Structural Features Of Precipitating Clouds Observed By Geostationary Satellite And Dual-frequency Radar

Precipitation is one of the most common weather events in our daily life.It plays an extremely important role in the water cycle and earth radiation budget,and is closely related to regional and global climate change.Meanwhile,precipitation is very complex,which includes various types of precipitation such as frontal precipitation,topographic precipitation,convective precipitation,cyclonic precipitation,etc.precipitation of various types has unique thermo-dynamic and microphysical processes.By understanding precipitating cloud features of different types,we can get better insight into the formation and development process of precipitation clouds,and then provide factual bisis for the preciptiation prediciton.In this thesis,using data from Global Precipitation Mission(GPM)Dual-frequency Precipitation Radar(DPR),Himawari-8 advanced Himawari image(AHI)and other platforms form 2014-2018,we firstly analyzed the differences of DPR's various level 2 precipitation products,and then focused on the characteristics of three types of precipitations,including topographic precipitation in the south slope of Himalayas,precipitations influenced by cloud life cycle in the east China,and extratropical cyclonic precipitation in the north Pacific storm track.The main conclusions of this thesis are listed as follows:1.Differences of DPR's level 2 precipitation productsBased on different scan modes and retrieval methods,GPM DPR provides users three single-frequency products KaHS,KaMS,and KuPR as well as dual-frequency product DPR MS.Using case and statistical analysis,it is shown that KaHS presents the highest storm top height,which is 0.1 km higher than that of KuPR.KaHS shows great great advantages in observing weak precipitations(<0.5 mm/h),while it underestimates intense preciptiations(>10 mm/h).KuPR inherits the good perfomance of Tropical Rainfal Measurement Mission(TRMM)preciptaiton radar(PR)on intense precipitations,but is restricted in observing weak precipitations.KaMS omits large amount of weak precipitations as well as underestimates intense precipitations,hense it is not suitable to be used independently.The precipitation retrieval algorithm of DPR MS is highly self-governed and performs well in retrieving both weak and intense precipitations,while DPR_MS's storm top height mainly relys on KuPR's echo top height.In addition,DPR_MS can also provide users dual-frequency Droplet Size Distribution(DSD)information.2.Topographic preciptiations over the southern HimalayasIn this section,precipitating systems over the southern Himalayas were firstly identified using GPM DPR data,and then categorized into five classes according to surface flow from the ERA-interim data.The surface flow is introduced to indicate the precipitation triggers,which is validated in this study.The five classes are upslope class,down slope class,easterly circumfluent class,westerly circumfluent class,and light flow class,respectively.The precipitating systems of the upslope class were triggered by the heat pump effect.They occurred mostly in the afternoon at moderate altitude of the slopes.The preciptiting systems of the downslope class were forced by the valley wind during the night.They were distributed uniformly over the slopes and foothills,and had low near-surface droplet concentrations,small near-surface effective droplet radiuses,weak near-surface rain rates,and low rain top altitudes.The precipiting systems of two circumfluent classes were both triggered by the mechanical insulation of the Himalayas.The occurred mostly at the boundary of foothills and slopes in the morning or evening.As a result that the surface flow of easterly circumfluent class originated form the Bay of Bengal with abundant moisture,preciptitaion was therefore often accompanied by intense near-surface rain rates and high storm top altitudes.The precipitating systems of the light flow class were thought to be forced by the surface sensible heating,either intense or depressed.Influnced by the precipitating mechanism,they were companied by high storm top altitudes but weak near-surface rain rate.3.Life-cycle effect of cloud on the precipitations in the east ChinaWe identified precipitating systems from May to August 2016 using data from the GPM DPR instrument.Then,using this set of cases,Himawari-810.4-mmbrightness temperature data from before and after each precipitation event were used to identify three life stages of clouds:a developing stage,a mature stage,and a dissipating stage.Using statistical analysis and two case studies,we show that the precipitating systems at different life stages of the clouds have different systematic properties,including the area of precipitation,the convective ratio,the rain-top height,and the brightness temperature.The developing systems had the largest convective ratio,whereas the dissipating systems had the largest area of precipitation.The life stage of the cloud also influenced the vertical structure of the precipitation.The microphysical processes within each stage were unique,leading to various properties of the droplets in precipitation.The developing systems had large,but sparse,droplets;the mature systems had large and dense droplets;and the dissipating systems had small and sparse droplets.Our results suggest that the different properties of precipitating systems in each life cycle stage of clouds are linked to the cloud water content and the upward motion of air.4.Extratropical cyclonic precipitations in the northern Pacific storm trackUsing data from GPM DPR and ERA-interim,we carry out a statistical study on the precipitation features of extratropical cyclones in the northern Pacific storm track region.Extratropical cyclones were classified into 4 categories including developing,mature,dissipating,and short-term ones due to their life stages.Our results show that extratropical cyclones of all categories had a "comma" rainband and precipitations most frequently occurred northeast of the cyclonic center.The extratropical cyclones promote precipitation to the east of their centers,but suppress precipitation to the west.Precipitation to the east of the extratropical cyclones had larger and more condensed droplets,a stronger intensity,and a higher rain-top than the local seasonal average,while the opposite characteristics were seen to the west.Our results suggest that the different types of vertical air motion and moisture content in these two regions induced by the frontal structure of extratropical cyclones play important roles in the different impact of extratropical cyclones.Furthermore,extratropical cyclones of variant life stage had different degrees of impact on precipitations:the highest in developing stage,followed by mature stage,and the weakest in dissipating stage.