An Unexpected Peak in Daytime Convection Initiation Weakens Diurnal Amplitude of Tropical Oceanic Precipitation and Cloud Cover

Abstract Earth system models (ESM) are still deficient in their representation of the diurnal cycle of tropical oceanic cloud cover and rain, underestimating cloud cover throughout the diurnal cycle and simulating an overnight rainfall peak that is slightly too early. To better understand the diurnal cycle of tropical oceanic rain and cloud cover, the diurnal cycle of deep convective system (DCS) initiation and the subsequent later‐stage accumulation of rainfall resulting from systems initiating at earlier times is analyzed using Lagrangian‐tracked DCSs. The Tracking Of Organized Convection Algorithm through 3D segmentatioN (TOOCAN) DCSs are matched to the Integrated Multi‐satellitE Retrieval for GPM rainfall product and binned by their hour of initiation (in local solar time) to evaluate morphological characteristics and contributions to rain and cloud cover diurnal cycles. Two peaks of DCS initiation are observed: an anticipated overnight peak and an unexpected late morning peak that is earlier than the expected afternoon peak in surface heating. DCSs initiated within the daytime peak have similar morphologies to DCSs initiated overnight and significantly contribute to the afternoon rain and cloud cover likely important for explaining the decreased amplitude of the over‐ocean diurnal cycle. When daytime‐initiated DCSs are excluded from the computation of the precipitation diurnal cycle, we find a closer resemblance to the NASA‐GISS ESM simulated diurnal cycle amplitude, suggesting that daytime DCS initiations may be too few or not maintained in ESMs that exhibit an over‐ocean diurnal cycle amplitude that exceeds observational estimates.