Abstract:This paper evaluates the future projection of heavy rainfall events in the middle and lower reaches of the Yangtze River valley based on outputs of eight coupled models attending the Coupled Model Intercomparison Project phase 5(CMIP5) from IPCC AR5.The experiments under different representative concentration pathways(RCPs) are compared with each other,and with the previous CMIP3 experiments as well.The outputs from the historical simulation of CMIP5 are also utilized as a base to derive future trends.The results suggest an agreement among all the CMIP5 models,in that both the strength and the occurrence frequency of heavy rainfall events are projected to increase in the 21st century relative to the last twenty years of the 20th century(1980—1999).In contrast,the strength increase in the east of the region is even greater than that in the west.Besides,the interannual variability of heavy rainfall events is also projected to enhance in the future.As for different RCPs,the projected increases in the strength and occurrence frequency of heavy rainfall events in RCP2.6 and RCP8.5 are greater than those in RCP4.5.In comparison to CMIP3,the projected increases in the strength and occurrence frequency are even larger,albeit a significant difference in the spatial distribution in the latter projection.The projected maximum increase in the rainfall amplitude in CMIP3 is located in the central region,while it is in the east of the region in CMIP5.

Abstract:Based on the summer(June—August) precipitation data from 11 stations over Yangtze-Huaihe valley from 1951 to 2010,the northern hemisphere mean sea level pressure field data provided by NCAR and the west Pacific subtropical high indexes,the interannual variability of the quasi-biennial oscillation(QBO) of the summer precipitation and its relationship with east Asia summer monsoon and west Pacific subtropical high were discussed by using Morlet wavelet transform,cross wavelet transform and correlation analysis method.The results showed that QBO component was very important in the interannual oscillation of summer precipitation field in Yangtze-Huaihe region,which experienced a course of changing from strong to weak,and then to strong again.In addition,the contemporaneous correlation between precipitation and QBO of summer monsoon intensity as well as subtropical high ridge was good.Their mutual impact was also shown in the interannual scale and there was obvious lagged and leading correlation respectively in four-year and one-year scales.

Abstract:Based on the ground meteorological indicators,the climate indexes and the NOAA reanalysis data during 1960—2012,spring-drought-period(April—May) monthly precipitation amounts in Jilin Province are analyzed by using power spectrum analysis,time-scale decomposition,cross-examination stepwise regression analysis,etc.This paper aims to find proper potential annual influence factors and decadal ones.The results show that April—May precipitation in Jilin Province has two significant periods,namely,2—4 years and about 10 years.In terms of the decadal scale,precipitation in April is closely related to the Southern Hemisphere Annular Mode Index in March and the 850 hPa meridional wind in March over the high-latitude area in East Russia,while that in May is related to the Northern Hemisphere Annular Mode Index in May and the Pacific mid-high-latitude circulations in April.As for the interannual scale,precipitation in April has close relationship with the Multivariate ENSO Index in March,the local relative humidity in April and the 850 hPa meridional wind in April over coastal areas in East and North China,while that in May does with the contemporary North Atlantic Oscillation Index,the local relative humidity and the surface pressure.The coefficients of correlation between the real values and the fitted ones are 0.67(April) and 0.81(May) separately,and proper potential influence factors play more important roles than the model structure.

Abstract:By using regional climate model(RegCM3),summer rainfalls over North China during 1991 to 2002 were simulated.The model's capability to reproduce the different time scale features of rainfall and temperature had been evaluated based on station observations.Results showed that there were some differences between the model result and the observation in the spatial distribution of summer rainfall.The model can well reproduce the rainfall over Hetao and south of Huanghe river basin,but it overestimated the rainfall in regions along Taihang Mountain and the coastal regions.The model can well reproduce the spatial pattern of temperature.The simulated temperature in Shanxi and southern regions was cooler than the observation.It also well revealed the inter-annual variation of summer rainfall and temperature,such as anomalies in some special years.The daily variation of rainfall and temperature,as well as the peak and valley value evolution of daily rainfall,were also successfully simulated.The model can also reproduce the time,location and intensity during the heavy rainfall process in typical cases.Unfortunately,the rainfall was overestimated in the model.It requires further work to investigate whether the deficiency was caused by the complex topography or cloud-radiation parameterization scheme.

