Arctic sea ice may be declining faster than expected : study

Simplicissimus 25/10/2017

Arctic sea ice may be declining faster than expected: study
▻https://www.reuters.com/article/us-canada-arctic-research/arctic-sea-ice-may-be-declining-faster-than-expected-study-idUSKBN1CT2JD

https://s3.reutersmedia.net/resources/r/?m=02&d=20171024&t=2&i=1206815049&w=&fh=545px&fw=&ll=&pl=&sq=&r=LYNXMPED9N1JJ#.jpg

FILE PHOTO: A Russian border mark is pictured at the Nagurskoye military base in Alexandra Land on the remote Arctic islands of Franz Josef Land, Russia March 29, 2017. Picture taken March 29, 2017.
REUTERS/Sergei Karpukhin

Arctic sea ice may be thinning faster than predicted because salty snow on the surface of the ice skews the accuracy of satellite measurements, a new study from the University of Calgary said on Tuesday.
The report from the Canadian university’s Cryosphere Climate Research Group published in the academic journal Geophysical Research Letters found satellite estimates for the thickness of seasonal sea ice have been overestimated by up to 25 percent.
That means the Arctic Ocean could be ice-free much sooner than some scientific predictions, which forecast sea ice will first disappear completely during summer months between 2040 and 2050, according to lead author Vishnu Nandan.

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Simplicissimus @simplicissimus 25/10/2017

Effect of Snow Salinity on CryoSat-2 Arctic First-Year Sea Ice Freeboard Measurements - Nandan - 2017 - Geophysical Research Letters - Wiley Online Library
►http://onlinelibrary.wiley.com/doi/10.1002/2017GL074506/full
Abstract
The European Space Agency’s CryoSat-2 satellite mission provides radar altimeter data that are used to derive estimates of sea ice thickness and volume. These data are crucial to understanding recent variability and changes in Arctic sea ice. Sea ice thickness retrievals at the CryoSat-2 frequency require accurate measurements of sea ice freeboard, assumed to be attainable when the main radar scattering horizon is at the snow/sea ice interface. Using an extensive snow thermophysical property dataset from late winter conditions in the Canadian Arctic, we examine the role of saline snow on first-year sea ice (FYI), with respect to its effect on the location of the main radar scattering horizon, its ability to decrease radar penetration depth, and its impact on FYI thickness estimates. Based on the dielectric properties of saline snow commonly found on FYI, we quantify the vertical shift in the main scattering horizon. This is found to be approximately 0.07 m. We propose a thickness-dependent snow salinity correction factor for FYI freeboard estimates. This significantly reduces CryoSat-2 FYI retrieval error. Relative error reductions of ~11% are found for an ice thickness of 0.95 m and ~25% for 0.7 m. Our method also helps to close the uncertainty gap between SMOS and CryoSat-2 thin ice thickness retrievals. Our results indicate that snow salinity should be considered for FYI freeboard estimates.

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Dror@sinehebdo @sinehebdo 29/10/2017

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