divergence in the large scale flow filed are favorable for the rainfall occurrence,where the strongest water vapor transfer from 850 hPa is necessary.On the basis of energy analysis,not only a high Kindex value all over the Jiangsu Province,but also substantial energy accumulation in the north and middle of Jiangsu provides the instability condition for the precipitation.In addition,the coupling of helicity with a negative(positive) value at upper(lower) levels is the dynamical mechanism to activize and maintain such a low pressure torrential rainfall.

Abstract:A heavy torrential rainfall process during August 17 and 18,2009 is analyzed by using both normal and abnormal data such as radar data.The results show that:1) the torrential rainfall mainly occurred in the border district of northwest subtropical high when the trough moved eastward and the subtropical high moved backward to the south;2) some thermal environmental indexes like CAPE presented good corresponding relationship with intensive rainfalls in south Shandong province;3)distribution of precipitation was profoundly affected by the topographic condition;the complex topography of mountains in Shandong Province can lead to significant precipitation amplification and block the movement of the convective systems;4) low jet stream and train effects existed in the torrential rainfall;the strong radarecho lasting for a long time is the main reason for the heavy rain in Feixian;the strong southerly flow and the thick moist air are the leading factors for the torrential rainfall;5) the theory of the impact of terrain on precipitation well explains the distribution of precipitation in this torrential rainfall progress;6) the special terrain of Feixian contributes to the heavy rainfall greatly.Radar data is a good supplement to normal observational data.The impact of terrain exerts important influence on strong precipitation and its distribution.

Abstract:From the factors leading to a disaster,those more directly related with heavy rain disasters can be collected by analyzing the relationship between the heavy rain and the subsequent disaster loss systematically.An evaluation model of regional heavy rain strength is established by using the methods of normal distribution probability density function and minimum distance.On that basis,by using the analogy method,a model for quantitative preestimate of heavy rain disaster loss from May to September in Hubei Province is established by analyzing the similarities in the disaster loss in some heavy rain cases in history.It shows that analogy method is practical in quantitative preestimate of heavy rain disaster loss according to the test results from 2008 to 2009.

Abstract:A new atmospheric correction algorithm based on dark object method and the look up table developed from MODTRAN model was introduced for Landsat images in the paper.The infomation of the satellite remote sensing images was used to support the atmospheric correction.The algorithm was applied to the Landsat ETM+imagery and comparisons show that the influence on Landsat imagery caused by molecules,water vapor,ozone,and aerosol particles in the atmosphere was effectively reduced after the correction.The surface reflectivity was more precisely,which is beneficial for remote sensing information extraction and thematic interpretation.