Vertical Air Motion Retrievals From Airborne W-Band Cloud Radar

Chen, Haonan; Fairall, Christopher W; Williams, Christopher; Thompson, Elizabeth J

Citeable URL: https://scholar.colorado.edu/concern/articles/5h73px98r

Abstract

In-cloud vertical air motion is a key parameter to describe cloud dynamics and lifecycles. Short-wavelength ( Ka - and W -band) radars are often used to observe clouds and extract the vertical air motion from the radar-measured Doppler velocity. However, the vertical air motion retrieval techniques developed using ground-based radar Doppler spectrum may be problematic for airborne cloud radars due to nonideal radar system performance (e.g., receiver saturation) and the Doppler velocity measurement uncertainties caused by aircraft motion, aircraft speed, and the large aircraft motion induced horizontal wind. This article presents a new and simple approach for estimating the in-cloud vertical air motion using airborne W -band radar measurements, which is applicable to cloud measurements without precipitation or with weak precipitation. In particular, a power-law relation between cloud and precipitation particle fall speed and attenuation corrected radar reflectivity is established first. Then, the particle fall speeds estimated from radar reflectivity using the established power-law relation are compared with the radar-measured Doppler velocities to derive the vertical air motions. This technique is demonstrated with W -band airborne radar measurements from the National Oceanic and Atmospheric Administration Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign from January to February 2020, which was designed to investigate atmospheric shallow convection and air-sea interaction in the tropical North Atlantic east of Barbados. The retrieved in-cloud air motion is compared with results reported in the literature for a nearby domain, suggesting that this simple retrieval technique performs reasonably well. Since this approach is applicable for airborne radar measurements with high-frequency noises, it can be used as an effective tool for investigating the mean profile of vertical air motion.

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