Atmos. Chem. Phys. Discuss., 11, 597-625, 2011
© Author(s) 2011. This work is distributed
under the Creative Commons Attribution 3.0 License.
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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.
An analysis of cloud overlap at a midlatitude atmospheric observation facility
L. Oreopoulos1 and P. M. Norris2,3
1Laboratory for Atmospheres, NASA-GSFC, Greenbelt, MD, USA
2Global Modeling and Assimilation Office, NASA-GSFC, Greenbelt, MD, USA
3GEST, University of Maryland Baltimore County, Baltimore, MD, USA

Abstract. An analysis of cloud overlap based on high temporal and vertical resolution retrievals of cloud condensate from a suite of ground instruments is performed at a mid-latitude observational facility. Two facets of overlap are investigated: cloud fraction overlap, expressed in terms of a parameter "alpha" indicating the relative contributions of maximum and random overlap, and overlap of horizontal distributions of condendsate, expressed in terms of the correlation coefficient of condensate ranks. The degree of proximity to the random and maximum overlap assumptions is also expressed in terms of a decorrelation length, a convenient scalar parameter that emerges under the assumption that overlap parameters decay exponentially with separation distance. Both cloud fraction overlap and condensate overlap show significant seasonal variations with a clear tendency for overlap to be closer to maximum for summer months. A tendency for more maximum overlap is also observed as the size of the domain used to define cloud fractions increases. These dependencies are significantly weaker for rank correlations. Hitherto unexplored overlap parameter dependencies are investigated by analyzing mean parameter value differences at fixed separation distance within different layers of the atmospheric column, and by searching for possible systematic relationships between alpha and rank correlation. We find that for the same separation distance the overlap parameters are significantly distinct in different atmospheric layers, and that a tendency exists for random cloud fraction overlap to be generally in sync with more random overlap of condensate ranks.

Citation: Oreopoulos, L. and Norris, P. M.: An analysis of cloud overlap at a midlatitude atmospheric observation facility, Atmos. Chem. Phys. Discuss., 11, 597-625, doi:10.5194/acpd-11-597-2011, 2011.
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