Abstract:The masoscale WRF model is used to simulate Typhoon Matsa that occurred over the western North Pacific in August 2005.The simulation data are applied to a barotropic shallow water equation to study the barotropic characteristic wave structures and their stabilities when Matsa reaches its peak.The results show that there are counterclockwise-propagating external inertial-gravity waves and vortex Rossby waves inside Matsa,which have different structures and stabilities.The external inertial-gravity waves occur the outer part of Matsa,and their growth rate increases as wavelength reduces,and the wave phase speed over the outer part is 48.9-68.5 m·s^-1.The Rossby waves appear over the 200 km of center area,and their wave number-3 is the most unstable,with 5 m·s^-1 phase speed at the 100 km radius.In addition,the perturbation wind fields of the external inertial-gravity waves are generally perpendicular to the height fields,and the ratio of perturbed divergence to perturbed vorticity is over 3 and could be up to 10³,indicating that the waves are associated with divergence.The perturbed wind fields of the Rossby waves are generally parallel to the height fields,the ratio of perturbed divergence to perturbed vorticity is 10^-1-10^-2,and the waves are related to vorticity,which is intimately associated with tangential propagation of spiral rainbands.

Abstract:Assimilation of ATOVS(Advanced TIROS Operational Vertical Sounder) microwave radiance data is implemented in WRF-EnSRF(Weather Research and Forecasting-Ensemble Square-Root Filter) system to test its capacity of satellite data assimilation and its simulation performance in a rainstorm.The ATOVS data assimilation experiment and the control experiment are performed to simulate a rainstorm process in Guangdong region on 6-7 June 2008.Results show that,assimilating the radiance data,it can enrich temperature information in the upper troposphere and humidity information in the mid-lower troposphere,and improve initial wind field.Both experiments have well simulated the main rainfall area and period,but the simulations of the rain storm and large rain storm in the control experiment are not good enough.In contrast,the assimilation experiment can improve the simulations of location,intensity and range of the strong precipitation center,which is more accordant with the observed precipitation.

Abstract:In this paper,5 kinds of observational data and the RAMS(regional atmospheric modeling system) modeling results are used to investigate a dense sea fog event over the Yellow Sea from 2 to 5 May 2009.The results show that:1) a high-pressure system,to some extent,controlled the evolution and impelled the dissipation of the sea fog,which was rare in past researches;2) the morphological variation of the sea fog was in accordance with the temperature difference of 1-3℃ between the air and sea surface over the north part of the Yellow Sea,which proved the important role of temperature difference between the air and sea surface in sea fogs;3) the simulated pattern of fog top height calculated from the model agrees well with the sea fog region identified from the visible satellite imagery,which was an evidence to show the ability of the RAMS to simulate sea fog events.

Abstract:Temperature anomaly series at 160 stations of China in winter(December,January and February) from 1951 to 2010 are processed by the station homogeneity adjustment scheme.The adjusted series for dealing with the variance heterogeneity distribution caused by station network heterogeneity are more effective.EOF(empirical orthogonal function) analysis method is used to study the original and adjusted temperature anomaly series.Results show that:1)There is better organization for high absolute value areas of the first two typical fields of the adjusted data than those of the original data because the high absolute value areas of the typical fields locate mainly in the three north region(Northwest China,North China and Northeast China) and the Tibetan Plateau,which are consistent with the high value areas of mean square deviation field.2)The evolution features of main mode time coefficients of before and after adjustment are similar r_h≥0.886,h=1,2),but the variance contribution of linear and interdecadal components of the first two time coefficients for the adjusted data much more focus on the first mode.3)The linear components of the first typical fields and their time coefficients for the adjusted data can display the main strong warming areas over China in winter during the past 60 years,and their interdecadal components are more consistent with the evident interdecadal variation areas over China than those of the original.

Abstract:The extreme cold and snow weather occurred at the mid-latitudes of Northern Hemisphere in December 2009.Based on the NCEP/NCAR reanalysis data,this paper studies the characteristics of stratospheric AO(Arctic Oscillation) abnormal signal downward propagation and its influence on the extreme weather,and the planetary wave propagation mechanism related to the abnormal signal downward.It shows that:1)The Arctic Oscillation(AO) plays an important role in this cold event,and its anomalous negative signal occurs and maintains in the stratosphere during the preceding November.In the early December,the associated anomalies spread into the troposphere and then propagates fast onto the surface,which leads to remarkably positive(negative) geopotential height and temperature anomalies in the northern polar(mid-latitude) region in the whole troposphere in December.2)Induced by the negative AO signal,the anomalous northerlies dominate the eastern Asia and the west part of the Northern America during the early December,facilitating the extreme cold condition in these areas.The associated northwesterly anomalies in the Europe and the strengthened cold Mongolian high also result in the prevalence of low temperature in the northern Eurasian continent during the mid-to-late December.3)The stationary planetary wave propagation into the stratosphere is extremely strong at the high-mid latitudes of Northern Hemisphere in November,which induces negative AO anomaly in the stratosphere.Accompanied by weakening of the planetary wave upward propagation during the following December,the negative AO anomaly exhibits from the upper troposphere to surface,leading to cold-condition circulation anomalies.

