Abstract:Using the high resolution simulations of WRF model and the calculation scheme of grid-based moist available energy,this paper analyzes the space-time evolution characteristics of moist available energy in the occurrence and development processes of a strong rainfall weather during the Jianghuai Meiyu period,and qualitatively and quantitatively discusses the interaction mechanism of the transition term,the advection term and the vertical transport term in the energy equation from the energy budget balance.Results show that,in the strong rainfall process,the space-time characteristics of moist available energy have good corresponding relations with the occurrence and development of heavy rain.The range of 40×10⁴ J·hPa^-1·m^-2 contour of 800 hPa moist available energy in the lower troposphere and the contour extending to near 500 hPa can be used as necessary conditions for the heavy rainfall occurrence.The rapid energy accumulation at 2—3 h before heavy rain and its impact on the moving direction of rainfall areas have a good indicative function to rainstorm forecast.The horizontal and vertical transport and transition of moist available energy ensure the energy accumulation and the energy increase in the middle troposphere,which provide sufficient energy for the occurrence and maintenance of heavy rain.

Abstract:The new generation mesoscale model WRF is used to simulate a typical thunderstorm process in Ningbo area on 24 June 2006,and the impacts of land surface parameterization schemes(Noah and RUC) on numerical simulation of the thunderstorm process are tested.The results show that,for surface thermodynamic field before the thunderstorm happened,the simulated results with Noah scheme are more close to the observations.However,with RUC scheme,the simulated results do not reflect the diversity of underlying surface coverage and the impacts of city underlying surface,and the difference between rural and urban areas is not obvious.The start and development processes simulated by Noah scheme are more reasonable,and the results simulated by RUC scheme describe the key stages in the evolution process of thunderstorm well,such as three merging processes.Because the considered factors and physical process parameterizations are different,the strength and center of accumulated precipitation simulated by Noah scheme are more consistent with the observations than those simulated by RUC scheme.The duration of thunderstorm is strongly sensitive to land surface process parameterization,and both durations simulated by the two schemes are longer than actual duration of the thunderstorm to different degree.Whatever the land cover category in Ningbo area,the sensible heat flux(latent heat flux) simulated by Noah scheme is greater than(less than) that simulated by RUC scheme during the day.

Abstract:Based on the NCEP/NCAR daily reanalysis data and observational rainfall data from 1961 to 2010,24 persistent heavy rain events are selected in the first rainy season in South China,and the beginning dates of annual South China summer monsoon rainfall(SCSMR) are chosen according to the basic criterion.According to the SCSMR beginning date and the average circulation pattern of South Asia High(SAH) at 150 hPa during a heavy rain event,the 24 persistent heavy rain events fall into four categories,including east SAH pattern before SCSMR,east SAH pattern after SCSMR,belt SAH pattern after SCSMR,and west SAH pattern after SCSMR.Among them,west SAH pattern after SCSMR is the most with the longest average duration.The same points of persistent heavy rain events in all SAH patterns show that:The center of both high frequency and large rainfall locates near northeast Guangdong Province;During the heavy rain,South China geopotential height increases at 150 hPa but decreases at 500 hPa;South China lies in the 150 hPa divergence zone to south side of westerly jet;The southwesterly is obvious over coastal area of South China at 850 hPa,and the low level convergence over northeast South China is the most obvious;Precipitable water vapor(PWV) over coastal area of both Guangdong and Guangxi provinces is the most.Direction of water vapor transportation integrated from surface to 300 hPa is mainly southwest over South China.The differences show that the mean rainfall is the least in the west SAH pattern after SCSMR;The easterly jet over the Indian Ocean emerges in both the belt and the west SAH patterns after SCSMR;PWV in the patterns after SCSMR is larger than that in the pattern before SCSMR over the coastal area of both Guangdong and Guangxi provinces.