Abstract:Based on NCEP/NCAR monthly reanalysis data from 1948 to 2012,the interdecadal variation of summer water vapor transport over eastern China is investigated using the 9-yr moving average,EOF analysis and compositive analysis methods.Results show that summer(June—August) water vapor transport is characterized with a turning point from strong to weak around 1975.The abnormal area of water vapor transport mainly locates in the eastern China.Water vapor transport from South China Sea to eastern China has interdecadal variation in June.Water vapor transport from the Bay of Bengal,South China Sea and western Pacific in July(Indian Ocean,South China Sea and western Pacific in August) to eastern China also has interdecadal variation.Distribution of summer water vapor transport flux vectors is consistent with that of the first component of interdecadal water vapor transport before and after the interdecadal variation.Significant water vapor flux convergence zone locates in the southwest to the northeast China.In the northern Yangtze River,water vapor convergences(divergence) are caused by the wind field convergence(divergence) and the water vapor advection,but in the southern Yangtze River,which is mainly caused by the wind field convergence(divergence).

Abstract:Using mesoscale simulation WRF model,the formation and development of a southwest vortex occurred over Sichuan province on June 30 and July 1,2008 were investigated.The results indicated that the southwest vortex primarily emerged at 850 hPa and then formed at 700 hPa after several hours.The formation of the southwest vortex at 850 hPa was directly connected with low-level jet.The diagnostic analysis of ω equation showed that the horizontal advection of vorticity and divergence mainly influenced the formation of the southwest vortex at 850 hPa while latent heat release was not important to its genesis.The results also indicated that the latent heating was the key factor for the formation of the southwest vortex at 700 hPa.The dry sensitive experiment further confirmed that latent heat release had little influence on the southwest vortex at 850 hPa,but it caused strong convergence of cyclonic shear circulation and finally formed the vortex at 700 hPa.

Abstract:The Weather Research and Forecasting model(WRF) was used to simulate the formation process of Meiyu in 2004 and the impact of urbanization on precipitation and the vertical structure of the Meiyu front was analyzed in detail.After changing urban to cropland,the simulated precipitation at rainfall centers on June 14 decreased obviously,while the precipitation over the area northwest to it increased.The thermal structure of Meiyu front was similar to that in the control experiment,but the intensity of the high value scope of the pseudo equivalent potential temperature,ascending motion,convective instability and moisture were weaker.The location of the frontal zone was slightly north than in the control test.On June 15,the simulated precipitation at the rainfall center in the middle of Anhui Province also decreased,and the precipitation over the area west to it increased.The structure of the Meiyu front and the location of frontal zone were similar to those in the control run,but the low value scope of the pseudo equivalent potential temperature(336 K) at 800 hPa was larger,almost covering 26—32°N,resulting in lower convective instability over the high value region of the pseudo equivalent potential temperature.

Abstract:The process of a brief heavy rainfall on 8—9 August 2007 over the Central Shaanxi Plain was analyzed using the T213 data and high space and time resolution data including automatic meteorological observing station data.The results indicate that the brief heavy rainfall occurred under favorable large-scale ciuculation backgrounds,including the break of high-pressured dam,which resulted from the development merge of Qingqhai-Tibet Plain pressure and the west Pacific Ocean subtropical high in the middle level at 500 hPa,right flank divergence field of westerly jet entrance region in the upper level at 250 hPa and the shear line's development in the low level at 700 hPa.The amount of water vapor in storm experienced changes of decrease,sudden increase and fast decrease,which owed to wind direction fast changes at the low level.The vapor accumulation from surrounding areas of the Center Shaanxi Plain,which was achieved through the easterly current,had provided sufficient vapor and potential instability for the occurrence of the heavy rainstorm.The vapor increased so fast that the rainstorm occurred suddenly,and the rapid decrease of vapor made the rainfall last shortly.The dynamic mechanism of rainstorm was the formation of intense “pavement pumping” effect,the secondary circulation circle and the asymmetric structure between the strong vertical upward movement and the weak dowdward movement due to the development of the upper anticyclone vorticity.The automatic meteorological observing satation data and satellite image data showed that the heavy rainfall was caused by the occurrence and development of MαCS,which came from the mergence and development of MβCS.The convective cells merged,developed and enhanced individually to form the different precipitation centers at Qishan,Liquan and Gaoling.The development of the convective cells resulted from the surface mesoscale convergence system.The changes of strength of the precipitation had a good corresponding relationship with that of the surface mesoscale convergence system.The formation and development of the ground mesoscale convergence systems may be the trigger and development mechanism for the heavy rainfall.

