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云微物理参数的准确获取对辐射收支计算具有重要的研究意义。本研究首先基于新一代静止气象卫星葵花-8(Himawari-8)数据,结合辐射传输理论与最优化反演方法反演获得了水云和冰云的光学厚度和粒子有效半径,并将反演结果与MODIS二级云产品进行了对比,发现两者具有较好的一致性。之后,利用反演获得的云光学厚度和粒子有效半径进一步计算获得了地表和大气层顶的短波辐射强迫,并将结果与CERES三级辐射产品进行了对比,发现本研究计算得到的结果与CERES产品均具有较高的相关性,地表和大气层顶短波辐射强迫相关系数R分别高达0.97和0.98,均方根误差RMSE分别为15 Wm-2和15.6Wm-2,表明具有较高的精度。本文在以往地表短波辐射估算研究基础上,首次将非球形冰晶模型Voronoi拓展至卫星的地表以及大气层顶短波辐射强迫的估算,并通过CERES辐射产品证实了其有效性,该研究可为后续完整辐射收支(短波、长波)估算提供重要参考。相关产品详见CARE主页(http://www.slrss.cn/care/)。
Abstract: Objective: The accurate acquisition of cloud microphysical parameters, cloud optical thickness (COT) and cloud effective radius (CER), is of great significance to the calculation of surface or top-of-atmosphere (TOA) radiation budget. However, most of the studies consider little about the cloud phase. Even if the cloud phase state is considered, the ice cloud is assumed to be spherical, which brings errors to the subsequent radiation calculation. In addition, few studies focus on shortwave radiation forcing (SWRF) from satellites, but on downward shortwave radiation at the surface. To solve above problems, this study proposes methods for retrieving COT and CER for water and ice clouds as well as estimation of SWRF from the Himawri-8 satellite. Method: In this study, we proposed a novel method for retrieval of COT and CER for water and ice clouds from the new-generation geostationary satellite Himawari-8 measurements, based on the radiative transfer theory and optimal method. The irregularly shaped model named Voronoi, which was widely used in Japan Aerospace Exploration Agency (JAXA) satellite missions like Himawari-8, GCOMC-C, etc., was used in our ice cloud model. In addition, a method for estimation of SWRF at the surface and the TOA was proposed, based on the look-up-table (calculated by the radiative transfer model - RSTAT) method, as inputs of retrieved COT and CER above. Finally, validation of retrieved COT and CER from Himawari-8 in this study was performed with Moderate-resolution Imaging Spectroradiometer (MODIS) collection-6 (C6) cloud product, as well as estimated SWRF from Himawari-8 by this study with Clouds and the Earth’s Radiant Energy System (CERES) level-3 (L3) SYN product, respectively. Result: Validation with MODIS C6 cloud product for 4 days in different seasons (2016-01-01, 2016-04-01, 2016-07-01, 2016-10-01) shows that our retrieved COT and CER for water and ice clouds from Himawari-8 have a good agreement with MODIS product, with correlation coefficient (R) values of COT of 0.68 and 0.77, respectively. While for CER, due to the different ice cloud model used in MODIS and this study show a lower R value. While for validation of SWRF with the CERES L3 SYN product, estimated SWRF at the surface and the TOA by this study show very good agreement, with R values of 0.97 and 0.98, root-mean-square-error (RMSE) values of 15.0 Wm-2 and 16.6 Wm-2. While, mean-bias-error (MBE) values of -5.6 Wm-2 and -8.5 Wm-2 indict that our SWRF results have a slightly under-estimation. Conclusion: Our proposed methods for retrieving COT and CER, as well as SWRF at the surface and the TOA from Himawari-8 are effective. Although our ice cloud model (Voronoi) is different with MODIS, the finial SWRF validation still shows that our cloud products have high accuracy in other aspects. This research can provide important reference for the subsequent full radiation budget (shortwave plus longwave) estimation. Detailed products please see our homepage (http://www.slrss.cn/care_zh/). Key words: Himawari-8, cloud optical thickness, cloud effective radius, shortwave radiation forcing Supported by National Natural Science Foundation of China (No. 42025504, 91837204, 41701406); Second Tibetan Plateau Scientific Expedition and Research Program (STEP) (No. 2019QZKK0206); National Key Research and Development Program of China (No. 2017YFA0603502)