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The Relationships Between Cloud Top Radiative Cooling Rates, Surface Latent Heat Fluxes, and Cloud‐Base Heights in Marine Stratocumulus
Author(s) -
Zheng Youtong,
Rosenfeld Daniel,
Li Zhanqing
Publication year - 2018
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2018jd028579
Subject(s) - latent heat , environmental science , marine stratocumulus , atmospheric sciences , cloud forcing , radiative cooling , longwave , climatology , cloud base , meteorology , radiative transfer , radiative forcing , cloud computing , geology , geography , aerosol , physics , quantum mechanics , computer science , operating system
Cloud top radiative cooling (CTRC) drives turbulence in marine boundary layers (MBLs) topped by stratocumulus clouds. This study examines the role of CTRC in regulating the surface‐cloud coupling, surface latent heat fluxes, and cloud base height by exploiting a 6‐month worth of shipborne observations over the subtropical northeast Pacific in combination with geostationary satellite data. We find that owning to the prevailing equatorward flow that advects stratocumulus clouds over warmer sea surfaces, the vast majority of the decoupled stratocumulus decks are fed by divergence from the tops of underlying cumulus, forming cumulus‐coupled MBL. The cumulus‐coupled and well‐mixed MBL dominate the subtropical MBL regimes. We find that strong CTRC favors greater (smaller) occurrence frequency of well‐mixed (cumulus‐coupled) MBLs. In well‐mixed MBLs, strong CTRC enhances entrainment of dry free‐tropospheric air, desiccates the MBL, increases the surface latent heat fluxes, and elevates the cloud‐base height. This is demonstrated by the observed covariabilities between the CTRC rate and surface latent heat fluxes and cloud‐base height. The relationships are more statistically significant in conditions where the inversion strength is relatively weak, and thus, the entrainment is more effective. In cumulus‐coupled MBLs, however, the influence of CTRC in regulating the surface moisture is not detected by the ship observations. The much greater latent heat fluxes than the CTRC rate in cumulus‐coupled MBLs suggest stronger surface forcing, which substantially tames the footprint of CTRC.