Tropical cyclone formation regions in CMIP5 models: a global performance assessment and projected changes
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Tropical cyclone formation regions in CMIP5 models: a global performance assessment and projected changes K. J. Tory1 · H. Ye1 · G. Brunet1 Received: 11 April 2020 / Accepted: 23 August 2020 © The Author(s) 2020
Abstract Tropical Cyclone (TC) formation regions are analysed in twelve CMIP5 models using a recently developed diagnostic that provides a model-performance summary in a single image for the mid-summer TC season. A subjective assessment provides an indication of how well the models perform in each TC basin throughout the globe, and which basins can be used to determine possible changes in TC formation regions in a warmer climate. The analysis is necessarily succinct so that seven basins in twelve models can be examined. Consequently, basin performance was reduced to an assessment of two common problems specific to each basin. Basins that were not too adversely affected were included in the projection exercise. The North Indian basin was excluded because the mid-summer analysis period covers a lull in TC activity. Surprisingly, the North Atlantic basin also had to be excluded, because all twelve models failed the performance assessment. A slight poleward expansion in the western North Pacific and an expansion towards the Hawaiian Islands in the eastern North Pacific is plausible in the future, while a contraction in the TC formation regions in the eastern South Indian and western South Pacific basins would reduce the Australian region TC formation area. More than half the models were too active in the eastern South Pacific and South Atlantic basins. However, projections based on the remaining models suggest these basins will remain hostile for TC formation in the future. These southern hemisphere changes are consistent with existing projections of fewer southern hemisphere TCs in a future warming world
1 Introduction Projections of fewer tropical cyclones (TC) globally in a warming world have been consistent for more than a decade now (e.g., Knutson et al. 2010, 2019; Walsh et al. 2015). However, most global coupled ocean–atmosphere climate models continue to struggle to reproduce realistic TC climatologies in some basins, including the very active North Atlantic basin, which casts doubt on any projections made for these specific basins. Confidence in projections can be improved if it can be established how realistic model TC formation is, and if we can understand why TC formation climatologies change between future and present-day scenarios (Tory et al. 2018, hereafter T18). In order to answer these questions T18 sought to identify a set of basic parameters that define where TCs can and cannot form (TC formation boundaries) and identify fundamental atmospheric * K. J. Tory [email protected] 1
and oceanic climate circulations that determine the global distribution of these parameters. In this paper the T18 TC formation boundary parameters are applied to a selection of Phase 5 of the Coupled Model Intercomparison Project (CMIP5, Taylor et al. 2012) models during the peak summer TC seasons (i.e., J
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