Abstract:On the basis of optimizing WRF ensemble square-root filter assimilation system with two-way nesting forecasting scheme and radar data quality control scheme,which also integrates multi-physics ensemble integral scheme,a new ensemble initial perturbation scheme with perturbed potential and stream functions is introduced.This new scheme has smaller perturbed scale and more obvious physical meaning.With direct assimilation of Doppler radar data on the landfalling of typhoon Saomai,this paper compares the impacts of the new perturbation scheme,the background error covariance random perturbation scheme and the whole space random perturbation scheme on the ensemble filter assimilation.Result shows that all three initial perturbation schemes can improve typhoon structure,but the assimilation effect of the new scheme is more distinct due to smaller scale and better physical structure,which can improve the forecasting quality of typhoon track,center minimum pressure,maximum wind speed and precipitation.

Abstract:Based on the daily temperature data from 1951 to 2010,and the longitudes/latitudes/altitudes of 753 stations in China,the relocation point of each station is determined.By using the t-test method and the difference method of standard normal homogeneity test(SNHT),this paper studies the impact of relocation on homogeneity of annual mean temperature over China and corrects the inhomogeneous temperature series.Results show that the data of 714 stations are gotten by linking the series of business substitution station.Only 148 of 714 stations have not been relocated,and the other 566 stations have been relocated for 950 times.The t-test shows that the 235 of 950 times relocations lead to significant differences of annual mean temperature.The SNHT test shows that the 237 of 950 times inhomogeneities of annual mean temperature are caused by the relocations,where the 79 times temperature should be adjusted more than 0.5℃.The 84% inhomogeneous series by the relocations could be relatively adjusted to homogeneous series by adding a coefficient.

Abstract:By using the non-hydrostatic mesoscale numerical model ARPS(Advanced Regional Prediction System),the high-resolution simulation of landfalling process of the strong tropical storm Bilis in 2006,especially the rainfall amplification process after its landfall,is carried out,and comparisons are taken between observations and simulations.Furthermore,the diagnostic analysis by using the high-resolution simulation data is performed to study the rainfall amplification process.Results show that the ARPS reproduces well the landfalling process of Bilis and the rainfall amplification process after its landfall located at the edge of Guangdong,Jiangxi and Hunan Provinces.The large value regions of both the vertical divergence flux and the moist potential vorticity agree fairly well with the location of the rainfall amplification.Both of them have pretty good indicative meanings to the location of heavy rainfall,in which the vertical divergence flux is better.The moist potential vorticity indicates well not only the distribution associated with the rainfall amplification but also the distribution associated with Bilis in 2006.

Abstract:The conservative physical quantities,dry energy potential vorticity(DEPV) and wet energy vorticity(WEPV),which combine the energy synoptic meteorology with dynamics of the atmosphere,are derived from the basic atmospheric motion equation and the concept of total atmospheric energy.It is found that the energy potential vorticity(EPV) expressed by the static temperature is easier in mathematical computation with clearer physical meaning.DEPV and WEPV are applied to diagnose a typical thunder wind case in Hubei in 2007.It shows that both DEPV and WEPV could forebode the thunder wind weather.The enhancing and descending of DEPV in the upper troposphere increase unstable energy in the middle and lower troposphere,which promotes the thunder wind.It indicates that the thunder wind will occur in the superposition between the high WEPV region in the lower troposphere and the baroclinic system.

Abstract:Based on the 10-15 days extended range ensemble forecasts of CMC,ECMWF,UKMO and NCEP in the TIGGE dataset,the multi-model ensemble forecasts of surface air temperature in the Northern Hemisphere middle latitudes during the period from 1 July to 30 September 2008 have been conducted by using EMN(Ensemble Mean),BREM(Bias-Removed Ensemble Mean) and SUP(Multi-model Superensemble),respectively.Meanwhile,the Talagrand distribution,ensemble spread,and RMS error are utilized to evaluate the forecast skills of each single forecast system.As is known that the precision of daily forecasts in extended range is relatively low,people pay more attention to the prediction precision of weather process in extended range.The daily data of each single forecast system and the daily observed data are processed by the moving average method.The processed data are also conducted with multi-model ensemble means.Finally,the training period of SUP is tested.Results show that four single forecast system’s ensemble spread are low compared with RMS error.ECMWF is the best single system,NCEP follows and UKMO is the worst.The forecast skills of EMN,BREM and SUP are all higher than single system and SUP is the best ensemble method.Moving average methods further improve the forecast skill of surface air temperature and the longer of moving step is,the better of the prediction results are.For the training period of SUP about daily and 3-day moving average,75 days are the best training period for 10-12 d forecasts and 35 days are the best for 13-15 d forecasts.For 5-day and 7-day moving average,the best training period is 35 days at all forecasting time.

