Abstract:This paper reviews recent progresses in the study on intraseasonal variability of Tibetan Plateau snow cover (TPSC) and its influence.TPSC is unstable and frequently in short duration.Such unique characteristics may lead to fast variation in TPSC within a seasonal period.Surface air temperature (SAT) and precipitation are factors governing TPSC variation on the intraseasonal time scale.The direct relationships of TPSC with SAT and precipitation are the result of intraseasonal variation in regional atmospheric circulation.The intraseasonal variation of TPSC is also related to the large-scale atmospheric circulation.The Madden-Julian Oscillation,the Arctic Oscillation and the North Atlantic Oscillation can explain some of the intraseasonal variability of TPSC.The atmospheric response to intraseasonal variability of TPSC is rapidly through snow-albedo effect.The intraseasonal variability of TPSC influences regional and downstream atmospheres,which leads to changes in East Asian trough and westerly jet.Such variations of atmosphere result from anomalous thermal advection from the Tibetan Plateau forced by TPSC.Due to the significant influence of intraseasonal variability of TPSC,better TPSC initialization and forecast can improve subseasonal forecast.

Abstract:Arctic sea ice continues to shrinking with the global warming,creating a significant chance to shipping on the Arctic routes.However,some issues still hinder the opening of Arctic shipping routes.Especially,the navigation safety is threatened by the uncertainty of sea ice prediction due to the complex physical mechanism of sea ice change.In recent years,deep learning algorithms,having excellence in tackling nonlinear fitting problems,have shown increased evidence of potential to address the problem of sea ice prediction.This paper provides a critical review of existing deep learning methods developed for sea ice prediction.First,the deficiency of numerical model in sea ice prediction was analyzed,leading out the advantage of deep learning methods.Second,the limitations of adopting deep learning methods only were pointed out in light of the characteristics of sea ice.Finally,the possible paths to adopting specialized knowledge of meteorology and oceanography into deep learning methods so as to provide a better prediction model were discussed.

Abstract:In so far,the post-seasonal best track datasets given by each regional center are used as the true values of tropical cyclone forecast performance verification and analysis.Operationally,the verification regards real-time positioning as the true values as a result of the best track datasets published after one year,which leads to an obvious inevitable error.Consequently,different organizations give out distinct forecast performance,which causes confusions.In order to analyze the bias in forecast performance verifications by using the real-time/initial positioning and the best track datasets as the "true values" respectively and assess the possible effect of positioning error on forecast performance,this paper firstly investigates the bias between the best track datasets and the real-time/initial positioning (i.e.the positioning error) and its distribution characteristics,then analyzes the difference when using the real-time/initial positioning and the best track datasets as the "true values" to calculate the forecast errors respectively,and finally preliminarily assesses the sensitivity of forecast performance to positioning error based on the most basic CLIPER (Climatology and Persistence) forecast method.Results show that when the best track datasets from CMA-STI are taken as the "true values",the average positioning error is 24.3 km from 2013 to 2019,and when the datasets from RSMC-Tokyo are taken as the "true values",the error is 26.2 km.It found that the positioning error is closely related to the intensity.The positioning error in tropical storm stage is 35.7-41.1 km,while that in super typhoon stage is only 7.5-8.3 km.Within 96 h lead time,the average forecast error calculated with the best track datasets as the "true values" is slightly less than that calculated with the real-time/initial positioning as the "true values",but the stronger the intensity,the smaller the difference.The positioning error has a significant impact on the forecast performance in a short lead time.

Abstract:In this study,the environment of 796 tropical cyclones genesis (TCG) from 1979 to 2013 is assessed,via the categorization system developed by Yoshida and Ishikawa (2013),into five flow large-scale circulation patterns:monsoon shear line (SL),monsoon confluence region (CR),monsoon gyre (GY),easterly wave (EW) and preexisting tropical cyclone (PTC).The SL,CR and GY are related to the circulation pattern of monsoon trough among them.It is shown that most of the tropical cyclones are associated with circulation pattern of monsoon trough (such as SL-41%,CR-20% and GY-6%),and the TCG location and strength characteristics of TCs with each pattern is discussed.Based on the classification results,is found that the anomalies of the circulation pattern related to the monsoon trough and PTC are the main causes of the abnormal TCG frequency,and the possible physical origin thereof is given preliminarily.

