Preprints
https://doi.org/10.5194/acp-2022-136
https://doi.org/10.5194/acp-2022-136
 
09 Mar 2022
09 Mar 2022
Status: this preprint is currently under review for the journal ACP.

Highly supercooled riming and unusual triple-frequency radar signatures over Antarctica

Frédéric Tridon1,a, Israel Silber2, Alessandro Battaglia3,4, Stefan Kneifel1, Ann Fridlind5, Petros Kalogeras4, and Ranvir Dhillon4 Frédéric Tridon et al.
  • 1Institute for Geophysics and Meteorology, University of Cologne, Cologne, Germany
  • 2Department of Meteorology and Atmospheric Science, Pennsylvania State University, University Park, PA, USA
  • 3DIATI, Politecnico di Torino, Turin, Italy
  • 4University of Leicester, Leicester, UK
  • 5NASA Goddard Institute for Space Studies, New York, NY, USA
  • anow at: DIATI, Politecnico di Torino, Turin, Italy

Abstract. Riming of ice crystals by supercooled water droplets is an efficient ice growth process, but its basic properties are still poorly known. While it has been shown to contribute significantly to surface precipitation at mid-latitudes, little is known about its occurrence at high latitudes. In Antarctica, two competing effects can influence the occurrence of riming: the scarcity of supercooled liquid water clouds due to the extremely low tropospheric temperatures and the low aerosol concentration, which may lead to the formation of fewer and larger supercooled drops potentially resulting in an enhanced riming efficiency.

In this work, by exploiting the deployment of an unprecedented number of multi-wavelength active and passive remote sensing systems (including triple-frequency radar measurements) in West Antarctica, during the Atmospheric Radiation Measurements West Antarctic Radiation Experiment (AWARE) field campaign, we evaluate the importance of riming incidence in Antarctica and find that riming occurs at much lower temperatures compared to the mid-latitudes.

We then focus on a case study featuring a persistent layer of unexpectedly pronounced triple-frequency radar signatures but only a relatively modest amount of supercooled liquid water. In-depth analysis of the radar observations suggests that such signatures can only be explained by the combined effects of moderately rimed aggregates or similarly shaped florid polycrystals and a narrow particle size distribution (PSD). Simulations of this case study performed with a 1D bin model %by introducing an additional class corresponding to rimed ice indicate that similar triple frequency radar observations can be reproduced when narrow PSDs are simulated. Such narrow PSDs can in turn be explained by two key factors: (i) the presence of a shallow homogeneous droplet or humidified aerosol freezing layer aloft seeding an underlying supercooled liquid layer, and (ii) the absence of turbulent mixing throughout a stable polar atmosphere that sustains narrow PSDs, as hydrometeors grow from the nucleation region aloft to several millimeter ice particles, by vapor deposition and then riming.

Frédéric Tridon et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-136', Anonymous Referee #1, 29 Mar 2022
  • RC2: 'Comment on acp-2022-136', Anonymous Referee #2, 26 Apr 2022

Frédéric Tridon et al.

Frédéric Tridon et al.

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Short summary
The role of ice precipitation in the Earth water budget is not well known because ice particles are complex, and their formation involves intricate processes. Riming of ice crystals by supercooled water droplets is an efficient process, but little is known about its importance at high latitudes. In this work, by exploiting the deployment of an unprecedented number of remote sensing systems in Antarctica, we find that riming occurs at much lower temperatures compared to the mid-latitudes.
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