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https://doi.org/10.5194/acp-2020-993
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-993
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  12 Oct 2020

12 Oct 2020

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This preprint is currently under review for the journal ACP.

The Prevalence of Precipitation from Polar Supercooled Clouds

Israel Silber1, Ann M. Fridlind2, Johannes Verlinde1, Andrew S. Ackerman2, Grégory V. Cesana2,3, and Daniel A. Knopf4 Israel Silber et al.
  • 1Department of Meteorology and Atmospheric Science, Pennsylvania State University, University Park, PA, USA
  • 2NASA Goddard Institute for Space Studies, New York, NY, USA
  • 3Center for Climate Systems Research, Earth Institute, Columbia University, New York, NY, USA
  • 4School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY, USA

Abstract. Supercooled clouds substantially impact polar surface energy budgets but large-scale models often underestimate their occurrence, which motivates accurately establishing metrics of basic processes. An analysis of long-term measurements at Utqiaġvik, Alaska, and McMurdo Station, Antarctica, combines lidar-validated use of soundings to identify supercooled cloud layers and colocated ground-based profiling radar measurements to quantify cloud base precipitation. We find that more than 85 % (75 %) of sampled supercooled layers are precipitating over the Arctic (Antarctic) site, with more than 75 % (50 %) precipitating continuously to the surface. Such high frequencies can be reconciled with substantially lesser spaceborne estimates by considering differences in radar hydrometeor detection sensitivity. While ice precipitation into supercooled clouds from aloft is common, we also find that the great majority of supercooled cloud layers without ice falling into them are themselves continuously generating precipitation. Such sustained primary ice formation is consistent with continuous activation of immersion-mode ice nucleating particles (INPs), suggesting that supercooled cloud formation is a principal gateway to ice formation at temperatures greater than ~ −38 °C over polar regions. The prevalence of weak precipitation fluxes is also consistent with supercooled cloud longevity, and with well-observed and widely simulated case studies. An analysis of colocated microwave radiometer retrievals suggests that weak precipitation fluxes can be nonetheless consequential to moisture budgets for supercooled clouds owing to small liquid water paths. Finally, we suggest that these ground-based precipitation rate statistics offer valuable guidance for improving the representation of polar cloud processes in large-scale models.

Israel Silber et al.

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Israel Silber et al.

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Short summary
Long-term ground-based radar and sounding measurements over Alaska (Antarctica) indicate that more than 85 % (75 %) of supercooled clouds are precipitating at cloud base, and 75 % (50 %) are precipitating to the surface. Such high prevalence is reconciled with lesser spaceborne estimates by considering radar sensitivity. Results provide a strong observational constraint for polar cloud processes in large-scale models.
Long-term ground-based radar and sounding measurements over Alaska (Antarctica) indicate that...
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