Global Character of Latent Heat Release in Oceanic Warm Rain Systems

Abstract

Warm rain plays an important role in Earth's water and energy cycles. Little is known, however, about the global character of latent heat release from warm rain regimes owing to a lack of satellite observations with sufficient sensitivity to this often light, sometimes isolated, precipitation. The Wisconsin Algorithm for Latent heating and Rainfall Using Satellites (WALSRUS) utilizes CloudSat's W-band Cloud Profiling Radar to estimate vertical profiles of latent heating, surface rainfall rate, and related processes across all oceanic warm rain regimes. This study examines a 4-year climatology of monthly mean WALRUS estimates to document the global character of latent heating in oceanic warm rain and quantify the sensitivity of underlying condensation and evaporation processes to bulk properties of the large-scale environment. Warm rain is found to make up 9.2% of oceanic global rainfall and 13.9% of oceanic tropical rainfall. Convective warm rain contributes 36% of rain accumulation and 50% of column latent heating even though its occurrence frequency is only 11%. Net pressure-weighted column-integrated latent heating from warm rain condensation averages 0.15 K day−1 of atmospheric heating, with nearly equal contribution from convective and shallow warm rain. While warm rain is found throughout the globe, the Intertropical Convergence Zone is a notable warm rain hot spot peaking near 1 K day−1. The mean height of the maximum condensation in warm rain is 1.5 ± 0.6 km and found to be generally invariant to atmospheric stability. On the other hand, the depth of the entrainment cooling layer decreases with increasing inversion strength.