Abstract:Based on TBB data in summer from 2007 to 2011,Banded MCSs(BM) over the Tibet Plateau with stable characteristics are screened out and classified.Causes for BM are discussed in different types by combining with NCEP data and HYSPLIT model.Results show that 37 cases of BM with stable characteristics fall into three types according to their shapes:North convex type(NCT),south boundary type(SBT) and zonal type(ZT).NCT BM are the most while ZT BM are the fewest.These BM occur in 30% time of the whole summer,especially in nearly 50% time of July.The main causes for BM include South Asia high and jet stream on upper level,shear line with convergence at 500 hPa and the air of high temperature and humidity in the south of shear line.At 500 hPa,ZT BM commonly occur between westerly airflow in north side of plateau and eastern airflow in south side of plateau.NCT BM occur under the synoptic situation that there is lank westerly airflow in northern plateau,strong trough in Bay of Bengal and influence of flow from southwest by south on eastern and southern plateau.In the process of SBT BM,there is usually northwest airflow over the plateau and strong cyclone in the south in Bay of Bengal.There are four vapor divergence regions around the plateau and vapor in convective zone mainly derives from south side of southwest edge and southeastern plateau.

Abstract:By simulating the dynamic and structural characteristics of water eddies in a limited area,the paper analyzed the functions of impact factors like non-uniform wind field,water jet current,their superposition,environmental boundary,Coriolis force and etc.The eddies generated by wind fields are of larger size and deeper depth.Cyclone is of concave surface and anticyclone is of convex surface.The eddies generated by water jet appear on both sides of the jet and accord with the jet thickness.Their size is smaller and thickness is shallower,but their flow and strength are stronger.Topographic boundary plays a guiding role in the movement of eddy.The Coriolis force in the Northern Hemisphere is beneficial for the enhancement of negative eddy.Meantime the potential function presenting convergence and divergence of eddies for cyclone is stronger than that for anticyclone.It is more effective to cause the vertical upward motion for cyclone than to cause the downward motion for anticyclone.When non-uniform wind field overlapped water jet,the number of eddies increase,their size decreases and their patterns at bottom are of more obvious difference from those on the surface layer.There are many types of eddy structures:for some the whole layer is consistent;for some others consistency only existence on the upper layer;for still some others the upper and lower circulations reverse,etc;The eddies generated by wind field are mainly barotropic,the eddies forced by water jet are manly baroclinic.In kinetic energy exchange,it happens that the barotropic kinetic energy transforms into baroclinic kinetic energy at barotropic eddy area,and the barotropic kinetic energy transforms into baroclinic kinetic energy at baroclinic eddy area.Both kinetic energy transformations are beneficial for the maintenance of the two kinds of eddies.

Abstract:Spatial and temporal variations of spring frost are identified based on the historical measurements from 35 meteorological stations in Jiangsu Province from 1961 to 2008.Then,using the climate data projected by models in "WCRP" coupled model intercomparison program-phase 3,the future trend of spring frost is analyzed under different climate conditions.Results show that,in recent 48 years,the date of final spring frost come earlier significantly in Jiangsu Province.Meanwhile,the days of spring frost decrease markedly.Both the date of final spring frost and the days of spring frost change abruptly in the late 1990s.Future global climate change will considerably cause the date of final spring frost to end earlier.Compared with the average date from 1961 to 1999,the date of final spring frost will be 4.6—9.6 d and 14.6—17.7 d earlier in 2020s and 2060s under the condition of moderate emission(A1B),7.3—11.3 d and 12.8—16.5 d earlier in 2020s and 2060s under the condition of high emission(A2),and 5.3—10.2 d and 9.4—14.2 d earlier in 2020s and 2060s under the condition of low emission(B1),respectively.

