Forecast Impact of FORMOSAT‐7/COSMIC‐2 GNSS Radio Occultation Measurements,Atmospheric Science Letters

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Forecast Impact of FORMOSAT‐7/COSMIC‐2 GNSS Radio Occultation Measurements
Atmospheric Science Letters ( IF 2.0 ) Pub Date : 2020-11-23 , DOI: 10.1002/asl.1019
Benjamin Ruston ₁ , Sean Healy ₂

Affiliation

The FORMOSAT‐7/COSMIC‐2 GNSS‐RO mission was launched on June 25, 2019, and it has provided a large increase in the number of GNSS‐RO observations available for operational numerical weather prediction (NWP) in the latitude band between ±40°. A key aim of this mission has been to improve the GNSS‐RO measurement quality in the lower and middle troposphere. In this study, we summarize the impact of the FORMOSAT‐7/COSMIC‐2 measurements in two independent NWP systems, which are now assimilating these measurements operationally. These are the United States Navy Global Environmental Model (NAVGEM) and the European Center for Medium‐Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS). Both systems employ a 4‐dimensional variational system (4D‐Var), and assimilate GNSS‐RO bending angles. The experiments cover the period January to March 2020. The impact of the FORMOSAT‐7/COSMIC‐2 measurements is assessed using improvements in short‐range forecast departures to other observations such as radiosonde and radiances, forecast error statistics against a verifying analysis, and adjoint based Forecast Sensitivity to Observation Impact (FSOI) estimates. The FORMOSAT‐7/COSMIC‐2 measurement has a clear impact on stratospheric temperatures and winds in the tropics. A novel finding is that the measurements also improve the tropical tropospheric humidity fit to radiosondes, and the fit to tropospheric radiances sensitive to humidity. To date, the impact of GNSS‐RO on humidity has been difficult to demonstrate in well constrained, operational NWP systems assimilating the full suite of observations. The results are achieved with a conservative assimilation approach which extended the quality control and observation error assignments used for the previous COSMIC receivers; further, possible improvements to the assimilation strategy are noted.

中文翻译：

FORMOSAT-7 / COSMIC-2 GNSS无线电掩星测量的预测影响

FORMOSAT-7 / COSMIC-2 GNSS-RO任务于2019年6月25日启动，它为可用于在±之间的纬度范围内运行数字天气预报（NWP）的GNSS-RO观测数量提供了大量增加。 40°。该任务的主要目的是提高对流层中低层的GNSS-RO测量质量。在这项研究中，我们总结了FORMOSAT-7 / COSMIC-2测量在两个独立的NWP系统中的影响，这些系统现在在操作上可以同化这些测量。它们是美国海军全球环境模型（NAVGEM）和欧洲中距离天气预报中心（ECMWF）综合预报系统（IFS）。两种系统均采用4维变化系统（4D-Var），并吸收GNSS-RO弯曲角。实验涵盖了从2020年1月到2020年3月的时间。FORMOSAT-7/ COSMIC-2测量的影响是通过对其他观测值（如探空仪和辐射率）的短期预报偏离的改进，对验证分析的预报误差统计以及基于伴随的预测对观测影响的敏感性（FSOI）估计。FORMOSAT-7 / COSMIC-2的测量对热带平流层的温度和风有明显的影响。一个新颖的发现是，这些测量还提高了对流探空仪对热带对流层湿度的适应性以及对湿度敏感的对流层辐射度的适应性。迄今为止，很难在高度约束的，可操作的NWP系统中证明GNSS-RO对湿度的影响，并吸收整套观测结果。通过保守的同化方法获得了结果，该方法扩展了先前COSMIC接收机使用的质量控制和观察误差分配；此外，还指出了对同化策略的可能改进。

更新日期：2020-11-23

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