Abstract:South China is one of the most frequent drought and flood areas in China.The main characteristics of precipitation in South China are long rainy season and large rainfall.Studying the distribution characteristics and variation rules of spring precipitation in South China can be used as a basis for the allocation and utilization of precipitation resources in spring and the early warning of drought and flood in South China.Most studies have mainly focused on the characteristics of spring precipitation and its influencing factors in South China at present,while there are few studies about the interdecadal variation of spring precipitation in South China.Interdecadal climate change is the background of monthly,seasonal and interannual climate changes and forecasts,and also affects climate change over a longer period of time.It is one of the key issues of climate change.So this paper intends to study the interdecadal variation of spring precipitation in South China,and the corresponding characteristics of atmospheric circulation and sea surface temperature(SST) anomaly.
To investigate the subject of spring precipitation of 48 stations in South China,its interdecadal variation characteristics and its relationships with atmospheric circulation and SST,the daily precipitation data in China,NCEP/NCAR reanalysis data,and Pacific Decadal Oscillation(PDO) index and SST data provided from NOAA during 1960-2010 are used.This paper uses the common meteorological statistical methods and diagnostic analysis methods.
It is found that spring precipitation in South China has experienced three stages:during 1960-1971,the precipitation is less than normal;during 1972-1992,it is more than normal;during 1993-2010,it is still less than normal,but the reduction degree is weaker than that in the first stage.There are great differences in the circulation background fields among the different stages of interdecadal variation of spring precipitation in South China.In the first stage,the westerly is flat at 500 hPa,which is not helpful for the north cold air southward.The warm air mass is not active with the anomalous divergence of water vapor flux divergence in South China,so the precipitation is less than normal.In the second stage,the ridge over the north of Tibetan Plateau is stronger at 500 hPa,which is favorable for the north cold air southward.The southward cold air joins the active warm moist air mass in South China,combining with the anomalous convergence of water vapor,thus the precipitation is more than normal.In the third stage,the trough and ridge system of the westerly wind is stronger at 500 hPa,which is good for the northern strong cold air southward.The southern branch trough in the Bay of Bengal fills up,which is not helpful to the southern warm moist air moving to South China.These conditions result in less precipitation in spring.Furthermore,the precipitation in South China has a positive correlation with PDO index.In the view of seasonal changes,there exists the most significant correlation between PDO index in previous autumn and precipitation in South China in spring on the interdecadal time scale.In the view of different stages of interdecadal variation of spring precipitation in South China,the positive correlation of PDO index and spring precipitation in South China is the most obvious during 1960-1971.

Abstract:The midlatitude cyclone is a low-pressure vortex with strong baroclinicity that occurs in the mid-to high latitudes in the Southern and Northern Hemispheres.Some studies show that significant changes in the cyclone activity and atmospheric circulation over East Asia have occurred over the past decades.The statistical characteristics of the midlatitude cyclone were analyzed manually in the past,while this method is time-consuming and relies on the subjective experience of researcher.The objective cyclone identification and tracking method is widely used to research on detecting cyclone activities with the development of reanalysis data and numerical model in recent years.The features of precipitation in Northeast China in spring and summer and its relationships with mid-to high latitude circulation systems are well studied.The cold vortex in Northeast China is considered as the key component,while midlatitude cyclone also plays an important role in rainy season.In this study,based on the 4 times daily ERA-Interim mean sea level pressure reanalysis data,using the objective cyclone identification and tracking method,the characteristics of mid-latitude extra-tropical cyclone activity in East Asia in spring and summer during 1979-2013 and its linkage with concurrent rainfall in Northeast China are analyzed.The results show that East Asian mid-latitude cyclones generate in the middle of Mongolia and to the east of Altai Mountains,and move to the north of Heilongjiang province.The cyclone increases gradually to the maximum to the west of Greater Khingan Mountains and dissipates thereafter.The region of cyclone activity in spring is larger than that in summer,and the cyclone is also stronger in spring.While the lifetimes of cyclone are similar in different seasons,the maximum standard deviation of cyclone frequency and intensity are both located in central Mongolia,which indicates that both the most frequent cyclone activity and the greatest variation of cyclone activity happen there.Therefore,Mongolia was selected as the representative area for the abnormal activity of midlatitude cyclone in East Asia.The cyclone numbers in spring and summer in this key area (40-50°N,80-140°E) both display linear decreased trend in the late 35 a.The correlation between the cyclone activity and rainfall in Northeast China is positive in both seasons,but the reasons are different.During the strong cyclone activity years,the cyclonic circulation over Northeast China benefits the increase of spring rainfall,and the increase of summer rainfall mainly depends on the anomalous westerly moist transport.

