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Fair - Weather Cumuli Climatology at the TWP ARM Site

Kollias, P. and Albrecht B.A., University of Miami
Twelfth Atmospheric Radiation Measurement (ARM) Science Team Meeting

Fair-weather cumuli are fundamental in regulating the vertical structure of water vapor and entropy in the lowest 2 km of the Earths atmosphere over vast areas of the oceans. Over two years of data from the mm-wavelength cloud radar, at the Nauru (TWP-ARM) site, are analyzed and a statistical description of the field of fair weather cumulus is inferred. Frequency diagrams of cloud thickness, fractional coverage, updraft-downdraft magnitudes and cloud reflectivity are calculated for four different classes of fair weather cumuli. Seasonal patterns are identified and their relationship to the thermodynamic structure of the boundary layer (wet-dry periods) is investigated. The boundary layer is predominately stable. As a result of the thermodynamic state of the boundary layer, the shallow boundary layer clouds observed over the ARM-TWP site are a manifestation of the growing thermal in the mixed layer. This study provides an observational data set appropriate for testing fair weather cumulus realizations in LES.

Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).