Estimating turbulence characteristics with the Wyoming Cloud Radar

Marie Lothon

NCAR

In summer, marine stratocumulus often cover extensive areas of the subtropical oceans off the west coasts of the main continents. Their major effect on the global radiation budget has led to focused studies to better understand the processes that control their evolution. One of these was the DYCOMS-II experiment, which took place off the coast of California in the summer of 2001. During this experiment, the 3 mm Wyoming Cloud Radar (WCR) was mounted on the NCAR C-130 aircraft with both downward- and backward-looking antennas, with an angle of 32.5 degrees between them. Reflectivity and Doppler velocities were measured along both beams. Our aim here is to delineate turbulence structure as a function of height throughout the drizzling marine boundary layer.

We want to deduce the turbulence characteristics from the fine-structure of the Doppler velocity field, especially turbulence dissipation and integral scales. One essential step for this study is to appraise the fluctuations in Doppler velocity due to the fluctuations in the terminal fall velocity of hydrometeors. Using microphysics probe measurements, we estimated this contribution from the spatial distribution of the drop counts in each bin. As a second important step, we also studied the effect of the velocity averaging within the pulse resolution volume. Although the WCR dissipation estimates still need to be corrected for these effects, a comparison of turbulence characteristics with in situ measurements using the aircraft air motion sensing system will be shown.