Convectively Coupled Kelvin Waves over the Congo Basin: Modulation by Land Characteristics
Convectively coupled Kelvin waves (CCKWs) are a prominent mode of tropical variability that organize convection and modulate rainfall, providing an important source of synoptic-to-subseasonal predictability. Most current understanding of CCKW structure and evolution is derived from oceanic environments, where surface conditions are relatively uniform and wave–convection coupling is coherent. Over land, however, strong diurnal variability, heterogeneous surface properties, and complex terrain introduce additional processes that can substantially modify this coupling. Using reanalysis and satellite observations, we show that CCKWs over the Congo Basin depart from the canonical ocean-based framework. The typical shallow–congestus–deep convective transition is weak, with limited shallow cloud development ahead of the active phase, particularly during daytime. Surface latent heat flux anomalies occur in phase with enhanced incoming solar radiation, indicating a thermodynamically driven response rather than the wind-stress-dominated mechanism common over oceans. During the suppressed phase, reduced cloud cover allows increased solar radiation to warm the surface, strengthening latent heat fluxes and promoting boundary-layer growth and moistening. These processes progressively erode convective inhibition from below, while free-tropospheric adjustment becomes dominant only near the convective peak, implying a distinct pathway of convective preconditioning over land. Topography and diurnally forced circulations further modulate wave evolution by locally triggering convection ahead of the large-scale active phase, partially offsetting wave-scale inhibition and advancing convective maxima. This work demonstrates that land-atmosphere interactions substantially reshape CCKW structure and convection over Central Africa, highlighting the limitations of ocean-based Kelvin-wave frameworks for continental environments.