Modulation of environmental conditions on the significant difference in the super cyclone formation rate during the pre- and post-monsoon seasons over the Bay of Bengal

Abstract

Unlike other tropical ocean basins, the Bay of Bengal (BoB) has two tropical cyclone (TC) seasons: a pre-monsoon season (Pre-MS) and a post-monsoon season (Post-MS). More interestingly, during the period from 1981 to 2016, the global maximum and minimum formation rates of super cyclones (SCs, categories 4 and 5) occurred in the Pre-MS and Post-MS, respectively, in the BoB. Methods including Butterworth filter, box difference index analysis and quantitative diagnosis were utilized herein to detect what and how background environmental factors cause significantly different SC formation rates between the Pre- and Post-MS. Diagnosis results revealed that the vertical temperature difference (VTD) mainly determines whether TCs can develop into SCs during the Post-MS, similar to Pre-MS. It’s in agreement with previous studies demonstrating that the VTD is controlled by the low-level temperature during the Post-MS but is determined by the upper-level temperature during the Pre-MS. The results also revealed that the background sea surface temperature is much higher in the Pre-MS than in the Post-MS and forces higher 1000 hPa-level air temperature. Additionally, there is higher saturated specific humidity (qs) due to the higher temperature in the Pre-MS. The differences in the bottom-level temperature and qs cooperate to predominantly contribute to the significant difference in Vpot2, which could denote the maximum potential intensity of TC, eventually leading to the remarkably different SC formation rates between the Pre- and Post-MS in the BoB.

Interannual variability of the double easterly jets over the tropical western Pacific and their effects on tropical cyclone genesis

“…The relative contribution of each above‐mentioned physical process, could be measured by applying logarithms onto Equation (), following Li et al . (2020): …”

“…where V S =2:0 +0:1 × jvws 200 −vws 850 j represents the vertical wind shear (mÁs −1 ) between 200 and 850 hPa; U y =5:5 − ∂u 500 ∂y × 10 5 denotes the meridional gradient of zonal wind at 500 hPa; ω is the vertical velocity at 500 hPa; ζ a =5:5 +j ζ 850 + f ð Þ× 10 5 j represents the absolute vorticity at 850 hPa and f is the Coriolis parameter. The relative contribution of each above-mentioned physical process, could be measured by applying logarithms onto Equation (1), following Li et al (2020):…”

Analysis of Climate Change Induced Parameters of South-Eastern Coastal Islands of Bangladesh: Comparison from 1977 to 2017

“…On the other hand, the Southern and Eastern part of Kutubdia emerges to be gifted for wind electricity generation using large turbines where wind power density at the height of 50 m or higher is found to be above 200 W/m 2 annually over the year September 1996 to August 1997. It is found that at 30 m height, the coast side of Kutubdia should be sustainable for small turbines [27].…”

How Well do High-resolution Global Climate Models (GCMs) Simulate Tropical Cyclones in the Bay of Bengal?

“…One peak is in the pre-monsoon transition period (April-May) and another peak is in the post-monsoon transition period (October-November) (Li et al 2013). In this paper, we use the term super cyclone ratio to refer to the ratio of the super cyclone frequency (with super cyclones defined as those having a maximum sustained windspeed ≥ 60 m s −1 , Li et al 2021) to the total TC frequency. Interestingly, the pre-monsoon and post-monsoon transition periods are very different in terms of TC intensification; during the premonsoon and post-monsoon periods, respectively, the BoB experiences the highest and lowest super cyclone ratio (Li et al 2021) in the world.…”

“…In this paper, we use the term super cyclone ratio to refer to the ratio of the super cyclone frequency (with super cyclones defined as those having a maximum sustained windspeed ≥ 60 m s −1 , Li et al 2021) to the total TC frequency. Interestingly, the pre-monsoon and post-monsoon transition periods are very different in terms of TC intensification; during the premonsoon and post-monsoon periods, respectively, the BoB experiences the highest and lowest super cyclone ratio (Li et al 2021) in the world. However, both the annual cyclone frequency and average intensity are found to be higher in the post-monsoon (even though the super cyclone ratio is higher in pre-monsoon) than in the pre-monsoon season (Li et al 2013;Vissa et al 2013).…”