Abstract:The soil moisture over the Tibetan Plateau(TP),collectively affected by the snow cover and permafrost,has a long memory of wet and dry of land surface processes.Therefore,the soil moisture over TP,as an important factor of climate change,could be used to forecast the precipitation pattern in East China.However,because of rare observation stations over TP,the soil moisture observation in long time series is very deficient over TP.It leads to most of recent studies were based on reanalysis data,modeling data and satellite remote sensing data(named substitute data).Moreover,their findings were uncertain and different from the others.Therefore,in this study,studies about the applicability of various kinds of substitute data are summarized firstly,then characteristic of the soil moisture over TP as well as its climate effect are discussed.1) Comparison shows that current substitute data of soil moisture has significant over -or under- valuation over TP.Different conclusion could be drew according to various evaluation indicators and interpolation methods.Comparatively speaking,soil moisture products of SSM/I and FY 3B are in good correlation with observations.2) Soil moisture over TP has significant variations in multi-time timescale and remarkable spatial inhomogeneity in decadal trend pattern and interannual characteristic.There is significant ascending trend in spring soil moisture over TP based on SSM/I,in agreement with remarkable warming over TP.Two large interannual variation centers exit in east and west TP,whose related latent heat flux and sensible heating flux could motivate teleconnection wave train to affect precipitation anomaly in Yangtze River.3) Previous studies is different with each other about the effect of soil moisture over TP on precipitation over East China.One of the possible reason is that their substitute data is various with different applicability.Another reason may be the spatial inhomogeneity ignored in modeling design.Related issues need further research.

Abstract:Using the NCEP/NCAR monthly mean reanalysis data for the period of 1979—2014,CMAP(CPC Merged Analysis of Precipitation) precipitation data,in situ observational data at 160 stations in China,SST(Sea Surface Temperature) data provided by British Hadley Centre as well as CRU high-resolution surface temperature data by the University of East Anglia,this paper has investigated the migration of atmospheric mass over regions between Asia and North Pacific in boreal summer and its associations with climate anomalies by employing some statistical methods.
An index based on surface air pressure anomaly is defined to describe the Migration of Atmospheric Mass over regions between Lands and Oceans(MAMLO) on interannual time-scale.It is found that an anti-phase variation of anomalous atmospheric mass exists between mid-high latitudes in Asia and mid-low latitudes in North Pacific.This anti-phase relation can also be referred to Asia-North Pacific teleconnection pattern(ANPT).The summer MAMLO index varies with a dominant period of three years,a slowly decreasing trend,and distinct interdecadal variations in the study period.The ANPT is formed due to three factors.Firstly,the atmospheric mass fluxes anomalously diverge in lower and converge in upper troposphere in Siberia,and in North Pacific the opposite situations are observed,forming the anomalous vertical circulation characterized by anomalous downward motion in Asia and upward motion in Pacific,which links surface pressure variations along with horizontal circulation changes between Asia and Pacific.Secondly,MAMLO is mainly dominated by the contrast of anomalous heating between lands and oceans.Water vapor content is higher over the subtropical Pacific than that over eastern Asia,facilitating the atmosphere to absorb surface long wave radiation and solar short wave radiation over oceans more than over Asia continent.The striking contrast of the anomalous atmospheric diabatic heating between Asia and North Pacific is in favor of driving atmospheric mass to exchange between them.Thirdly,the energy dispersion of quasi-stationary Rossby wave also plays an important role in the anomalous loss and accumulation of atmospheric mass.
MAMLO is closely related to the summer climate anomalies in Eurasia and Pacific.When the MAMLO index is positive,the precipitation decreases significantly in Siberia,the southern area of Europe and the east coast of China,as opposed to the increase over northern China,the Hawaiian Islands and the south of Gulf of Alaska.At the same time,the temperature increases obviously over the West Siberian Plain and the central and eastern Pacific,along with the anomalous decrease in much of Eurasia,northern China and Northwest Pacific.Further researches by use of observational data over Chinese 160 stations conclusively indicate that correlations of MAMLO with variations of anomalous precipitation and temperature are particularly significant in China.When the MAMLO index is positive(negative),precipitation increases(decreases) and surface temperature decreases(increases) prominently over northern China.Instead,there is a decrease(an increase) in precipitation and an increase(a decrease) in surface temperature over southern China.
All the results above are helpful for us to better understand the mechanisms behind circulation changes and the causes of climate anomalies in Eurasia and Pacific during boreal summer and to provide useful clues to prediction of the summer climate anomalies.

