Indian Institute of Tropical Meteorology, Ministry of Earth Sciences, Pune, India.
Department of Atmospheric and Space Sciences, Savitribai Phule Pune University, Pune, India.
Sci Rep. 2021 Feb 11;11(1):3607. doi: 10.1038/s41598-021-82680-9.
Cyclone Fani, in April 2019, was the strongest pre-monsoon cyclone to form in the Bay of Bengal after 1994. It underwent rapid intensification and intensified quickly to an extremely severe cyclone. It maintained a wind speed of ≥ 51 m s (≥ 100 knots) for a record time period of 36 h. The total lifespan of the cyclone was double than the climatological lifespan. Also, the duration of the cyclone in its extremely severe phase and the accumulated cyclone energy were significantly larger than the climatological records for the pre-monsoon season. In the current study, we investigate the ocean-atmospheric conditions that led to its genesis, rapid intensification and long lifespan. Our analysis shows that the Madden Julian Oscillation and anomalous high sea surface temperatures provided conducive dynamic and thermodynamic conditions for the genesis of cyclone Fani, despite forming very close to the equator where cyclogenesis is generally unlikely. Further, favourable ocean subsurface conditions and the presence of a warm core eddy in the region led to its rapid intensification to an extremely severe cyclone. A large area of warm ocean surface and subsurface temperatures aided the cyclone to maintain very high wind speed for a record time period. The vital role of the ocean surface and the subsurface in the genesis and the intensification highlights the need to efficiently incorporate ocean initial conditions (surface and sub-surface) and ocean-atmosphere coupling in the operational cyclone forecasting framework.
2019 年 4 月，“法尼”气旋是 1994 年以来孟加拉湾形成的最强的前季风气旋。它经历了快速增强，并迅速增强为极强气旋。它的风速持续了≥51m/s（≥100 节），创下了 36 小时的纪录。气旋的总寿命是气候寿命的两倍。此外，气旋在极强阶段的持续时间和累积气旋能量明显大于前季风季节的气候记录。在本研究中，我们调查了导致其产生、快速增强和长寿命的海洋-大气条件。我们的分析表明，Madden Julian 振荡和异常高的海面温度为气旋“法尼”的产生提供了有利的动力和热力学条件，尽管它形成的地点非常接近赤道，通常情况下不太可能形成气旋。此外，有利的海洋次表层条件和该地区存在暖核涡流导致气旋迅速增强为极强气旋。大面积温暖的海洋表面和次表层温度使气旋能够以创纪录的时间保持非常高的风速。海洋表面和次表层在气旋的产生和增强中起着至关重要的作用，这凸显了在业务气旋预报框架中有效纳入海洋初始条件（表面和次表面）和海洋-大气耦合的必要性。
