Abstract:Based on the NCEP/NCAR daily reanalysis data from 1958 to 2008,this paper studies the subtropical high indexes in the winter of 2007/2008(a serious cold rain-snow frost disaster occurred in southern China),El Nino/La Nina events average,and 50-yr average(from 1958 to 2007).Then,the cross wavelet and wavelet coherence techniques are introduced to analyse the relativity and the difference of subtropical high indexes,and the influence of subtropical high on atmospheric circulation in different periods including the El Nino/La Nina periods and the usual years.Some meaning characters of subtropical high activity and corresponding subtropical circulation are revealed in the winter of 2007/2008,such as the position of subtropical high moves northward in the winter of La Nina event average,especially in the winter of mean-strong La Nina event.

Abstract:Interannual variability of the South-Asian high(SAH) establishment over the Indo-China Peninsula(ICP) from April to May and its relation to southern Asian summer monsoon are investigated by using NCEP/NCAR daily reanalysis and out-going longwave radiation(OLR) data from 1979 to 2008.It is found that the duration of the SAH establishment is relatively long(short) in the early(delayed)-establishment years.The upper tropospheric anti-cyclone over the ICP is stronger(weaker) in the early(delayed) years.Before the SAH establishment,the center of the anti-cyclone to the east of the Philippines is to the west of its normal location in the early years.But in the delayed years,there is not a closed anti-cyclone over the western Pacific before the SAH establishment.The time of the SAH establishment is closely associated with the convective development over the ICP.The earlier (later) convective flourish is corresponding to the earlier(later) SAH establishment.The onset of southern Asian summer monsoon in early-establishment years is significantly different from the delayed years.The earlier(later) SAH establishment is followed by the earlier(later) onset of the Bay of Bengal(BOB)-ICP summer monsoon and the South China Sea summer monsoon.Accordingly,the time of the SAH establishment over the ICP plays an indicative role in the subsequent onset of the southern Asian summer monsoon.

Abstract:By using the WRF(weather research and forecasting) model,the paper simulated the seasonal tropical cyclone activity over western North Pacific from 1 July to 30 September 2006.Results show that:1) the simulated total number of Typhoons is close to that from Best-track data set.The simulated landfall TC number is less than that of real Typhoon number and it is the same for separate monthly landfall number.The simulated intensity of Typhoons is weaker than that from Best-track data set;2) the model shows better ability in reproducing Typhoon and the height and wind vertical shear fields in July,but the ability tends to be weaker as the model time increases.This suggests that the model can be used to simulate the feature of seasonal tropical cyclone activity but the time limit needs further exploration.

Abstract:Interaction between El Niño of the tropical Pacific and Indian Ocean Dipole was studied on the basis of the monthly NCEP/NCAR reanalysis dataset and GISST data.There was an obvious jump in this interaction relationship between Dipole and ENSO events before and after 1961.The analysis results based on the CCM3(community climate model version 3) model are summarized as follows:the interaction of El Nio upon Indian Ocean Dipole mode was very weak during the phase between 1930 and 1961.But from 1962 to 2001,Indian Ocean Dipole mode provided favorable conditions for Pacific warm events.The Walker circulation over the tropical Pacific and the vertical zonal monsoon circulation over the tropical Indian Ocean coupled well over the oceanic continent.The warm events over the Pacific also provided favorable conditions for Indian Ocean Dipole mode from 1962 to 2001.

Abstract:Base on NCEP/NCAR skin temperature (land surface temperature or skin temperature,LST) and ERA40 reanalysis surface soil temperature (ECMWF-STL1) data,the differences and similarities in spring and summer land surface thermal conditions are evaluated from the aspects of their spatial distribution and variability.Results show that:1) Temperature decreasing from the equator to the poles is found in the climatological distribution of spring land surface thermal conditions from both datasets.However,ECMWF-STL1 has higher temperatures than LST in mid-low latitude regions but lower in high latitude regions.In summer,the distributions of the multi-year mean of the thermal conditions of the global land surface that two data sets reflected are similar except for that over the Greenland.2) In spring,both of the inter-annual variability of ECMWF-STL1 and LST in high latitude of the Northern Hemisphere is larger than that in other regions.The inter-annual variability of ECMWF-STL1 is stronger than that of LST in northern Eurasia but shows an opposite pattern in the south part.In summer,significant inter-annual variability are found in central Africa,north Eurasia and some parts of the Americas,while there are evident differences in temperature variability in the North and South America areas between the two datasets.3) The first mode of EOF analysis suggests that a reversed phase of spring thermal condition variation between North and South Eurasia exists in both datasets.But the spatial patterns of thermal anomalies described by those two datasets are almost opposite in North America and Australia.In summer,the characteristics of two datasets are similar in Eurasian and Africa while not much the same in other regions.4) In spring,the significant warming happens in the high latitudes of Eurasia.Compared with LST,the warming trend of ECMWF-STL1 in northern Eurasia is more significant,while cooling trend in southern is relatively weak.In summer,the spatial pattern of the warming trend of ECMWF-STL1 is similar to that of LST,but with smaller values than LST.In short,the thermal conditions described by two datasets are almost consistent in most area of Africa and Eurasia,but show evident different in Australia,Greenland,America and especially over the Tibetan Plateau.