Abstract:In this paper,the WRF-Chem model was used to analyze the temporal and spatial variations of the near-surface concentrations of ozone(O₃),nitrogen dioxide(NO₂) and fine particulate matter(PM_2.5) over the Beijing-Tianjin-Hebei region in August 2007.The simulation results were compared with surface observations.It was indicated that the model could reproduce the temporal and spatial variations of O₃ and PM_2.5 reasonably well and successfully reflect several pollution events in August 2007.However,the model's performance was relatively poor for NO₂.The correlation coefficients between the model simulations and the observations were 0.69—0.86 for O₃,0.44—0.49 for PM_2.5 and 0.27—0.43 for NO₂.In August,the monthly mean concentration of O₃ in Beijing and Tianjin was relatively low at about 30×10^-9 whereas relatively high O₃ concentration (about 60×10^-9) was predicted in the west of the Beijing-Tianjin-Hebei region and over the Bohai Bay.The PM_2.5 showed higher concentration levels in the south than in the north within the Beijing-Tianjin-Hebei region with the monthly mean concentrations ranging from 120 to 240 μg/m³.The monthly mean O₃ concentration at 14:00 BST in August was about 60×10^-9 in Beijing and Tianjin,which was lower than those in the surrounding areas.The mean PM_2.5 concentrations at 14:00 BST showed higher levels(100—120 μg/m³) in the southern parts of the Hebei province and the Bohai Bay areas.An O₃ pollution episode occurred on August 17 when the air temperature in Beijing reached 33 ℃ at 14:00 BST,resulting in high concentration of O₃(80×10^-9—110×10^-9).Meanwhile,due to the combined effects of local emission,chemical reaction and trans-boundary transport,the PM_2.5 concentration in the west and the north of the Bohai bay was as high as over 120 μg/m³,in which the secondary aerosols formed through chemical reactions,the primary anthropogenic aerosols released directly and sea salt aerosols accounted for about 50—100 μg/m³,10—20 μg/m³ and 1—7 μg/m³,respectively.Thus,the secondary aerosols were the main contributor to PM_2.5 in these areas during this episode.

Abstract:In order to understand the characteristics and sources of ozone(O₃) at Guangmingding peak of Mt.Huang,a typical site of high-altitude area in Eastern China,the data of O₃ concentration (observed during April 18—July 28,2008 and May 19—August 20,2009) were analyzed by using a statistical method (Kolmogorov-Zurbenko filter) and numerical simulation(Weather Research and Forecasting Model) in this paper.The results showed that the value of monthly averaged O₃ concentration of May,June and July were 107.73,101.93 and 68.02 μg·m^-3,respectively;the O₃ concentration in May and June was 25—60 μg·m^-3,which was higher than other Base Stations in China(except Shangdianzi) and Antarctic.However,the O₃ concentration in July was relatively close to that of other stations.The O₃ concentration was relatively at a higher level than in other areas during this period,but over-standard concentration events occurred rarely,which only accounted for 3.9% of the observation time.The diurnal variation of O₃ presented a multi-peak distribution,and the peak value of O₃ appeared from 21:00 to 06:00(Beijing Standard Time,the same below) with a tiny amplitude of 15—20 μg·m^-3 in a day.After simulating the variation of some parameters such as the height of tropopause and clear air turbulence over the area,the result showed that the concentration of O₃ was relative with the fold of tropopause.The O₃ concentration was the highest on sunny days,the lowest on rainy days and median on foggy and cloudy days.There was an obviously negative correlation between O₃ and temperature,relative humid and other pollution gases(CO,NO and NO₂),while it had a relatively weaker correlation with the wind speed.The O₃ distributed evenly during circle wind period in May (the wind direction was dominated by northwest in daytime and by south in nighttime).However,the O₃ concentration was higher during north wind period than that in south wind period in June and July(the wind direction was dominated by southwest both in daytime and nighttime).The raw data of O₃ were decomposed into different components by using the KZ filter.The results showed that the local O₃ concentration was mainly controlled by low frequency component(C_BL component),and the rest high frequency components(C_SY,C_DU and C_ID components) only made it fluctuate around the baseline.Finally,the contribution of C_SY,C_DU and C_ID components to C_BL component was quantitative analyzed during the two over-standard events that occurred during May 28—31,2009,and June 12—15,2009,respectively.

