Abstract:Based on the NCEP-CFSR(National Centers for Environmental Prediction Climate Forecast System Reanalysis) reanalysis dataset and WRF model,this paper studies the formation process of initial vortex of tropical cyclone Nargis over the Bay of Bengal(BOB) in April 2008.Results indicate that the initial disturbance of Nargis,which is found in the northern Pulau Sumatera Island,is probably triggered by the equatorial westerly jet associated with an eastward MJO event over Indian Ocean.On the other hand,the easterly jet(22—25 April),which originated from mid-latitudes,passed by South China Sea and entered into BOB,plays an important role to intensify the initial disturbance to be a tropical depression.When the cold easterly jet enters into the eastern BOB,the available potential energy of low level atmosphere converts into the total kinetic energy by increasing sea surface sensible heating,then the low level cyclonic circulation increases rapidly,and the initial disturbance moves northwestward and finally develops into a tropical depression.Through the sensitive experiments with WRF model,it has further proved that the initial disturbance of Nargis will not develop to be a tropical depression if the easterly jet is very weak.

Abstract:Based on the AVHRR high-resolution sea surface temperatures and the tropical cyclone(TC) dataset of Japan Meteorological Agency during 1982—2008,statistical analyses are firstly performed to study effects of Kuroshio over East China Sea on TCs in summer(JJA).The statistical analyses reveal that thirty percent of TC cases are strengthened when they pass the key Kuroshio region,while ninety percent of TC cases across the warm tongue of Kuroshio are intensified.Then,based on the composite analysis method,six rapidly intensified TCs are selected to study the effect mechanism of Kuroshio enhancing TCs,indicating that the increased heat fluxes along the warm tongue of Kuroshio play an important role in strengthening the intensity of TCs.Finally,a mesoscale numerical model(WRF) is used to study the effect of Kuroshio on TC Noguri—a typical intensified case in 2002.The WRF model well reproduces the rapidly intensified process of Noguri when it passes the warm tongue of Kuroshio.Two sensitivity experiments are designed to further explore the influence of the warm tongue on the intensity of TC with different sea surface temperatures.Numerical results show that the enhanced effect by the warm tongue of Kuroshio is much larger than the weakened effect by cold water due to TC-induced upwelling.As a result,the warm tongue of Kuroshio excites cumulus convection and then enhances intensity of TC through increasing sea surface heat fluxes.

Abstract:The tropical cyclone frequencies in the northwestern Pacific in 2010 and 1998 are far less than the normal frequency,so the diagnostic analyses are performed on relationships between ENSO events,East Asian summer monsoon circulation anomalies and the tropical cyclone frequency anomalies based on the data of serially numbered typhoons in the northwestern Pacific,the data derived from NCEP/NCAR reanalysis dataset and the interpolated outgoing longwave radiation(OLR) data provided by NOAA.The synoptic images of the main memberships of East Asian summer monsoon system influencing the tropical cyclone frequency are given:From spring to summer,the sea surface temperature in the equatorial eastern Pacific is warmer,Hadley circulation is stronger,and Walker circulation is weaker;the West Pacific subtropical high is intensified and moves westward;the monsoon trough extends southward without eastward and westward spread;the cross-equatorial flow in South China Sea and the western Pacific is weaker;the abnormal apparent heat source and apparent moist sink extends southward,and the tropical convective activity is not active in South China Sea and the Philippines,but it is active in south of the equator;therefore the tropical cyclone frequency is significantly less than the normal and the tropical cyclone moves westward.

Abstract:The high-resolution numerical simulations of Hurricane Bonnie(1998) are used to analyze its intensity and structure changes in relation to its associated inertial stability under the influence of intense vertical wind shear during three different stages of its life cycle.Results show that Bonnie has high asymmetry and experiences an eyewall displacement cycle during its rapid intensifying stage.During its rapid structure change stage,the development of high inertial stability is consistent with the change in hurricane inner core size.The inertially stable region,which is usually present inside the eyewall,provides resistance to radial motions,and plays an important role in reducing the influence of vertical wind shear.The inertially stable region reduces the Rossby radius of deformation,and concentrates the latent heating,which is beneficial to the enhancing of the hurricane.This is an important factor in the development of inner core region of the hurricane.

Abstract:Based on the infrared satellite images of MTSAT2 and NCEP/NCAR reanalysis data,this paper studies the cause of abnormal track of tropical cyclone Meranti(2010).The track of Meranti consists of three stages:the westward moving phase,the rotating phase and the northward moving phase.Results show that the environmental steering flow plays a key role in the westward moving phase and the northward moving phase,and the asymmetric structure of Meranti also has a certain influence,whereas the influence of asymmetric convection system is weak.The asymmetric convection system plays a main role in the rotating phase,including interaction of Meranti with two neighboring meso-scale vortices,the Meranti escaping northeastward in the binary vortex process and so on.It also shows that the fractal dimension of Meranti border line in the rotating phase is obviously different from that in the westward or northward moving phase,which is significantly lower with notable fluctuations.

