Abstract:Based on the daily NCEP/NCAR reanalysis data,this paper analyzes the extra-tropical low-frequency oscillation(atmospheric angular momentum budget and mountain torque) and AO(Atlantic Oscillation) indices in winter.Power spectrum analysis and correlation analysis show that the dominant variations of them occur in 30-60 d band,and the variation of atmospheric angular momentum budget has positive correlation with the variation of mountain torque and also responds to the variation of AO significantly.Dynamic diagnostic analysis shows that the mountain torque of the two major NH mountain ranges influences zonal atmospheric angular momentum(zonal westerly),and the subtropical westerly and the north-south westerly dipole structure change,so the strength of AO changes.In comparison with the Rockies,the Himalayas play a important role in AO variation.The dynamic diagnosis of the Himalayas ranges shows that,during the period of high(low) AO indices,the quasi-stationary planetary waves forced by the Himalayas ranges influence subtropical westerly,and the subtropical westerly weakens(strengthens) and the high-latitude westerly strengthens(weakens),so AO strengthens(weakens) and the polar vortex in the stratosphere strengthens(weakens).The strong(weak) center of polar vortex tends to Northeast Asia.

Abstract:Based on the NCEP/NCAR reanalysis and surface air temperature data recorded by University of Delaware,the interannual variation of tropical upper tropospheric trough(TUTT) over the northern Pacific in summer and its causes,together with its relationship with the surface air temperature over the North America,are investigated.Results indicate that the TUTT experiences a marked interannual variation during the period of 1979-2010 with two main periodicities of quasi-4 and quasi-5 years.Results also show that the TUTT intensity is highly negatively correlated with the surface air temperature over the southeast part of North America.As the summer TUTT increases(decreases) in intensity,the geopotential height in the upper-middle troposphere over southeast part of North America decreases(increases),thus the high which dominates over the southeast part of North America is correspondingly weakened(enhanced),leading to a decrease(an increase) in surface air temperature there.In addition,the interannual variation of TUTT is highly related to both the SST anomalies over the tropical Indian Ocean and SST anomalies over the tropical western Atlantic Ocean in summer,however,the former plays a dominant role.The increase of SST anomalies over the tropical Indian Ocean in summer would heat the overlying atmosphere and excite the eastward-propagating Kelvin waves to east of the equatorial Indian Ocean,and cause increase in geopotential heights of middle and eastern Pacific,thus induce the weak of TUTT intensity;and vice versa.

Abstract:Based on the daily precipitation data of 122 stations in Northeast China(NEC),the NCEP/NCAR reanalysis data and the monthly temperature data of 160 stations from NCC(National Climate Center) during 1961-2010,this paper reveals the rainfall patterns of NEC in June,July and August and analyzes the characteristics of abnormal atmospheric circulation.Results indicate that the precipitation of NEC can be divided into the consistent rainfall pattern(more rainfall pattern or less rainfall pattern) and the south-north anti-phase rainfall pattern(southern rainfall pattern or northern rainfall pattern) in June and August,and the consistent rainfall pattern(more rainfall pattern or less rainfall pattern) and the east-west anti-phase rainfall pattern(eastern rainfall pattern or western rainfall pattern) in July.In addition,the precipitation of NEC in June is related to Northeast cold vortex(the stronger cold vortex,the more rainfall),and the south-north anti-phase rainfall pattern is affected by the abnormal Okhotsk blocking high.The precipitation of NEC in July and August is related to East Asian summer monsoon,and the consistent rainfall pattern is affected by both the location of western Pacific subtropical high and the the wave train propagating eastward along the upper westerly jet stream,while the south-north(east-west) anti-phase rainfall pattern is affected by the intensity of western Pacific subtropical high.

Abstract:Based on the NCEP/NCAR daily reanalysis datasets(2.5°×2.5°) and the daily precipitation datasets of 743 meteorological stations in China in June during 1979-2007,the characteristics of the synoptic scale wave train and its impact on Meiyu in the middle and lower reaches of the Yangtze River are investigated by the correlation analysis method,the synthetic analysis method,etc.Results indicate that,when the precipitation is less in the middle and lower reaches of the Yangtze River in June,there is a synoptic scale wave train over East Asia and West Pacific.The wave train has both shorter duration and extended distance(from Hetao area of the Yellow River to the middle and lower reaches of the Yangtze River,to South China Sea,and to the Philippine Sea),and is stronger only below 500 hPa.Diagnosis and case analyses show that,when the wave train is especially notable,the Meiyu rainfall obviously decreases in the middle and lower reaches of the Yangze River and increases in the south region.It shows that the wave train has an important indicative significance for the precipitation prediction in the middle and lower reaches of the Yangtze River.