Abstract:By using a one-dimensional raindrop category model and taking the aircraft observations of raindrop size distribution in the air and meteorological elements' profiles in the boundary layer as the initial background field,the evolution of raindrop size distribution during the falling process was simulated and analyzed.The results showed that the one-dimensional raindrop category model could simulate the evaporation,coalescence and breakup processes of the raindrop properly.The simulated raindrop spectra presented a multi-peak distribution.Evaporation would make the diameters of raindrops smaller.It affected small size raindrops more seriously than big size raindrops and increased the concentration of number of medium-sized raindrops,but it would not to change the overall spectral shape of raindrops.The multi-peak raindrop size distribution was caused by the coalescence and breakup mechanism,which were key factors in the change of raindrop spectra.

Abstract:Using the Doppler radar data and simulated results of the mesoscale model WRF(Weather Research and Forecasting),this paper studies a precipitation process induced by convective and stratiform mixed clouds in Taiyuan and its surrounding areas during 9—10 May 2009.Results show that the local convection clouds are developed in the formation stage of convective and stratiform mixed clouds.With development and strengthening of the convection,the convective and stratiform mixed clouds are formed in a wider range,by means of merging process between the enhanced convection clouds and the ambient clouds.The merging process includes the local single cells merging,the cloud clusters merging and the high cores merging in convective and stratiform mixed clouds.The single cells merging and cloud clusters merging can bring about the explosive growth of clouds with a sharp increase in graupel content and rain water content.The high cores merging in convective and stratiform mixed clouds can enlarge the rainfall area rather than the rainfall strength.The depression inverted trough and the weak cold font are main influencing factors of formation and maintenance of the convective and stratiform mixed clouds.The depression inverted trough is beneficial to the accumulation of large-range convective energy in the lower layer and the wind shear is favorable to the development and merging of cloud clusters at a short distance.The dynamic and thermal effects of mountainous region promote the formation and strengthening of local single cells and strong centers in the mixed clouds.

Abstract:By referring to the Meiyu indexes and taking Guixi,Dexing,Yushan Quzhou and Longquan as representative stations,ESRS(the early summer rainy season) indexes have been set.From 1961 to 2010,the general beginning and ending days were 10 June and 1 July respectively,about 8 days before the Meiyu period in the Yangtze-Huaihe River basin.The average duration of ESRS was 20.5 days and there were 15.5 rainy days in this period.The beginning days experienced a "V" pattern variation while the ending days presented a "spindle" oscillation process,and there were no obvious increase or decrease tendencies for the durations of ESRS and the number of rainy days in the last 50 years.Nevertheless,there were apparent variations in the annual durations of ESRS and the number of rainy days during 1980s,and ESRS was relatively weak during 1960s and after 2000.Besides the general circulations over West Pacific and Tibet Plateau,that over the Ural region was the most important factor affecting the starting time of ESRS.The general circulations over the Arctic Pole in the Eastern Hemisphere,West Pacific at low and middle latitudes,and Okhotsk Sea affect the intensity of ESRS obviously.

Abstract:Based on the daily reanalysis data of European Center for Medium Weather Forecast (ERA-40),by using local energy change equations to calculate the seasonal variation of the local energy in different tropospheric layers over the North Pacific storm track,the role of internal dynamic mechanism in the maintainance of the track is discussed in detail.Results show that the seasonal variation of eddy kinetic energy can well reflect the phenomenon of midwinter suppression of the North Pacific storm track,which,with an occurrence probability of nearly 80%,is most prominent on the upper levels of the troposphere and was the strongest through the mid and late 1970s to the early 1980s.As viewed from the simultaneous variation of each energy terms averaged over the track,by adding up the stronger loss resulted from the larger decrease of the baroclinic energy conversion and eddy ageostrophic geopotential flux and the weaker gain resulted from the smaller decrease of the barotropic energy conversion,the remarkable net loss of the eddy kinetic energy during midwinter is possibly the direct reason for midwinter suppression of the North Pacific storm track.

