Spatial and temporal variability of snowfall over Greenland from CloudSat observations
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Published:2019-06-21
Issue:12
Volume:19
Page:8101-8121
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ISSN:1680-7324
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Container-title:Atmospheric Chemistry and Physics
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language:en
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Short-container-title:Atmos. Chem. Phys.
Author:
Bennartz RalfORCID, Fell FrankORCID, Pettersen ClaireORCID, Shupe Matthew D.ORCID, Schuettemeyer Dirk
Abstract
Abstract. We use the CloudSat 2006–2016 data record 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 m
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 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−1
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−1 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−1, depending on the assumed snowpack density and from CloudSat 23±4.5 cm yr−1. The annual cycle at Summit is generally similar between
all data sources, with the exception of ERA-Interim reanalysis, which shows
the aforementioned underestimation during summer months.
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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