Synergistic radar and sub-millimeter radiometer retrievals of ice hydrometeors in mid-latitude frontal cloud systems

Simon Pfreundschuh,Manfred Brath,Stefan A Buehler,Patrick Eriksson,Florian Ewald,Stuart Fox,Richard Cotton,David Duncan

doi:10.5194/amt-15-677-2022

Abstract

Abstract. Accurate measurements of ice hydrometeors are required to improve the representation of clouds and precipitation in weather and climate models. In this study, a newly developed, synergistic retrieval algorithm that combines radar with passive millimeter and sub-millimeter observations is applied to observations of three frontally generated, mid-latitude cloud systems in order to validate the retrieval and assess its capabilities to constrain the properties of ice hydrometeors. To account for uncertainty in the assumed shapes of ice particles, the retrieval is run multiple times while the shape is varied. Good agreement with in situ measurements of ice water content and particle concentrations for particle maximum diameters larger than 200 µm is found for one of the flights for the large plate aggregate and the six-bullet rosette shapes. The variational retrieval fits the observations well, although small systematic deviations are observed for some of the sub-millimeter channels pointing towards issues with the sensor calibration or the modeling of gas absorption. For one of the flights the quality of the fit to the observations exhibits a weak dependency on the assumed ice particle shape, indicating that the employed combination of observations may provide limited information on the shape of ice particles in the observed clouds. Compared to a radar-only retrieval, the results show an improved sensitivity of the synergistic retrieval to the microphysical properties of ice hydrometeors at the base of the cloud. Our findings indicate that the synergy between active and passive microwave observations may improve remote-sensing measurements of ice hydrometeors and thus help to reduce uncertainties that affect currently available data products. Due to the increased sensitivity to their microphysical properties, the retrieval may also be a valuable tool to study ice hydrometeors in field campaigns. The good fits obtained to the observations increase confidence in the modeling of clouds in the Atmospheric Radiative Transfer Simulator and the corresponding single scattering database, which were used to implement the retrieval forward model. Our results demonstrate the suitability of these tools to produce realistic simulations for upcoming sub-millimeter sensors such as the Ice Cloud Image or the Arctic Weather Satellite.

Highlights

The representation of clouds in climate models remains an important issue that causes significant uncertainties in their predictions (Zelinka et al, 2020)
For flight B984, the radar residuals show some scattered deviations located at the edge of the cloud, which are likely discretization artifacts
The main result from the experiments presented in this study is that we were able to find two ice particle shapes, the large plate aggregate and the six-bullet rosette, for which the results of the combined retrieval were consistent with the observations as well as the in situ-measured ice water content (IWC) and particle size distributions (PSDs) for flight B984

Summary

Introduction

The representation of clouds in climate models remains an important issue that causes significant uncertainties in their predictions (Zelinka et al, 2020). Improving and validating these models requires measurements that accurately characterize the distribution of hydrometeors in the atmosphere. At regional and global scales, such observations can be obtained efficiently only through remote sensing. Currently available remote-sensing observations do not constrain. S. Pfreundschuh et al.: Synergistic radar and sub-millimeter radiometer retrievals of ice hydrometeors the distribution of ice in the atmosphere well (Waliser et al, 2009; Eliasson et al, 2011; Duncan and Eriksson, 2018)

Objectives

Results

Discussion

Conclusion