Abstract:Using the data of Doppler radar and the cloud paramters products retrieved from FY-2E geostationary satellite data and MODIS Polar-orbiting satellite data,this paper analyzes the structure and transformation of cloud and precipitation in the extreme torrential rain process in Beijing on 21 July 2012.It shows that three stages of the precipitation process have different vertical structures of cloud and precipitation.1)In the warm area convective precipitation stage,the precipitation starts with the warm rain process.The rain drops grow quickly with significant coagulation in the warm cloud area,and the warm rain process is important for precipitation.With the development of cloud,the cold rain process is intensified.T-Re analysis shows that cloud droplets grow quickly below -10 ℃ level with significant condensation-coagulation.There is a deep zone of mixed phase above -10 ℃ level,with the top of cloud dominated by ice particles,and cloud water converts to rainfall quickly.2)In the front convective precipitation stage,the liquid MCC(Mesoscale Convective Complex) system with highly organization and low centroid is the main precipitation system with high rainfall intensity.The echo intensity increases quickly at ice-water mixed layer,and the freezing layer is the key area of rain microphysical process.The rain drops grow quickly with significant coagulation in the warm cloud area,but the broken or evaporation is not obvious.3)In the backward front precipitation stage,the ice particles increase quickly at near 0 ℃ level by coagulating cloud water.There is obvious evaporation in the early precipitation process.With the development of cloud,cloud water is less in the warm cloud area,and the rain drops can not grow without effective coagulation.

Abstract:Based on the NCEP/NCAR daily sea level pressure data,the Lamb-Jenkinson atmospheric circulation type method is used to define summer atmospheric circulation types over the Huaihe River valley,and a summer precipitation trend forecast model is established by the successive regression method.Results show that the main circulation types impacting on the summer climate over the Huaihe River valley are the southerly,southwesterly,southeasterly and cyclone types,and they have obvious interannual and interdecadal characteristics.The summer precipitation trend forecast model established by the circulation types over the Huaihe River valley has a good forecast skill.

Abstract:Based on the daily surface temperature data at 384 stations of China and the NCEP/NCAR daily reanalysis data from 1960 to 2010,this paper analyzes the frequency and intensity characteristics of cold air activity in China.Results show that both frequency and intensity of cold air activity at single station in northern China are higher than those in southern China.Based on the invading routes of cold air,northern China is divided into three subareas,in which the most cold air activity occurs in November,and southern China is divided into two areas by 25°N,in which more cold air occurs in December and January.On the interannual scale,both frequency and intensity of cold air activity decrease.On the interdecadal scale,the frequency variations of cold air activity in the five areas are inconsistent,while the intensity variations weaken from 1960s to 1980s.The frequency of nationwide cold air activity decreases in both 1960s and 1990s,while the interdecadal variation of northern cold air activity frequency is weak.Compared with the normal years,when Eurasia surface cold high pressure strengthens(weakens),surface temperature in most parts of China decreases(increases) and East Asia trough strengthens(weakens) at 500 hPa,the frequency of cold air acitivity is higher(lower) in the corresponding years.

Abstract:Based on the NCEP/NCAR 6-hourly sea level pressure reanalysis data from 1980 to 2012 and a defined method to objectively identify cyclones,this paper has analyzed the climatic characteristics and interannual(interdecadal) variations of frequency and intensity of cyclone activities over the Changjiang-Huaihe River basin in late spring and early summer.Results show that there is an obvious high-frequency cyclone activity center in Changjiang-Huaihe River basin from May to July.It lies between Dongting Lake and Poyang Lake from May to June,and moves northward in July,with a higher frequency to the south of Huaihe River.The frequency and intensity of cyclones over Changjiang-Huaihe River basin decrease from 1980s to 1990s,and increase in the first decade of 21st century.The stable longwave circulation structure appears at 500 hPa in whether more cyclone frequency years or less,but there are obvious differences between them.Two southern troughs appear in the Arabian Sea and the Bay of Bengal in the more cyclone years,while only one appears in the Bay of Bengal in the less cyclone years.In the more cyclone years,there is an abnormal convergence center with cyclonic circulation in the lower troposphere from South China to Changjiang-Huaihe River basin,while an abnormal divergence appears in the upper troposphere.Because the abnormal disturbance of westerlies along subtropical jet stream spreads energy to East Asia,the abnormal cyclonic circulation appears in eastern regions.Such circulation structure provides some advantages for the cyclones over Changjiang-Huaihe River basin.