Abstract:By using the surface observational data at high spatial and temporal resolutions together with simulations of the Weather Research and Forecasting model,the characteristics of atmospheric boundary layer and mechanisms of two different types of MCSs(mesoscale convective systems) which led to the Meiyu front rainstorm that occurred over the Yangtze River basin during 29-30 June 2009 are analyzed,focusing on sea level pressure field,boundary layer cold pool,dryline and its effect in MCS.The results show that there are obvious differences for the sea level pressure fields corresponding to the two distinct MCSs (referred as MCS1 and MCS2).MCS1 corresponds to boundary layer convergence line while MCS2 is composed of a mesolow and a mesohigh which are located in front of and behind the severe convective zone,respectively.The severe convective zone occurred in the transition zone between the mesolow and mesohigh.The boundary layer convergence line is an important factor in maintaining MCS1.The convergence between the boundary outflow before the boundary layer cold pool caused by the developing process of MCS1 and lower-layer wind triggered MCS2.The mesoscale dryline in the transition zone was an important characteristic of MCS2.

Abstract:Using the radar data,surface data and upper air data and NCEP (6-hr interval) reanalysis data on 26 cases of thunderstorm from 2003 to 2009 in eastern Hubei Province,the radar echoes caused thunderstorm gale are divided to three types,namely single-cell thunderstorm,bow thunderstorm and squall-line thunderstorm according to the morphology features of radar echoes.This paper statistically analyses the characteristics of radar base reflectivity,echo tops,vertical integrated liquid,mid-altitude radial convergence,inflow jet,mesocyclone and atmospheric conditions of the three types,and establishes the three radar echo conceptual models based on the evolution of radar echoes caused thunderstorm gale.Results show that the bow thunderstorm and squall line thunderstorm can be warned about 30 min in advance,but it is difficulty to advance the warning of single-cell thunderstorm.

Abstract:Based on the satellite water vapor image combining with visible picture and radar data and conventional observation,the paper analyzed the strong convective system in Peixian of Jiangsu Province on 5 June 2009.The results show that the junctions of satellite water vapor imagery abnormal dynamic areas and convection systems as well as the two convection cloud clusters effluent boundary in the visible image produced the strong convection weather such as tornado easily.The water vapor conveyors in the water vapor imagery were consistent with convection cloud systems in the visible image.Water vapor imagery feature is connected with the large scale weather process which resulted in vertical motion and air current deformation field.The water vapor imagery stands for dynamic feature of hightroposphere.Strong convection often occurs in the low brightness temperature cloud clusters.High space-time resolution satellite and radar image can reflect the strong convective system very well and offset the insufficiency of conventional observation to provide a reference for the short-time weather forecasting.

Abstract:Cloud is critical in understanding the current climate and it plays an important role in simulating potential climate change.The U.S.Department of Energy(DOE) atmospheric radiation measurement (ARM) AMF explored field campaigns that took place in Shouxian in the east of China for the first time in 2008.Based on the observational data,the study presents some preliminary results like cloud height and cloud thickness as well as cloud’s radiative features in Shouxian during late autumn and early winter.It was found that the occurrence of clouds took 76.3% of the observational days and 54.0% of the observational time.Middle cloud(M) and high cloud(H) occupied 76.7% of all the clouds.The weather system is the dominant modulator in cloud formation in Shouxian.In addition,there were more middle clouds(M) transforming into precipitation cloud(P) than low(L) and high cloud(H),which is about 67.7%.Precipitation occurring in the afternoon took 47.8% of all the precipitation cloud.Aerosol affected the distribution of precipitation cloud obviously.The reduced daily mean shortwave radiation caused by the cloud and aerosol was about-99.1 W/m² with aerosol contributing 25.1% of the value.We quantitatively estimate there are obvious differences in the surface radiation budget caused by the clouds of different heights and thicknesses.P cloud produces the largest cooling effect (-201.9 W/m²) while the thickness of less than 2 km H cloud has the smallest cooling effect (-32.9 W/m²).There are evident differences between ground site observation and MODIS data estimation,whose value could be-1.9—-36.9 W/m².

Abstract:Based on the precipitation data,Doppler radar data and sounding figures,the paper statistically tests the effect of artificial precipitation enhancement by using a self-developed effect-evaluating software system.By comparing the differences of Doppler radar echo characteristics between the target clouds and the contrast clouds,the effect of rain enhancement is studied by evaluating the multi-point operations in the west part of Hainan Province on August 11,2010.The results show that the effect of seeding starts in half an hour after seeding in the target area and reaches the peak.Compared with the contrast clouds,the increase rates are larger for such parameters as the maximum echo intensity,the stronger echo area,echo tops and the values of the vertically integrated liquid water content of the target cloud.The results also indicate that the seeding operations indeed extend the life of the target clouds.

