Abstract:Infrared(IR) observations from Spinning Enhanced Visible and Infrared Imager(SEVIRI) on board Meteosat Second Generation(MSG)-2 satellite are assimilated into NCEP(National Centers for Environmental Prediction) global data assimilation system(GDAS).The assimilation of current Geostationary Operational Environmental Satellite(GOES) Imager data was also reinvestigated.The Community Radiative Transfer Model(CRTM) was used as observation operator for the simulation of SEVIRI radiance observations.The CRTM was enhanced with several critical components for IR radiance simulation,such as a dynamically-updated land surface emissivity data,as well as fast and accurate gaseous absorption modules.The Global Space-Based Inter-Calibration System(GSICS) calibration corrections were applied to improve the simulation of SEVIRI and GOES Imager radiances.Preliminary results show that inclusions of the SEVIRI radiances at water vapor channels(6.25 and 7.35 μm) and CO₂channel(13.40 μm) in Global Forecast System(GFS) produced significant positive impacts on the six-day forecasts.Assimilation of other five SEVIRI IR window channels in GFS reduces the positive impact.By applying GSICS calibration algorithm to correct SEVIRI and GOES-12 Imager observations biases,the impacts on GFS forecast were improved.Further studies are being carried out to improve the effective assimilation of SEVIRI IR window channels radiances.

Abstract:A process of severe convection occurring in Shanghai on August 25,2010 is analyzed by using LAPS(local analysis and prediction system) analysis field to assimilate various meteorological data.Results showed that the storm was trigged directly by mesoscale convergence systems on middle and lower layers.The convergence lines on surface developed into strong ones in the formation stage and became the major triggering mechanism of the mesoscale vertical circulation.In the meantime,the vertical structure contributed to the mesoscale convection development because of the convergence on middle layer and the divergence on high layer.The prominent updraft zone located near the storm center,and the relative humidity grew significantly on middle and high layers.In the mature stage,the downdraft drag,which occurred on low layer near the storm centre,made the updraft more slantwise.The mesoscale circulation structure and moisture supply were destroyed in the decaying stage,and the vertical structure was contrary to that in the formation stage.The LAPS analysis field has an advantage in spatial and temporal resolution,which well revealed the spatial structure and development process of meso and small scale systems in the mesoscale analysis.

Abstract:By using outgoing longwave radiation(OLR) data from National Oceanic and Atmospheric Administration(NOAA),daily wind (850 hPa) data from European Center for Medium-Range Weather Forecasting(ECMWF) and tropical cyclones(TC) data from Joint Typhoon Warning Center(JTWC),the impact of quasi-biweekly oscillation(QBW) on tropical cyclone activity over the western North Pacific(WNP) is studied in this paper.The index of 10 to 20-day oscillation is defined by referring to the Madden-Julian oscillation(MJO) index proposed by Wheeler and Hendon(2004).The analysis shows that TCs always occur in the area where convection is active.During QBW-phase1,the southeasterly of the western North Pacific subtropical high is weakened by the anticyclone-circulation of QBW.The westward (northwestward) moving TCs tend to change their tracks to the west of 140°E.During QBW-phase3,with the southeasterly of the western North Pacific subtropical high strengthened by the cyclone-circulation of QBW,TCs tend to change their tracks to the east of 140°E.Case studies of some TCs are discussed in this paper.The results show that TCs may present sudden poleward track change while its center overlaps with the center of the cyclone-circulations (anticyclone-circulations) of QBW.

Abstract:Based on the lightning data by the World Wide Lightning Location Network(WWLLN) and the typhoon data from Typhoon Institute of Shanghai Meteorological Bureau,the paper presents the lightning activity characteristics and the relationship between the lightning frequency and the maximum winds of 55 typhoons occurring over the western Pacific during 2005 and 2010.The results show that over the west Pacific,there are three distinct lightning flash regions in mature typhoons.One significant maximum in the eyewall regions about 20-40 km away from the center;the other two are located in outer rainbands (280-340 km and 440-580 km from the center).Most typhoons have lightning activity peaks before the maximum winds.The lag times ranges from 0 to 24 hours and the average lag times is 26.6 h.Therefore,the frequency of lightning activity is,to some degree,an indicator for the typhoon intensity development within 24 h.

Abstract:Two ensemble simulations for 22 boreal-summer seasons (1979-2000) are conducted by the Community Atmosphere Model version 3 (CAM3) with the specified observed sea surface temperature(SST).Impacts of surface soil moisture(SSM) on the simulation of potential predictability of East Asian summer climate are investigated by the model with interannually varying SSM(ISSM) and climatological SSM(CSSM),respectively,based on the variance analysis method.Results show that,under the specified observed SST,the potential predictability of East Asian summer climate simulated by the CAM3 with ISSM is better than that with CSSM over East Asia,especially over Northwest China.The potential predictability of summer precipitation and air temperature over Northwest China from ISSM simulations is 0.1 higher than that from CSSM simulations.A possible mechanism of influence of soil moisture on potential predictability of summer climate in Northwest China is proposed.The interannual variability of ground evaporation and surface turbulent heat flux can be simulated by CAM3 with ISSM better than with CSSM in Northwest China,leading to the model forecast skill of the summer climate improved by the model with ISSM.

