Abstract:By using the monthly surface ozone data collected at remote sites over East Asia(EA) and related wind field and precipitation data,this paper studies the ozone seasonal cycle,interannual variation characteristics and their relations to EA monsoon,and the main factors influencing the surface ozone.The results show that the spring maximum and summer minimum of surface ozone occurs widely across mid-latitudes in the North Hemisphere at remote sites,including most parts of EA.However,the surface ozone has a summer maximum in the region of 33-43°N over EA,and a later winter/early spring maximum in south of 20°N over EA.These ozone seasonal cycle features were mainly controlled by the seasonal transitions of East Asia winter/summer monsoon circulations.The latitudinal differences of appearing time of surface ozone peaks in spring over EA Pacific Rim regions are closely related to the differences of pollutants transport path and strength from Asian continental.The analysis of seasonal variations of potential vorticity,upper air jet stream around tropopause,and the variation of vertical circulations shows that the winter and spring are the strongest periods of air mass transport from stratosphere to troposphere.However,the transport from stratosphere to troposphere is weakest from May to November and has lower impact on surface ozone.The interannual variations of EA summer monsoon onset(time and strength) and patterns of circulation are the main reasons of surface ozone interannual variations in spring and summer over EA Pacific Rim regions.The other factors for surface ozone variation could be attributed to monsoon precipitations,cloud effects on photochemistry and the stratosphere-troposphere transport.

Abstract:Base on the thunderstorm days,hail days and hail damage area data in east agricultural region of Qinghai Province from June to September from 1961 to 2010,the climate change trend,regressive analysis and significance test methods are used to analyse the tendency of thunderstorm days and hail days in recent fifty years.The natural variation tendency of hail days is forecasted with the optimum fitting value of thunderstorm days tendency as independent variable.The effect of artificial hail suppression under the background of climate change is qualitatively illustrated based on the significant difference between the tendency and natural trend of hail days.Meanwhile,the effect of artificial hail suppression is quantitatively analyzed based on the regressive analysis and significance test of the thunderstorm days and hail damage area.Results show that:1)The hail days has no an obvious decreasing trend from 1961 to 1990 under the same trend of background of climate change,therefore the artificial hail suppression effect is not remarkable.In contrast,the change trend of hail days from 1991 to 2010 decreases notably,with a significance level of 0.001,proving that the artificial hail suppression effect is remarkable. 2)There exists some fluctuations in some years,but the average rate of artificial hail suppression and mitigation is 52.6% with the 95% confidence level in east agricultural area of Qinghai Province from 1991 to 2010.

Abstract:Using a DMT(Droplet Measurement Technologies) continuous flow streamwise thermal gradient cloud condensation nuclei (CCN) counter,the aircraft and ground measurements of CCN over some regions of North China are conducted.The field observations show that,due to the severe air pollution,CCN number concentration in Taiyuan city is higher than that in Shijiazhuang city.Daily mean and maximum CCN number concentrations increase with the supersaturation.With the influence of meteorological factors and human activities,the variations of CCN number concentration display a distinctive diurnal cycle including two apparent peaks.Precipitation has an obvious scavenging effect on the ground CCN.The ground CCN spectra can be derived from the expression N=CS^k.The fitting spectra parameters C(more than 2 200 cm^-3) and k(less than 1) represent the continental characteristic of CCN in Taiyuan city.The CCN is mainly transported from surface and CCN number concentration decreases with the height.Long-distance transportation of particles provides secondary source for CCN when the upper wind direction changes.The cloud has a definite depletion effect on CCN particles so that CCN decreases obviously in clouds.

Abstract:Using the routine meteorological measurements and supersonic measurements at Dunhuang Gobi site in June 2004 and August 2008 as an example,This paper analyses the general process of summer heat transfer and its characteristics over a Gobi underlying surface in the arid region of Northwest China.Observation qualities of turbulent fluxes and measured surface energy closure are first evaluated,indicating that the system in the site measures well during the daytime overall.The typical diurnal variations of surface energy fluxes in summer show that the latent heat flux is generally little and can be ignored.In the daytime,both downward solar radiation and upward longwave radiation near surface are strong,and surface net radiation is mainly transformed into sensible heat flux(e.g.,mean surface net radiation and sensible heat flux at noon at Dunhuang Gobi site can reach more than 380 W·m^-2 and 250 W·m^-2,respectively).Soil releases energy to balance surface radiation cooling in the nighttime,and sensible heat flux is a little less than 0.The frequently occurred free convection activity near-ground is found in the daytime,which influences the observation quality of momentum flux.It can effectively transfer near-ground heat into upper air and contributes to the super depth of the atmospheric boundary layer.The characteristics of momentum roughness length and thermodynamic roughness length over the Gobi surface are further researched.The momentum roughness length at Dunhuang Gobi site is determined as 0.6 mm.The thermodynamic roughness length is an order of magnitude lower than the momentum roughness length,which agrees with the primary understanding of thermodynamic transport characteristics over the arid region.

