A satellite and reanalysis view of cloud organization, thermodynamic, and dynamic variability within the subtropical marine boundary layer

Other literature type English OPEN
Kahn, Brian H. ; Matheou, Georgios ; Yue, Qing ; Fauchez, Thomas ; Fetzer, Eric J. ; Lebsock, Matthew ; Martins, João ; Schreier, Mathias M. ; Suzuki, Kentaroh ; Teixeira, João (2017)

The global-scale patterns and covariances of subtropical marine boundary layer (MBL) cloud fraction and spatial organization with atmospheric thermodynamic and dynamic fields remain poorly understood. We describe a novel approach that leverages coincident NASA A-train and the Modern Era Retrospective-Analysis for Research and Applications (MERRA) data to quantify the relationships in the subtropical MBL derived at the native pixel and grid resolution. Four subtropical oceanic regions that capture transitions from closed-cell stratocumulus to open-cell trade cumulus are investigated. We define stratocumulus and cumulus regimes based exclusively from infrared-based thermodynamic phase. Visible reflectances are normally distributed within stratocumulus and are increasingly skewed away from the coast where disorganized cumulus dominates. Increases in MBL depth, wind speed and effective radius (r<sub>e</sub>), and reductions in 700&ndash;1000&thinsp;hPa moist static energy differences and 700 and 850&thinsp;hPa vertical velocity, correspond with increases in reflectance skewness. We posit that a more robust representation of the cloudy MBL is obtained using visible reflectance rather than retrievals of optical thickness that are limited to a smaller subset of cumulus. An increase in re within shallow cumulus is strongly related to higher MBL wind speeds that further correspond to increased precipitation occurrence according to CloudSat. Our results are consistent with surface-based observations and suggest that the combination of A-train and MERRA data sets have potential to add global context to our process understanding of the subtropical cumulus-dominated MBL.
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