Abstract:In order to study the relationship between soil moisture and summer precipitation on the Qinghai Tibet Plateau in spring,the relationship between soil moisture and summer (May to September) plateau precipitation was analyzed by using era interim soil moisture data from 1979 to 2019 and the observed precipitation data of 109 stations in the same period,which was then verified through a series of sensitivity numerical experiments.The results show that there is a significant positive correlation between surface soil moisture (0-28 cm) in late spring (May) and plateau precipitation in early summer (June).In addition,the North-South reverse mode of soil moisture corresponds to the north-south dipole mode of plateau precipitation in early summer,and there are two high correlation regions.Secondly,an index reflecting the soil moisture gradient at the end of spring is defined.The Smg_Index is the negative correlation between the time series of the first mode of precipitation in June,and this relationship has become more significant since the mid-90s.According to the numerical sensitivity test,after Smg_Index doubled,the surrounding atmosphere converged to the center of the plateau by enhancing the plateau heat source,thereby causing increase of atmospheric temperature and humidity in the Tanggula mountains in the center of the plateau,in turn resulting in an obvious increase of precipitation.However,this mechanism does not play a significant role in dry years.

Abstract:In the present paper,the spatial and temporal distribution characteristics of warm-sector rainstorm (WR) cases which have occurred in the southern part of the Yangtze River during the period of 2008-2018 are analyzed,and the underlying contributing factors are investigated using NCEP/NCAR reanalysis data and FY2E TBB data.There are a total 65 warm-sector rainstorm (WR) cases which occurred in the southern part of the Yangtze River during the period of 2008-2018,which can be divided into four types:shearline,subtropical high (SH),interaction between shearline and SH,and southwest low-level jet.These can be further subdivided into warm shearline,cold shearline,interaction between warm shearline and SH,interaction between cold shearline and SH,SH margin,SH internal and southwest low-level jet.Among these seven types,the cold shearline type has the greatest number and widest distribution,while the southwest low-level jet type has the smallest number.In addition,precipitation in the warm shearline type exhibits the characteristic of extremity.Warm-sector rainstorms in the southern part of the Yangtze River are mostly found in the inland plains,which are independent of those occurring in southern China.Among the middle level weather systems,WRs are mostly affected by the northeast cold vortex,followed by plateau systems.WRs are often accompanied by low-level jets,and have a much higher probability to occur in spring and early summer than in boreal summer.Two water vapor transport channels which affect the WR both transport water vapor to the southern part of the Yangtze River via the southwest low-level jets.With the exceptions of the SWLLJ and SH internal types,the other WRs in the southern part of the Yangtze River are characterized by obvious CAPE and K index,low CIN and LI,while LCL is in the range of 920-980 hPa,LFC 800-900 hPa,Thetase 340-360 K and H0 4,500-5,500 m.

Abstract:By using of National Centers for Environmental Prediction/Department of Energy reanalysis data,through some statistical methods,such as empirical orthogonal function analysis,composite analysis,regression analysis,we research the variation of wintertime Middle East subtropical westerly Jet stream (MEJ) core location based on the interannual time scale.The link between the interannual variations of MEJ core location and the atmospheric circulation is studied,and the critical circulation factors associated with the interannual variations of MEJ core location are found out.The east-west movement of the MEJ core is very pronounced.MEJ core extends from 17.5°E to 67.5°E,which spans 50 longitudes in the east-west direction.MEJ core's location shows apparent interannual variation features.There is closed relation between the variation of MEJ core location and East Atlantic teleconnection (EA) and Mediterranean Convergence (MC) anomaly.When EA is robust,negative 200 hPa geopotential height anomaly occurs in the middle and high latitudes of the North Atlantic,and positive anomaly exists in the subtropical North Atlantic,northern Africa,and southern Europe.The geopotential height anomaly distribution with positive in the south and negative in the north makes the 200 hPa zonal wind at the western MEJ axis week under direct dynamical effect.Furthermore,through Ekman pumping to bring secondary circulation,the anomalous geopotential height with positive EA phase produces convergence wind anomaly in the Mediterranean Sea at the high level of troposphere,which strengthens MC with a positive anomalous vorticity source in the Mediterranean.Eastward propagating Rossby wave activities along Asian-African subtropical westerly jet motivated by vorticity source are anomalous,making the zonal wind at the eastern MEJ axis strong under the interaction of current flow and wave.The above process shows the indirect effect of EA on MEJ.Under the joint influence of EA and MC anomaly,200 hPa zonal wind weakens at the west part of the MEJ axis and strengthens at the east part,which makes MEJ core eastward movement.Vice versa.Moreover,besides the EA's effect,other atmospheric circulation factors in middle and high latitudes maybe impact the MC anomaly.