Abstract:Changes of soil moisture over China along with global warming are explored through comparing the control and double CO₂ experiments in 10 coupled models participating in the 4th Assessment Report(AR4) of Intergovernmental Panel on Climate Change(IPCC).The results show that the summer monsoon enhances and the winter monsoon weakens over East Asia under the global warming.More water vapor is transported to China during both winter and summer.Precipitation increases in almost all area of China except for the Yangtze River in summer and South China in winter.The difference between precipitation and evaporation(P-E) during summer displays an increase over Northeast and southern China,and a decrease extending from the Yangtze River to Northwest China.During winter,almost all models simulate an increasing(a decreasing) P-E over northern (southern) China.Under the global warming,changes in precipitation,evaporation,runoff and snow melting over China collectively cause an increase in soil moisture over arid region,and the increase is stronger in winter than that in summer.However,the soil moisture decreases over other regions.These results are based on multi-model ensemble mean,which is of value to some degree for future climate prediction;whereas these models exhibit variety and uncertainty.

Abstract:Based on the NCEP/NCAR reanalysis and NOAA OLR data,this paper studies the relationship between the establishment of South Asian high(SAH) over the Indo-China Peninsula(ICP) and the splitting of 500 hPa subtropical high over the Bay of Bengal(BOB) in springtime.Results show that,before the establishment of SAH,the convective activity extends northward from the "Maritime Continent" and establishes initially over the ICP.In concert with this,a local anti-Hadley cell displays in the mid-lower tropospheres over BOB due to the sensible heating induced by the Tibet Plateau.This local meridional cell results in a descending center near the 15°N of BOB from 500 hPa to 700 hPa,which suppresses the development of convective activity and thus becomes unfavorable for the splitting of 500 hPa subtropical high in this region.After the establishment of SAH over ICP,a strong divergence centre shows in the upper troposphere over BOB,accompanied by disappearance of the mid-low tropospheres descending center near the 15°N of BOB.Consistent with this,convective activity develops over BOB and coincides with increasing of precipitation and releasing of latent heating.This induces a diabatic maximum center at 500 hPa and thus intercepts the ridge of subtropical high over BOB.Therefore,the divergence effect induced by the upper SAH establishment possibly triggers the establishment of convective activity and the splitting of 500 hPa subtropical high over BOB.

Abstract:Daily precipitation data of 89 stations in South China from 1969 to 2008,provided by the China National Meteorological Information Center,are used to investigate the spatial and temporal features of the extreme precipitation during the post-flood season (July-September) in South China.Results show that:1)The spatial distributions of the average annual total precipitation amount,heavy precipitation amount,precipitation frequency,heavy precipitation frequency and rainstorm frequency are basically in agreement with that of the extreme precipitation threshold during the post-flood season in South China,with larger values in the south of Guangdong and Guangxi,and the southwest of Fujian.Heavy precipitation amount,precipitation frequency and rainstorm frequency have a great influence on the spatial distribution of the total precipitation.Heavy precipitation amount,heavy precipitation frequency and rainstorm frequency have implications for the temporal variation of total precipitation.2)The regional averaged extreme precipitation of South China during the post-flood season shows an obvious interdecadal change around 1992,and the remarkable increase takes place for the mean values and variance of all the indices except for precipitation frequency,indicating that the drought and flood disasters have increased since 1993.In addition,the total precipitation and precipitation frequency decrease in the two stages(before 1992 and after 1993),with some differences for the notable decreasing regions.