Abstract:Based on hourly precipitation observation data during the warm season(May to September) of 2005-2014 from 69 gauge stations in Jiangsu,the spatial and temporal distributions of short-time heavy rainfall(≥ 20 mm/h) have been analyzed,which showed obvious heterogeneity in space and time.The occurrence frequency of short-time heavy rainfall in northern Jiangsu area was higher than that in the southern region,and its most active region is located in the western area along Huaihe River.Meanwhile,extreme short-time rainfall events(≥ 50 mm/h) frequently occurred in the eastern Huaibei with concentrated rainfall distributions.The occurrence frequency of short-time heavy rainfall showed the decreasing trend in the past decade,especially in northern Jiangsu.In general,July was the most active month of short-time heavy rainfall,and the extreme short-time rainfall events occurred most frequently in August.The pentad short-time heavy rainfall evolved with the phase variations that the frequency of short-time heavy rainfall increased rapidly during Meiyu season with the peak in the second pentad of July,and then the frequency of extreme short-time rainfall events increased obviously during mid-summer and reached its peak in the third pentad of August.In average,the diurnal variations of short-time heavy rainfall showed a double-peak pattern,with the highest peak around 17:00 BST and the secondary peak around 07:00 BST,while extreme short-time heavy rainfall events tended to occur in the afternoon.The diurnal variations of short-time heavy rainfall also demonstrated obvious sub-seasonal variability and spatial differences.It had a single peak in early morning during Meiyu season and a single peak in the evening during mid-summer.From the south to the north of Jiangsu,the diurnal pattern evolved from a single peak to double and multiple peaks.The peak appeared mostly in the afternoon in the southern area of Huaihe River,while mainly appeared during the night to early morning in the northern area of Huaihe River.

Abstract:In this study,based on the monthly sea surface temperature data and daily rainfall of 753 stations over China,11 subdivisions of summer rainfall in eastern China were found by using the rotated empirical orthogonal function(REOF),and other methods.The 11 subdivisions of summer rainfall were shown by statistical methods to be independent from each other,which differs from the three types of summer rainfall patterns of eastern China,thus representing the connection of summer rainfall in eastern China.Based on the interdecadal variation of the relationship between ENSO and 11 subdivisions of summer rainfall,three categories of the correlation between SSTA in the Niño3 region and summer rainfall were defined by means of moving correlation,composite analysis,etc.:In the first category,the correlation is always very week in the long term,such as in northeastern China,the middle and lower reaches of the Yangtze River,south of the Yangtze River,the Fujian-Jiangxi area,and the Qiongzhou Rim strait.In the second category,the significant correlation is fairly stable,such as in the Hetao area and middle and lower reaches of the Yellow River.In the third category,the relationship shows noticeable changes,as such as in the Liaoning-Jilin,Yellow River-Huaihe River,Huaihe River and Guangdong-Guangxi areas.In the fourth category,the abrupt year of the interdecadal variation of the relationship between ENSO and four subdivisions of summer rainfall in eastern China differ.The correlation between SSTA in the Nino3 region and the summer rainfall in the Guangdong-Guangxi area abruptly changed in 1975.However,the relationship between ENSO and summer rainfall in the Liaoning-Jilin and Yellow River-Huaihe River areas was weak after 1980.The interdecadal variation of the relationship between ENSO and summer rainfall of the Huaihe River occurred around 1985.

