Studies have shown that assimilating the radio occultation (RO) observations, including those from the FORMOSAT-3/COSMIC (constellation observing systems for meteorology, ionosphere, and climate) (FS3-C), provides positive impacts on tropical cyclone (TC) forecasts. The FS3-C's successor, the FORMOSAT-7/COSMIC-2 (FS7-C2), provides denser spatial data coverage over the Tropics and Subtropics, where severe weather systems often occur. This study investigates the impact of FS7-C2 refractivity profiles on the prediction of TC genesis. A quick observing system simulation experiment is conducted for the period when Hurricanes Helene and Gordon (2006) occurred over the North Atlantic Ocean using a regional ensemble data assimilation system. Though assimilating FS3-C or FS7-C2 ROs successfully reproduces Helene's development, assimilating FS7-C2 ROs better captures the genesis and development of Gordon with abundant moisture and vorticity in Gordon's core region, providing conditions favorable for the development of deep convection. A minimum area-mean total precipitable water vapor of 54 mm, as well as the existence of mid-level cyclonic vorticity (e.g., 500 hPa), at the storm core region in the initial condition is required for forecasting Gordon's genesis. Also, the assimilation of FS7-C2 ROs in our experiments reduces the 500 hPa geopotential error by 22% and improves probabilistic quantitative precipitation forecast compared with assimilating FS3-C ROs. Two sensitivity tests are conducted to evaluate the impact of low-level negatively biased FS7-C2 RO profiles and the removal of FS7-C2 data below 3 km on Gordon's genesis. The former test does not degrade Gordon's genesis forecast skills due to a dipole error correlation between the background ROs and the moisture field over an observed RO profile near Gordon. The latter test does degrade Gordon's forecast skills but is still better than the assimilation of FS3-C ROs since the features of low-level moisture and mid-level vorticity are preserved to some extent.

中文翻译：

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了解同化 FORMOSAT-7/COSMIC-2 无线电掩星折射率对热带气旋形成的影响：以飓风戈登 (2006) 为案例研究的观测系统模拟实验

研究表明，同化无线电掩星 (RO) 观测，包括来自 FORMOSAT-3/COSMIC（气象、电离层和气候星座观测系统）(FS3-C) 的观测，对热带气旋 (TC) 预报产生积极影响. FS3-C 的继任者 FORMOSAT-7/COSMIC-2 (FS7-C2) 在经常出现恶劣天气系统的热带和亚热带地区提供更密集的空间数据覆盖。本研究调查了 FS7-C2 折射率剖面对 TC 成因预测的影响。针对飓风“海伦”和“戈登”发生期间进行了快速观测系统模拟实验(2006) 使用区域集合数据同化系统发生在北大西洋上空。虽然同化 FS3-C 或 FS7-C2 ROs 成功再现了Helene的发育过程，但同化 FS7-C2 ROs 更好地捕获了Gordon核心区水分和涡度丰富的Gordon的成因和发展，为深部发育提供了有利条件对流。预报戈登需要初始条件下风暴核心区的最小面积平均总可降水量为 54 毫米，以及存在中层气旋涡度（例如 500 hPa）的起源。此外，与同化 FS3-C ROs 相比，在我们的实验中同化 FS7-C2 ROs 将 500 hPa 位势误差减少了 22%，并提高了概率定量降水预报。进行了两项敏感性测试，以评估低水平负偏 FS7-C2 RO 剖面和去除 3 公里以下的 FS7-C2 数据对戈登起源的影响。由于背景 RO 与戈登附近观察到的 RO 剖面上的水分场之间的偶极误差相关性，前一个测试不会降低Gordon的成因预测技能。后一个测试确实降低了戈登的预报技巧，但仍优于 FS3-C RO 的同化，一定程度上保留了低层水汽和中层涡度的特征。