Abstract:Based on the observed daily maximum,minimum temperatures and daily precipitation data at the 29 meteorological stations which locate in the Yangtze and Huaihe River Basins as well as the daily NCEP reanalysis data,the statistical downscaling model(SDSM),which is a combination of multiple linear regression and stochastic weather generator,has been used to calibrate the parameters of SDSM at each station.Subsequently the statistical downscaling model is applied to construct scenarios of the climate extremes during the end of the 21st century by using predictor sets simulated by two GCMs (i.e.HadCM3 and CGCM3,hereafter referred to as SDSM-HadCM3 and SDSM-CGCM3,respectively) forced by the special report on emission scenarios(SRES) A2.Future scenarios of the climate extremes such as heat waves and intensity precipitation in the 21st century at the 29 meteorological stations are constructed.The evaluation of simulated extreme indices of temperature and precipitation for the current climate shows that the downscaled temperature-related indices match the observations well,and SDSM can modify the systematic cold biases of the AOGCMs.For example,compared with the raw CGCM3,SDSM can reduce the "cold bias" of the winter maximum and minimum temperature by 3℃ and 4.5℃,respectively.For indices of precipitation extremes,most AOGCMs tend to underestimate the intensity,but SDSM improves this significantly.The bias of simple daily intensity index(I_SDI) in summer for SDSM is -6%,while that of CGCM3 is as high as-60.6%.Overall,compared with the AOGCMs,the downscaling model really has "added values".Scenario results using A2 emissions show that in all seasons there is a significantly increase of mean daily-maximum and minimum temperature at the 29 meteorological stations,accompanied by a decrease of the number of frost days and an increase of the heat wave duration.For instance,the frost days in winter are projected to a significantly decrease of 5-25 days at the 29 stations while the heat wave duration in summer increases by about 4-14 days.There is good agreement in the direction and magnitude of the projected changes of temperature-related indices between the two driving AOGCMs.A warming environment will also give rise to changes in extreme precipitation events such as the maximum 5-day precipitation and the heavy rainfall proportion (R_95t).Precipitation extremes are projected to increase at most of the 29 meteorological stations in a quite consistent manner between the two global scenarios.For example,the R_95t in summer is projected to increases by 26% and 27% by SDSM-HadCM3 and SDSM-CGCM3,respectively.

Abstract:Using the daily rainfall data of 90 stations in East China from 1960 to 2009,the interdecadal changes of occurrence frequency and intensity of precipitation extremes in boreal summer(June-July-August) in East China in recent five decades are investigated.Results show that there are significant interdecadal changes of the precipitation extremes in the past 50 years.In recent 20 years,the precipitation extremes occur more frequently than those in the earlier 30 years,and more and stronger extreme precipitation events are observed in 1990s.In East China,the extreme events of precipitation processes last usually less than 9 days.However,the extreme events of continuous rainy days last usually more than 9 days.Relative to the other regions in East China,the more precipitation processes with higher persistence and stronger intensity occur in Fujian Province.The largest extreme rainfall appear in conjunction part of Jiangxi and Anhui provinces.Zones where the extreme events of precipitation occur more frequently moves interdecadally in meridional direction.The north-south shifts of the zones mentioned above are also observed in the extreme events of daily precipitation and precipitation processes.Interestingly,there exist two frequent occurrence zones of precipitation extreme events over the south and north of Yangtze River,respectively.The two zones get closer to each other and even merge into one in some decades,and get distant from each other in other decades,which is observed in the last three decades.

Abstract:This paper discusses the modulation effect of Quasi-biweekly oscillation of cross-equatorial flow on typhoon tracks over the Western North Pacific by using the tropical cyclones (TCs) data from the American Joint Typhoon Warning Center (JTWC) and NCEP/NCAR reanalysis wind data.The typhoon tracks are divided into seven types and the evolution of low-frequency circulation in the period of the atmospheric quasi-biweekly oscillation(QBWO) is synthetically analyzed through the methods of lead and lag regression.The results show that the meridional wind and cross-equatorial flow at 925 hPa bear the characteristics of periodic oscillations of 10 to 20 days and it is useful in forecasting the typhoon tracks over Northwest Pacific.In the equatorial region of North Pacific,the low-frequency cross-equatorial flow and meridional wind can influence the low-frequency cyclone and anticyclone and modulate the typhoon tracks by regulating the position and strength of intertropical convergence zone(ITCZ).The component of the strong northward low-frequency cross-equatorial flow is beneficial for the low-frequency cyclone,and makes the ITCZ move northward.Typhoons can move along the zone of the ITCZ.The component of weak northward low-frequency flow or of southward low-frequency flow goes against the movement of typhoons.

Abstract:In this paper,the temporal and spatial characteristics of urban heat island effect in Tianjin city in the year 2008 were analyzed by using the observation data and the 6 h ground general data from 14 automatic meteorological stations in Tianjin.The results showed that the urban heat island effect in Tianjin not only had significant diurnal,monthly,seasonal and annual variation characteristics,but also was closely related to the method to choose urban and suburban stations.Finally,the relationship between urban heat island intensity and cloud,wind,humidity was analyzed by using the multiple linear regression analysis method.It was found that the wind speed was a dominant meteorological factor,but the overall impact of the meteorological elements on the urban heat island effect in Tianjin was relatively limited.

Abstract:The problem of thresholds' uncertainty in satellite cloud imagery classification has been resolved using a technique based on the information of image entropy.Based on the Kapur technique of image entropy,the cloud imageries are classified into several kinds automatically.And the nine thresholds selected as the classification results are analyzed.With the nine thresholds,the cloudy imageries are classified into ten cloud layers.And the cloud classification method is realized.During the storm rainfall of the first ten days of July 2007 in Huaihe River Basin,the method is applied and the results are compared with the enhancement technology of infrared image in GOES User's Guide.The results show that the method is useful for analyzing ground precipitation based on satellite image.