Research On Aerosol Direct Radiative Forcing And Cloud Parameters Retrieval Over Eastern China

Clouds and aerosols are important components of the earth-atmosphere system,which play non-negligible roles in the earth-atmosphere radiation budget.By directly and indirectly effect,aerosols can modulate the earth's radiation budget,which may further influence climate change,atmospheric stability and regional air quality.Radiation,latent heat and forced convection are three main mechanisms of cloud radiative effect.In addition,clouds can form precipitation which can directly influence the global water cycle.Eastern China?EC?is located in the Asia monsoon region,therefore,the weather and climate,the distribution and expansion of aerosols,clouds and precipitation will inevitably be influenced by monsoon circulations.Anthropogenic aerosol loading in eastern China has rapidly increased in response to the similarly rapid industrialization and urbanization in this region over the past decades,which has caused serious environmental and climatic problems.Therefore,investigating the temporal-spatial distribution characteristics and the climatic effects of clouds and aerosols are of great scientific significance to us to fully understand the climate characteristics of eastern China,which may further help to improve the living conditions of humans and help the government to make the right policy.Based on multi-year ground-based and satellite-based aerosol observations,the climatic distributions,the inter-annual and the seasonal variations of aerosols in eastern China are first analysed.Then,taking eastern China as an example application,a grid-cell method of aerosol direct radiative forcing calculation is examined using the SBDART transfer model with inputs from MODIS and AERONET observations and reanalysis data.Finally,based on the Himawari-8 satellite observations and the BSR algorithm,the cloud parameters of a weather process in eastern China are retrieved,which will lay the foundation for the accurate calculation of cloud radiative effect.The main results are as follows:?1?Based on the MODIS observations from 2001-2014,the temporal-spatial distribution characteristics of AOD are explored in eastern ChinaHigh AOD centers of east Asia are observed in EC including the north China plain?NCP?and the Yangtze-river delta?YRD?,Sichuan basin,and the pearl river delta,while low aerosol loading centers are mainly located in the northwest and the northeast region of China.Moreover,the area and the intensity of high-value centers in east Asia are larger during spring and summer than those in autumn and winter.Regional mean AOD values present obvious upward trends during winter in east Asia,and during all four seasons in EC,NCP and the YRD.In addition,AOD value in east Asia peaks in spring and minimizes in autumn.However,AOD values are the largest in summer and the lowest in winter in the other areas.?2?Using the ground-based aerosol observations,the temporal-spatial distribution characteristics of aerosol SSA and ASY are investigated in eastern ChinaThe aerosol SSA?ASY?values in north eastern China?NEC?are the largest in summer and the lowest in winter.In south eastern China?SEC?,however,the largest and the lowest aerosol SSA values occur in summer and in winter,respectively,and ASY value is at its maximum during summer and its minimum during winter.Besides,SSA values of urban sites are smaller than those in rural sites.Moreover,there are obvious intra-seasonal variations of SSA in summer and the regional differences are larger in summer.The seasonal variations of ASY values are smaller than SSA values,and ASY values peak from May to August.Aerosol SSA exhibits distinct inter-annual variations,however,the amplitudes are larger in summer and autumn.?3?Using aerosol observations,the simulations of ADRF are carried out,which reveals the temporal-spatial variations of grid-cell ADRF in eastern ChinaTaking a pollution episode and a clean episode as examples,the results suggest that values and the ranges of high-value centers of AOD in the pollution episode are larger than those in the clean episode.The backward trajectories of the two episodes indicate that the aerosols sources are the same in the NEC and SEC in the clean episode.In contrast,the aerosols come from different areas to NEC and SEC of the pollution episode.The ADRF of the two episodes show that the distributions of ADRF are similar to those of AOD,and the intensity of ADRF is stronger in the pollution episode.The aerosol optical parameters in winter and summer in eastern China during 2006-2014 are analysed,which reveals that the values of AOD,SSA,and ASY are larger in summer than those in winter.Aerosol induce negative forcing at the TOA and the surface during both winter and summer,which may be responsible for the decrease in surface temperature and the increase in surface relative humidity.Values of ADRF vary from-40W/m₂ to-140W/m₂ at the surface,which are four times stronger than those at the TOA.Both AOD and ADRF present strong inter-annual variations;however,their amplitudes are larger in summer.Moreover,influenced by monsoon activities,spatial distributions of AOD and ADRF between strong and weak monsoon years exhibit significant differences.For most areas of eastern China,the AOD values are larger and the intensity of ADRF is stronger in winter strong monsoon years and in summer weak monsoon years.?4?Based on Himawari-8 observations and BSR algorithm,cloud parameters are retrievaledThe 1.6?m channel reflectivity is also sensitive to the change of cloud phase and the surface type.Compared to the relative azimuth angle,the change in solar zenith angle and satellite zenith angle play more important roles in the value of the reflectivity of 0.64 micron and the 1.6 micron channel.Taking the case inApril 15th 2016 as an example.The result indicates that ice clouds are mainly spread over subtropical land area,and its 0.64?m channel reflectivity is 0.2?0.4,the 1.6?m channel reflectivity is 0.1?0.2 and the brightness temperature?TB?is 220K?230K.Mixed clouds,with the largest area,the 0.64?m channel reflectivity is larger than 0.2,the 1.6?m channel reflectivity is 0.05?0.4 and the TB is within 240K?270K.Water clouds are mainly found in ocean area,and the 0.64?m channel and the 1.6?m channel reflectivity are all over 0.2,the TB is from 273K to 290K.Then the cloud parameters of ice and water clouds are retrieved and analysed.The CER of ice clouds are larger than 10?m while the CER of water cloud is below 10?m.The COD of ice clouds are above 15 and parts of them even larger than 50.However,the COD of water clouds are almost within 10?20,except for the areas where the 0.64?m channel reflectivity is larger.In terms of the CWP,the CWP of ice clouds?greater than 200g/m₂?are larger than those of water clouds?less than 100g/m₂?.