Climatological features of rapidly intensifying tropical cyclones in the North Indian Ocean

M. Ranalkar, Ram Kumar Giri, Kamaljit Ray
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Abstract

The study investigates the climatological variation of rapidly intensifying tropical cyclones (RITCs) developed in the North Indian Ocean (NIO) using observational and reanalysis data from 1982 to 2020. The analysis reveals that out of 153 tropical cyclones (TC) developed in the NIO, 59 TCs underwent rapid intensification (RI). The monthly variation of RITCs exhibited bimodal distribution with a primary peak in November and a secondary peak in May. The percentage of RITCs during April–June is higher as compared to October–December. The study identifies the core zones of RI initiation in the Arabian Sea (AS) and the Bay of Bengal (BoB), respectively. The occurrences of RITCs over the AS have been observed to increase since 2000. Over 65% of RITCs occurred within 12 h of TC formation, and the duration of RI varies from 24 to 48 h. TCs with lifetime maximum intensity (LMI) less than 55 kt have not undergone RI. The trend in the 95th percentile of 24‐h intensity changes is positive but insignificant (p‐value >0.05) in the AS, and for the BoB, it is negative and significant (p‐value <0.05). We infer that there has been an insignificant increase in the 95th percentile of 24‐h intensity change at the rate of 0.32 kt per year in the AS and a significant decrease in the 95th percentile of 24‐h intensity change at the rate of −0.21 kt per year in the BoB. The analysis further reveals that during the RI phase the composite SST of RITCs exceeds 30°C in the core zone, and the mid‐tropospheric (700–500 hPa) relative humidity at the centre of RITCs is high, preventing the intrusion of dry air from the west and aiding in the sustenance and intensification of TCs. The study not only provides insight into the climatology of RITCs in the NIO but also delineates the interplay of large‐scale atmospheric and oceanic parameters in fostering rapid intensification of TCs.
北印度洋快速增强的热带气旋的气候特征
该研究利用 1982 年至 2020 年的观测和再分析数据,研究了北印度洋(NIO)出现的快速增强热带气旋(RITCs)的气候学变化。分析表明,在北印度洋生成的 153 个热带气旋中,有 59 个热带气旋经历了快速增强(RI)。RITC 的月变化呈双峰分布,主峰在 11 月,次峰在 5 月。与 10 月至 12 月相比,4 月至 6 月的 RITC 百分比更高。该研究分别确定了阿拉伯海(AS)和孟加拉湾(BoB)的 RI 起始核心区。据观测,自 2000 年以来,RITCs 在阿拉伯海上空的发生率呈上升趋势。超过 65% 的 RITC 发生在 TC 形成后的 12 小时内,RI 持续时间从 24 小时到 48 小时不等。在 AS 中,24 小时强度变化的第 95 百分位数趋势为正但不显著(p 值 >0.05),而在 BoB 中,趋势为负且显著(p 值 <0.05)。我们推断,在 AS 中,24 小时强度变化的第 95 百分位数以每年 0.32 千吨的速度增加,但不显著;在 BoB 中,24 小时强度变化的第 95 百分位数以每年-0.21 千吨的速度显著下降。分析进一步表明,在RI阶段,RITCs核心区的综合SST超过30°C,RITCs中心的对流层中层(700-500 hPa)相对湿度较高,阻止了西部干燥空气的侵入,有助于TCs的维持和加强。该研究不仅有助于深入了解北印度洋区域热带气旋的气候学特征,而且还描述了大尺度大气和海洋参数在促进热带气旋快速增强方面的相互作用。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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