Abstract:The multiyear mean climatological and interannual variations of the summertime atmospheric stability associated with the heating and aerosol optical depth(AOD) have been investigated using the NCEP/NCAR reanalysis data and the aerosol data of MODIS satellite over the eastern China during 1979—2008.Results show that the spatial distribution of atmospheric stability in the planetary boundary layer is inhomogeneous,and it exhibits interannual variations.The mean climatology of atmospheric stability is found to be in association with the mean climatological distributions of the diabatic heating and aerosol optical depth(AOD).Three principal modes of the anomalous overall Richardson number(Ri_b) in East China are found by performing the empirical orthogonal function analysis.It is indicated that different leading modes of Ri_b are closely related to the summer monsoon circulation anomalies,especially the P-J type teleconnection pattern and the western Pacific subtropical high,which may play a very important role in the stability change of the boundary atmosphere in East China.

Abstract:The relationship between 10—30 d low-frequency oscillation and the rainfall over Changjiang-Huaihe River Valley during Meiyu period is analyzed by using the 756 stations' daily precipitation data in China and the NCEP/NCAR daily reanalysis data from 1961 to 2010.The results show that a 10—30 d periodic variation is obvious in the flood years during Meiyu period.The activeness and break of rainfall over Changjiang-Huaihe river valley during Meiyu period is also closely associated with the low-frequency oscillations' northward and westward propagation.During Meiyu period in flood years,the rainfall over Changjiang-Huaihe river valley is influenced by the low-frequency anticyclone over the South China Sea and the low-frequency cyclone over the Sea of Japan in the lower troposphere,which modulate the western North Pacific subtropical high to extend westward or to retreat eastward,and thus affect the water vapor transport and confluence of cold and warm air in Changjiang-Huaihe river valley.In the upper troposphere,the low-frequency anticyclone and cyclone in mid-latitude area over Asian mainland influence the position of South Asian High,which leads to the intensity changes of low-frequency rainfall over Changjiang-Huaihe river valley.

Abstract:A heavy rainfall event,which was mainly caused by typhoon Haiou,subtropical high and weak cold air,occurred in Shandong Province on 17—19 August 2008.A vortex in the low-troposphere is the maker of the heavy rainfall event.The structure and mechanism of the mesoscale vortex were studied by using routine observational data and the simulated data from mesoscale model WRF (Weather Research and Forecasting).The results show that the eastward movement of the mesoscale vortex was accompanied by a process that a new vortex center came into being and combined with the old vortex instead of a simple movement along the shear line.The mesoscale vortex formed in the convection area with obvious temperature rising,deep saturated layer and rising motion.After the formation of the mesoscale vortex,downdraft dominated the center of the vortex,convection area moved to its east part and the rainfall area lay in its northeast and southeast quadrants.The cold pool near boundary layer,dry intrusion between 600 hPa and 400 hPa,weak wind area between 900 hPa and 850 hPa as well as the coupling between low level jets(LLJ) and upper level jets are important characteristics of the mesoscale vortex during its generating and developing phases.During the fading stage of the mesoscale vortex,downdraft became strong and deep,and LLJ and the outflow of upper level weakened obviously.The analysis of vorticity equation suggests that divergence term and tilting term in the low-troposphere,horizontal advection term and convection term in the mid-troposphere are the main contributors for the positive vorticity.The horizontal convergence in low levels and the transportation of vorticity from low levels to high levels are beneficial for the formation and development of mesoscale vortex.The increase of positive vorticity in low levels is partly caused by the transformation from horizontal vorticity to vertical vorticity.The tilting term is very important for the formation of mesoscale vortex.In the later phase of its formation,the weakening of the low level convergence,high level divergence and the vertical transportation led to the weakness of positive vorticity,and thus the weakness of the mesoscale vortex.

Abstract:The illustrations with the map of China as base map are common in meteorological papers.Based on the standard expression form of the attached map of South China Sea Islands in the map of China,using the GrADS(Grid Analysis and Display System) software,this paper describes a program of *.gs file in detail,which can correctly draw the attached map of South China Sea Islands in the map of China.It is beneficial to the reference of scientific workers and the standard drawing of the attached map.