Evaluation of vertical velocity and air density correction assumptions using collocated 94-GHz radar and Doppler lidar in light rain

Vertical velocity retrievals have been identified as beneficial for the improvement of climate modeling efforts, with recent emphasis calling for accurate retrievals within precipitating clouds and deep convective storms. Nevertheless, the most mature and accurate retrievals for absolute vertical velocity measurement are available only within nonprecipitating environments. For many radar-based velocity retrievals, these efforts require significant averaging and/or restrictive assumptions for the fall speeds of hydrometeors at altitude.

Under certain light rain conditions, two established technologies for vertical velocity retrievals are simultaneously available. Doppler lidars are capable of accurate true air motion retrievals unaffected by air density assumptions and limited only by eventual attenuation in heavier rainfall and cloud. Vertically-pointing 94-GHz radar retrieval techniques are less sensitive to attenuation in rain and capitalize on nonRayleigh scattering of select raindrop sizes to perform accurate drop fall speed to air motion conversions. However, air density and drop fall speed conversions, to the accuracies claimed by 94-GHz retrieval efforts, have not been fully vetted for light precipitating conditions.

We explore the performance of both Lidar and 94-GHz radar techniques for vertical velocity retrievals under light rain conditions under which both systems are viable. Observations are performed using collocated systems at the ARM central facility in Lamont, Oklahoma during the MC3E field campaign in 2011 for which high resolution temporal atmospheric sounding information was also simultaneously available.