Abstract:Based on the ensemble forecasting data of China Meteorological Administration(CMA),European Centre for Medium Range Weather Forecasts(ECMWF),Japan Meteorological Agency(JMA),U.S.National Centers for Environmental Prediction(NCEP),and United Kingdom Met Office(UKMO) in the TIGGE datasets,the multimodel ensemble forecasting techniques have been investigated.Results show that the multimodel ensemble forecasts are superior to that of the individual model.However,the improvement of multimodel ensemble forecast skill is different for different meteorological elements.The multimodel superensemble with running training period(R-SUP) has the best performance for surface air temperature in the Northern Hemisphere.For precipitation forecast in the Northern Hemisphere,the bias-removed ensemble mean(BREM) is more skillful and stable than every single model.In addition,the multimodel ensemble forecasting experiments of extreme weather event with freezing rain and snow over southern China during early 2008 have been conducted by using BREM with running training period(R-BREM).Taking root-mean-square errors(RMSEs) of ECMWF 96 h forecasts as the criterion,the forecast lead time of surface air temperature over the southeastern coast of China may be prolonged from 96 h to 192 h by using the R-BREM technique.And the threat scores(TS) of the light and moderate rain forecasts have been significantly improved except for some particular lead time.

Abstract:Aiming at such complexity and uncertainty problems as the influence of equatorial sea surface temperature(SST) on West Pacific subtropical high,by introducing the fuzzy mapping idea and ANFIS(Adaptive-Netwook-Based Fuzzy Inference System) technique,the response trend and degree of West Pacific subtropical high intensity to the thermal pattern and shift of SST in equatorial eastern Pacific,western Pacific,and equatorial Indian ocean are analysed and discussed.Results show that the enhancing(weakening) response of subtropical high is corresponding to the SST cooling(warming) in equatorial eastern Pacific,and the response amplitude weakens(enhances) with time.The weakening(enhancing) response of subtropical high is corresponding to the SST cooling(warming) in equatorial Indian ocean,and the response amplitude is far less than that to the SST in equatorial eastern Pacific.The different response trends of subtropical high are corresponding to the different pace warming in equatorial western Pacific,viz.the rapid(slow) warming of SST in western Pacific is suitable for the weakening(enhancing) of subtropical high,and the delayed enhancing response is corresponding to the SST cooling in equatorial western Pacific.Some new viewpoints are introduced as follows:the SST shift range and rate are the key impact factors of subtropical high aberrance,and their influences are more notable than those of basic thermal status of equatorial SST.

Abstract:In modern variational data assimilation system,the background error covariance determines the space distribution of observation information and analysis increment balance between control variables.Based on the NMC(National Meteorology Centre) method,a new multivariable balance constraint operator is designed,and the forecast difference fields of WRF model from 2 June to 9 August 2009 are used to simulate the new background error covariance.In physical transformation,the multivariable balance constraint operator is built among control variables including relative humidity.The empirical orthogonal function method and the recursive filter are used to simulate the vertical and horizontal error covariances of control variables (ψ,χ_u,T_u,h_ru,p_su)^T, respectively.The results of single observation test show that observation information has been passed between the wet and dry variables with new background error covariance,and the increment distribution of relative humidity is similar to the temperature.

Abstract:The effects of regional SST(sea surface temperature) anomaly on interdecadal variation of East Asian summer monsoon(EASM) are investigated based on the observed monthly SSTs in different sea waters(global,extra-tropical,tropical,tropical Indian Ocean-Pacific,tropical Indian Ocean,and tropical Pacific) during 1950-2000.The observed SSTs are used to drive the NCAR CAM3 global atmospheric circulation model in a separate way,followed by long-term multiple group integrations in comparison to ERA-40 and NCEP/NCAR reanalysis data.Numerical simulations show that the SST changes of global,tropical,tropical Indian Ocean-Pacific,and tropical Pacific exert important impacts upon the interdecadal variability of EASM,reproducing the observed interdecadal weakening happened in the mid-late 1970s.Their simulated summer circulation anomalies in the strong and weak EASM years differ greatly,in better agreement with observations.Tropical Pacific is the key region to impact the interdecadal variation of EASM.Extra-tropical SSTA has weaker effect on the interdecadal variation of EASM.The tropical Indian SST-driven simulations reveal an interdecadal strengthening of EASM since the mid-late 1970s opposed to the impact of tropical Pacific SSTA,i.e.,the EASM interdecadal strengthening(weakening) is responded to the interdecadal warm(cold) SSTA in the tropical Indian Ocean.As a background,the interdecadal variation of SST in tropical Pacific has important effect upon the interdecadal weakening of EASM in the mid-late of 1970s.