Abstract:Huaihe River is one of the main rivers in China.It lies between the Yellow River and Yangtze River.Since ancient times,floods and droughts occurred frequently in Huaihe River Basin with significant casualties and economic losses.In developing measures for disaster prevention or emergency response for disaster relief,the study of floods and droughts caused by precipitation anomaly in Huaihe River Basin should be strengthened.Based on the observation dataset,this study not only defines the precipitation transition events from spring to summer,but also produces its intensity using total seasonal precipitation.The precipitation transition from spring to summer is analyzed by using the 30 gauge stations in Huaihe River Basin during 1961-2014.The typical patterns of Wet-Wet and Dry-Wet transitions generally occurred and their intensities were stronger in the past 54 years.The results indicate that temporal variation of transition event shows interannual and interdecadal variabilities.The significant decrease trend of transition frequency is detected during 1961-1979 and 2000-2010,but it has increased in recent years.The transitions often occur in more than one-third stations over half sample periods.This study applies the Season-reliant Empirical Orthogonal Function(S-EOF) analysis to detect major modes of seasonal precipitation.Based on S-EOF method,the cumulative variance contribution of the first mode is up to 34.4%.The principal component 1(PC1) illustrates the continuous positive precipitation anomaly in spring and summer in most areas,and it is worthy to notice the rising of its time coefficient in past few years.Otherwise,transition from negative to positive precipitation anomaly and interdecadal variation of time coefficient are shown by PC2.Furthermore,results show that PC1 relates to continuous El Niño event from early winter to spring,positive East Asian subtropical westerly anomaly at 200 hPa in spring,positive Indian Ocean Dipole and south wind anomaly at 850 hPa over eastern China from spring to summer.The reverse occurs during a continuous negative phase scenario.The negative SSTA in eastern coast of China,the significant changes of northward East Asian subtropical westerly,and the shift of meridional wind anomaly at 850 hPa over southeastern China cross seasons play important roles in the occurrence of PC2 in Huaihe River.

Abstract:Based on the statistical characteristics of rainstorm location and trajectory of the cyclone in the Huaihe River Basin during Meiyu period,the schemes of WRF numerical simulation are designed and the purpose is to investigate the orographic forcing mechanism of terrain of Dabie Mountains on the shallow rainstorm cyclone.Results show that:1)In the three simulation experiments,the eastward speed of cyclone is the fastest in the experiment without terrain of Dabie Mountains,the slowest for the cyclone going around northern mountains,and the medium for the cyclone passing over mountains.Without terrain of Dabie Mountains,the trajectory of the cyclone is obviously in the south of the trajectory of cyclone going around northern mountains,showing that the cyclone has a feature of moving along lowland.With inverted terrain of Dabie Mountains,affected by the large-scale mountain,the cyclone is forced to go around northern mountains,with a more north trajectory than those of the cyclone passing over mountain and the cyclone in experiment without terrain of Dabie Mountains.2)The effect of mountain on cyclone intensity is that it can offset and reduce the intensity when the cyclone going around northern mountains with an anticyclonic trajectory.In the experiment without terrain of Dabie Mountains,the cyclone maintains its intensity by self-system and is stronger than the cyclone going around northern mountains.When the cyclone has passed over the ridge of mountain,it has a double intensity,because the cyclone experienced a potential vorticity conservation process in front of and behind the ridge.3)The forced ascending motion of mountain with a large gradient is larger than the systematic uplift of cyclone.The vertical upward velocity with both mountain forcing and cyclonic convergence can increase nearly one times.4)The enhancing of total vorticity behind the ridge of mountain mainly shows that the low-level vorticity advection,twisting and divergence terms have marked increase,and their increments can reach up to one times,but the changes of the terms are small in the middle level.5)The strong rainfall usually happens in the north part of cyclone where the south jet met the east flow of the cyclone,indicating that a warning area of strong rainfall locates in the north part of rainstorm cyclone in the Huaihe River Basin.6)By the topographic forcing on eastward trajectory of cyclone,the mountains can further influence the north-south location of rainstorm zone.