Abstract:Based on a high resolution numerical simulation of the flash-flooding rainstorm process in Guangxi in June 2008,the evolution of the inner structure and dynamical features of the mesoscale vortex,which caused the heavy rainfall,have been investigated in terms of movement and continued development process.
By means of synoptic analysis,it is found that the mesoscale vortex was the main system leading to the rainstorm in Guangxi.The core of the rain band at different times mainly lied in the eastern part of the vortex within the range of 400 km,and the track and intensity of the rain band coincided with those of the vortex.The structure of the mesoscale vortex was especially distinct on 700 hPa,with the horizontal size ranging from 600 to 900 km.In addition,its move path could be divided into two stages:the southward moving stage and the eastward shifting stage.
Using the high-resolution model output data to analyze the inner subtle dynamic and thermodynamic structures of the mesoscale vortex,it is shown that strong ascending motion existed in the vortex center,which was quite beneficial to the formation of organized deep and moist convection systems.When the vortex reached its intensity peak,the vertical size of these convection systems could run through the entire troposphere,with the rotational motion and potential motion reaching the same magnitude.During the vortex's development process,the release of latent heat showed that there was an obvious warm core at the middle and high levels of the vortex center,and the stronger the vortex grew,the more distinct it became.Meanwhile,upward vertical transportation of warm wet flow,which was caused by strong convergence at low levels,signified that the vortex center attained high humidity.Influenced by the environment in the vortex's movement and development process,the redistribution of momentum,heat and moisture in the vortex center area took place as follows:(1)As the vortex moved southward along the Yunnan-GuizhouPlateau,its central pressure decreased and a uniform horizontal circulation was formed,with multiple strong convective systems evolving at the vortex center and on both sides.(2)As the vortex moved southward and approached the low-level jet(LLJ),the coupling effects of positive vorticity disturbance in the vortex center and positive vorticity shear on the left of the LLJ caused the vorticity to strengthen greatly,thus generating the maximum of vorticity and upward motion near the ground layer,which caused the moist convection and rainfall to both become the strongest in the vortex's center.(3)During the vortex's eastward movement stage,the influence of the LLJ became more important.In the eastern side of the vortex,the air was warm and wet,and possessed more convective instability energy,while stronger vertical movement and convective activity also appeared.Meanwhile,in the west,the air became significantly colder and drier,with almost no vertical movement or convective activity.Analysis of the three-dimensional flow field structure of the mesoscale vortex indicates that there were typical quasi-balanced dynamical features present in the mesoscale vortex,which could be described in detail by successively occurring long-lived organized deep moist convection systems,strong super-geostrophic flow with a large ageostrophic component,as well as intensive divergence which coexisted and had the same magnitude as the strong rotation during its lifetime.

Abstract:Based on the ensemble forecasts of 1—7 day daily accumulated precipitation from the European Centre for Medium-Range Weather Forecasts(ECMWF),Japan Meteorological Agency(JMA),National Centers for Environmental Prediction(NCEP) and UK Met Office(UKMO),with the hourly merged precipitation product over China as the observed data,the forecast of daily precipitation in China by means of statistical downscaling and the reconstruction of spatial and temporal correlation of the precipitation forecast were conducted.The statistical downscaling based on different categories of the rainfall was applied to improve the precipitation forecast.The Schaake Shuffle was used to reconstruct the spatial correlation and temporal persistence of the precipitation forecast.The results show that the forecasts after the regression based on the different categories of the rainfall are more accurate than the ones after the regression.Classifying the rainfall into different categories was not considered,due to the fact that the anomaly correlation coefficient becomes larger and the root-mean-square error becomes smaller.The spatial and temporal correlations after the reconstruction are quite close to the observed ones.