Abstract:Based on U.S.NCEP/NCAR reanalysis data and Northern polar vortex intensity data from China National Climate Center,with correlation analysis and composite analysis,the effect of Northern polar vortex intensity on North Pacific storm track and its possible physical mechanism are studied.Conclusions are drawn as follows:In the years when Northern polar vortex is stronger(weaker),North Pacific storm track is also stronger(weaker).The stronger(weaker) North Hemisphere polar vortex will enhance(decrease) storm track and disturbance kinetic energy in the storm track area.In the years when Northern polar vortex is stronger(weaker),the synoptic-scale disturbance meridional and vertical heat transports are stronger(weaker) than mean,and the synoptic-scale disturbance transport of westerly momentum is stronger(weaker) significantly.Further investigation shows that the anomalous changes of polar vortex give rise to change in the upper level geopotential heights over the Eurasian continent and its downstream Pacific ocean,then change the East Asia westerly jet and the baroclinicity in the upstream of the storm track,and finally the storm track.

Abstract:The climatic and anomalous characteristics of summer atmospheric heat source in Lhasa are investigated by using the daily atmospheric heat source data from 1950 to 2006.On this basis,the basic features of 10-20 d oscillation of summer atmospheric heat source in Lhasa are analyzed especially.The results are as follows:1)The climatic mean of summer atmospheric heat source in Lhasa is 88 W·m^-2,which is obviously lower than that in the Asia monsoon trough area.So Lhasa is an atmospheric heat source area with the general intensity.But the summer atmospheric heat source in Lhasa shows an obvious declining tendency in the mid-1990s,and it is close to 0 at the beginning of 21 century.2)The intensity of 10-20 d oscillation is about two times as much as the mean intensity of the intraseasonal oscillations of summer atmospheric heat source in Lhasa from 1950 to 2006.The significant 33 years account for 57.6% of the total 57 years,so the 10-20 d oscillation is an important component for intraseasonal oscillations of the summer atmospheric heat source in Lhasa.3)There is an obvious intraseasonal variation for 10-20 d oscillation of summer atmospheric heat source in Lhasa,which is the strongest during the 20 days before or after the beginning of July.There is also an obvious interdecadal variation,with two stronger stages from the end of 1950s to the middle of 1960s,and from 1980s to the early of 1990s.

Abstract:The capability of CENTURY model in simultating the vegetation Net Primary Productivity(NPP) in China was evaluated,and the response of vegetation NPP in China to variations of CO₂ concentration,temperature and precipitation from 1981 to 2008 was investigated.Results show that NPP in China exhibts various responses to different climatic factors.The variation of CO₂ concentration has no evident effect on the annual coefficient of NPP variation,but can increases the annual trend coefficient of NPP in most areas of China.Temperature can significantly affect the annual coefficient of NPP variation in high-mid latitudes of China,but,for the whole country,the impact of temperature change is less significant than that of precipitation change.The main controlling climatic factor impacting the trend of NPP is precipitation.In addition,it is found that the distribution of response of NPP trend to combination of temperature and precipitation seems to be similar to that caused by precipitation variation alone.

Abstract:Based on the precipitation data at 160 stations in China and the NCEP/NCAR reanalysis data during 1951-2011,this paper studies the interannual variability of winter precipitation over southeastern China and associated circulation and water vapor transport characteristics.Results show that interannual variation of winter precipitation over southeastern China is significant.When the precipitation anomaly is positive(negative),the sea level pressure anomalies are negative (positive) of Mongolian high and over southern China,and positive(negative) in the adjacent sea area of Asia;At 500 hPa,the high pressure ridge near the Balkhash Lake and East Asia trough both are weaker(stronger);westerly jet of Eastern Asia is weaker(stronger),and westerly jet of the Middle East is stronger(weaker).There is a significant abnormal ascending(sinking) motion over 20-30°N eastern China and an abnormal sinking(ascending) motion in low latitudes.Two dominating water vapor transports affect winter precipitation over southeastern China.Firstly,a water vapor transport comes from the south branch airflow of the westerlies around the Tibetan Plateau,by Arabian Sea and the Bay of Bengal,to South China.Secondly,a water vapor transport comes from the low-latitude western Pacific,by South China Sea,to Southwest China.In addition,there is a negative correlation between East Asian winter monsoon index and winter precipitation over southeastern China.