Abstract:Based on the NCEP/NCAR reanalysis data,the FY2E-TBB data and the precipitation observed by meteorological stations,the general circulation and precipitation before and after South China Sea(SCS) summer monsoon onset of 2011 are analyzed.Results show that the convective activity first appears in the Bengal Bay,then extends to SCS in 2011.Meanwhile,South Asia high moves to the northern Indo-China peninsula and the western Pacific subtropical high withdraws eastward from SCS,and SCS summer monsoon breaks out in the fourth pentad of May(the 28th pentad of 2011).After the monsoon onset,the India-Bengal Bay summer monsoon trough forms,and the southwest flow prevails in lower troposphere over most of SCS,coupling with abrupt changes of both the convective rainfall and the circulation over SCS.With the progress of monsoon activity,the rainbelt moves northward and the great precipitation appears over the middle and lower reaches of the Yangtze River where the rainy season begins.It is found that both the SCS summer monsoon and the Meiyu over the middle and lower reaches of the Yangtze River are influenced by the subtropical high.There is an obvious negative correlation between intensity of Meiyu over the middle and lower reaches of the Yangtze River and that of SCS summer monsoon,but there is a remarkable positive correlation between onset time of the Meiyu and that of SCS summer monsoon.SCS summer monsoon is weaker and its onset time is earlier,while Meiyu precipitation over the middle and lower reaches of the Yangtze River is heavier and its onset time is earlier in 2011.

Abstract:Based on the NCEP/NCAR 1°×1° gridded analysis data per 6 hours and the best track data from JTWC,the temporal and spatial distribution characteristics as well as the value of the divergent wind surrounding 118 tropical cyclones in the range of 100°E to 180°E in the northern hemisphere from May to September during 2004-2010 were statistically analyzed.TCs can be divided into seven types according to different influence systems,and the first four categories take up more than 91.5% of the total number,which are 1) cross-equatorial flow type;2) equal cross-equatorial flow and subtropical high type;3) strong cross-equatorial flow and weak subtropical high type;4) subtropical high type.Centered on TC,areas within 500 kilometers away from the closed vortex of the new TCs are affected by subtropical high in the first quadrant,by subtropical high and continental high in the second quadrant,by cross-equatorial flow in the third quadrant,and mostly affected by cross-equatorial flow and seldom by subtropical high in the fourth quadrant.As for the regional average divergent wind values,the effect intensity of cross-equatorial flow varies in the range of 1.4-3.5 m·s^-1,and the effect intensity of subtropical high varies in the range of 0.7-1.2 m·s^-1.By conducting both control test and sensitivity test on TC 0704,we know that another new TC will still generate in few days after removing the TC,which proves the surrounding systems play an important role in TC genesis.

Abstract:The influences of sea surface temperature(SST) anomaly in the North tropical Atlantic(NTA) during boreal summer(June-October) on tropical cyclone(TC) formation over the western North Pacific(WNP),and the underlying physical mechanisms are investigated using TC best track data sets,Hadley SST data and NCEP/NCAR reanalysis data for the period of 1979-2012.A significant negative correlation between WNP TC genesis frequency and simultaneous June-October NTA SST anomalies are demonstrated.The results suggest that the NTA SST warming produces a pair of low-level anomalous circulations,with an anomalous cyclonic circulation over the tropical Atlantic/eastern Pacific,and an anomalous anticyclonic circulation over the WNP.This anticyclonic circulation anomaly suppresses convection and barotropic energy conversion from large-scale flow,reduces low-level cyclonic vorticity and midtropospheric humidity,thus greatly inhibits the TC genesis over the WNP;and vice versa.