Abstract:A study of the relationship between tropical disturbance and distant rainstorm events in the region of 0°-50°N,90°-150°E during May to September in the period 2006-2011 was performed,while typical cases were selected for statistical analysis and numerical simulation.The results are as follows:(1)Under the background of favorable atmospheric conditions,a tropical disturbancewhose intensity is lower than a tropical depressioncan also cause distant heavy rainfall combining with the effect of mid-latitude systems.The statistics suggest that 21 events can be divided into three categories according to the type of moisture channel on 850 hPa:"S" pattern moisture channel,double moisture channel and northwestward moisture channel.The distant heavy rainfall events with "S" pattern moisture channel occur most frequently and the distant heavy rainfall events occur most frequently in July.The composite analysis of the three types shows that the formation of the remote heavy rainfall is closely related to the atmospheric circulation formed by the mid-latitude systems,tropical disturbance and subtropical high.The mid-latitude systems provide a favorable background of atmospheric circulation and the distant heavy rainfall occurs in the area with high moisture flux,which indicates the importance of moisture transportation.(2)The composite analysis of low-level jet of having or not having distant heavy rainfall shows that the southerly low-level jet located in the east of the tropical disturbance plays an important role in the formation of the distant heavy rainfall and is the key to make a connection between the low-latitude and mid-latitude systems regardless of the tropical disturbance intensity.The diagnosis and numerical study of a case with "S" pattern moisture channel further indicates that the southerly low-level jet is the main channel of transporting moisture to the mid-latitude rainstorm area and its intensity is one of the main factors affecting the distant rainstorm intensity.(3)The diagnosis of a case with "S" pattern moisture channel also indicates that the low-level jet between the tropical disturbance and subtropical high is the main energy channel that transports abundant energy to the distant rainstorm area.So the low-level jet not only contributes to the northward moisture transport but also the energy transport to the distant rainstorm area.(4)Sensitivity experiments show that the tropical disturbance can also induce the propagation of Rossby wave energy towards the northeast,the intensity of which is proportional to the intensity of the tropical disturbance,thus affecting the distant rainfall distribution.Wave trains can not form after removing the tropical disturbance,which is not beneficial to the dispersion of wave energy and the development of the distant rainfall.

Abstract:Understanding the predictability of a numerical model is an essential step before that model is added to a super ensemble prediction system.It is also very important for the development of that model.But forecast noise easily hinders the thorough understanding of the predictability of a model.The forecast always consists of useful forecast information and forecast noises,but sometimes,the proportion of forecast noises are remarkable big,especially for the primary stage of the model development.The forecast will be far apart from the observation when the forecast noises are stronger than the useful forecast information.The predictability evaluation should focus on the useful forecast information which is only decided by the physical characteristics and dynamic properties of the model.Then a valuable statistical correction method is necessary for the reasonable evaluation of the model predictability.This paper evaluates the predictability of three Atmospheric General Circulation Models(AGCM) and seven Coupled General Circulation Models(CGCM) before and after the statistical correction.We selected three AGCMs of Institute of Atmospheric Physics(IAP),for the comparison,seven CGCMs were also selected from the Development of a European Multimodel Ensemble System for Seasonal-to-Interannual Prediction project (DEMETER),the potential predictability of these AGCMs and CGCMs on summer rainfall in tropical regions,especially in the tropical western Pacific region is evaluated.Results indicate that:All of these models are able to reproduce well the spatial features of mean rainfall of the past 20 years,but there are obviously differences between models for precipitation anomalies.In order to reduce the distraction of noises,the Singular Value Decomposition(SVD) method is used to estimate the predictability of models for main spatial features of observed precipitation anomalies.IAP 9-AGCM has the maximum similarity of the first