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Estimating the Decoupling Degree of Subtropical Marine Stratocumulus Decks From Satellite
Author(s) -
Zheng Youtong,
Rosenfeld Daniel,
Li Zhanqing
Publication year - 2018
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2018gl078382
Subject(s) - advection , decoupling (probability) , subtropics , environmental science , submarine pipeline , satellite , meteorology , marine stratocumulus , climatology , atmospheric sciences , geology , oceanography , geography , physics , control engineering , astronomy , fishery , biology , engineering , aerosol , thermodynamics
The decoupling degree of stratocumulus (Sc) decks is an important quantity dictating evolutions of Sc. In subtropical oceans, the Sc decoupling is a key intermediate process of the Sc‐to‐cumulus transitions, a persistent phenomenon that is not fully understood. This study introduces a new approach for estimating the degree of decoupling of subtropical Sc decks using passive satellite sensors. This method is limited to regions where Sc decks are advected over progressively warmer water. This is most common in the subtropics. The estimation concept is that decoupled Sc clouds under cold‐advection conditions are fed by spreading of the tops of cumulus clouds that are coupled. The cumulus clouds constitute a much larger liquid water path over small areas, which is identified by a positive skewness of the liquid water path, a quantity measurable from high‐resolution satellite data. The decoupling degree here is defined as the difference between the Sc cloud‐base height and lifting condensation level that is the cumulus cloud‐base height under cold‐advection conditions. This concept and the satellite‐based estimations are supported by ship measurements over the Northeast Pacific. One‐year climatology of the satellite‐inferred decoupling degree was generated over the same region, revealing a coherent pattern of offshore decoupling, consistent with previous theory and field‐campaign observations.