Abstract:The superensemble (SUP) hindcastof the surface air temperature over East Asia and its surrounding areas was conducted based on the CMIP5 runs of 15 climate system models. The ERA data of the monthly surface air temperature were used as observed values, and root-mean-square error (RMSE), anomaly correlation coefficient (ACC), and mean absolute error (MAE) were chosen to evaluate the hindcast skills of individual models, the multimodel ensemble mean (EMN) and SUP techniques. The results show that the length of the training period has influence on the hindcast results. The RMSE decreases and the ACC increases as the training period length increases within some ranges. However, the hindcast errors will not decrease or even increase when the training period reaches a particular length. All of the 15 individual models can hindcast with some skills the surface air temperature over East Asia and its surrounding areas, its interannual variation and spatial distribution. Nevertheless, the hindcast skills are different for different models, among which the CCSM4 model has the highest hindcast skill. Multimodel ensemble techniques are superior to individual models in terms of the hindcast skills. The SUP technique has higher hindcast skill than the EMN. The regionally averaged RMSE of the SUP hindcast is around 0.43℃, suggesting that the SUP improves the hindcast skill of the surface air temperature considerably.

Abstract:Taking into account both IASI instrument characteristics and the specific circumstance of GRAPES,a bias correction scheme applicable to operational system is developed for IASI radiances.The scheme utilizes a scan correction and an air-mass correction.Figures show that instead of latitudinal dependency for microwave radiances bias,there is a different scan bias for each of the 2x2 IASI pixels.Scan bias between limb and nadir measurements can be removed with the view angle as independent variable,while the smaller amplitude pixel-to-pixel bias avoided by the way of thinning.Air-mass bias is corrected according to the weather condition at that time,which can be quantitatively represented with predictors computed from the background field.Four predictors are used,including 1000~300 hPa thickness,200~50 hPa thickness,50~20 hPa thickness,and model surface temperature.Verification results show that biases can be controlled stably at a relatively low level for a long time and the correction effects are significant.

Abstract:The hybrid ensemble transform Kalman filter-three-dimensional variational data assimilation (Hybrid ETKF-3DVAR)method is used to assimilate the simulated Doppler radial velocity observations based on Weather research and forecasting (WRF)model.The hybrid scheme updates the ensemble mean using a hybrid ensemble and static background-error covariance on the basis of 3DVAR framework.The ensemble perturbations in the hybrid scheme are updated by the ETKF scheme,which updates the background perturbation through a transform matrix.The results show that Hybrid ETKF-3DVAR provides more accurate analysis than traditional 3DVAR.Additionally,significant positive impact from the hybrid data assimilation is found in vortex structure and position as well as the track forecast.It is found that such positive improvements are mostly provided by the flow-dependent covariance other than the use of ensemble mean by comparing the results from 3DVAR and the HybridS experiment,which uses static background-error covariance and ensemble mean as the first guess.

Abstract:Based on the TOPEX/Poseidon(T/P) satellite sea level anomaly(SLA) data during 1993-2012 and FSCR(Climate Forecast System Reanalysis) wind data,the temporal-spatial features of sea level of Yellow Sea and East China Sea within the 20 years are analyzed.The impacts of wind fields within different periods on the sea level are investigated,and the possible mechanisms of sea level change of short duration are studied by FVCOM(Finite Volume Community Ocean Model).The results show that the average sea level of Yellow Sea and East China Sea in recent 20 years is high in southern and low in northern;seasonal wind fields near the sea surface with coastal distribution and sea water thermal swelling together force the sea level plus deviations in summer and autumn,and minus deviations in winter and spring.The average wind speed near the sea surface is gradually decreasing and the sea level rising speed is about 2.9 mm/a during the 20 years.The short duration actions of wind field mainly present as disastrous wind events.According to statistics,both the summer typhoon and the winter cold wave show a trend of decrease in frequency and increase in intensity during the 20 years.The FVCOM model is used to simulate and analyze the sea level changes of Yellow Sea-East China Sea under typhoon and cold wave impacts,and results show that the strong typhoon wind creates the divergent cyclone vortex of sea current with sea level of negative low surface center,while the strong cold wave wind from north creates the anti-cyclone vortex of sea current with sea level of positive high surface center.The strong sea current areas in the two types of vortexes increase the sea surface gradient.Due to the unstable sea temperature profile with depth and the active convection impact caused by the winter cold wave,the kinetic energy and momentum were transported downwards more faster in depth and intensity,compared with that of summer typhoon.