SVD modes to the observed one,which means IAP 9-AGCM can reproduce the main feature of observed precipitation anomalies over the tropical western Pacific,the two IAP 2-level models also have similar spatial features,but the spatial characteristics of forecasted precipitation anomalies shift to the east about 20 degree.In the ocean area,the spatial features of CGCMs' anomalous precipitation are more similar to the observation than AGCMs',but for the west of 140E,CGCMs' anomalous precipitation are remarkable difference from those observed features,it may due to the complex topography,lots of small islands on this area could reduce the performance of the coupling between atmospheric models and ocean models.Considering the good ability of AGCMs,it reproduces the most important spatial feature of the observed precipitation anomalies which is a statistical correction method based on Empirical Orthogonal Function(EOF) analysis method is applied to hindcasts of the ten models.We calculate the Abnormal Correlation Coefficient(ACC) between observations and forecasts before and after the statistical correction.Due to the weak of rainfall intensity and the spatial shifting,the original ACCs of IAP AGCMs are remarkable lower than CGCMs',but after statistical corrections based on EOF,AGCMs show similar good ACCs of CGCM.The statistical correction method also improves ACCs of some of CGCMs,but it does not work when the original ACC is good enough.It implies that the improvement of predictability will ultimately depend on the progresses of researches on numerical models.With the successive improvement of IAP AGCM,the most obvious advance of summer rainfall appears in the tropical western Pacific,but in the eastern Pacific,hindcast precipitation anomaly remains weak.

Abstract:In this study,based on observations and numerical simulations,the squall line in front of the tropical cyclone in Hunan and Jiangxi Provinces of China,which preceded the super typhoon "Rammasun"(2014) was simulated and investigated,and the formation and development mechanism of this pre-TC squall line were discussed,as the vertical wind shear in this case was significantly weaker than the squall line in mid-latitude.The diagnostic analysis results showed the following:
Due to the fact that the typhoon moved northward and the subtropical anticyclone moved westward,the pressure gradient between them increased,which led to the enhancement of the low-level air current.The mid-and low-level wind field was a relatively homogeneous southwesterly flow in the area,which was influenced by the squall line,thus the wind direction and wind speed changes were not significant in the vertical direction.As a result,the low-and mid-level vertical shear before the squall line in front of the tropical cyclone were weaker than the mid-latitude squall line.Based on the mesoscale numerical model,the thermodynamic characteristics of the squall line at different stages under weak shear environment were analyzed emphatically.The results showed that the balance between the relatively weak vertical shear and weak cold pool led to the erect updraft of the squall line at the initial stage of the squall line in front of the tropical cyclone.Significant unstable environmental conditions at the leading edge of the squall line with cold and dry air overlapping warm and moist air were an important thermodynamic factor contributing to its development and enhancement.The horizontal wind shear on the right side of the typhoon inverted trough and the gust front which was formed by the low-level divergent airflow and middle-layer rear inflow jet in front of the squall line were the main dynamical factors related to its development.During the mature period,the gradual widening and strengthening of the cold pool on the rear side of the squall line and the squall line in front of the tropical cyclone away from the typhoon led to the decrease of moisture and energy supply.At the same time,the cold and dry air invasion in the mid-level behind the squall line strengthened and diffused toward the lower layer on the side of warm and moist air,which was associated with the warm and moist air flow updraft over the line tilted toward the cold pool side.Consequently,the vertical lifting weakened,which was not conducive to the formation of a new convective cell along the outflow boundary,and was detrimental to the development and maintenance of the squall line.These two features indicated the weakening of the squall line during this period.At the dissipation stage,the squall line moved too far away from the typhoon,and the influence of the typhoon on the squall line became extremely weak.Insufficient moisture supply and lifting led to the decay of the squall line in front of the tropical cyclone.

