P1.8 The transition from stratus topped to trade-wind cumulus topped marine boundary layer in global climate models

Monday, 9 June 2008
Johannes Karlsson, JPL, Pasadena, CA; and G. Svensson, J. Teixeira, and S. S. Cardoso

Large persistent decks of low, stratiform cloudiness can be found in the the eastern parts of the sub-tropical ocean basins. Due to large-scale subsidence and cold waters the marine boundary layer (MBL) is relatively shallow in these regions and upside down convection, triggered by the infrared cloud-top cooling are important for maintaining the well-mixed MBL. When the airmass is advected equatorward with the trade winds, it is exposed to increasing sea surface temperatures as well as decreasing subsidence. As a consequence of these changes in external forcing, the depth of the MBL is increasing and the stratus topped MBL evolves into a cumulus topped MBL.

We utilize data from the GCSS/WGNE Pacific Cross-section Intercomparison (GPCI) as well as satellite measurements, to investigate how well global models manage to simulate the above described cloud regime transition. We also distinguish the processes that are of importance for the growth of the MBL depth in the models.

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