Bruce A. Albrecht — University of Miami
Virendra Prakash Ghate — Argonne National Laboratory
Ming Fang — University of Miami
Category
Dynamics/Vertical Motion
Description
Time-height display. The upper panel is vertical velocity and the lower panel is the EDR calculated from spectrum width. The data were recorded by the SGP MMCR during 03:00 to 04:00 UTC on 26 March 2005.
Observations from the Atmospheric Radiation Measurement (ARM) millimeter wavelength cloud radar (MMCR) are used to examine the turbulence structure associated with 18 hours of stratocumulus observations over the Southern Great Plains site. The MMCR has a 0.2° angular resolution that limits the influence of shear and the coupled term on the spectrum width measurements and makes this radar particularly suitable for estimating turbulence in clouds. The magnitude of the energy dissipation rate (EDR) calculated from spectrum width agrees with that calculated from turbulent velocity power spectra. The EDR calculated from the spectrum width is more self-consistent, robust, and reliable than that from the resolvable velocity power spectra. Because moments are generated from an averaged Doppler spectrum, the single MMCR-measured spectrum width, as well as its spatial or temporal average, can be used to compute EDR. In the time-height display for the case investigated, updraft cores correspond to low EDR areas. Larger EDR values surround the updraft core and appear on the top and edges of the updraft core. In contrast to the updraft, the downdraft often corresponds to a large EDR area. These large and low EDR value areas constitute a wave train that is not easy to recognize in the velocity and reflectivity fields.
