Intraseasonal convection–circulation coupling in the Northern Hemisphere Tropics: A vorticity‐budget analysis

Abstract The complexities of convection–circulation coupling challenge understanding of the tropical atmosphere. This coupling is manifested in the vertical component of vorticity, which both aids and is modulated by convection. This study, for the first time, investigates the structure, maintenance, and propagation of vorticity associated with precipitating convection at various intraseasonal timescales (low‐frequency (LF), high‐frequency (HF), and synoptic‐scale events) for global tropical ocean basins during the boreal summer. Examining the vertically resolved vorticity budget for the European Centre for Medium‐Range Weather Forecasts Reanalysis Version 5 (ERA5), we show that the vorticity associated with precipitating convection intensifies progressively and becomes vertically uniform away from the Equator. For convective events closer to the Equator, vorticity is weakly associated with rainfall both temporally and spatially. In contrast, for convection sufficiently away from the Equator, rainfall and vorticity are spatially collocated and temporally in phase. Larger values of absolute vorticity and consequently higher boundary‐layer vortex stretching drive this stronger association farther away from the Equator. Maintenance of a vertically uniform vorticity structure is achieved by boundary‐layer vortex stretching and convection‐induced vertical advection of vorticity into the free troposphere. Despite quantitative differences, these findings hold across global ocean basins, and the dominance of vortex stretching and vertical advection persists across timescales. In contrast, the propagation characteristics of these vortices differ. LF events primarily propagate northward, while HF and synoptic events move northwestward. The mechanism for the northward propagation of LF vorticity in the Bay of Bengal is latitude‐dependent. Consistent with previous theories, vortex tilting makes substantial contributions to the propagation of vorticity close to the Equator. However, a different mechanism involving enhanced contributions from horizontal advection dominates when convection is farther poleward. This systematic evolution of convection–circulation coupling across timescales provides an important benchmark for covariation of precipitation, vertical vorticity, and velocity in climate models.