Abstract:Using the NCEP/NCAR reanalysis data during 1980-2004,some forcing factors,such as latent heat release from condensation and underlaying surface thermal differecence,are defined and their impacts on the south-to-north cross-equatorial flow are studied with diagnosis analysis and numerical simulation.Main conclusions are shown as follows:the cold Australia land always corresponds to strong Australian High or frequent cold air activities,which is favorable for the formation of strong cross-equatorial flow;the cold underlaying surface to the south of the channel is often accompanied by weak Walker circulation,which is also helpful for the establishment of strong cross-equatorial flow;the warm Indo-China peninsula and cold South China Sea,as well as the strong heat source near the Philippines,all can be associated with strong convergence zone in north hemisphere,which is advantageous for the formation of strong cross-equatorial flow.The features of forcing factors and circulation factors corresponding to weak south-to-north cross-equatorial flow are opposite to the above ones.

Abstract:By analyzing the daily precipitation data from 20:000 BST to next 20:00 BST in Henan, Shandong, Anhui and Jiangsu provinces, the persistent and strong precipitation process(PSPP) over the Huaihe River valley from 1961 and 2006 is defined. Based on the NCEP data, the synthesis method is used to analyse the variation characteristics of atmospheric circulation during and before the PSPP. Results show that,before and during the PSPP,1)The blocking high near the Ural Mountains becomes weaker,while the blocking high to the north of the Lake Baikal and near the Sea of Okhotsk becomes stronger; 2)The western Pacific subtropical high extends to the north and to the west at 500 hPa,whereas it shows obvious extension to the west and almost no extension to the north at 850 hPa;3)The scope of the South Asia high extends obviously. Especially, the height at 200 hPa over the north the Huaihe River valley increases dramatically, and the 200 hPa high level jet center over the East China-Japan changes remarkably as well.The low level jet at 850 hPa is related to the westward extension of the western Pacific subtropical high.And the weakening of the high pressure near the Ural Mountains, the southward-moving of the cold air, and the increase of east-west atmospheric pressure gradient are all beneficial to the formation of the low level jet.

Abstract:Using NCEP/NCAR spring daily reanalyzed data from 1948 to 2010 with the inverted arithmetic,the atmospheric heat sources in the Tibetan Plateau are computed.Then the characteristics of climate change of the heat sources and the relationship of their anomalies with the previous winter general circulation are analyzed.The results are summarized as follows:in spring,the eastern and western parts of the Tibetan Plateau are the active variation zones of heat source.And it is found that the distributions of the spring heat source over the western and eastern parts of the plateau are opposite to each other.The spring heat anomaly over the plateau is influenced by the East Asian winter monsoon.

Abstract:By using the daily icing data of ice station and the related station data of Erlangshan Mountains in Sichuan Province in winter of 2001-2009,relationships between the icing thickness and some meteorological factors are analyzed based on the identified conductor icing factors and the constructed icing theory model.It is found that the icing increase is not well related to an individual meteorological factor,for example,vapor pressure and wind speed.An attempt to define water vapor transport index combined with some meteorological factors is employed and the index couples closely with the icing increase ratio.Finally,a conductor icing model is built according to the parameters of conventional meteorological observations including wind speed,temperature and vapor pressure.Comparison of the comprehensive fitting ice cover thickness with the observed one shows that the better fitting results can be achieved to serve project applications.

Abstract:By using the direct homogeneity test (based on the observation data and the t test) and 3 indirect homogeneity methods(including SNHT,PMTT and PMFT),time series of annual mean wind speed at 2 meteorological stations,Tianchang and Susong,from 1957 to 2010,have been tested respectively.The results show that station relocation,observational environment change,instruments updating and measurements variation can all influence the homogeneity of the mean wind speed,and the impact of measurements updating is the most prominent factor.Because based on observation data from meteorological stations,the results of direct test is more reliable.However,SNHT,PMTT and PMFT are effective in identifying the change-points,but the missing ratio is also of a high degree.Thus,to test mean wind speed homogeneity,if the observation data from meteorological stations are correct and intact,the direct test should be used firstly and then other methods can be used additionally.

