Abstract
The present study investigates the effect of increasing sea surface temperatures (SSTs) on tropical cyclone (TC) frequency using the high-resolution Australian Community Climate and Earth-System Simulator (ACCESS) model. We examine environmental conditions leading to changes in TC frequency in aqua-planet global climate model simulations with globally uniform sea surface temperatures (SSTs). Two different TC tracking schemes are used. The Commonwealth Scientific and Industrial Research Organization (CSIRO) scheme (a resolution-dependent scheme) detects TCs that resemble observed storms, while the Okubo–Weiss zeta parameter (OWZP) tracking scheme (a resolution-independent scheme) detects the locations within “marsupial pouches” that are favorable for TC formation. Both schemes indicate a decrease in the global mean TC frequency with increased saturation deficit and static stability of the atmosphere. The OWZP scheme shows a poleward shift in the genesis locations with rising temperatures, due to lower vertical wind shear. We also observe an overall decrease in the formation of tropical depressions (TDs) with increased temperatures, both for those that develop into TCs and non-developing cases. The environmental variations at the time of TD genesis between the developing and the non-developing tropical depressions identify the Okubo–Weiss (OW) parameter and omega (vertical mass flux) as significant influencing variables. Initial vortices with lower vorticity or with weaker upward mass flux do not develop into TCs due to environments with higher saturation deficit and stronger static stability of the atmosphere. The latitudinal variations in the large-scale environmental conditions account for the latitudinal differences in the TC frequency in the OWZP scheme.
Highlights
Tropical cyclones (TCs) cause severe socio-economic losses, mainly in coastal communities
We remove the Okubo–Weiss zeta parameter (OWZP) storms below a limit of boxaveraged lifetime maximum 10 m/s wind speed for further analysis of TCs to remove the secondary peak in the bi-modal distribution of intensities shown in Figure 1a and focus on the arguably more realistic, more intense storms
The SST25 experiment is considered as the control experiment, for which we found a global mean number of 3218 TCs
Summary
Tropical cyclones (TCs) cause severe socio-economic losses, mainly in coastal communities. A recent generation of climate models has produced simulations with a reasonable geographical distribution and seasonal variability of TCs but have uncertainties in the simulated intensity due to its sensitivity to the representation of sub-grid scale processes and horizontal resolution [1,2,3,4,5,6,7,8,9,10,11]. From these studies, it can be noted that there are differences in the processes governing TC formation versus intensification.
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