Abstract:Numerous studies have shown that the structure and intensity of tropical cyclones have been restricted by themselves,as well as the interaction between the airflow and boundary layer,the thermal variations of the sea,and so on.With the numerical model widely used in the weather forecast,there has been increasingly great attention paid to the parameterization scheme of the atmospheric model.Numerous findings have shown that the various physical parameterization processes have obvious effects on simulating tropical cyclones.The impacts of the cloud-radiative forcing(CRF) on tropical cyclones is a complicated process,depending on the cloud microphysics parameterization model.Different aerosol distributions hold different CRF.Some studies have shown that solar radiation affects the structure and tracks of tropical cyclones,in which case the CRF will remain a key overhang.Therefore,this work carries out the study of the sensitivity of cloud radiation on the effects of tropical cyclones,and discusses the possible influences of cloud radiation on the development and structure of typhoons.
In order to highlight the influences of CRF on TC,as well as to avoid the disturbance of uncertainty random circumstance factors such as underlying surface and the interaction between TC and environment,two sets of sensitivity simulations were conducted using the high-resolution Weather Research and Forecasting(WRF) model(WRF-ARW)(version 3.3.1).The simulations were solved using bidirectional double nesting,in which every domain had a 241×241 grid point,the horizontal resolution ratio was 9 km and 3 km,and the vertical direction was divided into 28 layers.The cloud microphysical scheme adopted WSM6.The initial conditions originate from an ideal cyclonic vortex which was symmetric.The initial wind speed was 8 ms^-1,and the maximum wind radius was 125 km.The tangential wind speed of the initial vortex decreased with height.For the sake of simplicity,this paper uses the f plane.The latitude of the center was 15°N.The underlying surface was a uniform ocean,the sea surface temperature was set to 29℃,and the influence of large-scale atmosphere was neglected.According to the setting wind field,the quality field and thermodynamics field elements were obtained by solving the nonlinear equilibrium equation.The cloud-radiative forcing(CRF) in the WRF was controlled by the namelist parameter “iCloud”.When iCloud=1,the CRF effect was considered in the simulation.Conversely,when iCloud=0,the CRF effects were excluded.Through the comparison of the above two simulations,we can obtain the influence of the CRF effect on the development of TC.
The results show that,mainly by changing the tropical cyclone radiation distribution,the CRF had an effect on the convective activity,as well as the tropical cyclone structure and size.In the development process,the strong cooling along the anvil top and weak warming in the cloudy regions under the forcing of cloud and radiation could reduce the static stability at the middle-upper levels,while the change of the middle-lower levels was relatively less significant.The convective activity of the tropical cyclone was enhanced by the CRF.The tropical cyclone developed faster and had a larger size in the case with the CRF than without it.In view of the considerable impacts of the CRF on the size and strength of tropical cyclone,it is necessary to pay more attention to the CRF in the numerical prediction of tropical cyclones.

Abstract:This paper has carried out the statistical and diagnostic analyses of development of cyclones in east sea area of China in spring from 2008 to 2014.Results show that the cyclones in east sea area of China in spring are shallow low-pressure systems.The vertical stretching height of the cyclones is below 600 hPa and the horizontal scale is less than 1 500 km.The strong weather with strong winds,big waves and heavy precipitation is mainly located in the southeast of the cyclone.The high wind jet region of cyclonic circulation of each level,which forms in the southeast of the cyclone,is called the cyclone jet.From the top to the lower,the jet axis of cyclone rotates counterclockwise in the vertical direction,which forms a funnel shape of cyclone with big top and small bottom.Cyclonic shear on the left side of cyclone jet is conducive to the maintenance of intensity of cyclone center,and the cyclonic shear on the left side of upper cyclone jets is correspond to the velocity convergence zone in the front of lower cyclone jets,which is beneficial for the cyclonic dynamic pumping and the strong vertical ascending motion in the southeast of the cyclone.The cyclone jets at different levels are configured to support the asymmetric structure of the cyclone and lead to the asymmetric distribution of cyclonic elements.Cyclone jet transports vertical helicity,horizontal helicity and sufficient water vapor into the cyclone and they are strongly lifted in the southeast of the cyclone,which enhances the release of condensation latent heat and prompts the development of cyclone and the strong weather area occurred in the southeast of the cyclone from thermal and dynamic aspects.The sea surface frontal temperature distribution in spring is beneficial to the enhancement of the cyclone jet,which reinforces the baroclinicity of the cyclone through non-adiabatic cooling in the northwest and non-adiabatic heating in the southeast of the cyclone.Environmenal westerly jet stream at high altitude is located in the right side of the cyclone,forming the whole deviation wind convergence,which effectively enhances the low level cyclone jet.Meanwhile,the momentum transports downward from the upper level and locates in the west side of the cyclone,leading to the development of weak current(i.e.the sinking branch of spiral structure of the cyclone) in the northwest of the cyclone,and then enhancing the spiral circulation of the whole cyclone,which makes the cyclone jet also begin to strengthen from the lower level.

