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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 07 Jan 2019

Research article | 07 Jan 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Spatial and temporal variability of snowfall over Greenland from CloudSat observations

Ralf Bennartz1,2, Frank Fell3, Claire Pettersen2, Matthew D. Shupe4, and Dirk Schuettemeyer5 Ralf Bennartz et al.
  • 1Earth and Environmental Sciences Department, Vanderbilt University, Nashville, Tennessee, USA
  • 2Space Science and Engineering Center, University of Wisconsin – Madison, Madison, Wisconsin, USA
  • 3Informus GmbH, Berlin, Germany
  • 4Physical Sciences Division, Cooperative Institute for Research in Environmental Science and NOAA Earth System Research Laboratory, Boulder, Colorado, USA
  • 5ESA-ESTEC, Nordwijk, The Netherlands

Abstract. We use the CloudSat data record 2006–2016 to estimate snowfall over the Greenland Ice Sheet (GrIS). We first evaluate CloudSat snowfall retrievals with respect to remaining ground-clutter issues. Comparing CloudSat observations to the GrIS topography (obtained from airborne altimetry measurements during IceBridge) we find that at the edges of the GrIS spurious high snowfall retrievals caused by ground clutter occasionally affect the operational snowfall product. After correcting for this effect, the height of the lowest valid CloudSat observation is about 1200 meters above the local topography as defined by IceBridge. We then use ground-based Millimeter Wavelength Cloud Radar (MMCR) observations obtained from the Integrated Characterization of Energy, Clouds, Atmospheric state, and Precipitation at Summit, Greenland (ICECAPS) experiment to devise a simple, empirical correction to account for precipitation processes occurring between the height of the observed CloudSat reflectivities and the snowfall near the surface. Using the height-corrected, clutter-cleared CloudSat reflectivities we next evaluate various Z-S relationships in terms of snowfall accumulation at Summit through comparison with weekly stake field observations of snow accumulation available since 2007. Using a set of three Z-S relationships that best agree with the observed accumulation at Summit, we then calculate the annual cycle snowfall over the entire GrIS as well as over different drainage areas and compare the so-derived mean values and annual cycles of snowfall to ERA-Interim reanalysis. We find the annual mean snowfall over the GrIS inferred from CloudSat to be 34 ± 7.5 cm/yr liquid equivalent (where the uncertainty is determined by the range in values between the three different Z-S relationships used). In comparison, the ERA-Interim reanalysis product only yields 30 cm/yr liquid equivalent snowfall, where the majority of the underestimation in the reanalysis appears to occur in the summer months over the higher GrIS and appears to be related to shallow precipitation events. Comparing all available estimates of snowfall accumulation at Summit Station, we find the annually averaged liquid equivalent snowfall from the stake field to be between 20 and 24 cm/yr, depending on the assumed snowpack density, and from CloudSat 23 ± 4.5 cm/yr. The annual cycle at Summit is generally similar between all data sources, with the exception of ERA-Interim reanalysis, which shows the aforementioned under-estimation during summer months.

Ralf Bennartz et al.
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Ralf Bennartz et al.
Ralf Bennartz et al.
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Publications Copernicus
Short summary
The Greenland Ice Sheet (GrIS) is rapidly melting. Snowfall is the only source of ice mass over the GrIS. We use satellite observations to assess how much snow on average falls over the GrIS and what the annual cycle and spatial distribution of snowfall is. We find the annual mean snowfall over the GrIS inferred from CloudSat to be 34 ± 7.5 cm/yr liquid equivalent. To our knowledge, this study is the first to address snowfall over the GrIS using CloudSat observations.
The Greenland Ice Sheet (GrIS) is rapidly melting. Snowfall is the only source of ice mass over...