Abstract
Abstract. A new version of sea ice motion and age products includes several significant upgrades in processing, corrects known issues with the previous version, and updates the time series through 2018, with regular updates planned for the future. First, we provide a history of these NASA products distributed at the National Snow and Ice Data Center. Then we discuss the improvements to the algorithms, provide validation results for the new (Version 4) and older versions, and intercompare the two. While Version 4 algorithm changes were significant, the impact on the products is relatively minor, particularly for more recent years. The changes in Version 4 reduce motion biases by ∼ 0.01 to 0.02 cm s−1 and error standard deviations by ∼ 0.3 cm s−1. Overall, ice speed increased in Version 4 over Version 3 by 0.5 to 2.0 cm s−1 over most of the time series. Version 4 shows a higher positive trend for the Arctic of 0.21 cm s−1 per decade compared to 0.13 cm s−1 per decade for Version 3. The new version of ice age estimates indicates more older ice than Version 3, especially earlier in the record, but similar trends toward less multiyear ice. Changes in sea ice motion and age derived from the product show a significant shift in the Arctic ice cover, from a pack with a high concentration of older ice to a sea ice cover dominated by first-year ice, which is more susceptible to summer melt. We also observe an increase in the speed of the ice over the time series ≥ 30 years, which has been shown in other studies and is anticipated with the annual decrease in sea ice extent.
Highlights
Arctic sea ice conditions have undergone significant changes in recent years, with dramatic reductions in the overall ice extent, ice age, and ice thickness
One explanation for the stronger decline in ice thickness is the preferential loss of thicker, old ice in comparison with relatively thin first-year ice
– Removed erroneous buoy and AVHRRderived motions – Updated buoys motions through most recent date – Derived sea ice mask from NSIDC1 product instead of internally derived concentration estimates – Used GDAL2 library to interpolate SSM/I fields from polar stereographic to EASEGrid – Improved browse images
Summary
Arctic sea ice conditions have undergone significant changes in recent years, with dramatic reductions in the overall ice extent, ice age, and ice thickness. These data have been connected to the satellite altimetry record (Kwok, 2018) to create an intermittent longterm time series over part of the Arctic While these direct ice thickness estimates are useful, such products lack the longterm and/or the basin-wide coverage that is available from the multi-decadal sea ice age record. A medium-resolution OSI SAF product based on visible and infrared sensor inputs provides daily coverage at 20 km spatial resolution (Dybkjaer, 2018) Another product, developed by the French National Institute for Ocean Science (IFREMER), combines passive-microwave and scatterometer inputs to produce 3 d motion estimates (GirardArduin and Ezraty, 2012). Because the ice age product is produced by utilizing the sea ice motion product, we outline the production of the motion product first
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