Abstract:A rainstorm process in north Shaanxi on 27 July 2012 is studied by using the 1°×1° NCEP/NCAR reanalysis data,observed surface precipitation data and black-body temperature(TBB) data from FY-2E satellite.The rainstorm process is simulated by WRF(Weather Research Forecasting) mesoscale numerical model and diagnostic analysis is made by using WRF model outputs.Results show that the rainstorm took place in regions between the northwest marginal zone of the western Pacific subtropical high and the Baikal cyclone.In the middle and low layers,the water vapor originated from the Bay of Bengal,passed the eastern Tibetan Plateau and arrived in north Shaanxi.The process from the small non-organized cloud clusters to self-organized cloud clusters stimulated the development of mesoscale convection system.Near the trough line,the mesoscale gravity wave could be caused by geostrophic adjustment in the right of jet stream exit region at 200 hPa.The energy of downward propagation of mesoscale gravity wave was absorbed by the atmospheric neutral layer near surface,which leaded to the convection development in lower atmosphere layer,and promoted the genesis and development of rainstorm.

Abstract:Using the NCAR Community Atmosphere Model(CAM4.0),two sensitivity experiments integrated 25 years are performed under the conditions of potential vegetation and current vegetation,respectively.The possible influences of the land-use change(LUC) on the land surface energy balance,hydrological cycle and climate over East Asia are investigated.Results show that the current LUC featured by rapid forest degradation and cropland increasing significantly alters the land surface characteristics,leading to increase of surface albedo in all seasons over East Asia,which in turn changes the surface energy balance and hydrological cycle over the region in winter and spring.In addition,impacts of large-scale LUC on the general circulation over East Asia are also detected.Current LUC tends to cause evidently stronger winter monsoon circulation and slightly enhanced summer monsoon.No evident changes of air temperature induced by current LUC are found,but more(less) spring precipitation happens in the north(south) of East Asia under the impacts of LUC.

Abstract:The ensemble hindcast experiments of 11 members in summer(JJA) of 22 years were conducted by the BCC_AGCM2.0(T106L26) developed by National Climate Center.The capability of prediction in 500 hPa geopotential height,precipitation,and 2 m air temperature were tested by the cross validation and root mean square error methods.Results indicate that the model shows a good performance of 500 hPa geopotential height in the tropical region,oceans and parts of Eurasia.The simulation of precipitation over the mid-lower reaches of Yangtze River and most parts of South China has considerable reliability.The correlation coefficients of the 2 m air temperature anomalies in most parts of northern China are positive and pass the local significance test at 90% confidence level.However,the results in southern China are needed to be improved.Meanwhile,the ensemble forecast is much better than the single-sample prediction.The forecasting results can be improved by using the higher resolution atmospheric general circulation model.

Abstract:Based on the NCEP/NCAR reanalysis monthly height data from 500 to 10 hPa(total 12 layers) in winter from 1948/1949 to 2009/2010,three polar vortex circulation indices of Northern Hemisphere are calaulated,which are the area index(S),the strength index(P),and the center position index(λ_c,φ_c) including longitude and latitude.The vertically seasonal,monthly and abnormal changes of Northern Hemisphere polar vortex are analyzed.Results show that the changes of polar vortex area and strength are different not only in the different heights,but also in the appearance time of the intraseasonal maximum.Correlation between the polar vortex area and strength is not significant,therefore they can be seemed as two independent indices.There are also differences of the area and strength interdecadal trends between in the upper layer and in the lower layer,and their abnormal changes are complicated.The changes of the center positions in both the upper and lower layers are identical.The changes are mainly located in the north of 80°N of the eastern hemisphere.Around the North Pole,the polar vortex longitude change is much more severe than the latitude change.The interdecadal change of latitude is significant,and the polar vortex is obviously southward in recent 10 years.On the whole,the position of polar vortex center from 500 hPa to 10 hPa varys in counterclockwise direction,and the radius increases with height.

