Reduction in the tropical high cloud fraction in response to an indirect weakening of the Hadley cell

Natchiar, S. R. M., Webb, M. J., Lambert, F. H., Vallis, G. K., Morcrette, C. J., Holloway, C. E. ORCID: https://orcid.org/0000-0001-9903-8989, Sergeev, D. E. and Boutle, I. (2024) Reduction in the tropical high cloud fraction in response to an indirect weakening of the Hadley cell. Journal of Advances in Modeling Earth Systems, 16 (5). e2023MS003985. ISSN 1942-2466 doi: 10.1029/2023MS003985

Abstract/Summary

Tropical high cloud cover decreases with surface warming in most general circulation models. This reduction, according to the “stability-iris” hypothesis, is thermodynamically controlled and linked to a decrease in the radiatively-driven clear-sky convergence, when the peak anvil clouds rise because of the rising isotherms. The influence of the large-scale dynamical changes on the tropical high cloud fraction remains difficult to disentangle from the local thermodynamic influence, given that the mean meridional circulation remains inextricably tied to the local thermodynamic structure of the atmosphere. However, using idealized general circulation model (GCM) simulations, we propose a novel method to segregate the dynamical impact from the thermodynamic impact on the tropical high cloud fraction. To this end, our investigation primarily focuses on the mechanisms underpinning changes in the high cloud cover in the deep tropics in response to extratropical surface warming, when the tropical sea surface temperatures remain invariant. Net convective detrainment of ice cloud condensates decreases at the peak detrainment region, without a rise in its altitude. We also find that the importance of depositional growth of ice cloud condensates in controlling the high cloud fraction response in the deep tropics varies with altitude.

Item Type	Article
URI	https://reading-clone.eprints-hosting.org/id/eprint/116165
Identification Number/DOI	10.1029/2023MS003985
Refereed	Yes
Divisions	Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
Publisher	American Geophysical Union
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