Tropical cyclone (TC) Amphan is analyzed in terms of the various factors that governed the intensification process associated with it and compared with Fani. Furthermore, the TC radial characteristics and ocean productivity are examined. Notably, both TCs formed in the Bay of Bengal during the pre‐monsoon seasons of 2020 and 2019, respectively. For this study, both ocean and atmospheric parameters from various sources including global analyses, satellite observations, and outputs from Model for Prediction Across Scales‐Atmosphere (MPAS‐A) and Advanced Research Weather Research and Forecasting (WRF‐ARW), are considered. The results indicate a gradual decrease in vertical wind shear during Fani. In the case of Amphan, the increase in mid‐tropospheric relative humidity values is found to be substantial. The sea surface cooling after the passage of Amphan was higher than in the case of Fani. The higher sea surface temperature in the Amphan case corresponds to the lower aerosol loading (partly because of lockdown measures) than that of Fani in the pre‐cyclone phase. And the decrease (increase) in aerosol loading coincides with an increase (decrease) in the direct radiative forcing at the ocean surface. The Madden–Julian Oscillation played a greater role in the cyclogenesis of Fani, but Kelvin waves offered a major support in the case of Amphan. The warmer sea surface, higher tropical cyclone heat potential, and conducive ocean and atmospheric setting together supported the further intensification of Amphan to the supercyclone stage. The difference in chlorophyll concentration showed a significant variation, with higher positive values seen in the case of Amphan implicating greater vertical mixing. The numerical modeling effort indicated superior performance of MPAS‐A compared to WRF‐ARW in simulating the radial parameters of the TCs.

中文翻译：

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比较与孟加拉湾两次明显增强的季风前热带气旋相关的大气和海洋特征

根据控制与其相关的强化过程的各种因素对热带气旋 (TC) Amphan 进行了分析，并与 Fani 进行了比较。此外，还考察了TC径向特征和海洋生产力。值得注意的是，这两个热带气旋分别于 2020 年和 2019 年季风前季节在孟加拉湾形成。在这项研究中，考虑了来自各种来源的海洋和大气参数，包括全球分析、卫星观测以及跨尺度大气预测模型（MPAS-A）和高级研究天气研究和预报（WRF-ARW）的输出。结果表明，法尼期间垂直风切变逐渐减少。就安芬而言，对流层中层相对湿度值的增加非常显着。安攀经过后海面冷却程度高于法尼。与气旋前阶段的法尼相比，安攀情况下较高的海面温度对应于较低的气溶胶负荷（部分原因是封锁措施）。气溶胶负荷的减少（增加）与海洋表面直接辐射强迫的增加（减少）一致。马登-朱利安振荡在 Fani 的气旋发生中发挥了更大的作用，但开尔文波在 Amphan 的情况下提供了主要支持。温暖的海面、较高的热带气旋热势以及有利的海洋和大气环境共同支持了安攀进一步增强至超级气旋阶段。叶绿素浓度的差异显示出显着的变化，在 Amphan 的情况下看到较高的正值意味着更大的垂直混合。数值建模工作表明，与 WRF-ARW 相比，MPAS-A 在模拟 TC 的径向参数方面具有优越的性能。