Abstract:This paper extracts 1 295 TC edges from 1 295 IR images of 69 TCs during 2006-2010,and calculates the fractal dimension of the edges using the compasses method.The 1 295 TC edge fractal dimension are sorted in descending order and classified into five categories,denoted by A,B,C,D and E,which are in the same frequencies.The fractal dimension mean value of the five categories are 1.21,1.26,1.29,1.33 and 1.40,respectively.Then we find five samples nearest to the five averages.The IR images and TBB contour map of the five samples show that the edges of TCs are more rough and non-circular,and the structures of TCs are more complicated,as the increase of the fractal dimension.All above indicate that the fractal dimension of TC edges can quantitatively describe the complex degree of TC to some extent.

Abstract:Based on the tropical cyclone best track data from the Joint Typhoon Warning Center (JTWC) and the NCEP/NCAR reanalysis data from 1980 to 2009,we set a threshold for rapid intensification tropical cyclones (RITC) as 35 kn,which was the magnitude of intensity change of tropical cyclones in a period of 24 h with the accumulative probability of 96% over the western North Pacific.According to zonal wind shear between 200 hPa and 850 hPa,the paper divided the vertical wind shear (WS) into the westerly vertical wind shear (WWS) and easterly vertical wind shear (EWS) and compared the characteristics of rapid intensification of tropical cyclones in EWSwith those inWWS.The results show that about 70% of RITCs occur inEWS.There are most RITCs in September,whose initial intensity are between 65 and 70 kn.In largeEWS,abundant vapor comes from southwest at 850 hPa.At 500 hPa and 200 hPa,the Pacific subtropical anticyclone is strong and the ridge line is situated in north area.The temperature in outflow layer is below -79 ℃.In large WWS,the water vapor is from southeast at 850 hPa.At 500 hPa,subtropical high is split into several centers.Compared with that of the former,the divergence field of RITCs at 200 hPa is weaker.And the temperature in outflow layer is about -76 ℃.

Abstract:Based on Doppler radar data,meteorological satellite data,automatic weather station data and the NCEP/NCAR(1°×1°) reanalysis data,this paper studies the circulation background,internal structure and evolution of the meso-scale convective systems in a storm rainfall far distant from typhoon in Anhui Province.Results show that:1)The easterly airstream around lower typhoon transports moisture and heat to rainstorm area,which results in the enhancement of atmospheric instability in the mid-latitude area.While the ascending motion in front of the westerly trough is beneficial to the development of low layer convergence and the maintenance of vertical motion in the rainstorm area.2)The strong precipitation process consists of two meso-β scale convective systems(MβCSs),whose generation and maintenance lead to longer time maintenance of the heavy rainfall.3)Radar echoes and ground factors show that the strong precipitation is caused by two meso-β scale convective systems.There are different reasons for the frontogenesis of mesoscale convective system,but the development of convection systems is relevant to the surface mesoscale convergence line and the strengthened mesoscale low pressure.Meso-γ scale strong convection systems are the direct reason of local rainfall peak.4)There is a interaction between the middle latitude synoptical system and the circulation of the typhoon outer region in the two strong precipitation processes.The triggering of low layer cold air and the strengthening of southwest warm and wet airflow in front of the westerly trough enhance the precipitation obviously.5)On the Doppler radar radial velocity images,the strengthening of meso-β scale convective systems is closely related to the strengthening of low layer warm and wet airflow.The formation of meso-γ scale convective systems is caused by small scale wind speed convergence.