Abstract:Based on regular observational data and NCEP/NCAR reanalysis data,the dynamical mechanism of an extraordinary snowstorm during 3—4 March 2007 over the south of Northeast China was analyzed.The results showed that the region around the shear line at 850 hPa,which played a significant role in convergence and lifting,corresponded to the center of the heavy snow and it was also the main influencing system and the key factor for the successful forecast of the event.Vorticity variability could not only reflect the physical mechanism of the formation and development of the snowstorm shear,but also predict the position and intensity of the heavy snowstorm.Among all the factors affecting vorticity,the strong convergence terms in positive voritcity regions at 700 hPa to 900 hPa was the main forcing source of positive voritcity tendency.When voritcity on lower level increased,it transported upwards and made the system develop,which illustrated the function of the main system dynamically.The absolute vorticity advection was related with the movement of trough and its intensity varieties on different levels,which reflected vertical changes of the influencing system on different levels during the snowstorm.The twisting term played a negative role on low level,which meant that the upwards movement distributed asymmetrically in horizontal direction which formed negative vorticity and it negatively affected the development of the snowstorm system.

Abstract:Based on Doppler radar data,wind profiler radar data and high-density observations of AWSs(automatic weather stations),a heavy rainfall event in Tianjin during 25—26 July 2012 is investigated.Results show that:(1)The radar echo shows the high centroid structure during the heavy rainfall event,and the cyclonic convergence with updraft is closely linked with rear downdraft,indicating that the convection has certain organizations and the strong rain echo will not be weakened in a certain time so the heavy rainfall will be continued.The maintenance and extended height of adverse wind region can be used as a threatened signal of heavy rainfall.(2)The surface convergence line is in good agreement with “train effect” area on the radar echo map.The mesoscale surface convergence center and the steady maintenance of meso- and micro-scale convergence are important factors affecting the rainstorm.(3)The disturbance process of low level jet and boundary layer jet can be analyzed in detail based on the wind profile data.The jet is significantly strengthened before the heavy rainstorm,which is consistent with “train effect” on the radar echo map,but can be warned more earlier than radar.The enhanced characteristics of low level jet and boundary layer jet from the wind profiler radar have a good indicative significance for the short-term weather forecast of heavy rainfall.

Abstract:Based on the conventional weather observational data from 54 meteorological stations in Jiangsu Province from 1960 to 2009,the daily potential evapotranspiration at different stations in this province was calculated by Penman-Monteith Equation.Relative moisture index(I_RM),an index reflecting arid and moist climate characteristics,was used to evaluate the arid and moist climate conditions in a region.The daily I_RM values at different stations in the province were computed from the observed precipitation and the calculated evapotranspiration.According to the Chinese Meteorological Drought Grades in the National Standard GB/T20481-2006 of China,the computed I_RM values were classified into three grades and the different statistical parameters of I_RM were used to analyze the arid and moist characteristics in different regions of Jiangsu Province.The research results indicate:1) In a year,the semi-arid area and the moist area occupied a half of the total area in Jiangsu province respectively.Among them,the northern side of the Huaihe River,the north part of the region between the Yangtze River and the Huaihe River and the north part of the coastal region were semi-arid area and the south part between the Yangtze River and the Huaihe River,the south part of the coastal region,the valley of the Yangtze River and the south part of Jiangsu Province were the moist area;2) The precipitation and the potential evapotranspiration in a region were the two key factors influencing the relative moisture index and the climatic dryness and wetness characteristics in the region.The change of precipitation played a dominant role in the tempo-spatial changes of I_RM and the variation of the potential evapotranspiration played an auxiliary effect;3) In winter,there was the most obvious arid and moist contrast between the south and north parts of Jiangsu Province while it was the least in summer.The scope of moist area was largest in summer but it was smallest in autumn.The scope of semi-arid area was largest in autumn but it had no distribution in summer.The scope of arid area was largest in spring but there were no arid area in summer and autumn.The climate in Jiangsu Province was moistest in summer but it was aridest in spring;4) The annual change of I_RM presented a single peak on the north side of the Huaihe River and the coastal region and there were two peaks in the region between the Yangtze River and the Huaihe River,the Valley of the Yangtze River and the south part of Jiangsu Province.The interannual variability of I_RM was largest in the coastal region but it was smallest in the valley of the Yangtze River.

