Detecting Arctic Icing Events From Space

Winter ice in northwest Alaska. NPS / Kyle Joly.

Icing — also called rain-on-snow — events can hit plants and animals hard. For caribou, the ice crusts they leave make it hard to reach their main winter food, lichens growing close to the ground, and breaking through crusts makes travel more costly in energy. As the Arctic warms rapidly, icing may become more frequent and widespread.

Long-term monitoring of icing is still a young science. An international team of researchers, including the National Park Service, found that combining different satellite sensors detected icing events across the Arctic effectively — tools that could fill data gaps and improve understanding of long-term trends.

The study

In summary, the team's paper reports:

• The problem. Rain-on-snow happens in midwinter across much of the Arctic. It changes the snowpack and, at worst, forms ice layers that affect wildlife, plants and soils long after the rain.
• The tools. Satellite microwave observations can reveal these events. Only Ku-band radar (scatterometer) had been used across the whole Arctic, and its data are limited, so the team tested other frequencies and both active (radar) and passive sensors, with an eye to higher-resolution records.
• How it works. Radar time series can capture the change in snow structure an event leaves, even with gaps in the data, and help judge how severe it was; active and passive sensors can also detect wet snow during an event if a pass happens at the right time.
• C-band radar was of special interest because data are plentiful at resolutions from 10 metres to 12.5 kilometres. Its sensitivity to temperature is a problem, but combining it with a passive microwave wet-snow indicator (from the ASCAT and SMOS satellites) addresses it.
• Checking it. Results were compared with snow-pit records, caribou migration data and Ku-band products. Ice crusts were found in the snow after detected events, with 82 percent overall accuracy; the more events in a winter, the larger that season's rise in C-band backscatter.
• Impacts. Events detected on the Yamal and Seward peninsulas had severe effects on reindeer and caribou through ice crusts.
• Next steps. Sentinel-1 radar looks promising for mapping ice layers in finer detail. The team recommends fusing several kinds of satellite microwave data into a climate data record, allowing for their differences; retrieval is most robust in the tundra, where sensors agree.

Sources

• National Park Service, "Detecting Icing Events." https://www.nps.gov/articles/000/detecting-icing-events.htm
• Bartsch, A., Bergstedt, H., Pointner, G., Muri, X., Rautiainen, K., Leppänen, L., Joly, K., Sokolov, A., Orekhov, P., Ehrich, D., and Soininen, E.M., 2023, "Towards long-term records of rain-on-snow events across the Arctic from satellite data," The Cryosphere 17(2): 889–915.
• Further reading suggested by the NPS: Ed Struzik, "Rain Comes to the Arctic, With a Cascade of Troubling Changes," Yale Environment 360, February 20, 2024.
• Words on this page from people and organisations outside the federal government are paraphrased; rewritten in hubnx's own words.