Abstract:At present,the global climate models have some limitations on the ability to simulate and hindcast the climate characteristics of the East Asian monsoon region,as well as the complex terrain.The numerical simulation and prediction using the fully coupled model is a promising method in the study of climate change.Coupled Model Intercomparison Project Phase 5(CMIP5),includes a fully coupled model of decadal return testing,which is the latest version of the major international advanced models,much better than the previous model.The return performance of the model is mainly reflected in two aspects:climate mean and climate variability,in which the model of climate change can be reasonably rewarded in order to predict the future climate effectively.Most of these studies focused on the assessment of climate change trends and climate averages.Ensemble forecasting can effectively cope with the uncertainty of model prediction.Some studies have pointed out that the multi-model ensemble has more reliable simulation ability than the single model in the contemporary climate of East Asia.BMA is a pre-processing method of ensemble forecasting,which can provide more accurate prediction,and studies have shown that BMA is better than simple multi-mode ensemble average.Based on the CMIP5 which runs of 10 climate system models for the surface air temperature hindcast,the multi-model ensemble(EMN) and Bayesian model averaging(BMA) prediction of the surface air temperature have been conducted.In terms of the variance distribution,the spatial and temporal distribution of the surface air temperature variation as well as the periodic oscillation characteristics,the skills of single models,EMN,BMA hindcasts are reasonably good by using EOF analysis and Morlet wavelet analysis.The results show that each single model,EMN and BMA can hindcast the variance distribution quite well for the period of 1981-2010.Among them BMA provides the best hindcast.EOF analysis indicates that each single model,EMN and BMA can hindcast two leading modes of the surface air temperature anomalies over East Asia.The models MIROC5 can not only hindcast the trend,but also hindcast the detrended variability fairly well.Although most single models and their multi-model ensembles are able to hindcast the trend of the surface air temperature over East Asia,it is still difficult to hindcast the interannual and interdecadal variability.Wavelet analysis suggests that CMCC-CM model systems can hindcast the quasi-quadrennial oscillation reasonably well,which is associated with that of the NCEP data.Multimodel ensemble mean and BMA are not able to hindcast the periodic variation characteristics of the surface air temperature principal components.

Abstract:East Asian region is one of the largest monsoon regions in the world,and East Asian winter monsoon(EAWM) plays an important role in the regional climate.Anthropogenic sulfate and black carbon(BC) are most important radiation active aerosols in East Asia.The interaction between aerosols and East Asian monsoon climate has received more and more attention in recent years.In this study,the impact of increase in anthropogenic aerosols on EAWM over eastern China are investigated using the NCAR Community Atmospheric Model version 5.1(CAM5.1),a state-of-the-art climate model considering aerosol direct,semi-direct and indirect effects.The effects of increase in anthropogenic sulfate,BC and both of them on EAWM are decomposed from different sensitivity simulations by changing anthropogenic aerosol emission sources in eastern China,and the experiments differed only in the aerosol and precursor gas emissions.CAM5.1 can generally capture the main features of winter atmospheric circulation in East Asia.
