Millimeter-Wavelength Radar Observations of Updrafts, Downdrafts and Turbulence in Fair Weather Cumuli

Millimeter-wavelength Doppler radars are ideal tools for studying dynamical processes in fair-weather cumuli. In this paper we use observations made with a surface-based, upward-facing 94 GHz Doppler radar to examine the vertical structure of updrafts and downdrafts in fair weather cumuli and to provide a more general characterization of the turbulence structure of the clouds. Observations at high temporal sampling (1-sec dwell, 1-sec signal processing) provide Doppler spectra through the depth of fair-weather cumuli as they pass over the radar. Samples from a large number of clouds were segregated to obtain the mean characteristics associated with both active and passive cloud elements. Active clouds sampled typically indicate adiabatic cores with downdrafts along the cloud boundaries and within the cloud that detrains below the trade inversion. Statistical characterizations of the clouds include statistics on Doppler moments as a function of cloud thickness, updraft/downdraft magnitudes, cloud-top entrainment events, and turbulence intensity. Attempts are in progress to document the three-dimensional structure of fair weather clouds by cross-plane scanning of ± 5-10 ^o