Abstract:In order to analyze the influence of initial atmospheric conditions on short-term climate numerical prediction,two different sets of ensemble hindcasting experiments were performed with IAP9L2x2.5-AGCM(a grid-point Atmospheric General Circulation Model which was developed by the Institute of Atmospheric Physics,the Chinese Academy of Sciences) forced by observed and climatic surface sea temperature(SST),sea ice respectively for seventeen years(1988—2004).In each set of the experiment,there were three tests under three different initial atmospheric conditions,namely,NCEP-Ⅱdata,smoothed 5-day NCEP-Ⅱdata and smoothed 11-day NCEP-Ⅱdata.The method of correlation analysis was used here.The results showed that the influence of initial atmospheric conditions on short-term climate prediction in the extratropical areas is greater than that in the tropical areas.As to summer in East Asia(China),the initial atmospheric conditions of smoothed 5-day NCEP-Ⅱ data performed better than smoothed 11-day NCEP-Ⅱdata and NCEP-Ⅱdata(adopted by real-time prediction at present) by comparing the temporal anomaly correlation and the average of spatial anomaly correlation of meteorological elements during the 17 years.In contrast to the initial atmospheric conditions adopted at present,the work in this paper unveiled some useful information that is suitable for short term prediction for IAP 9L2°×2.5°-AGCM,which is valuable.

Abstract:In this paper,the Weather Research and Forecast Model(WRF) is coupled with Surface-Layer Scheme,Single-Layer Urban Canopy Model and Mingle-Layer Urban Canopy Model respectively to evaluate the simulation effect of various parameterizations on the weather conditions on 1 August 2007 in Nanjing.The best urban parameterization scheme is coupled into WRF to study the impact of land cover change on the Urban Heat Island(UHI) effect in Nanjing.Results show that the Mingle-Layer Urban Canopy Model shows the best simulation effect for surface temperature and 10m wind field.Urbanization makes surface air temperature increase over the region,especially at night and thus intensifies the UHI effect.After urbanization,the wind speed in the downtown area decreases obviously while the Urban Heat Circulation occurs more apparently.There also exists the downstream effect of UHI in Nanjing.

Abstract:Studies have shown that large-scale monsoon gyre activity is closely associated with tropical cyclogenesis over the western North Pacific.In this study,two cases of monsoon gyre activities in 2002 and 2009 were first examined.It was found that a monsoon gyre can be linked to the formation of one or more tropical cyclones,which usually occur near or to the east of the gyre center.Further analysis of the monsoon gyre activity during the period of 2000—2009 indicates that tropical cyclogenesis mainly occurs near or to the east of the gyre center,although the definition of a monsoon gyre depends on its duration and the circulation intensity.It is suggested that the tropical cyclogensis may be associated with the Rossby wave energy dispersion of monsoon gyres.

Abstract:Considering the required fixed-point and hourly wind speed forecast for the wind power prediction in wind farm,numerical prediction of wind velocity from the MM5 lattice point output released by the Central Meteorological station was interpolated into of an anemometer tower at a certain height in a wind farm along the coast of Fujian in this paper.Through error analysis of forecast results,we found that there were some systematic errors due to special underlying surface at the junction of land and sea.According to the lag correlation of the error and the real-time meteorological data from the anemometer tower,weinvestigated dynamic correction methods for numerical prediction of wind velocity from the MM5 using earlier error observations and anemometer tower turbulent indicators,and established revised equations.The average absolute error of the revised wind velocity forecast was reduced by 31%—54% and the accuracy of prediction was improved effectively.

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