Abstract:Based on the aerosol scattering properties observed by the integrating Nephelometer in the north suburb of Nanjing in spring 2011,combined with data of PM_2.5 mass concentration,visibility and routine weather observation,the variation features of aerosol scattering coefficients and its correlation with PM_2.5 mass concentration and visibility were analyzed.Results show that the mean aerosol scattering coefficient is 311.5±173.3 Mm^-1 and the maximum frequency distribution of hourly mean scattering coefficient is 100-200 Mm^-1.The diurnal variation of aerosol scattering coefficient is obvious,and higher(lower) in the morning and evening(at noon and in the afternoon).The trend variation of scattering coefficient shows an agreement with the mass concentration of PM_2.5,and a negative correlation with the visibility.The daily mean aerosol scattering coefficient in the hazy day is up to 700.5±341.4 Mm^-1,and the maximum value reaches about 1 900 Mm^-1.The analysis of ground observations,NCEP/NCAR reanalysis data and simulated back trajectories of air parcels shows that the air parcels mainly come from south and southeast of Nanjing in the hazy day.

Abstract:Based on the water surface spectral data in Taihu Lake area and MODIS remote sensing image data on the same day,this paper retrieved the aerosol optical depth(AOD) in Taihu Lake area by using the radiative transfer model 6S and selecting the user-defined aerosol model.The retrieved AOD data and the AOD data measured by CE318 were applied to the atmospheric correction in Taihu Lake area,respectively,so the two different water reflectivities were gotten and compared with the measured water reflectivity.Results show that the distribution of retrieved AOD in Taihu Lake area is reasonable,which is mainly caused by the developed industry and the more serious pollution in the north of Taihu Lake.The differences of retrieved data induced by the spectral absorption coefficients of particulate and the apparent reflectivity received by the satellite lead to the nonuniform distribution of retrieved AOD.It is more accurate by using the AOD retrieved by MODIS data to do the atmospheric correction.The method and results will be helpful for the retrieval of AOD and the accuracy of atmospheric correction.

Abstract:Based on the MM5 model with four different cloud microphysical schemes(Duhia simple ice,Reisner mix phase,Reisner2 graupel and Schultz microphysical schemes),numerical simulations are carried out to study the cloud physical processes in a rainfall event over Qilian Mountains during 12-13 July 2002.Comparisons among the experiments and against the observations indicate that the simulated rainfall area from the four cloud physical processes are further south than the observed one.Except Reisner2 graupel scheme,other three schemes have little effect on the center of rainfall area,and the intensity of precipitation center is not sensitive to cloud microphysical processes.The explicit precipitation and parameterize precipitation depend on different cloud microphysical processes.Cloud microphysical processes impact on the occurrence time and intensity of strong precipitation by affecting the occurrence/development times and intensity of dynamic conditions.Analysis of the cloud microphysical parameters shows that the processes of the parameters concerned with precipitation are different for the four different schemes.For Duhia simple ice scheme,rain water and cloud water are primary.For Reisner mix phase scheme,the collection of rain water,cloud water,snow and graupel may paly a main role for precipitation,and the coagulation of ice crystal is relatively weak.For Reisner2 graupel scheme,rain water,cloud water,snow,ice and graupel all are concerned with collection and accretion processes.For Schultz microphysical scheme,the collection of ice,snow and graupel is more significant.

Abstract:Based on a test platform of the X-band fully solid-state weather radar at Key Laboratory of Atmospheric Sounding of China Meteorological Administration,this paper introduces that the combination working mode is designed to detect the blind spot of radar near-field detection,which is caused by wide pulse,under the condition of 50 m radar detection distance resolution.This paper mainly analyzes the impact of time sidelobe leaked by main-lobe on detection range of the meteorological echo intensity.Transmission Amplitude Taper will improve the level of sidelobe compression under the loss of peak emission power,however,it is not suitable for limited peak power and low compression factor.Furthermore,an adaptive method is introduced to suppress sidelobe.The simulations show that,using the method,the peak sidelobe suppression is nearly -50 dB,and the main-lobe broadening coefficient is close to 1.Compared with the classic matching method and hamming weighted method,it will improve about 4 dB for the weak signals detection.Finally,based on the analysis of radar detectable maximum distance,the precipitation detection capability of the X-band radar is compared with the 713 radar in a field observation case.It shows that the X-band solid-state radar can detect precipitation echoes stronger than 10 dBz within 150 km.