This paper describes the impact of direct assimilation of Indian Ocean Data Coverage (IODC) Meteosat-8 SEVIRI Clear Sky Brightness Temperatures (CSBTs) and the Atmospheric Motion Vectors (AMVs) in a 4D-Var framework through a set of Observing System Experiments (OSEs) during May 2018. Meteosat-8 located at 3.5°E was relocated to 41.5°E and fully functional over the IODC region since February 2017. The impact of CSBTs from selected infra-red and water vapor channels of SEVIRI and AMVs derived from visible, infrared and water vapor channels is studied through identical OSEs using National centre for Medium Range Weather Forecast (NCMRWF) Unified Model (NCUM) assimilation and forecast system. The study discovered that the analysis increments of humidity and temperature are largely driven by AMVs rather than the CSBTs over the IODC region. The complementarity of AMV and CSBT assimilation is noticed in the wind analysis. Humidity forecasts from NCUM in the medium range show that the CSBT contribution is less than that of AMVs. CSBT assimilation showed near neutral impact in the temperature forecasts; however, it has contributed significantly to the wind forecast, at different pressure levels. Impact parameter estimated based on European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 global reanalysis shows that Meteosat-8 AMV assimilation produced noticeable improvement over the Indian Ocean region, particularly in the lower and upper tropospheric levels. Results from this study indicate the importance of wind assimilation over the Tropics, compared to the use of CSBTs. Though the AMV assimilation improved the humidity and wind fields, the statistical skill scores analyzed during the extreme precipitation event associated with two cyclones during the study period show that the precipitation over the IODC region is predicted well when the AMVs are denied from the assimilation.

本文描述了通过一组观测系统实验 (OSE) 在 4D-Var 框架中直接同化印度洋数据覆盖 (IODC) Meteosat-8 SEVIRI 晴空亮度温度 (CSBT) 和大气运动矢量 (AMV) 的影响) 在 2018 年 5 月期间。位于 3.5°E 的 Meteosat-8 被重新定位到 41.5°E 并自 2017 年 2 月起在 IODC 区域完全运行。来自 SEVIRI 和 AMV 的选定红外和水蒸气通道的 CSBT 的影响来自可见光使用国家中期天气预报中心 (NCMRWF) 统一模型 (NCUM) 同化和预报系统，通过相同的 OSE 研究红外和水蒸气通道。该研究发现，湿度和温度的分析增量主要由 AMV 而非 IODC 区域上的 CSBT 驱动。在风分析中注意到 AMV 和 CSBT 同化的互补性。来自 NCUM 的中等湿度预测表明，CSBT 的贡献小于 AMV。CSBT 同化在温度预测中显示出近乎中性的影响；然而，它对不同压力水平的风预测做出了重大贡献。根据欧洲中期天气预报中心 (ECMWF) ERA5 全球再分析估计的影响参数表明，Meteosat-8 AMV 同化对印度洋地区产生了显着的改善，特别是在对流层下层和上层。这项研究的结果表明，与使用 CSBT 相比，热带地区风同化的重要性。尽管 AMV 同化改善了湿度和风场，