Abstract:Nanjing is one of the most important industrial cities in China,and its local land cover and environment have been modified over the past several decades.In this paper,with three scenarios(URBA,NURBA,URBNA) integrated by the WRF model,we investigate the effects of aerosol and urban expansion to boundary layer meteorology over Nanjing,China,with the aim of comparing the effects of aerosol and urban expansion during a heat wave,and discuss the feedback between them.Through the observed data validating the variable 2 m temperature and 2 m relative humidity from the model,the WRF model is capable of capturing the features of urban meteorological variables in the Nanjing region during a hot weather episode.Based on the Aerosol-Aware Thompson microphysical scheme and two types of aerosol(ice-friendly aerosol N_IFA and water-friendly aerosol N_WFA),the cooling effect caused by aerosol is apparent and dominate at daytime.The radiative forcing leads to a decrease of -0.11 ℃ in 2 m temperature and -12 W/m² in net radiation at daytime,both of which peak at 0800 LST and 1800 LST.The surface air temperature of Nanjing increases by 1.7 ℃ due to urban expansion.This in turn leads to an increase in wind speed of around 0.8 m/s,for which the increase due to heat island effect is greater than the decreased due to surface roughness.As for the 2 m temperature,the urbanization-warming effect is stronger than the aerosol-cooling effect under a hot weather episode.The latent heat flux decreases and sensible heat flux increases in the daytime,resulting in a warmer atmospheric temperature(below 1.6 km) in the daytime than in the nighttime.Urban-induced local updraft brings the aerosol to a greater height,especially in the daytime.As a result,a positive feedback may exist between the aerosol and the stability of the urban boundary layer.It is important to note that the warming effect of black carbon is not considered in this paper.

Abstract:China is located in an area of complex climate in Asia.Its rainy season mainly appears in summer.And the frequent floods caused by extreme rainfalls have brought serious impacts and heavy losses to the economic development and people’s lives.So it is necessary to know the temporal and spatial distribution of the extreme rainfalls in Eastern China.At present,there are many probability models on extreme value theory research.Among these models,the Generalized Pareto Distribution(GPD) is often used by researchers to study extreme rainfalls.In this paper,based on the daily rainfall data from 429 stations with no missing over Eastern China from May to September during 1961 and 2012,GPD is used to study the spatial distribution of extreme rainfall statistical characteristics in these 52 years,as well as in El Niño developing and decaying years.The causes of the extreme rainfalls are also discussed.The results show that:(1)The thresholds decrease roughly from southeast to northwest.And the largest value of the thresholds is in southern Guangdong,which means there are more rainfalls in summer there than other places.Besides,southern Guangdong is close to the Pearl River,which leads to higher probabilities of flood disasters in summer.The trends of thresholds are basically positive over Eastern China.(2)The largest values of scale parameter are in South China,which means there are higher probabilities of maximum rainfalls.The trends of scale parameter are positive in most places to the south of the Yellow River.And the probabilities of maximum rainfalls are increasing in these places.Besides,thresholds and the trends of scale parameter of the stations located along the Yangtze River are large.So we should pay great attention to the flood disasters occurring in these places.(3)In the summer of El Niño developing years,there is cyclone circulation anomaly in western Pacific.And the Southeast China is under the influence of north wind anomaly on the west of the cyclone,which leads to less rainfalls in most places over Eastern China.The values of scale parameter are smaller in most places in the north area than usual,especially in Neimenggu.In these places,the probabilities of maximum rainfalls are limited.There are more probabilities of record-breaking maximum rainfalls only in southeastern Fujian and west central Heilongjiang.(4)In El Niño decaying years,there is anticyclone circulation anomaly in western Pacific.The Southeast China is under the influence of south wind anomaly on the west of the anticyclone.And the area of west Pacific subtropical high is large,which leads to more rainfalls in most places over Eastern China.The values of scale parameter are larger in most places over Eastern China than usual,except in northwestern Heilongjiang,west-central Neimenggu,southern Hebei,northern Jiangsu,southern Yunnan and so on.The probability of severe flooding disasters is large in east central Guangdong and at the junction of Anhui,Hubei,and Jiangxi.

