| Cloud optical thickness(?c)and particle effective radius(Re)are two key parameters of cloud optics/Microphysics,which are important to maintain the Earth Radiation Balance,study the mechanism of heavy precipitation and improve the global climate model.At present,the methods of detecting microphysics mainly include raindrop spectrum,aircraft observation,radar and satellite.Satellites are becoming more and more important tools because of their advantages of wide observation range,continuous whole range and uniform data.The temporal resolution of the old generation of geostationary satellites is high,but the spatial resolution is limited.The new generation of geostationary satellites launched in recent years has greatly improved the space-time resolution of observations.Based on the AHI multispectral data from a new generation geostationary satellite Himawari-8,a method for simultaneous retrieval of cloud optical thickness and effective radius of cloud-top particles is developed.A product with a spatial resolution of 2 km and a temporal resolution of 30 minutes was obtained.In order to verify the accuracy of the retrieval results,this paper evaluates the retrieval products with MODIS cloud products and aircraft observation data,and analyzes the possible sources of the deviation.Finally,a case of weather protection is analyzed by using the retrieval product.The cloud optical thickness and effective radius are evaluated by using MODIS C6 cloud products and aircraft data,and the results are in good agreement.Compared with MODIS,the ? c retrieval result of ocean is better than that of land,and the Re retrieval result of water cloud is better than that of ice cloud.The correlation coefficient of Re is 0.90 compared with that of aircraft observation.Comparing with MODIS,the source of the deviation is analyzed,and it is found that the Re retrieval deviation is related to cloud optical thickness.For thin cloud(especially cirrus cloud),the retrieval deviation is large,and the retrieval precision is improved after removing thin cirrus cloud.This is mainly because the radiation below the thin cloud penetrates the cloud more easily,thus interfering with the radiation observed by the satellite.Moreover,for thin clouds,the retrie'val of effective radius is no longer independent of the retrieval of optical thickness,and sometimes the retrieval solution is not unique.The ?c retrieval deviation is influenced by MODIS and AHI zenith angle(except for the ice cloud).When the zenith angle of satellite is more than 40,the number of pixels with an absolute value of ? c deviation greater than 20 increases.This is mainly due to the inhomogeneity of cloud in the three-dimensional structure,especially in the vertical structure.Different views of AHI and MODIS will result in different retrieval results.In addition,the channel wavelength,the retrieval algorithm and the space-time matching method are also the possible factors of the retrieval deviation.Finally,the retrieval product is applied to the case analysis of Tianjin National Games opening ceremony on August 27,2017.The movement of cloud from west to east slightly to north can be clearly seen through the time evolution of the cloud particle effective radius and cloud optical thickness at half-hour intervals.The optical thickness of these clouds is thicker and the cloud top particle effective radius is larger.The T-Re diagram of the two regions of the seeding was analyzed,and it was found that after the seeding,compared with before the seeding.(2)It was found that the maximum cloud-top height decreased and the minimum cloud-top height increased in region 1.The change of the minimum cloud-top height in region 2 was not obvious and the maximum cloud-top height increased.(2)The number of pixels of small particles with effective radius less than 30?m was increased after seeding in both regions.In particular,in region 2,the effective radius of most of pixels is concentrated near 10 ?m after catalysis.(3)with the development of seeding,the slope of the curve in both regions shows a decreasing trend and gradually inclines towards Re. |
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