Improved rain rate and drop size retrievals from airborne Doppler radar

Abstract

Abstract. Satellite remote sensing of rain is important for quantifying the hydrological cycle, atmospheric energy budget, and cloud and precipitation processes; however, radar retrievals of rain rate are sensitive to assumptions about the raindrop size distribution. The upcoming EarthCARE satellite will feature a 94 GHz Doppler radar alongside lidar and radiometer instruments, presenting opportunities for enhanced retrievals of the raindrop size distribution.We demonstrate the capability to retrieve rain rate as a function of drop size and drop number concentration from airborne 94 GHz Doppler radar measurements using CAP-TIVATE, the variational retrieval algorithm developed for EarthCARE. For a range of rain regimes observed during the Tropical Composition, Cloud and Climate Coupling field campaign, we explore the contributions of mean Doppler velocity and path-integrated attenuation (PIA) measurements to the retrieval of rain rate, and the retrievals are evaluated against independent measurements from an independent 9.6 GHz Doppler radar. The retrieved drop number concentrations vary over 5 orders of magnitude between very light rain from melting ice and warm rain from liquid clouds. In light rain conditions mean Doppler velocity facilitates estimates of rain rate without PIA, suggesting the possibility of EarthCARE rain rate estimates over land; in moderate warm rain, drop number concentration can be retrieved without mean Doppler velocity, with possible applications to CloudSat.

On the distinctiveness of oceanic raindrop regimes

“…increasing from about 3.5 to 4.0. This is roughly in line with the a priori N w used for rain by Mason et al (2017) of 3.9e3, or 3.59 in log space. It is noted that the distributions of D m and µ are not particularly Gaussian, with the means and medians separate, and N w only moderately Gaussian in log space.…”

Retrievals of Riming and Snow Density From Vertically Pointing Doppler Radars

“…The CAPTIVATE retrieval framework (Mason et al, ) has been developed for radar‐lidar‐radiometer synergy retrievals from EarthCARE (Illingworth et al, ). CAPTIVATE therefore includes instrument forward models for the Doppler radar and high‐spectral resolution lidar (HSRL) aboard EarthCARE but is also designed to be easily configurable for active and passive sensors on ground‐based and airborne platforms.…”

The Microphysics of Stratiform Precipitation During OLYMPEX: Compatibility Between Triple‐Frequency Radar and Airborne In Situ Observations

“…A more quantitative assessment can be drawn by exploiting the outputs of the retrieval algorithm developed in this study. It is based on optimal estimation (Rodgers, ), which has been already successfully applied in the area of cloud and precipitation remote sensing (e.g., by Battaglia, Mroz, Lang, et al, ; Battaglia, Mroz, Tanelli et al, ; Delanoë & Hogan, ; Grecu et al, ; Mace et al, ; Mason et al, ; Mason et al, ; Munchak & Kummerow, ; Tridon & Battaglia, ; Tridon et al, ). While multifrequency radar observations are the backbone of this retrieval methodology, it can also easily assimilate vertically integrated information such as the path integrated attenuation (PIA) such as in Battaglia, Mroz, Lang, et al ().…”

“…By exploiting the frequency dependence of the interaction between hydrometeors and microwave radiation (Lhermitte, ), multifrequency radars have the potential to provide improved profiles of precipitation rates and of the microphysical properties of the ice and rain particle size distributions (PSDs). Previously, several multifrequency cloud radar techniques have been proposed to derive precipitating ice (Leinonen et al, ; Mason et al, ; Matrosov, ; Turk et al, ) and rain (Firda et al, ; Mason et al, ; Tridon et al, ) in stratiform systems, but few of them provide a simultaneous description of the ice and rain profile (Gaussiat et al, ; Grecu et al, ; ; Seto et al, ). Three points make such a retrieval challenging: The properties of ice crystals are extremely variable (size, shape, and structure), which makes their microwave scattering properties complex.…”