Dynamical propagation and growth mechanisms for convectively coupled equatorial Kelvin waves over the Indian Ocean

Matthews, Adrian J. ORCID: https://orcid.org/0000-0003-0492-1168 (2021) Dynamical propagation and growth mechanisms for convectively coupled equatorial Kelvin waves over the Indian Ocean. Quarterly Journal of the Royal Meteorological Society, 147 (741). pp. 4310-4336. ISSN 0035-9009

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Convectively coupled equatorial Kelvin waves (CCKWs) are high-impact tropical weather systems that can lead to severe flooding over the Maritime Continent. Here, a vorticity budget for CCKWs over the Indian Ocean is constructed using reanalysis data, to identify the basic mechanisms of eastward propagation and growth. The budget is reasonably well closed, with a small residual/sub-gridscale term. In the lower troposphere, CCKWs behave like strongly modified theoretical equatorial Kelvin waves. Vortex stretching, from the divergence of the Kelvin wave acting on planetary vorticity (the -fD term), is the sole mechanism by which the vorticity structure of a theoretical Kelvin wave propagates eastward. In the lower and middle troposphere, this term is also the key mechanism for the eastward propagation of CCKWs but, due to subtleties in its structure and phasing linked to a combination of modal structures, it also contributes to growth. Unlike in the theoretical Kelvin wave, other vorticity source terms also play a role in the propagation and growth of CCKWs. In particular, vortex stretching from relative vorticity (the -zeta D term) is the largest source term, and this leads strongly to growth, through interactions between the background and perturbation vorticity and divergence. Horizontal vorticity advection by the background flow contributes to propagation, and also acts to retard the growth of the CCKW. The sum of the source terms in this complex vorticity budget leads to eastward propagation and growth of CCKWs. The structure and vorticity budget of CCKWs in the upper troposphere is quite unlike that of a Kelvin wave, and appears to arise as a forced response to the lower tropospheric structure. The implications for numerical weather prediction and climate simulations are discussed.

Item Type: Article
Additional Information: Funding Information: UK Natural Environment Research Council through the Equatorial Line Observations project and the TerraMaris project, NE/R012431/1; NE/R016704/1. Data availability: The ERA‐Interim data were provided by the Centre for Environmental Data Analysis. The 3B42 data were provided by the NASA/Goddard Space Flight Center and PPS, which develop and compute the 3B42 dataset as a contribution to the TRMM project, and are archived at the NASA GES DISC. Acknowledgement: The research presented in this paper was carried out on the High Performance Computing Cluster supported by the Research Computing Service at the University of East Anglia.
Uncontrolled Keywords: kelvin wave,eastward propagation,equatorial wave,growth rate,tropical weather system,vorticity budget,atmospheric science ,/dk/atira/pure/subjectarea/asjc/1900/1902
Faculty \ School: Faculty of Science > School of Environmental Sciences
Faculty of Science > School of Natural Sciences
University of East Anglia Research Groups/Centres > Theme - ClimateUEA
UEA Research Groups: Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences
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Depositing User: LivePure Connector
Date Deposited: 06 Oct 2021 01:58
Last Modified: 20 Mar 2023 08:35
URI: https://ueaeprints.uea.ac.uk/id/eprint/81558
DOI: 10.1002/qj.4179

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