Abstract:Based on the NCEP/NCAR,ERA-40 reanalysis datasets and 160 stations precipitation data in China in summer(July and August),by means of correlation analysis,composite analysis and other methods,the interannual relationship between Mascarene High(MH) and summer precipitation in North China and it's interdecadal variability are analyzed.Results show that there is significant negative correlation between the MH and summer precipitation in North China in interannual time scale and that this negative correlation relationship began to diminish since 1974.During the stronger period(1951-1973),significant negative correlation center between the MH and summer precipitation over eastern China was mainly located in North China,while during the weaker period(1974-2011),the negative correlation between the MH and summer precipitation over North China became weaker,and significant positive correlation center was observed in the middle and lower reaches of the Yangtze river.The cause for interdecadal variability between MH and summer precipitation in North China is as follows:when Eastern China is(not) influenced by the stronger anomalous south wind coming from MH,summer precipitation in North China is more(less),and the relationship between MH and summer precipitation in North China is in stronger(weaker) period.The interdecadal variability of inter-annual relationship between MH and summer precipitation in North China is one of the causes for the floods in Southeast China and droughts in Northeast China since the mid-1970s.

Abstract:Using tropopause pressure data and upper temperature data of 14 sounding stations over the Tibetan Plateau from 1979 to 2008,the relationships between two types of tropopause heights and upper air temperature in different seasons are analyzed.Based on these,the coupling connection between ascending motion(total ozone) and tropopause height is discussed by monthly NCEP/NCAR reanalysis data from NOAA and monthly TOMS/SBUV total ozone data from NASA.The results indicate that the first(second) tropopause is at 300-200 hPa(near 100 hPa) over the year.The seasonal,interannual variations and long-term trend of the two types of tropopause heights display closely opposite relation to those of temperature at their corresponding altitudes,respectively,namely the higher(lower) tropopause height,the lower(higher) temperature at the corresponding altitude.The ascending motion is conducive to the rising of the tropopause height,especially the ascending motion at about 200 hPa(100 hPa) is helpful to the rising of the first(second) tropopause height.There is an obvious negative correlation between the total ozone and the second tropopause height at each season.The second tropopause rises(reduces) with the losing(increasing) of total ozone over the Tibetan Plateau.In recent years,the second tropopause height clearly lifts with the reducing of the total ozone.

Abstract:Based on the observed daily temperature data from 62 stations in North China and NCEP/NCAR reanalysis data from 1961 to 2008,the characteristics of negative accumulated temperature (NAT) change in North China and its circulation background were studied through methods such as EOF,REOF,and wavelet analysis.Results show that:1) the NAT in North China increased consistently,especially in Northern Shanxi Province;2) The NAT in North China can be divided into two subdivisions because the NAT increasing amplitudes were different in east and west.There were both abrupt changes in the west and east of North China,occurring in 1988 and 1986 respectively.A 3-6 years' cycle period was found in the west of North China while it was 2-4 years in the east of North China;3) Changes of Northern Hemisphere winter atmospheric circulation had a close relation with the NAT anomalies in North China.Further composite analysis showed that cold periods were represented by stronger Siberian High,colder winter in North China and larger NAT’s absolute value near the ground while the main influence systems were the East Asian trough and Ural ridge in the middle troposphere.The stronger Ural ridge and the deeper East Asia trough made the cold air activity stronger in North China.In warm periods,it was the opposite situation.

Abstract:A thunderstorm ensemble forecasting approach is performed by the ensemble analysis of the cloud model’s forecast results according to the initial condition aggregation provided by the grid forecast results of the mesoscale non-hydrostatic WRF model.The approach is applied to forecast the characteristics of thunderstorm around Nanjing one day in advance and is verified by the Doppler radar data of the thunderstorms in summer in Nanjing.Results show that the intensity and distribution of thunderstorms over the research area is reasonably predicted one day in advance.It is particularly good to forecast the distribution of the strong thunderstorms by using the ensemble forecasting technique.Moreover,the application of the PDF(probability density function)of thunderstorms’ duration into the probability forecasting of the influenced area of thunderstorms improves the radar’s warning and monitoring capacity of local thunderstorms.