Abstract:An objective discriminating method of cyclone(the cyclone phase space method) is introduced.Based on the NCEP-FNL reanalysis data,two Jiang-Huai cyclones are studied with the objective method,which verifies the features of structure evolution and precipitation distribution of Jiang-Huai cyclones.Results show that the objective method has a good indicative significance for the structure evolution of two Jiang-Huai cyclones.There is a good corresponding relation between the low level thermal wind parameter and the minimum pressure.The significant decline of low level thermal asymmetry parameter and the decrease of low level cold core have an obvious indicative significance for main precipitation period.This objective method is obviously better than the diagnosis method based on the temperature advection dipole used before in the weather analysis.This method also has some deficiencies and needs to be improved.It is suitable for grid data,easy to calculate,and convenient for operational use too.

Abstract:Based on monthly rainfall data of CMAP and reanalyses of NCEP/NCAR from 1979 to 2010,the meridional shifting of East Asian jet stream(EAJ) in upper troposphere and its regional climate impacts have been investigated.An index is defined to describe the meridional shifts of EAJ.The results have demonstrated that there is notable interannual variability for EAJ,with periodicities of 2—3 a and 8 a.When the EAJ locates at latitudes more northern than normal(more southern than normal),the wave-like anomalous rainfall pattern signed with the positive—negative—positive(negative—positive—negative) signs is observed form lower to higher latitudes in East Asia sector along with negative(positive) anomalies of temperature in subtropical western Pacific,and simultaneously significant positive(negative) anomalies in regions including the eastern and northern parts of China and Japan.In region of the eastern parts of Siberia,negative(positive) anomalies are also found.Although in years when the position of East Asian jet shifts anomalously,circulation anomalies look equivalent barotropic.The meridional shifting of EAJ and the temperature anomalies in the regions from the middle-lower reaches of Yangtze River in China eastward to Japan are found to be related to the anomalous meridional circulation induced possibly by the anomalous diabatic heating in tropic regions including the western Pacific and the South China Sea,and related to the eastward propagation of mid-latitude wave energy.

Abstract:Based on the daily reanalysis data of European Center for Medium Weather Forecast(ERA-40) and the empirical orthogonal function(EOF) method,we find that the first mode depicts a meridional seesaw variation of the storm track,the second mode depicts the variation of the storm track against its climatological position and the third mode depicts a tri-polar oscillation.Further regression analysis shows that:When eastern storm track moves southward(northward),the sea surface temperature(SST) is of El Nino(La Nina) pattern,winter colder(warmer) sea surface is unusually low(high) upon the east and middle ocean tropic areas and middle-latitude North Pacific and middle troposphere is of positive(negative) Pacific-North American Pattern(PNA) teleconnection;when eastern storm track strengthens(weakens),SST of Kuroshio Current is warmer(colder) than usual,and middle troposphere is of positive(negative) West Pacific Pattern(WP) teleconnection;when eastern storm track presents the positive-negative-positive(negative-positive-negative) tri-polar oscillation from northwest to southeast,SST near Papua New Guinea is warmer(colder) than usual,SST near Hawaii is colder(warmer) than usual,colder(warmer) sea surface is unusually low(high),middle troposphere is positive(negative) similar to PNA Pacific-North American Pattern,teleconnection.All in all,time coefficients of different modes have significant correlation with the Aleutian Low(AL) index,PNA index,WP index,Nino3 index and the Kuroshio Current(KC) index respectively,which demonstrates the existence of the relationship between the east storm track and atmosphere as well as SST anomaly.

