Turbulence and microphysical retrievals using mm-wavelength Doppler spectra

Millimeter wavelength radars are among the new tools that have been developed to study boundary layer clouds over the past 15 years. In a vertical pointing mode, Doppler velocity spectra from these radars and the moments of these spectra have provided a detailed description of the updraft and downdraft structures in stratocumulus and fair-weather cumulus clouds. In this paper we review and develop new retrieval techniques of turbulence and microphysics using mm-wavelength radar Doppler spectra observations in a variety of continental and marine boundary layer clouds. In the first part, emphasis is given in the detection of wind shear zones and estimation of turbulence dissipation rates. Cloud droplets' are good tracers of turbulent air velocity in the same way that smoke particles reveal turbulent eddies in a smoke filled room. Thus observations of turbulence intensity (e.g. dissipation rate, e) inside the cloud, can be very useful in defining the field of kinetic energy dissipation in the cloud. Observations in fair-weather cumulus and stratocumulus show Doppler spectrum bimodality created by the presence of sharp vertical velocity gradients such as those in the region between adjacent updrafts and downdrafts. The high spectrum width values in these areas can be used for the identification of shear zones as the radar vertical beam scans the cloud. In the second part, the retrieval of cloud and drizzle size distributions using Doppler spectra are evaluated and the use of higher Doppler spectra moments (skewness and kyrtosis) is investigated through modeling and observations in marine stratocumulus clouds.