Abstract:Using the observation and reanalysis data for the period of 1900-2014,this study shows that the impacts of Atlantic Zonal Mode (AZM) on the interannual variations of Australian autumn precipitation can be modulated by Interdecadal Pacific Oscillation (IPO).It is revealed that,when the IPO is in the positive phase,the AZM decreases the autumn precipitation in central Australia,whereas,when the IPO is in the negative phase,the AZM increases the autumn precipitation in central and southern Australia.The reason for this is that,during the IPO positive phase,the anomalous warming and ascending motion in the tropical Atlantic related to the AZM induce anomalous descending motion over the tropical eastern Pacific,thereby leading to anomalous upward motion around the Maritime continent.The anomalous upward motion adjusts the local Hadley circulation and results in anomalous subsidence in central Australia.This,together with the anomalous anticyclone in the lower troposphere,the southeasterly anomalies of which along the northwestern frame hinder the transport of warm and humid water vapor from the tropical Indian Ocean,results in a precipitation deficit in central Australia.In contrast,during the IPO negative phase,due to the different basic state and stronger AZM amplitude when compared to those during the IPO positive phase,the Rossby wave in the mid-high latitudes of the Southern Hemisphere caused by the AZM induces a barotropic cyclone in Australia.The anomalous cyclone not only trigger the anomalous ascending motion,but also contribute to the greater transportation of warm moisture from the tropical Indian Ocean to central and southern Australia,by means of the anomalous northwester lies along the northwestern frame,in turn leading to surplus precipitation in this region.Therefore,the IPO modulates the AZM-Australian precipitation relationship by altering the basic state and AZM amplitude.

Abstract:Research of particles from cloud to rain is a fundamental approach to study the precipitation mechanism.Based on the cloud radar and dual-polarization precipitation radar data,this paper analyzes the echo characteristics and formation of a typical convective warm cloud precipitation process in Nanjing on August 9,2020.Using various radar parameters and fuzzy logic algorithm to identify the hydrometeor types,the evolution of hydrometeors in precipitation process is analyzed.Results show that the cloud with high precipitation efficiency behaves approximately a tropical structure with strong and low echo centricity.When the radar observes large spectrum width and linear depolarization ratio,strong updraft in the upper cloud and positive-negative velocity presenting vortex convergence,it indicates that heavy precipitation is about to occur.The precipitation particles identified by the fuzzy logic algorithm are mainly raindrops,with wet and dry snow particles at the top of the cloud.With a large number of cloud and precipitation particles in different sizes and complex orientations,the collision-coalescence process,as the main precipitation mechanism,is quickly completed under the action of the rising air flow and vortex convergence.

Abstract:To learn more about the performance of GRAPES_Meso 3 km (Global/Regional Assimilation and Prediction System) model for precipitation prediction in pre-rainy season in South China under complex topographical conditions,and to provide a reference for model development and business application,we divide the 86 stations in Guangdong Province into three sub-regions:the eastern coastal area,the western coastal region and the inland region according to the complex terrain characteristics of Guangdong Province and in combination with the distance from the coastline and the terrain characteristics of the station by using the hourly precipitation data of 86 stations in Guangdong Province and the multi-source fusion precipitation data of the National Meteorological Information Center.The binary event forecast verification methods are used for quantitative evaluation of precipitation forecast effect during the pre-rainy season from May 18 to June 18,2020 in South China.The results show that the refined precipitation prediction skills of GRAPES_Meso 3 km model are greatly affected by the complex terrain of Guangdong.The scores of prediction success index (TS) and equitable thread score (ETS) of 24-hour cumulative precipitation of light rain,moderate rain and heavy rain magnitude in the eastern coastal and inland areas of Guangdong are higher than those in the western coastal areas;although the rainstorm prediction scores have the same characteristics,the rainstorm forecast scores of the three-sub regions are generally low;from the perspective of 3 h cumulative precipitation forecast score,there are obvious diurnal variation characteristics in the three sub regions of the eastern coastal region,the western coastal region and the inland region,but the performance of the eastern coastal region and the western coastal region is different from that of the inland region.The precipitation forecast score of the eastern coastal region and the western coastal region is low at night (the forecast deviation is high),relatively high during the day (the forecast deviation is low),while that of the inland region is high at night (low forecast deviation),relatively low in the daytime (high forecast deviation).The reason for the relatively low prediction score in the western coastal region is that there is a weak wind shear in Guangdong during the test period,and most of the western coastal region is just controlled by the high temperature area in the south of the shear line,but the daily average temperature in the region simulated by the model is lower than the actual situation,resulting in more empty precipitation forecasts in the western coastal region,which reduces its precipitation prediction skills.

Abstract:Land surface temperature (LST) is a key parameter in the heat balance between surface and atmosphere,and plays an important role in climate,ecology,hydrology and other related research fields.In this paper,the brightness temperature data of the FY-3D microwave radiation imager (MWRI) from November 2019 to October 2020 are selected and preprocessed,including data resampling and abnormal pixel elimination.Next,the physical model of the UMT microwave retrieval algorithm is used to retrieve the surface temperature in China,and the retrieval results are verified and analyzed using the surface temperature products of the FY-3D microwave radiation imager and the actual measured values of 166 stations at the China Ground National Exchange Station.The results show that,compared with the surface temperature products of FY-3D microwave radiation imager,the UMT retrieval results can ensure the same retrieval accuracy,while also increasing the amount of data that can be acquired.In addition,in the verification of surface temperature retrieval results,including open water pixels,the accuracy of the UMT retrieval results increases with the increase in the fraction of open water.In the interval of (0.1-0.2),the root mean square error and unbiased root mean square error of the UMT retrieval results are the minimum,at 4.239℃ and 4.233℃,respectively.Even when the fraction of open water is large,the UMT retrieval results can still reflect the time series changes of the actual measured values.Finally,the UMT retrieval results can reflect the change trend and distribution pattern of land surface temperature in China,and can better supplement the data that missing within the area of FY-3D microwave radiation imager surface temperature products.