Abstract:As one of the means for bridging the gap between low resolution data obtained from weather models and those required in the basin scale,statistical downscaling has become an important field of study,due to its relative simplicity and practicability,along with its many flexible methods.More accurate forecast results can be obtained by the statistical downscaling method of establishing the function between the low-resolution raw model output and high-resolution prediction variables.With the partial correlation-based method,forcing factors are sought for the precipitation over the middle and lower reaches of the Yangtze River Basin in June and July,and a statistical downscaling model is established for the precipitation.The major forcing factors for the precipitation over the region include the 850 hPa geopotential height over the western Pacific(W_PH8) and the sea surface temperature in the Kuroshio extension(K_SST).The W_PH8 may indicate the influence of the western Pacific subtropical high on the rainfall,while the K_SST may reflect the variability of the Kuroshio extension.A regression statistical downscaling model based on W_PH8 and K_SST shows good performance in fitting the variability of early summer rainfall in the middle and lower reaches of the Yangtze River Basin,and the model also shows strong robustness in the independent validation.In the future the statistical downscaling model can be used for downscaling output from seasonal forecast numerical,and improving the middle and lower reaches of the Yangtze River Basin early summer rainfall prediction.

Abstract:Afro-Asian subtropical westerly jet stream in the Eastern Hemisphere is formed from West Africa through the Arabian Peninsula,South Asia and East Asia to the North Pacific.Currently,most studies on the Afro-Asian subtropical westerly jet streams have focused on the East Asian westerly jet stream,which lies in the eastern part of Eurasia,but less attention has been paid to the Middle East westerly jet stream(MEJ),which situates in the western part of Eurasia.The MEJ is an important circulation system that affects the climate of Northern Hemisphere’s mid-latitude regions and is closely related to the climate of China.Here,by means of National Centers for Environmental Prediction/National Center for Atmospheric Research monthly reanalysis data,and sunspot data provided by National Oceanic and Atmospheric Administration,the inter-annual variation characteristics of wintertime MEJ and solar cycle modulation of the relationship between North Atlantic Oscillation(NAO) and MEJ axis south-north shift are studied.The results show that wintertime MEJ axis north-south shift has obvious inter-annual variation feature.The spatial variation of MEJ manifests axis shift east-west out-phase(MEJAO) pattern and axis shift in-phase(MEJAI) pattern.Furthermore,solar activity has obvious 11-year period.In the high solar activity cases,the location of NAO’s spatial structure is more close to the continent that is situated near the east of North Atlantic,and there are opposite sea level pressure(SLP) anomalies at the north of Europe and Mediterranean Sea.Through Ekman pumping,these anomalous SLP can bring secondary circulation and Mediterranean convergence(MC) anomaly at the high level of troposphere.By Rossby wave train excited by anomalous MC,there are geopotential height anomalies in Iran Plateau at the high level of troposphere,which can lead to westerly opposite changes between south and north sides of eastern MEJ axis.In addition,there are geopotential height anomalies in southern Europe at the high level of troposphere,which can bring to westerly anomalies at north side of western MEJ axis.The distribution of westerly anomalies between south and north sides of the eastern MEJ axis is opposite to that of western MEJ axis,which is manifested MEJAO pattern.In the low solar activity cases,the spatial structure of NAO is located at the Atlantic,which is difficult to form MC anomaly.The relationship between NAO and MEJAO pattern is not obvious.Therefore,there is solar cycle modulation of the relationship between NAO and MEJ axis shift.

