Entraining Plume Model Assessment of the Convective Coupling of Equatorial Waves

Convectively coupled equatorial waves (CCEWs) exhibit a broad range of characteristics, modulate tropical and extratropical weather across a wide range of spatial and temporal scales, and continue to challenge global weather and climate models. While previous studies have documented the large-scale thermodynamic variations associated with CCEWs, the relative importance of moisture and/or temperature variations within the sub-cloud layer (SCL), boundary layer (BL) and lower free troposphere (LFT) for convective coupling have not been quantitatively assessed.

In this study, an entraining plume model is used to examine the relative roles of moisture and temperature variability within the SCL, BL and LFT for convective coupling within different CCEWs. Entraining plume estimates of lower tropospheric (1000 - 600 hPa) vertically integrated buoyancy (<B>) are calculated from ERA5 thermodynamic fields, and shown to be highly coherent with observed IMERG precipitation variability. Power and coherence analyses are used to assess the impacts of removing moisture and/or temperature variability from the SCL, BL, and/or LFT on the variability of <B> and its coherence with IMERG precipitation. Consistent with the findings of previous studies, temperature variability is found to play a more important role in the convective coupling of Kelvin waves and inertia-gravity waves than other CCEWs. While moisture variability within the BL is small relative to that occurring in the LFT, moisture variability within the BL plays a surprisingly large role in modulating <B> and its coherence with IMERG precipitation.