Atmos. Chem. Phys. Discuss., 11, 13469-13524, 2011
© Author(s) 2011. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Moisture and dynamical interactions maintaining decoupled Arctic mixed-phase stratocumulus in the presence of a humidity inversion
A. Solomon1,2, M. D. Shupe1,2, P. O. G. Persson1,2, and H. Morrison3
1CIRES, University of Colorado, Boulder, CO, USA
2Earth System Research Laboratory/NOAA, Boulder, CO, USA

Abstract. Observations suggest that processes maintaining subtropical and Arctic stratocumulus differ, due to the different environments in which they occur. For example, specific humidity inversions (specific humidity increasing with height) are frequently observed to occur coincident with temperature inversions in the Arctic, while they do not occur in the subtropics. In this study we use nested LES simulations of decoupled Arctic Mixed-Phase Stratocumulus (AMPS) clouds observed during the DOE Atmospheric Radiation Measurement Program's Indirect and SemiDirect Aerosol Campaign (ISDAC) to analyze budgets of water components, potential temperature, and turbulent kinetic energy. These analyses quantify the processes that maintain decoupled AMPS, including the role of the humidity inversions. The results show the maintenance of liquid clouds in both the shallow upper entrainment zone (temperature and humidity inversion) due to a down gradient transport of water vapor by turbulent fluxes into the cloud layer and direct condensation by radiative cooling, and in the updrafts of the mixed-layer eddies below cloud top due to buoyant destabilization. These processes cause at least 20 % of the cloud liquid water to extend into the inversion. The redistribution of water vapor from the top of the humidity inversion to the base of the humidity inversion maintains the cloud layer while the mixed layer-entrainment zone system is continually losing total water. In this decoupled system, the humidity inversion is the only source of water vapor for the cloud system since water vapor from the surface layer is not efficiently transported into the mixed layer. Sedimentation of ice is the dominant sink of moisture from the mixed layer.

Citation: Solomon, A., Shupe, M. D., Persson, P. O. G., and Morrison, H.: Moisture and dynamical interactions maintaining decoupled Arctic mixed-phase stratocumulus in the presence of a humidity inversion, Atmos. Chem. Phys. Discuss., 11, 13469-13524, doi:10.5194/acpd-11-13469-2011, 2011.
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