Abstract:In this study,based on the output of historical ocean temperature analysis program conducted by Japan Meteorological Agency and NCEP/NCAR reanalysis project,a relationship between tropical Pacific Subsurface Ocean Temperature Anomalies(SOTA) and East Asian Summer Monsoon(EASM) is proposed and investigated.The results indicated that there is a strong correlation between SOTA during winter and EASM.Among the three leading modes in the tropical Pacific subsurface temperature,the first mode has a dipole pattern,with warming in the eastern Pacific and cooling in the western Pacific,which is closely related to traditional El Niño,the western Pacific subtropical high(WPSH) is enhanced.An anomalous anticyclone with its southwesterly winds dominating over the western North Pacific,carrying abundant moisture to Yangtze River and Huaihe River Basin as well.Subsequently,it favors a positive precipitation anomaly along with a poor EASM,which in comparison with traditional El Niño,demonstrating that the impact of traditional El Niño is more significant than the EASM.The persistence of SOTA during winter could lead to form sustainable effects,affecting the general circulations over East Asian Pacific.When a continuous negative(positive) SOTA in the warm pool moves eastwards,the Sea Surface Temperature(SST) of East Pacific becomes cold(warm),while the strengthening of overturning due to the temperature of cold(warm) sea causes anomalies in the SST.Consequently,a meridional wave train appears over East Asia in the summer.Under the impact of an anomalous Western North Pacific anticyclone,it highly affects the atmospheric circulation and climate as well.

Abstract:Soil moisture is a significant variable in environmental studies(e.g.,numerical weather prediction,modeling climate change,runoff prediction,drought monitoring,etc.).It is the most important terrestrial water resource for ecosystems.In addition,the soil moisture correlates terrestrial water and energy cycles,thus,this is an important predictor for hydro meteorological processes(e.g.,precipitation,drought,and heat waves).However,currently,soil moisture is not defined as a conventional component for meteorological monitoring.Therefore,several studies were carried out which often didn't contain the soil moisture observations over the globe.In recent years,the soil moisture retrieval using satellite remote sensing technology has been widely developed.Microwave remote sensing of soil moisture has received great attentions and has shown appropriate prospects due to a number of unique features(e.g.,its atmospheric transparency and sensitivity to surface soil moisture).The Fengyun-3B(FY-3B) satellite,which is managed by China Meteorological Administration(CMA),and FY-3B is the second satellite in the third Fengyun series,carrying a multi-frequency passive microwave radiometer on-board,the Microwave Radiation Imager(MWRI).Based on the brightness temperature observations of MWRI,we attempted to retrieve the land surface soil moisture for the period of July 2011 to July 2014 over China.This was done using a radiative transfer model as well as further estimations of the soil moisture's systematic errors.Next,the soil moisture retrievals are compared with in-situ soil moisture observations obtained from the CMA's agrometeorological monitoring network,in addition to the reanalyzed soil moisture data derived from ERA-Interim and National Centers for Environmental Prediction(NCEP) databases.The spatial distribution of FY-3B soil moisture appears increasing gradually from the northwest to the northeast and southeast of China,that agrees well with the in-situ observations as well as reanalysis soil moisture.The systematic errors of FY-3B retrievals are closely correlated with the vegetation density.Where it is densely become vegetated,the systematic errors are largest(e.g.,over the southwest of China),while the systematic errors are smaller where it is drier.In terms of the seasonal variations,FY-3B soil moisture agrees well with the in-situ agrometeorological observations.In most parts of the China territory,these two datasets confirm a positive correlation;it demonstrates that the FY-3B soil moisture captures the properties of temporal variations in China,generally representing that the soil moisture is relatively high in winter,while there is a decline in spring and summer seasons.However,soil moisture declining in Spring and Summer is not surprising the scholars due to the terrestrial water balance.In warm seasons,there are more precipitations than in cold seasons;however,evapo transpiration is largely increased in warm seasons due to the increasing the atmospheric demand of water vapor.Therefore,in warm seasons,water stored in soil becomes even less than that of in cold seasons.This agreement with in-situ observations demonstrates that the obtained FY-3B soil moisture is quite plausible in terms of temporal variations.However,FY-3B soil moisture shows a strong but negative correlation with ERA-Interim and NCEP reanalyzed soil moisture where soil is relatively wet,reaching-0.8～-0.5 in south of China as well as some parts of northeast of China,where the reanalyzed data are negatively correlated with in-situ observations as well.This negative correlation is mainly attributed to the differences in seasonal variations where the climate is relatively wet;in such regions,the reanalyzed soil moisture data shows a relatively dry winter and wet summer,in contract with that of the in-situ observations.Eventually,it can be concluded that the reanalyzed soil moisture data derived from ERA and the NCEP contain considerable uncertainties in wet climate regions;consequently,those data should be used with great caution.In terms of the temporal variations,the achieved FY-3B soil moisture observations are prior to the reanalyzed soil moisture data.

