Monday, 24 October 2005
Alvarado F and Atria (Hotel Albuquerque at Old Town)
Two years of cold season boundary layer stratocumulus observed by Millimeter-Wave Cloud Radar (MMCR) over the ACRF (Atmospheric Radiation Measurement Program Climate Research Facility) in Northern Oklahoma have been analyzed to determine the characteristic structure and behavior of turbulence for the continental cloud-topped boundary layer. Analysis is confined to nondrizzling or lightly drizzling cloud systems for which precipitation does not unduly bias the Doppler velocity field. Under such assumptions the Doppler velocity field may be considered a proxy for vertical velocity. Although the scan strategy is optimized to detect a wide variety of tropospheric clouds, for many cases the radar is able to sample coherent eddy structures in cloud-topped boundary layers. Vertical velocity variance and skewness are contrasted to their counterparts in marine stratocumulus. Variance profiles show generally weaker turbulent intensity than is found in typical marine boundary layers, though this may be somewhat a consequence of the data averaging period. Variations in skewness imply that continental stratocumulus are driven by a combination of cloud-top radiative and surface forcing. Results from large eddy simulation show that the skewness profile is very sensitive to evaporation of droplets below cloud base.
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