Abstract:The Morrison's double-moment microphysics scheme is incorporated into the mesoscale model WRF V2.2 to simulate the weather process of snow and rain from 00:00 UTC 25 to 12:00 UTC 29 January 2008 in the southern China.Based on the correct simulation of the weather evolvement,the sensitivity experiments are used to research the impact of cloud droplet number concentration on accumulated precipitation in the microphysics schemes,showing that the impact is complicated and nonlinear.The microphysics properties in the weather process are analyzed in detail.The evolution of each hydrometeor class is analyzed to find out the effect of cloud droplet number concentration increase on the warm cloud and cold cloud precipitation processes.Results indicate that the higher cloud droplet number concentration is,the higher cloud water mixing ratio is,and the smaller cloud droplet size is.In addition,the response of rain droplet to cloud droplet number concentration is opposite to the response of cloud droplet.The higher cloud droplet number concentration is,the lower rain droplet number concentration is,and the lower rain water mixing ratio is,which leads to the warm cloud precipitation to be inhibited.Because of the increase of cloud droplet number concentration,the number concentration of ice crystal and snow have no obvious change.However,the mixing ratio of ice crystal and snow becomes higher as the cloud droplet number concentration increases,so the cold cloud precipitation is enhanced.This case is simulated by using different cloud droplet number concentration,the difference of total precipitations is less than 1%.In general,the precipitation decreases when the cloud droplet number concentration increases.The proportion of decrease of warm cloud precipitation is much higher than that of increase of cold cloud precipitation.However,in this case,the dominant process is cold cloud precipitation.The absolute values of decreased and increased precipitations are similar and of the same order of magnitude.The result of their counteraction is that the value of total simulated precipitation has no obvious change when the cloud droplet concentration increases.

Abstract:Based on the MFRSR(multi-filter rotating shadow-band radiometer)data observed at Taihu Site during May 16,2008 to April 17,2009,the aerosol optical depth (AOD) is retrieved and its statistical results at 415 nm,500 nm,615 nm,675 nm and 870 nm are given,as well as the statistical results of turbidity coefficient and Angstrom wavelength exponent.Results indicate that the maximum value of AOD at these five wavelengths are 1.9,1.6,1.3 and 1.2,respectively;The half width of spectrum distribution are 0.90,0.70,0.55,0.45 and 0.25,respectively;The AOD value at its frequency distribution peak are 0.750,0.550,0.475,0.425 and 0.425,respectively.The AOD value is largest in spring,smaller in summer,and smallest in winter at all these five wavelengths.The Angstrom turbidity coefficients range from 0 to 1.25,with 60% data larger than 0.4 and 97% data lager than 0.2;The Angstrom wavelength exponent in spring,summer,autumn and winter are 0 to 3.0,0 to 2.8,0.2 to 2.0,and 0.2 to 2.0,respectively.It reflects that atmosphere is polluted occasionally and influenced remarkable by anthropogenic sources.Considering the peak distribution of wavelength exponent,it is suggested that there are larger particles existing in spring and summer than in autumn and winter.

Abstract:In this paper,we analyzed the spatial distribution and temporal variance of lightning frequency by using lightning positioning data in China during 2008 and 2010.Based on Price's theory,we estimated the quantity of NOx emission produced by lightning (LNOx) and preliminarily analyzed the temporal and spatial distribution of LNOx.The results showed that lightning occurred more frequently in July and August and mainly in Guangzhou and Wuhan.LNOx was mainly distributed in the area of 25-40°N and 105-125°E.The quantity of LNOx in Wuhan,Guangzhou,Chengdu,Chongqing,Changsha,Nanjing and Nanchang are higher than that in other regions,and the maximum could reach up to 1.23×10⁷g each grid.August saw the highest yield while the second highest was July.Furthermore,the seasonal characteristics of LNOx distribution were obviously,and the percentages in spring,summer,autumn and winter were 4.8%,89.4%,5.3% and 0.5% respectively.LNOx mainly appeared in Guangzhou area in spring while in summer it moved northward and became wide and strong.The distribution area decreased in autumn and the maximum occurred in Guangzhou.In winter,the quantity of LNOx decreased significantly with its maximum appearing in the southwest of Wuhan.

Abstract:Based on the lightning location system data of Jiangsu Meteorological Bureau from 2006 to 2010,this paper analyses the seasonal,monthly and daily variations,and spatial distribution of lightning frequency,and the distribution interval of lightning intensity over the five representative areas (Nanjing,Suzhou,Xuzhou,Nantong and Lianyungang) in Jiangsu Province,which can reflect the distribution differences and characteristics of lightning activity.Results show that the negative lightning frequency are more than the positive in the five areas in four seasons.The monthly lightning frequency changes obviously in each area,and the peak appears in Nanjing in July and in the other areas in August.The daily variation of lightning frequency is obvious in each area,and the peak appears at 14:00-17:00 BST.The spatial distribution of lightning frequency are unbalanced in the whole province,and there are more (less) lightning in the southern (northern and central) Jiangsu,with many lightning density centers in parts of Nanjing,Zhenjiang and Changzhou.Most of lightning intensity centralize 20-50 kA,while there are very few for the lightning intensity more than 100 kA.Moreover,the positive lightning intensity is stronger than the negative.