| Clouds play a crucial role in the radiative budget balance of the Earth-atmosphere system.The spatiotemporal variations in cloud cover and cloud type impact the radiative budget balance,leading to consequential effects on the climate.Interactions with longwave and shortwave radiation vary with the cloud types,making it essential to quantify the radiative role of clouds in the Earth-atmosphere system.This topic is widely concerned by academic circles.The Tibetan Plateau(hereafter referred to as TP),often referred to as the "third pole" of the Earth,profoundly affect the climate of eastern China and even the world.Therefore,the researches of the cloud and radiation characteristics of TP have been attracted more attention.To reveal the spatiotemporal variation of cloud and radiative characteristics over the Tibetan Plateau.Based on the multi-satellite datasets and other auxiliary data,we focus on the spatial response functions of pixels of microwave radiometer and radiative energy imager,a gridding algorithm is studied to facilitate the integration of data from the satellite with reanalysis datasets,and the comparison between the datasets from different platforms.Then,we develop a cloud property retrieval algorithm,and the study of the validation of radiation flux from FengYun-4A is then carried out.We fully analyze the various characteristics of cloud and radiation over the TP during summer,including the cloud cover,total radiation budget,flux by cloud type,cloud radiative forcing,internal cloud radiation forcing,etc.The results of this paper provide insight into the cloud and radiative characteristics of the Tibetan Plateau during summer and serve as a reliable observational basis for numerical models simulation and other studies.The main results and innovations achieved in this thesis are as follows:1.In this paper,based on characteristics of the Global Precipitation Measurement Microwave Imager(GMI)18.7 GHz channel,the gridded datasets of two gridding process methods,namely the direct method(Mean)and the Backus-Gilbert(BG)method,are compared with the "true" value.For three ideal pixels’ sample intervals,namely edge(6.5 km×6.0 km),sud-edge(11.5 km×6.0 km),and center(13.0 km×6.0 km),the results show that the error of the direct method is relatively large.The BG method’s gridded data has significantly smaller errors than the former.It indicates that the BG method has a great advantage in the gridding process of those overlapped and low-resolution data such as GMI observations.This paper preliminarily applies the BG method to the gridded data of CERES footprints,and the result shows that the equivalent PSF of gridded data is more similar to the designed grid area.2.The cloud optical thickness and cloud effective particle radius are retrieved over TP using observations from the Advanced Geostationary Radiation Imager(AGRI),and the results are compared with similar widely accepted results from the ModerateResolution Imaging Spectroradiometer(MODIS)to confirm the quality of algorithm product.At the same time,this paper also compares the official AGRI outgoing longwave and shortwave radiation at the Top-of-Atmosphere(TOA)products with the widely accepted results from the Clouds and Earth’s Radiant Energy System(CERES)project by considering the Point Spread Function(PSF)of CERES.The results show that shortwave radiation of AGRI has a large systematic bias over clear and overcast scenes,which limits the application of this product.However,the systematic bias of AGRI longwave radiation is smaller.The results also show that the quality of longwave radiation products at nighttime is higher than that of the daytime.The error of daytime(nighttime)longwave cloud radiative forcing that is estimated by the AGRI products is about-4.37 W/m2±12.64 W/m2(-5.06 W/m2±9.39 W/m2).In this paper,we also point out that the PSF should be considered to compare two datasets from different instruments.3.This paper analyzes the cloud and radiative characteristics of 42 cloud types over TP and eastern China during the summer by using the CERES Flux by Cloud Type(FBCT)from 2003 to 2021,based on the cloud type definition of Internation Satellite Cloud Climate Program(ISCCP).The results show that the cloud cover by cloud types over TP is relatively concentrated,while the cloud cover by cloud types over eastern China is more widely distributed.The net cloud radiative forcing per percentile of the optically thin clouds(optical thickness less than 9.4)over TP are smaller than that over eastern China,while that of most optically thick(optical thickness not less than 9.4)clouds are larger than over eastern China.For the cloud types whose regression trend passes the 95%significance test,the high cloud cover over TP increase with the increase of the ERA5 2 m surface temperature,while most low cloud cover decrease.The optical thick cloud cover decreased and the thin cloud cover increase over eastern China.The total cloud radiative feedback of those clouds over two regions is positive by combining cloud regression trends with their net cloud radiative forcing per percentile,but the value is much larger over eastern China than over TP.4.The summer cloud and radiation diurnal variation of four subareas over TP from 2000 to 2020 are analyzed based on the hourly cloud and radiation data from CERES synoptic 1deg(SYN1deg).The results show that the differences between the centersouth(CS)subarea and the west(W)subarea are the greatest.The radiation budget diurnal variations of four subareas are dominated by solar shortwave radiation,and those are also influenced by the different cloud types.The results show that high clouds are most abundant in the CS subarea and those develop between 10:00 local time(LT)and 15:00 LT and gradually dissipate afterward.There are two high-frequency areas of low cloud cover over TP at nighttime,which are over the Kunlun Mountains and the southeastern TP.The cloud cover variations over those areas are different after sunrise.Due to the difference in cloud cover over different subareas,the radiative heating rates over those subareas are different.The vertical structure of the radiative heating rate of the atmosphere is heating in the upper layer(TOA～70 hPa),weak cooling in the middle layer(70～200 hPa),and strong cooling in the low layer(200～500 hPa),in the low layer,the radiative cooling rate over CS is weakest and is strongest over W.The vertical structure of internal cloud radiative forcing over W and center-north(CN)subareas is heating,constant or weak cooling,and cooling in the upper,middle,and low layers,respectively.The structure over CS and east(ETP)subareas is heating,cooling,and heating,respectively. |