Abstract:Based on slantwise vorticity development(SVD) theory,the possible dynamical mechanism of a persistent torrential rain which occurred in mid-June of 2008 was analyzed,and the role of low level jet (LLJ) in vorticity development was discussed.Meanwhile,several numerical simulations were performed to testify the rainstorm process based on MM5 and the results were further analyzed.The results indicate that:the development of low vortex from Tibetan Plateau was the primary cause for the precipitation in Guangxi and Guangdong at early stage.SVD took effect while moist isentropic surface tended to slope and air particles had relative motions along isentropic surface.With certain condition (C_M<0),the vorticity got a further development afterwards.Moreover,the enhancement of LLJ changed the atmospheric baroclinity and caused the vorticity to develop and move eastward,which was the main cause for the persistent torrential rain in Guangdong.The results of simulation control test well revealed the development process of the vortex and precipitation.The result of sensitive test showed that LLJ changed the stability of low level atmosphere and vertical shear of the wind,which meant that the baroclinity of the atmosphere was increasing.It thus made the mesoscale vortex develop further.

Abstract:Three-dimensional 4-day backward trajectories arriving in Lanzhou at 500m high were calculated every 6 h by using HYSPLIT-4 trajectory model in spring of 2001 to 2008.The 8 years were divided into two categories:high dust year (2001,2002,2004 and 2006) and low dust year (2003,2005,2007 and 2008).Cluster analysis,potential source contribution function (PSCF) model,and concentration-weighted trajectory (CWT) method were used to evaluate the transportation pathways and potential source regions of Lanzhou PM₁₀ pollution in spring.Results indicate that the western and northwestern pathways,respectively accounting for 33% and 19.4% of all trajectories,were major pathways leading to high springtime PM₁₀ loadings in Lanzhou in 2001,2002,2004 and 2006.However,the major pathways were the western and the northern pathways in 2003,2005,2007 and 2008,accounting for 23.6% and 18%,respectively.There were six potential source regions that had effect on PM₁₀concentration in Lanzhou,including Tarim Basin and Turpan Basin in Xinjiang,Qaidam Basin in Qinghai,Hexi Corridor in Gansu Province,the desert and gobi area in central and western Inner Mongolia.

Abstract:Field shading experiment was used to simulate reduced solar radiation at different percentages of 85%,80%,60%,40%,0% in winter wheat field.The activities of soil catalase,invertase,urease and the amount of available P,K,Fe,Mn were examined during different growth stages of winter wheat.Results show that different shading percentages delayed the winter wheat growing process to different degrees.The more the radiation decreased,the more significant the phonological delay was.The decrease of radiation at 60% and 80% promoted the activity of catalase near and away from the root zone of winter wheat.Reduced radiation significantly decreased soil urease and invertase activity in the late growth stages of winter wheat.The most significant invertase activity reduction occurred when the solar radiation was reduced by 80%.The reduced solar radiations decreased the urease activity in soil.The less radiation near the root zone decreased the amount of K,Fe,Mn,with a trend as follows: CK>40%>60%>80%.

Abstract:Based on the radiation data from May of 2009 to April of 2010 at Yangbajing in Tibet,the daily,monthly and seasonal variations of total radiation,ultraviolet radiation,long-wave radiation and net radiation were discussed and the frequency and reasons why the radiation exceeds the solar constant were analyzed.The results show that the total radiation,ultraviolet radiation,long-wave radiation and net radiation in Yangbajing area present obvious daily,monthly and seasonal variation characteristics.There is a positive correlation between the total radiation and ultraviolet radiation,between the total radiation and short-wave reflected radiation over earth surface and between the downward atmospheric radiation and long-wave reflected radiation over earth surface.

Abstract:A novel approach is proposed for cloud detection in satellite cloud image based on the improved Graph Cuts Model.10 gray features and 80 Gabor texture features were selected from two channels of FY-2C satellite image(infrared channel 1 and visible light channel),and the dimensions of feature vector were reduced to 9 by using PCA(principal component analysis).Then the similarity matrix was built up by those feature vectors.By using the spectral graph theoretic framework of Normalized Cuts,the cloud image was divided into 2 parts,the clear sky and the cloudy sky.Compared with the result of surface observation,the average consistency was 86.51%.The results demonstrate that this method is effective in cloud detection.

Abstract:Sunspot area is an important feature to measure the solar activities.Prediction of sunspot area can provide useful information for solar activities and space weather studies,etc.In this paper,we propose a smoothed monthly mean sunspot area prediction method by using an artificial neural network.The prediction model is built by training the area data before the twentieth solar cycle,and then it is used to forecast the data after the twenty-first solar cycle.We also consider the influence of different training steps and prediction steps respectively.The proposed method is able to exactly forecast the sunspot area of the next month,and the relative errors for different training steps are all less than 5%.However,the relative error will get larger if the prediction time is longer.