ABSTRACT

This paper describes the combined impact of clear sky hyperspectral radiances from four space-based instruments in the National Centre for Medium Range Weather Forecasting (NCMRWF) Unified Model (NCUM) 4D-Var assimilation and forecast system through Observing System Experiment (OSE) during May 2018. Radiances from four hyperspectral instruments, Atmospheric Infrared Sounder (AIRS) onboard EOS-AQUA satellite, Infrared Atmospheric Sounding Interferometer (IASI) onboard both MetOp-A and MetOp-B satellites and Cross-track Infrared Sounder (CrIS) onboard NPP satellite along with other conventional and satellite observations are assimilated in the first simulation (EXP), while the radiances from the four hyperspectral instruments were denied in the latter simulation (CNTL). The simulations run four assimilation cycles per day centred at 0000, 0600, 1200, and 1800 UTCs. 5-day forecasts based on the 0000 UTC initial conditions are generated from both EXP and CNTL. Results show that both O-B (Observation-Background) and O-A (Observation – Analysis) of other satellite radiances assimilated in EXP improved (in this case biases reduced) due to the assimilation of hyperspectral radiances. The impact of hyperspectral data assimilation in various forecast fields is estimated by computing Forecast Impact (FI) parameter with respect to an independent dataset, ERA5. Hyperspectral radiance assimilation improved both mass and wind forecasts in the short-range, and the FI degraded with higher lead time. There is a slight improvement in the precipitation over the Indian landmass due to the assimilation of hyperspectral radiances. Verification of model forecasts with radiosonde observations over the Indian region shows marginal improvement in the humidity and temperature forecasts due to the assimilation of hyperspectral radiances. Assimilation of hyperspectral radiances slightly improved the characteristics of two cyclones, Sagar and Mekunu, formed over the Arabian Sea during the study period. Both the experiments predicted early onset of monsoon 2018 than the IMD date of monsoon onset.

摘要

本文描述了国家中期天气预报中心 (NCMRWF) 统一模型 (NCUM) 4D-Var 同化和预报系统在 5 月期间通过观测系统实验 (OSE) 的四种天基仪器的晴空高光谱辐射的综合影响2018. 来自四种高光谱仪器的辐射，EOS-AQUA 卫星上的大气红外探测仪 (AIRS)、MetOp-A 和 MetOp-B 卫星上的红外大气探测干涉仪 (IASI) 以及 NPP 卫星上的跨轨红外探测仪 (CrIS) 沿在第一次模拟 (EXP) 中同化了其他常规和卫星观测结果，而在后一次模拟 (CNTL) 中拒绝了来自四个高光谱仪器的辐射。模拟每天运行四个同化周期，集中在 0000、0600、1200、和 1800 UTC。EXP 和 CNTL 生成基于 0000 UTC 初始条件的 5 天预测。结果表明，由于高光谱辐射的同化，在 EXP 中同化的其他卫星辐射的 OB（观测-背景）和 OA（观测-分析）都得到了改善（在这种情况下，偏差减少）。高光谱数据同化在各种预测领域的影响是通过计算与独立数据集 ERA5 相关的预测影响 (FI) 参数来估计的。高光谱辐射同化改善了短程质量和风的预报，FI随着提前期的延长而降低。由于高光谱辐射的同化，印度大陆的降水略有改善。对印度地区无线电探空仪观测对模型预测的验证表明，由于高光谱辐射的同化，湿度和温度预测略有改善。高光谱辐射的同化略微改善了研究期间在阿拉伯海形成的两个气旋 Sagar 和 Mekunu 的特征。两个实验都预测了 2018 年季风的开始时间比季风开始的 IMD 日期要早。