Abstract:Kelamayi has been affected by strong wind for many years,due to its leeward slope location.At present,the Kelamayi Meteorological Bureau has developed a high-resolution numerical prediction system,which can provide reference for strong wind forecast.In order to further improve the prediction effect of the system,a gravity wave drag (GWD) scheme application test has been carried out,schemes are designed.This includes shutting down the GWD in both domains of the model,opening the GWD in the outer domain while shutting down the GWD in the nested domain,and opening the GWD in both the outer and nested domains.The results show that,for the strong wind forecast of Kelamayi,located on the leeward slope,shutting down the GWD in both domains will trigger the downslope winds much earlier than the observation,while opening the GWD in the outer domain will delay the downslope winds to some extent,and opening the GWD in both domains will further delay the downslope winds and minimize the wind speed,so that the results are closer to reality.Although the GWD scheme can effectively improve the time and magnitude of the local gale forecast in Kelamayi City,for the station located on the non-mountain terrain,opening the GWD in the nested domain will yield a certain negative effect.In addition,the statistical results show that opening the GWD in the outer domain can significantly decrease the positive bias of wind forecast and decrease the RMSE,while opening the GWD in both the outside and nested domains will add a negative bias.According to the general verification result,the minimum error and a superior prediction effect can be obtained by turning on the GWD in the outer domain.

Abstract:Local climate zone (LCZ) scheme is a new method to construct urban high resolution land use classification (HRLUC) datasets.Based on the LCZ classification system,HRLUC datasets with building classification in 63 cities of China are produced.The original data are Landsat 8 satellite images and high resolution Google Earth images from 2017 to 2019,covering 51 933 training samples (>100 m×100 m) and 15 841 validation samples.The accuracy evaluation results show that the overall quality of HRLUC datasets in 63 cities of China is good,the overall accuracy is 72%-92%,and the average accuracy is 81%;The accuracy of urban land types is 59%-82%,and the average accuracy is 72%;The accuracy of natural land cover types is 71%-100%,and the average accuracy is 89%.Compared with similar studies,the accuracy of urban land types in this study is higher.In addition,based on the original LCZ classification system,construction zone is added as a basic type of urban LCZ classifications in China.24 of the 63 cities have the construction zone accounting for more than 5%,and the underlying surface of this type is mostly located at the junction of urban and suburban areas.

Abstract:In the present study,the aerosol optical properties,including aerosol optical depth (AOD),absorption aerosol optical depth (AAOD),Ångstr m exponent (α),volume size distribution (VSD) and single scattering albedo (SSA),for 10 cities in the West Asia region are analyzed in terms of seasonal,annual and diurnal scales based on the AERONET Level2 dataset during the period of 2010-2017.The results show that the respective averages of AOD,AAOD,α and SSA are 0.245±0.094,0.030±0.006,0.889±0.247 and 0.918±0.016,with the VSD exhibiting bimodal spectra.The results reveal significantly different features throughout the various seasons and regions.In general,the higher AOD occurs in spring and summer,while the lower one occurs in autumn and winter.As a result of dust storms,both the minimum of α and peak of volume concentration for coarse particles appear in spring.However,the maximum of α is regionally different,respectively exhibiting the maximum in winter and summer at the Arabian Peninsula and Mediterranean sites.At the Arabian Peninsula sites,the higher AAOD occurs in summer and autumn,while the lower one occurs in winter and spring.For the SSA of the Arabian Peninsula sites,the higher one is found in spring and summer,while the lower one occurs in autumn and winter.At the Mediterranean sites,the higher AAOD is shown in winter and spring,while the lower one occurs in summer and autumn.The region also shows the higher SSA in summer and autumn,with the lower one occurring in winter and spring.In addition,the diurnal variation characteristics of AOD also differ in these two regions.The diurnal variation of annual mean hourly AOD at the Arabian Peninsula sites is much more fluctuant than that at the Mediterranean sites.In addition,the AOD of desert sites exhibits higher values in the morning and evening,while being lower at noon.For the annual trend,aside from a significant decreasing trend of α occurring at TEP and AAOD at ERD,no obvious variation trend is shown for the optical properties at all of the sites.