In winter,the direct and 1st indirect effects of sulfate reduce the solar flux reaching the surface,leading to a reduction of air temperature of surface and low troposphere and an increase of sea level pressure over land.Adjustments in surface temperature and pressure fields result in a weakened wind field above 925 hPa.The gradient of pressure between land and sea is increased,which enhances EAWM.The large-scale precipitation in southern China is reduced by the 2nd indirect effects of sulfate,and the convective precipitation is reduced in northern China,which is caused by the changed circulation.In winter,the effects of BC reduce the solar flux reaching the surface,and increase the solar flux in the atmosphere by absorbing.The surface air temperature has an insignificant reduction because the semi-direct effects of BC partly offset the direct.The heating of the low troposphere leads to the enhanced convection and the increased convective precipitation in southern China.The changed circulation results in temperature increase in troposphere over China.Adjustments in surface temperature and pressure fields result in an enhanced north wind in northern China and a weakened wind field in southern China above 925 hPa.The effects of BC result to an enhanced(a weakened) EAWM in northern(southern) China.The effects of BC on cloud are different from sulfate,which come from the feedback of semi-direct effect and the changed circulation.The effects of total anthropogenic aerosols(both sulfate and BC aerosols) result in a weaker reduction of air temperature in winter,which are the common result of two kinds of aerosols.The convective and large-scale precipitations are both reduced in northern China,and the convective precipitation is increased in southern China.The changes in surface temperature and pressure fields also result in an enhanced wind field in northern China and a weakened wind field in southern China above 925 hPa.The effects of total anthropogenic aerosols also result in an enhanced(a weakened) EAWM in northern(southern) China.The effects of total anthropogenic aerosols on monsoon are not simply a linear summation between the two types of aerosols.

Abstract:The cloud vertical structure directly affect the atmospheric heating rate and exert great influence on atmospheric radiation and circulation.This paper focused on investigating the difference of the cloud vertical properties over two 4°×4° adjacent regions centered at(39.5°N,116°E) as E1 region and at(39.5°N,112°E) as E2 in North China.The CloudSat 2B products and the DARDAR products from Cloud-Aerosol-Water-Radiation Interactions(ICARE) from January 2008 to October 2014 were used to give a statistical analysis on the distribution characteristics of the cloud vertical structures and cloud microphysical parameters.
The CALIPSO level 2 products from June 2006 to September 2008 were used to analyze the statistical distribution characteristics of the cloud vertical structures.The latitudes of the two regions are different but the longitude ranges are the same.E1 is centered in the Jing-Jin-Ji metropolis circle where the atmospheric environment such as aerosol pollution levels and humidity conditions are different from that in E2.To investigate the impacts of aerosols on cloud distributions and other properties in different atmospheric environments,the two adjacent regions were selected and compared in terms of the distribution characteristics of the clouds in different temperatures which can reflect the cloud droplet phase.The statistical results show that:
1)The cloud structures of the two regions are obviously disparate in the mixed cloud layer(-40-0℃),warm cloud layer(>0℃) and ice cloud layer(<-40℃).The largest value of the cloud occurrence probability(COP) in E1 in the warm cloud layers appear in spring,which is 4.3 times of that in E2,and the largest one in E2 appears in autumn,which is 4.6 times of that in E1.The COP in the mixed cloud layers in E1 reaches the maximum in winter and in spring in E2 with 71% and 83% respectively.The COP in the ice cloud layers in E1 and E2 both reach maximum in spring with 29% and 16%.
2)There are obvious differences in seasons for the layer thicknesses of the COPs with high values.The layers with large COPs mainly appear in spring and winter in E1 or spring and summer in E2.The higher the height is,the smaller value of the reflectivity with higher cops.The largest reflectivity in E1 is stronger than that in E2 in autumn and winter.
3)The liquid water content(LWC),liquid effective radius(LRE),ice effective radius(IRE) and ice water content(IWC) in E2 are larger than those in E1,which is closely related to the stronger aerosol loading in E1.The statistical characteristics show that the interaction between aerosols and clouds has a complex feedback effect on the changes and liquid water content.The research results from the present study are expected to provide the knowledge that is needed for parameterizing cloud formation in climate models.