Abstract:An automatic identification method to identify tropical,convective and stratiform rainfall types by using the radar data like horizontal gradient,vertical gradient,echo top,VPR(vertical profile of radar reflectivity) is proposed in this paper.Based on the data of seven rainfall events observed by the radar in Guangzhou from May to August in 2008,the performance of this algorithm is compared with another method which only divides precipitation into two types of convective and stratiform.The results show that the method can automatically identify the distribution area of precipitation effectively.It can also improve the accuracy of radar-based quantitative precipitation estimation.

Abstract:A heavy fog event occurred in Nanjing area on 18—19 December 2007,lasting for 20 h,in which almost 1/3 time period was occupied by the super dense fog with visibility lower than 50 m.By using the field observational data in the north suburb of Nanjing during the fog event and NCEP reanalysis data,the evolution process,microphysical structure and boundary layer characteristics in the fog event are analyzed,and the causes of burst reinforcement of the ground fog are also discussed.Results show that the formation of fog is due to increasing moisture by southwest air current.Sufficient vapor is supplied by the advection transport and surface evaporation,and the inversion near bottom atmosphere uplifts and exists stably owing to warming effect of upper-layer air sinking,therefore the heavy fog can persist after sunrise.In the whole fog event,the temporal evolutions of fog droplet number concentration,average diameter and liquid water content are in agreement with each other,the average droplet spectrums all obey exponential decreased distribution,and fog droplets mainly concentrat in the section of smaller diameter.The two burst reinforcements of ground fog occur at nighttime,with all microphysical parameters increasing obviously and the droplet spectrum uplifting and broader.The burst reinforcements are mainly caused by sharp decline of temperature near surface,enhancement of inversion near bottom atmosphere,and increase of large aerosol particles which may act as condensation nuclei of fog droplets.

Abstract:Multi-temporal 8-day composite MODIS Surface Reflectance Product of 2009 were used to map the distribution of rice paddy in Henan Province.By taking into consideration the characteristic of rice cultivation and the rice growth patterns,a scheme for rice mapping has been proposed.In this scheme,to reduce the influence of factors like cloud,the time series of land surface water content index(I_LSW) and enhanced vegetation index(I_EV) were calculated from MODIS imagery and two different filters were applied to rebuild the time series data.Then,the principal component analysis method was employed to reduce the dimensionality of the times series data,with the first three components as I_LSW and I_EV respectively reserved as feature bands.Another feature band is the rice similarity index,which was obtained by calculating the similarity index between a standard rice growth curve of I_EV and the temporal curve of I_EV for each pixel.However,there were obvious differences in rice phenology between the north and south rice planting regions in Henan Province.Based on the obtained rice GPS samples,a standard rice growth curve of IEV was established for each region.Finally,support vector machine(SVM) classification method was used to retrieve rice distribution from the feature bands.The results showed that the obtained rice distribution in Henan Province is well consistent with the real situation.Rice mainly distributed on both sides of the Yellow river in the north of Henan Province,while it distributed along the Huaihe River or around large reservoirs in the south of Henan Province.Compared with the statistical data,the rice area obtained from MODIS data bears a mean relative error of 6.56%,and a Root Mean Square Error of 5.63 khm².Because of mixed pixels and dispersed rice distribution in some regions,the relative error can be larger than ±60%.However,the proposed rice mapping scheme based on the temporal MODIS data still shows its advantages in rice distribution mapping for large-scale areas.

Abstract:Using gale data (≥level 6 with ten minute average wind velocity≥10.8—13.8 m/s) of four meteorological stations in east Hexi corridor from 1971 to 2010,such climate characteristics as space and time distribution,intensity and endurance of the gales were analyzed systematically.The results show that gales mainly occur in the mountainous area and the edge of desert.Annual gale days and interdecadal gale days presents a reducing tendency.March to May is gale frequent period,which occupies 34.8%—56.8% of annual gale days.Then it is February,June and November.Gale days of different intensities vary a lot.The number of gale days reduces rapidly along with the elevation of gale intensity.Gale weather presents long-enduring characteristic and strong gale usually occur in sustained period of gale.Based on the daily data of ECMWF numerical forecast grid field at 20:00 BST from 2003 to 2007,forecast factor was initially elected by Press criterion and was further selected by stepwise regression forecast method.The gale forecast equations were built with optimal subset regression.The overall situation and the most superior significance forecast equations of the gale in every season in different areas were determined finally by the CSC double grading criterion.The forecast equations passed significance examination of α=0.01.Back substitution fitting rates of the prognostic equations were 66.7%—73.4% and forecast accuracy rates were 58.8%—67.5%,which achieved the forecast level to provide objective and effective instruction for gale forecast.The closest approaching principle was used to set forecast marginal value,ranks of gale forecast and early warning.