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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/tc-2019-223
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2019-223
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 21 Nov 2019

Submitted as: research article | 21 Nov 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal The Cryosphere (TC).

Satellite Observations of Snowfall Regimes over the Greenland Ice Sheet

Elin A. McIlhattan1, Claire Pettersen2, Norman B. Wood2, and Tristan S. L'Ecuyer1 Elin A. McIlhattan et al.
  • 1Department of Atmospheric and Oceanic Sciences, University of Wisconsin-Madison, Madison, Wisconsin, USA
  • 2Space Science and Engineering Center, University of Wisconsin-Madison, Madison, Wisconsin, USA

Abstract. The mass of the Greenland Ice Sheet (GIS) is decreasing due to surface melt and ice dynamics. Snowfall both adds mass to the GIS and has the capacity to reduce surface melt by increasing surface brightness, reflecting additional solar radiation back to space. This study leverages the synergy between two satellite instruments, CloudSat's Cloud Profiling Radar (CPR) and CALIPSO's Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), to identify snowfall cases over the GIS and partition them into two regimes: those associated with exclusively ice-phase cloud processes (IC) and those involving mixed-phase processes indicated by the presence of super-cooled liquid water (CLW). Overall, most CPR observations of snowfall over the GIS come from IC events (70 %), however, during the summer months, close to half of the snow observed is produced in CLW events (45 %). IC snowfall plays a dominant role in building the GIS, producing ~80 % of the total estimated 399 Gt yr−1 accumulation. Beyond the cloud phase that defines the snowfall regimes, the macrophysical cloud characteristics are distinct as well; the mean IC geometric cloud depth (~4 km) is consistently deeper than the CLW geometric cloud depth (~2 km), consistent with previous studies based on surface observations. Two-dimensional histograms of the vertical distribution of CPR reflectivities show that IC events demonstrate consistent growth toward the surface while CLW events do not. Analysis of ERA5 reanalyses shows that IC events are associated with cyclone activity and CLW events occur under large scale anomalous high pressure. Ground-based data is used to estimate the sensitivity of CloudSat's CPR to the two snowfall regimes, finding that the space-based radar is sensitive enough to detect ~95 % of IC snowfall cases and ~75 % of CLW snowfall cases seen at the surface.

Elin A. McIlhattan et al.
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Elin A. McIlhattan et al.
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Short summary
Snowfall builds the mass of the Greenland ice sheet (GIS) and reduces melt by brightening the surface. We present satellite observations of GIS snowfall events, divided into two regimes: those coincident with ice clouds and those coincident with mixed-phase clouds. Snowfall from ice clouds plays the dominant role in building the GIS, producing ~80 % of the total accumulation. The two regimes have similar snowfall frequency in summer, brightening the surface when solar insolation is at its peak.
Snowfall builds the mass of the Greenland ice sheet (GIS) and reduces melt by brightening the...
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