Abstract:Using the station data in Hebei area,a test analysis is maded on simulated results from China climate change projection data provided by National Climate Center.Results show that:1)July precipitation simulated by the regional model(RegMV) exists systematic deviation,which is larger in southern Zhangjiakou-Sangyang River basin and northern Zhangjiakou-Dam Plateau,but significantly smaller in Xinglong mountains east to Beijing and southeast coastal areas.2)July maximum temperature simulated by RegMV exists systematic deviation,which is significantly higher in Xinglong mountains east to Beijing and eastern plain region,but lower in southern Zhangjiakou-Sangyang River basin and eastern Taihang Mountains.3)January minimum temperature simulated by RegMV exists systematic deviation,which is higher in Xinglong mountains east to Beijing,North Taihang Mountains,and eastern plain region,but lower in southern Zhangjiakou-Sangyang River basin and eastern Taihang Mountains.4)The global model is difficult to describe terrain features of Hebei due to its low spatial resolution.Whether precipitation or temperature is simulated,the results are poor.The regional climate model has a certain improvement in describing terrain features of Hebei by improving the resolution,so its simulations have been improved significantly.However,due to the limit of the spatial resolution,such local terrain as Xinglong Mountains,Sangyang River basin,northern Taihang Mountains and other terrain are not well characterized,so the simulated results appear systematic deviation in these areas.It needs an improvement for the application of this set of data in Hebei area.

Abstract:Using NOAA Global Ocean Data Assimilation System(GODAS) monthly sea surface height(SSH) data,NCEP/NCAR monthly 850 hPa wind field reanalysis data,and monthly precipitation of 160 stations in China,the temporal and spatial characteristics of SSH interdecadal anomaly in the tropical Pacific and the relationships among SSH,850 hPa wind field and summer precipitation in eastern China are investigated.The results show that: 1)From autumn to winter,the main spatial pattern of SSH interdecadal anomaly in the tropical Pacific develops toward the similar “ENSO” pattern.From spring to summer,the similar “ENSO” pattern gradually decreases,and eventually disappears.An obvious SSH interdecadal turning in the tropical Pacific occurs around 1996.The SSH shows the low-east and high-west pattern since 1996,with some different evolutions in different seasons.2)A weak SSH fluctuation in summer over the tropical Pacific takes place around 1990,which continuously affects summer atmospheric circulation,weakens East Asian summer monsoon around 1992 and causes summer precipitation significantly abundant(deficient) in regions south of the Yellow River in eastern China,especially in South China(in Sichuan Basin and Northeast China).The substantive turning of SSH around 1996 exacerbates the above interdecadal variation trends of summer precipitation in China.

Abstract:The contribution of conventional observations on the east side of Tibetan Plateau to forecast error in WRF model is evaluated by using the WRFDA-FSO(Forecast Sensitivity to Observation) system from May to October in 2009 and 2010.Results show that,for the surface observations,the surface temperature contributes the major impact to the forecast error,the surface wind,surface pressure and water vapor contribute the minor impact,and the surface observations located in the regions(including eastern of Sichuan,most of Guangxi,and south edge of Yunnan) contribute the positive impact.For the sounding observations,the sounding temperature contributes the major impact to the forecast error,the sounding water vapor and sounding wind contribute minor impact,and the sounding observations located in the regions(including most of Yunnan,west edge of Guizhou,and northwest edge of Guangxi) contribute positive impact.After removing the surface and sounding observations,which contribute negative impact,the precipitation and temperature forecast are improved.

Abstract:Based on the raindrop size distribution data observed in a precipitation process in Mt. Huang in June 2011,this paper studies the characteristics of raindrop size distribution and microphysical parameters at different altitudes as well as the discrepancy.It shows that all of the microphysical diameter parameters are the highest in the mountainside and the lowest in the mountaintop.The rainfall intensity is the highest in the mountainside,while the number concentration is the highest in the mountaintop.On the one hand,it is the highest in the mountaintop and the lowest in the mountain bottom that the number density of raindrops with diameter less than 1 mm,which is related to evaporation and collision coalescence of small raindrops,on the other hand,the number density of raindrops with diameter larger than 1.5 mm in the mountainside is lager than that in the mountaintop or the mountain bottom,which may be due to the topographic forcing.The precipitation process can be divided to two stages based on the time series of each microphysical parameter.The values of each microphysical parameter in the first stage are obviously higher than those in the second stage.The rainfall intensity in the first stage is about three times larger than that in the second stage.There are approximate power function relationships between rainfall intensity and radar reflectivity,number concentration and maximum diameter,and the correlation between rainfall intensity and radar reflectivity is the best.

