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The seasonal variability in the characteristics and propagation of convectively coupled equatorial waves in the tropical Pacific Ocean
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DOI：10.1007/s00382-026-08341-7.png)
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Abstract
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In this study, we investigate contrasting behaviors in the structure, intensity, and propagation of equatorial Kelvin (EK), equatorial Rossby (ER), and mixed Rossby-gravity (MRG) waves over the tropical Pacific between boreal winter and summer. The EK and MRG waves propagate faster in boreal summer than in winter and exhibit stronger convective amplitude during summer. The ER wave shows little seasonal difference in phase speed (~ 5 m s−1) but has markedly stronger convection in winter. Horizontally, the EK and MRG waves exhibit only slight seasonal structural differences. The characteristic “swallowtail” convective envelope of ER waves arises from the bottom-up evolution of convective vertical structure along the wave’s propagation direction, and its seasonal asymmetry about the equator is driven by the northward migration of the ITCZ in boreal summer. Vertically, the EK wave exhibits a more pronounced “boomerang” structure in boreal summer due to stronger and deeper convective heating. The ER wave undergoes a fundamental transition from equivalent barotropic structure in boreal winter to first baroclinic mode in summer, governed by the weakening of background westerly vertical shear. The MRG wave similarly transitions from a near-barotropic structure in boreal winter to a boomerang-like first baroclinic structure in summer, attributable to the combined effects of weakened background westerly vertical shear and stronger convective heating. These findings demonstrate that equatorial wave characteristics are systematically modulated by the seasonally evolving background state, providing observational benchmarks for evaluating climate model simulations.
Keywords:
Equatorial Rossby waves
Equatorial Kelvin waves
Mixed Rossby-gravity waves
Seasonality
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