TY - JOUR
T1 - The Relationships Between Cloud Top Radiative Cooling Rates, Surface Latent Heat Fluxes, and Cloud-Base Heights in Marine Stratocumulus
AU - Zheng, Youtong
AU - Rosenfeld, Daniel
AU - Li, Zhanqing
N1 - Publisher Copyright:
©2018. American Geophysical Union. All Rights Reserved.
PY - 2018/10/27
Y1 - 2018/10/27
N2 - 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.
AB - 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.
KW - cloud-surface coupling
KW - marine stratocumulus
UR - http://www.scopus.com/inward/record.url?scp=85055651977&partnerID=8YFLogxK
U2 - 10.1029/2018JD028579
DO - 10.1029/2018JD028579
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AN - SCOPUS:85055651977
SN - 2169-897X
VL - 123
SP - 11,678-11,690
JO - Journal of Geophysical Research: Atmospheres
JF - Journal of Geophysical Research: Atmospheres
IS - 20
ER -