Abstract:A statistical analysis is done for Meiyu heavy rainfall over Changjiang-Huaihe valleys during 2007—2011 based on the daily precipitation data.It has been verified that there are two separate heavy rainfall regions over Changjiang and Huaihe valleys according to the rainfall frequency and distribution during Meiyu season.The two rainfall regions have their different features at prevailing meso-system,space structure,Meiyu front location,moisture transportation channel,rainstorm position,dry and cold air intrusion,southward movement of dry-cold momentum,etc.Under dominated dynamic circulations at high level,more low vortex heavy rainfall(77%) happened over Changjiang valley and more convergence line heavy rainfall(86%) happened over Huaihe valley.The prevailing shallow meso-systems cause the characteristics of Meiyu heavy rainfall with strong rainfall and weak wind.The low vortex over Changjiang valley brings moisture from both South Sea and East Sea,so it makes the heavy rainfall with a larger and wider covering area in Changjiang valley than that in Hauaihe valley.The convergence line in Hauaihe valley brings moisture from only South Sea.The dense zone of the potential pseudo-equivalent temperature isoline presents the Meiyu front and the leading edge of the dry and cold air,with an abrupt shape for the convergence line structure in Huaihe valley but a dry and moisture overlapped shape for the low vortex structure in Changjiang valley.On the north side of Meiyu front,the dry-cold intrusions from mid-high troposphere are downward,with a lower center position and a larger size in Changjiang valley than in Huaihe valley.The vertical distribution of moist potential vorticity shows that the heavy rainfall area is under the baroclinic part of moisture potential vorticity more than 0,a positive vorticity development area.The dry and cold momentum is presented by the baroclinic part of moisture potential vorticity less than 0,its centre transports downward and southward,and its south edge has indicative function to the position of heavy rainfall.The latitude effect and cold air density cause bigger southward velocity component of the dry and cold air mass momentum in Changjiang valley than in Huaihe valley.The combined effect of several influence factors(excluding the terrain factor) is benefit to the separation of heavy rainfall in Changjiang and huaihe valleys.

Abstract:Based on the MPL(micro pulse lidar) data over Shouxian area(32°33'30.18"N,116°46'55.02"E),Anhui Province from 14 May to 28 December 2008,this paper analyzes the diurnal variation of mixed layer height(MLH).Comparisons are made between MLHs retrieved by MPL retrieval methods(the gradient method,the inflection point method and the normalized gradient method) and MLH determined by the sounding data measured by SONDE.Results show that MLH retrieved from the lidar data using the gradient method are highly correlated with MLH measured by SONDE(the correlation coefficient is 0.976),and the gradient method is the most suitable retrieval algorithm in Shouxian area.The diurnal cycle of MLH on sunny days are retrieved by the gradient method,and the effect of meteorological conditions on MLH are also studied.Results show that the growth rate of MLH agrees well with the hourly increase of surface temperature one hour before.Surface wind speed and direction can also lead to rapid change of MLH.The development of MLH exhibits temporal behavior similar to that of the aerosol optical thickness,but with 0.5—3 h lag time.

Abstract:Based on QuikSCAT satellite remote sensing wind data over China offshore area(0°—45°N,105—135°E) during 2000—2009 and the wind results simulated by MM5 in 2007,through in-situ winds comparison,empirical orthogonal function(EOF) and singular value decomposition(SVD) methods,this paper studies the characteristics of QuikSCAT winds and MM5 simulations.Results show that the spatial distributions of two kinds of winds are similar and their speed variations are closely related.The spatial distribution of QuikSCAT winds is more reasonable and the magnitude of MM5 simulations is more reliable.With the PS(Pattern-Scaling) method,this paper extracts the spatial distribution from QuikSCAT winds and the magnitude from MM5 simulations,which shows that the spatial distribution is same as QuikSCAT winds and the magnitude of wind speed is equal to MM5 simulations.The preliminary test results show that the PS method can increase the accuracy of QuikSCAT winds in China offshore area.

Abstract:Global atmospheric temperature trends from the middle troposphere to the upper stratosphere are investigated based on the simulations from the Coupled Climate Model Inter-comparison Project phase 5(CMIP5) together with NOAA satellite observations from 1979 to 2005.Results show that the CMIP5 model simulations can reproduce the features of stratospheric cooling and tropospheric warming,which are consistent with the observations,but the CMIP5 simulations display different latitudinal-longitudinal patterns from SSU/MSU measurements,with significant discrepancies among the selected models.Compared with observations,the CMIP5 simulations significantly underestimate the stratospheric cooling in the tropics and substantially overestimate the cooling over the Antarctic in the MSU observations.The largest standard variation among the seven CMIP5 simulations is seen in both the south and north polar regions in the stratosphere,and the standard variation retains similar small values at all latitudes in the troposphere.