Abstract:The interannual variation of summer droughts in Xiangxi of Hunan Province is investigated,and the underlying causes for the drought events are explored,based on the drought index(CI) of Xiangxi,as well as the NCEP/NCAR reanalysis data and NOAA SST data.The CI is calculated by daily temperature and precipitation data from 1960 to 2013 recorded by 8 meteorological stations in Xiangxi.The results show that severe drought events occurred in summer of year 1961,1972,1981,1994,2009,and 2013,and the droughts are closely related to the mid-and high-latitude circulation anomaly patterns,and circulations at low latitudes and the tropics as well.The thermal external forcing near the Philippines from West Pacific to the Bay of Bengal,associated with the rainfall anomalies,is able to lead to the anomalous movement of the western Pacific Subtropical high,which probably results in the drought events.When the rainfall is positive with stronger than normal convection near the Philippines,the subtropical high moves northward anomaly and controls the Xiangxi area with less rainfall,then the drought will easily occur in Xiangxi.

Abstract:The distribution of haze days and air pollution index(API),and their relationship with meteorological elements were analyzed for Beijing,Nanjing,Shapingba district of Chongqing,and Guangzhou,using the MICAPS ground conventional observation data during 1994-2013 from 756 national base stations and the API data for 47 citiesduring 2002-2012 published by Ministry of Environmental Protection of the PRC.The results indicate thatthe haze and high API mainly occurs in central and eastern China;the annual frequency of haze days has begun to rise since 1998 and reached its maximum in 2013,and most haze occurs in January and least in August.While the annual frequency of high API is on the decline,and API is generally highest in December and lowest in August during the period of 2002-2012.The interannual and monthly variations of haze days and API are different forBeijing,Nanjing,Shapingba of Chongqing,and Guangzhou.As for the relationship between haze and meteorological elements,the results indicate that the relative humidity is generally high in the four large cities/district in haze days;when haze occurs,Beijing,Nanjing and Guangzhou,and Shapingba district of Chongqingare dominated by southwestly,southeastly,and northwestly wind,respectively,with wind speed mainly in the range of 1-4 m/s.Haze will easily occur inkatallobaric and stable lower atmosphere.The lower atmosphere stability(γ₈₅₀) is correlated negatively with API in Beijing and Shapingba district of Chongqing,while positively in Nanjing and Guangzhou.Multiple linear regression equations show that both thermal factor and dynamic factor have contributed to the visibility at haze days and API in winter in the four cities/district.

Abstract:By analyzing the variation rule of PM₁₀ concentration(concluded by a conversion of API(Air Pollution Index)) in Shanghai from 2001 to 2012,this paper establishes the remote sensing inversion model to measure PM₁₀ concentration in Shanghai.As indicated by the results,the following conclusions can be arrived at:1)There is a seasonal variation for PM₁₀ concentration in Shanghai,thus remote sensing inversion models in four seasons should be established,respectively.2)By probing into the correlation between MODIS AOD(Aerosol Optical Depth) products and PM₁₀ concentration,this paper arrives at the conclusion that only by going through aerosol vertical distribution and relative humidity error correction can AOD establish a preferable correlation with PM₁₀ concentration.3)Based on the aerosol vertical distribution and relative humidity error correction,all the four-season remote sensing inversion models established to measure the PM₁₀concentration in Shanghai have passed the test of fitting degree.Among them,the spring model uses the exponential function,the summer and autumn models apply the quadratic polynomial function,the winter model adopts the power function,and the yearly model uses the quadratic polynomial function.It is comparatively highly reliable to invert Shanghai PM₁₀ concentration using the four-season remote sensing inversion models.

Abstract:The wind tunnel experiments were carried out to study the impact of high-density building clusters and high-rise building on the wind environment,in case of different surface roughness and wind directions.The Shanghai Lujiazui Finance & Trade Zone and Shanghai Tower were selected as the test subject areas.The results show that the large wind area increases with the decrease of surface roughness,and the wind direction is easily affected by the building cluster distribution and arrangement.Under some conditions,the wind vector is varied at different height of high-rise building due to its inconsistent shape at upper and lower levels.According to a foreign wind environment comfort criteria on tall building,the average wind velocities at pedestrian level are evaluated,and three bad areas in aspect of wind environment are listed.

Abstract:The transitivity property of significant correlation between random variables is analyzed from geometric aspect.The geometric expression of the probability for the transitivity of significant correlation between random variables are derived with the sample capacity n≥3.Monte-Carlo method is used to validate the rationality of the geometric analysis and some discussions are given.