Abstract:Based on Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations(CALIPSO)Lidar level 2 aerosol data derived from the period of 2007—2014,in this study,the vertical distribution characteristics of aerosols observed in a haze event over North China and during December 2013 are analyzed.The results revealed that the aerosol extinction coefficients(σ) exponentially declinedwith altitudes.The annual mean of aerosol scale height is 2.48 km.Under 1 km,there isa layer of high σ value with the annual mean of 0.333 km^-1,representing maximum annual mean value in Winter and minimum one in Spring.The annual mean Particle Depolarization Ratio(PDR) shows an increase with the altitude,varying from 0.18 to 0.25.It is noteworthy that PDR ration is large in Spring,while it is small in Winter.The annual mean Color Ratio(CR) ranges from 0.7 to 0.8,gradually increasing with the altitude.In addition,CR shows declining the vertical distribution in Spring,while the trend inclines in other seasons.The polluted dust is the major aerosol type in the lower atmosphere.In Spring,the major aerosol type is dust,while the polluted dust is dominant in Summer and Autumn.In winter season,the major aerosol type is dust in middle and upper atmosphere,while the polluted dust is in lower layer.During a haze period,a homogeneous mixing layer with high σ exists below1 km.It shows that its value is three times of σ in a haze day in comparison with a clean day.Accordingly,the values of PDR and CR for the haze day are lower than those values in the clean day.Under 2 km,most of PDRs are below 0.2,and CRs are between 0.3 and 0.5.The polluted dust,which is the mixture of the remote transported dust and the local smoke particle,is the major aerosol type during a haze event.

Abstract:In this study,the time sequential images of the FY-2E VISSR(Visible and Infrared Spin Scan Radiometer) IR(Infrared) and WV(Water Vapor) bands are used to recognize and short-time forecast deep convective clouds.In many researches regarding the distinguishing of deep convective clouds from cirrus clouds,the BT (Brightness Temperature) threshold technique is a frequently applied method,of which the defect lies in its variance with time and space,rendering it difficult to find a proper threshold to all weather conditions.The fact that water vapor has strong absorption in the location of the WV band along with the vertical distribution of water vapor in the atmosphere makes it difficult for satellites to receive the radiation emitted at the WV band by clouds under the height of around 400 hPa and at ground,while the satellite detected energy of the IR band mainly originates from the middle-low level of atmosphere.With the aid of disparity in the radiation source,the increase in optical depth of high-level clouds leads to a gradual change in the distribution pattern of pixels of satellite images in IR-WV spectral space,which is invulnerable to time and space,in contrast to the BT threshold technique.In the present study,pixels are identified as deep convective clouds if the fitted slope of their IR and WV BT is greater than a given threshold.The backward trajectory method is used to predict the location and shape of the detected cloud in future hours.The motion vector field of the target area is retrieved using the cross-correlation method from two neighbouring images,with a time resolution of 30 minutes.The detection and forecast methods are applied to an MCC(Mesoscale Convective Complex) which occurred in southeastern China,and the evolution of the MCC during its entire lifecycle is obtained by the analysis of its cloud top TBB(Temperature of Black Body) distribution.The results show that the detection algorithm in this article,compared to other methods using IR data only,functions more effectively in discriminating thin cirrus from intense convective clouds,as well as in detecting convective clouds with lower height.The forecast approach performs well in a short time range,and the results are more accurate for clouds with large spatial dimensions than small ones.