Abstract:The temperature inversion in the boundary layer is an important indicator of atmospheric stability.The strong inversion may result in the accumulation of pollutants in the lower layer.In addition,the accumulation of strong inversion energy can also cause severe convective weather.All of these have a huge impact on the production of human life.In order to analyze the characteristics of temperature inversion in the boundary layer (below 2 km) over Nanjing City,this paper used the daily L-band radar data at 08:00 BST and 20:00 BST from 2010 to 2015.The frequency,intensity and thickness of ground temperature inversion and suspended inversion were analyzed in detail.The results reveal that the frequency of temperature inversion is high over Nanjing,up to 81.68%,including 23.9% ground inversion and 71.8% suspended inversion.The frequency of temperature inversion at 08:00 BST is higher than that at 20:00 BST.The temperature inversion occurs mostly in autumn and winter and rarely in summer.The inversion thickness is the lowest in summer and the maximum in winter and early spring.The inversion thickness at 08:00 BST is larger than that at 20:00 BST.The thickness of suspended inversion is larger than that of ground inversion.This phenomenon is due to the change of solar radiation.Solar radiation increases temperature at day time and strengthens the turbulence,resulting in the inversion weakened or disappeared.On the contrary,the ground temperature gradually decreased at night with the turbulence weakening,which resulting in the inversion intensity and thickness strengthened.The inversion intensity is weak in summer and strong in winter,which has an obvious seasonal variation.There is a little difference in inversion intensity between 08:00 BST and 20:00 BST.But the average of ground inversion intensity is 1.5 times of suspended inversion intensity.Most of strong inversion with intensity higher than 2℃/hm happened in winter.Based on the daily monitoring data of mass concentration of air pollutants in 2014 and 2015,the paper analyzed the relativity of pollutant mass concentration and inversion elements (inversion intensity and inversion thickness).The results reveal that the mass concentrations of pollutants (PM₁₀,PM_2.5,NO₂,SO₂ and CO) are in positive correlations with the inversion intensity and thickness.In other words,the stronger the inversion layer,the higher the pollutant mass concentration.The mass concentration of ozone is in a negative correlation with the inversion intensity and thickness,which is related to the diurnal variation of ozone mass concentration.Therefore,the atmosphere inversion in the low layer is one of important factors that influence the air quality.The changes of the inversion elements (inversion intensity and thickness) have certain directive significance to air quality forecast.

Abstract:With the accelerated pace of urbanization in Beijing,the expansion of urban scale outside the Third Ring Road in twentieth Century has been extremely rapid.That which has been suburban non-uniform underlying surface for the past 80 years has now developed into rough complex urban areas under the underlying surface,and corresponding increases in urban buildings and population density have also resulted in a significant increase in the surface dynamics of urban land.Displacement height(d) and surface roughness length(z₀) can be used to characterize the physical properties of the surface,and their size can directly affect the exchange between the ground and atmosphere fluxes,which in turn affects the physical and chemical conditions of the entire atmosphere.However,for urban underlying surfaces,it is often difficult to determine d and z₀ precisely because of their significant non-uniform surfaces(e.g.different shapes of houses and trees of different heights).Martano(2000) proposed a method for calculating d and z₀ based on monolayer observations.This method simplifies the mathematical problem of solving two-dimensional variables into one-dimensional variables by using the least squares method.Gao and Bian(2004) used this method and calculated the surrounding d and z₀ using the observation data of the Beijing 325 m meteorological tower in 2001,and obtained d=36.0 m,z₀=1.6 m.However,these two values were obtained more than a decade ago,thus it was necessary to reassess the two values due to the development of the area.As a follow-up study of Gao and Bian(2004),the present paper also uses Martano's method to calculate the d and z₀ around the tower by using the observation data of the 325 m meteorological tower in Beijing from January 2008 to March 2012.The core purpose of this paper is to obtain the displacement height d and surface roughness length z₀ around the tower,which can then be applied to the atmospheric numerical model,and be used to minimize the error caused by the inaccuracy of these two parameters.The study results show that,due to the heterogeneity of the underlying surface,both displacement height d and surface roughness length z₀ vary with the wind directions.From an average perspective,d=34.4 m and z₀=1.16 m are obtained as the representative values of the site for the years 2008-2012.By comparing the results obtained in this study with those from previous studies,it is shown that the zero-plane displacement d and aerodynamic roughness length z₀ at this site had increased before 2001,but have not since.Such a phenomenon is associated with the urbanization of the tower's surrounding areas.