Abstract:Based on the rainfall data at 160 stations of China,the NCEP/NCAR monthly reanalysis data,the monthly extended reconstructed sea surface temperature(ERSST) data supplied by NOAA and CPC(NOAA) indices,by using the EOF(empirical orthogonal function) analysis,this paper investigates JFMAM(January-May) precipitation patterns in the middle and low reaches of Yangtze River(MLRYR) during 1951—2013 and their causes.The results show that JFMAM precipitation of MLRYR has three EOF modes:the first mode with in-phase change,the second mode with north-south out-of-phase change,and the third mode with rainfall anormaly distribution along the Yangtze River.The aforementioned three modes are related to different circulaion anomalies.The maintenance of the anomalous circulations related to the three patterns are found to be related to,respectively,the perturbations originating from Europe and propagating easterward along the westerly belt,the wave train from Atlantic and passing through the Arctic areas to MLRYR,and the Northern Hemisphere Annual Mode.The in-phase rainfall pattern is well correlated with Nino3.4 index.The north-south out-of-phase pattern and the rainfall pattern along the Yangtze River are linked to sea surface temperature anomaly in the eastern Pacific.

Abstract:Based on the climatic data of station network in China,this paper briefly describes the relationship between the empirical orthogonal function(EOF) analysis method and the adjusted EOF(AEOF) analysis method,and gives schemes of analysis effect verification.Using EOF and AEOF methods,this paper analyses the anomalous summer air temperature series at 160 stations in China during 1951—2010.Results show that the mode square fitting rate and the cumulative mode square fitting rate of the first six modes by AEOF method are higher than those by EOF method.The fitting effect of the typical fields of first three modes by AEOF method on the mode square field of anomalous summer temperature series are better than that by EOF method.Therefore,the necessity of station homogeneity adjustment is demonstrated when EOF method is used,meanwhile the better adjustment effects using AEOF method are verified in the actual analysis.

Abstract:Using the observational daily precipitation data in South China during 1961—2012,this paper analyzes statistical characteristics of persistent heavy rainfall during the first rainy season in South China under the background of Pacific sea temperature fields on different time scales,and discusses the responses of low frequency cycle of precipitation during the first rainy season in South China to different sea surface temperature forcing,which can promote the development of extended-range forecast of the persistent heavy rainfall.Results show that there are higher occurring probability,stronger intensity and longer duration for the typical persistent heavy rainfall in the PDO(Pacific Decadal Oscillation) cold phase years than in the PDO warm phase years.Under the background of Pacific sea temperature fields on different time scales,the characteristics of the persistent heavy rainfall are different.During the PDO cold phase years combined with significant sea surface temperature anomalies in Nino region in winter and spring,the persistent heavy rainfall are stronger and longer.The external forcing of Pacific sea surface temperature fields on different time scales might have relationships with the low frequency cycles of precipitations during the first rainy season in South China,and further affect intensity and duration of the persistent heavy rainfall.

Abstract:This paper studies a thunderstorm event detected by Doppler Weather Radar(CIN RAD WSR/98D) in Tianjin on 13 August 2007,showing that the thunderstorm event is triggered by collision between sea breeze front and gust front over Bohai Bay.After the collided,new thunderstorm cells formed in the front of sea breeze front and gust front.The convection echo body intensifies in the back of gust front,and changes from theellipse echo to the typical bow echo.This paper applies the ground data of six factors at 36 automatic weather stations in Tianjin and the sounding data above 850 hPa in Beijing,forming new diagnostic data.Diagnostic analysis shows that there are strong low-level vertical wind shear and dew point temperature gradients in the front of sea breeze front detected by the Radar.The front edge of sea breeze front corresponds with the dense area of 0—3 km vertical wind shear gradient,and basically tallies with the rapid change zone of dew point temperature gradient.When the sea breeze front and the gust front collide,the 0—3 km vertical wind shear changes rapidly within 2 h with an obvious increasing trend,and CAPE(convective available potential energy) has significantly increased before the formation of thunderstorm.With the end of thunderstorm,above features will disappear.

Abstract:Based on the historical observation data of acid rain at Baoshan and Pudong in Shanghai,the long-term trend and formation of regional acid rain changes and the spatial distribution of precipitation acidity were analyzed.Generally speaking,precipitation at Baoshan site shows weak acidity,the mean rainfall pH is 5.21 and the mean acid rain rate is 24%.The inter-annual variation of rainfall pH shows a slightly downward trend.The electrical conductivity K increases obviously year by year with an average annual increase at 2 μs·cm^-1.The acid rain rate fluctuates from 8% in 2004 to 48% in 2009.The rainfall pH is usually lower in cold season and higher in warm season.It is the opposite for the electrical conductivity K.The average pH of acid rain in Pudong is 4.38,lower than that in Baoshan at 5.08.The acid rain rate in Pudong is 79.5%,much higher than that in Baoshan at 33%.Atmospheric pollutants SO₂,NO₂ and PM₁₀ concentrations are negatively correlated with rain pH and positively related to electrical conductivity.Atmospheric particulate pollutants,chemical composition,precipitation and wind direction exert important effects on the changes of precipitation pH and acid rain rate.