Exploiting Mie Scattering in KAZR Radial Velocities to Retrieve Air Motion and Raindrop Size Distributions

Williams, C. C., University of Colorado Boulder

Vertical Velocity

Convective Processes

Williams CR, RM Beauchamp, and V Chandrasekar. 2016. "Vertical Air Motions and Raindrop Size Distributions Estimated Using Mean Doppler Velocity Difference From 3- and 35-GHz Vertically Pointing Radars." IEEE Transactions on Geoscience and Remote Sensing, 54(10), 10.1109/tgrs.2016.2580526.


Top row: Observations from 3-GHz (cyan) and KAZR (black). Bottom row: Retrievals from new technique (red) and 449-MHz radar reference (black).


Top row: Observations from 3-GHz (cyan) and KAZR (black). Bottom row: Retrievals from new technique (red) and 449-MHz radar reference (black).

Science

In order to improve our modeling of raindrop breakup and coalescence processes, we need innovative retrieval techniques that convert ARM radar observations into vertical columns of air motion and raindrop size distributions (DSDs). A new retrieval technique (Williams et al. 2016) exploits the Mie scattering signatures in KAZR (Ka-band ARM Zenith Radar) to estimate air motion and raindrop size distributions.

Impact

Vertically pointing radars observe the net raindrop radial motion, which is a combination of falling raindrops embedded in updrafts and downdrafts. It is difficult to isolate air motion from raindrop motion using a single radar. By using two radars operating at different frequencies (which have difference sensitivities to Rayleigh and Mie scattering), differences in radial velocities are due to differences in the shape of the raindrop size distributions. Also, similar variations contained in both radial velocities are due to vertical air motion variations.

Summary

A new retrieval technique (Williams et al. 2016) estimating air motion and raindrop size distributions was developed and verified using 3- and 35-GHz radar observations collected during the MC3E field campaign. The retrieval technique can be applied to different pairs of ARM radar frequencies, included RWP (Radar Wind Profiler) and KAZR (0.915 and 35 GHz), RWP and W-band (0.915 and 95 GHz), and KAZR and W-band (35 and 95 GHz). The ability to retrieve air motion and raindrop size distributions from multiple sites over many seasons will help us investigate and improve model representations of raindrop breakup and coalescence processes.