Abstract:NCAR's community atmospheric model v3.0(CAM3.0) is used to explore the possible external forcing mechanism of North Pacific eastern-pattern storm track(EPST) in winter,when the storm track often has its strongest center located east of 160°W.This paper mainly focuses on the effect of positive(P) and negative(N) sea surface temperature anomaly(SSTA) in the middle-east equatorial Pacific(EP) and the Kuroshio Current(KC).Results show that EP-N SSTA has significant meaning for the emergence of EPST.The EP-N(P) and KC-P(N) SSTA can lead to the eastern(western) pattern of the storm track.The activity of storm track in eastern North Pacific may be caused by the enhancement of low level baroclinicity.Specifically,when there is the eastern(western) pattern,the westerly jet in eastern North Pacific,as well as the eddy baroclinicity,the transportation of synoptic-scale heat and momentum,and the feedback between eddy waves and mean flow increase(decrease),and v.v..Compared with EP,the atmospheric responses to SSTA in KC are more local and asymmetric with respect to the sign of SSTA,and KC-N SSTA mainly influences the entrance area of the storm track.

Abstract:Using the brightness temperature(TB) data of TRMM Microwave Imager(TMI) from 2007 to 2010,this paper establishes a method for estimating the intensity of tropical cyclone(TC) in Northwest Pacific,and tropical cyclones in 2010 are tested independently.Results show that the model fits well for those TCs,which are weaker than severe typhoon,with RMSE of about 5 m/s and mean absolute error of about 4 m/s.For theose TCs with strength between severe typhoon and super typhoon,the fitting error is bigger,with RMSEs of 9.65 and 6.60 m/s,and mean absolute error of 7.76 and 5.49 m/s,respectively.For theose TCs with intensity of strong typhoon and above,the fitting error in daytime(nighttime) decreases(increases),with minimum(maximum) error of 6 m/s(11.96 m/s),indicating that the estimate value is large(small) in daytime(nighttime).

Abstract:This study uses a ranking method to select some good and bad ensemble members from ensemble forecasts of the 2 m temperature above the ground in East Asia provided by European Centre for Medium-range Weather Forecasts(ECMWF) and United Kingdom Met Office(UKMO).The ensemble forecast products are taken from TIGGE archive for the period from June 8, 2007 to August 31,2007.The results show that the optimal selection method may reasonably select the ensemble members with higher and lower forecast skills for 24—96 h forecasts.Case study shows that the ensemble mean forecast of the optimally selected ensemble members may predict the extreme temperature quite well,and it performs better than the ensemble mean of all ensemble members.The forecast skill of the ECMWF ensemble forecast is higher than that of UKMO forecast in terms of the root-mean-square errors of the surface air temperature forecasts.

Abstract:Based on the ATMS(Advanced Technology Microwave Sounder) satellite microwave data during 1—30 August 2012,this paper analyzes the characteristics of data and does the bias correction tests in WRFDA,and verifies the impact of assimilation ATMS data on track forecasts of typhoons Kai-tak(the 13rd),Tembin(the 14th) and Bolaven(the 15th) in August 2012.Results show that,before the bias correction,the deviations for most ATMS sounding channels are less than those for corresponding AMSUA/MHS channels,except for some window channels and humidity channels.The bias variations across scan position for ATMS channels are less than those for corresponding AMSUA/MHS channels,so the data from all 96 scan positions for ATMS channels can be used.The biases are maximum for ATMS window channels and minimum for ATMS channels 6—10.After using the bias correction coefficients derived from ATMS microwave data,it can reduce the biases for temperature channels and humidity channels and improve the prediction of track and minmum pressure of typhoon compared to directly use the bias correction coefficients from NOAA-18.Case studies show that assimilation of ATMS satellite microwave data can improve the prediction of typhoon tracks.

Abstract:Based on the real-time observation data on 500 kV high voltage transmission lines in Hubei area in February 2008 and January 2009,MICAPS conventional meteorological data and NCEP reanalysis data,this paper studies the synoptic systems and meteorological conditions during the two wire icing processes.Results show that the deep low pressure trough at 500 hPa and low vortex with shear line at 850 hPa,which is close to Hubei area,have positive effects on ice thickness during the two icing processes.The air temperature and wind velocity play a leading role in the initial stage of the two icing processes.