Abstract:Based on the observations of 63 conventional meteorological stations and the investigated data of food-crops production in Jiangsu Province from 1986 to 2010,this paper studied the characteristics of climate change on three time scales in north,central and south Jiangsu,and the whole province.Based on the one-dimensional linear regression equation with the bootstrap resampling method,this paper studied the responses of the food-crops production to climate changes on the three time scales of crop-year(from November to October the next year),the growth seasons of summer(from Novemeber to May the next year) and autumn(from June to October) crops,and month.The influences of climate changes on the food-crops yield and the contributions of each climate factor in the past 25 years were quantitatively estimated.Results show that:1)In north,central and south Jiangsu,and the whole province,the climate factors are different on the time scales of crop-year,the growth season of summer and autumn crops and month,with some spatial-temporal differences.Under the combined impacts of the developing agricultural managements and technologies,and climate change,the food-crops yield per hectare in the four study areas increases significantly(p>0.01),with increasing trend of 66.89 kg·hm^-2·a^-1 in the whole province.2)Except that the response of the food-crops yield in south Jiangsu to climate change on the time scale of crop-year is not significant,the negative response of the food-crops yield to precipitation(the food-crops yield decreases when precipitation increases,and v.v.) can be found in the four study areas on the three time scales,indicating that precipitation variation plays an important role in the food-crops production.When precipitation increases(decreases),the food-crops yield in north and south Jiangsu,and Jiangsu decreases (increases),with the mean rates of 0.19%·(10 mm)^-1,0.09%·(10 mm)^-1 and 0.11%·(10 mm)^-1,respectively.3)Results of the three models show that the food-crops production in north and south Jiangsu,and Jiangsu all decreases due to climate change.Results of Model-C established by monthly climate factors reveal that climate change leads to the food-crops yield per hectare(total production) decrease of -6.51%·(10 a)^-1(-11.28×10⁸ kg·(10 a)^-1),-3.27%·(10 a)^-1(-2.36×10⁸ kg·(10 a)^-1) and-1.34%·(10 a)^-1(-4.45×10⁸ kg·(10 a)^-1) in north and south Jiangsu,and Jiangsu,respectively.Additionally,it is very necessary and critical to pay enough attention on the effects of monthly climate change in order to completely and systematically evaluate effects of climate change on food-crops production.

Abstract:In order to research the degree of social economic damage caused by tropical cyclones(TC) landing in Zhejiang Province and improve the service level of typhoon prevention and disaster reduction,this paper evaluates the disaster influence of TC occurred in Zhejiang Province from 1981 to 2007 by the fuzzy comprehensive evaluation method.In order to verify that the disaster effect assessment model is correct or not,the actual disaster situation of TC is evaluated,and the disaster influence index and the disaster index of TC are calculated and graded.Results show that the concordance rates between the disaster index and the disaster influence index can reach 92% for all samples.In addition,the correlation coefficient between the disaster influence index and the corresponding direct economic losses is 0.79.It indicates that the disaster effect assessment model can evaluate disaster influence of TC landing in Zhejiang Province.

Abstract:Based on the lightning data observed by SAFIR3000 lightning location system from 2005 to 2007 in Beijing and its circumjacent regions (Tianjin,Tangshan,Langfang,etc.),the temporal and spatial characteristics of intracloud(IC) flash and cloud-to-ground(CG) flash were analyzed.The results show that the time of high-frequency IC mainly occurs from 15:00 BST to 24:00 BST and the peak of the IC frequency appears at 19:00 BST.Most of IC flashes are prone to occur between June and August,and the peak occurs in July.The maximum of spatial density of IC mainly appears in the northeast of Beijing,the north of Tianjin and southwest of Chengde at the value of 30 times/(km²·a).The daily variation of average initiated height(MSL) of IC lightning is not obvious.The initiated height is the highest in summer,whereas it is the lowest in winter.The IC flashes mainly occur at the height of 9-10 km,which account for 10.97% of the total IC flashes.The high frequency time,months and high density area (at about 5 times/(km²·a)) of CG lightning are similar to those of IC lightning.However,a few differences appear between IC lightning and CG lightning.Firstly,the daily variation of IC has a single peak but that of CG has two peaks;secondly,both the beginning and ending time of IC’s high value are earlier than that of CG’s.In addition,the lightning density of the former is 5 times larger than the latter’s.The average percentage of+CG flashes in the total CG for three years is 16.44% and the percentage is lower in summer but higher in spring and autumn.In addition,its monthly variation has an inverse correlation with that of the+CG flashes frequency.The temporal-spatial distribution characteristics of total lightning are more similar to those of IC lightning.The high density areas of total lightning detected by SAFIR3000 are basically consistent with those detected by satellites.

Abstract:This paper reviews the research progress of ocean feedback to atmosphere in recent 10 years.Some main issues are addressed for further study,such as how to separate individual ocean influence on atmosphere anomaly in the observational researches effectively.Traditionally,the linear regression or partial correlation method is used to filter out the main interference factor.However,the method is valid only at the condition where we know the factor in prior,e.g.the ENSO signal is removed before assessing the ocean feedback in the mid-latitude.How about the other remote influence from the unknown ocean? A new method,the generalized equilibrium feedback assessment(GEFA),is used to separate each contribution of the individual ocean forcing automatically,without any prefiltering.Its validity is preliminarily proved in a simple thermal model and observations.Therefore,GEFA provides a useful tool for assessing the ocean feedback to the atmosphere.