The Gill and non-Gill equatorial wave circulations associated with convective variability over the subtropical western North Pacific

Atmospheric convection over the subtropical western North Pacific (SWNP) varies on time scales around 2 weeks with significant effects on local and remote circulation. Among unknown effects, coupling between the SWNP convection variability and equatorial wave circulation is poorly understood. This paper quantifies equatorial wave perturbations using a global, wave space regression between the 43-year outgoing longwave radiation data over the SWNP region and spectral expansion coefficients of tropospheric circulation from ERA5 reanalyses. The resulting tropical wave flow is divided between the Rossby and Kelvin waves, which constitute the Gill pattern of tropical wave response to heating, and mixed Rossby-gravity (MRG) and inertia-gravity (IG) waves, which are named non-Gill pattern. The non-Gill part in the upper tropical troposphere is shown to have as large amplitude as the Gill part of the response. In particular, the IG and MRG waves contribute most of the cross-equatorial circulation and the MRG wave signals have about 25% greater amplitude than the IG wave signals. As SWNP convection intensifies, the MRG wave northerly winds across the equator strengthen whereas the IG waves represent strengthening outflow over the SWNP region. The combined effect of the Kelvin and Rossby waves enhance the circulation on the equatorward side of the anticyclone over the SWNP region, with the three times stronger Rossby wave than Kelvin wave easterlies in the upper troposphere. In the weakening phase of the SWNP convection, the northerly IG flow in the southern Indian ocean is coupled with developing anticylonic circulation of Rossby waves, suggesting the effects on extratropics in austral winter. The results suggest a caution when using Gill solution for the interpretation of circulation associated with asymmetric heating sources in real atmosphere or its models.