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Abstract Snow is the most reflective natural surface on Earth. Since fresh snow on bare sea ice increases the surface albedo, the impact of summer snow accumulation can have a negative radiative forcing effect, which would inhibit sea ice surface melt and potentially slow sea‐ice loss. However, it is not well known how often, where, and when summer snowfall events occur on Arctic sea ice. In this study, we used in situ and model snow depth data paired with surface albedo and atmospheric conditions from satellite retrievals to characterize summer snow accumulation on Arctic sea ice from 2003 to 2017. We found that, across the Arctic, ∼2 snow accumulation events occurred on initially snow‐free conditions each year. The average snow depth and albedo increases were ∼2 cm and 0.08, respectively. 16.5% of the snow accumulation events were optically thick (>3 cm deep) and lasted 2.9 days longer than the average snow accumulation event (3.4 days). Based on a simple, multiple scattering radiative transfer model, we estimated a −0.086 ± 0.020 W m−2change in the annual average top‐of‐the‐atmosphere radiative forcing for summer snowfall events in 2003–2017. The following work provides new information on the frequency, distribution, and duration of observed snow accumulation events over Arctic sea ice in summer. Such results may be particularly useful in understanding the impacts of ephemeral summer weather on surface albedo and their propagating effects on the radiative forcing over Arctic sea ice, as well as assessing climate model simulations of summer atmosphere‐ice processes.
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A tale of Two Events: Arctic Rain-on-Snow Meteorological Drivers
Arctic warming may lead to altered occurrences and strengthening of extreme weather events. Arctic rain-on-snow (ROS) events are of a particular interest in this regard. ROS conditions generate hazards for the transportation sector, ranging from flooding and icing to airport closures, and can severely damage infrastructure through wet-snow avalanches. ROS events, and the resulting ice growth, interfere with foraging by reindeer, caribou, and musk oxen, heavily relied upon species among Indigenous peoples. There have been documented mass starvations of these animals due to ROS. This study addresses the meteorological setups of Arctic ROS events. We focus on cases for Iqaluit, Nunavut, in Canada and Nuuk, Greenland, using ERA5 atmospheric reanalysis, surface weather station data, and atmospheric soundings. At the synoptic scale, we find that blocking patterns play leading roles in ROS initiation, with atmospheric rivers contributing to both direct and indirect effects. Cyclone-induced low-level jets and resultant “warm noses” of higher air temperatures and elevated moisture transport are other key features in ROS generation. We conclude by postulating how climate change may alter the severity and frequency of Arctic ROS events, drawing on this improved knowledge of weather patterns leading to ROS conditions.
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- Award ID(s):
- 1928230
- PAR ID:
- 10442789
- Date Published:
- Journal Name:
- Annals of glaciology
- ISSN:
- 0260-3055
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Rain-on-snow (ROS) events can have adverse impacts on high-latitude ungulate populations when rain freezes in the snowpack, forming ice layers that block access to winter forage. In extreme cases, ROS events have led to mass die-offs. ROS events are linked to advection of warm and moist air, associated with extratropical cyclones. However, these conditions are common to many winter precipitation events, challenging our understanding of the particular conditions under which ROS events occur. This study uses the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) to differentiate ROS events in Alaska from precipitation events in which only snow falls on a preexisting snowpack [snow-on-snow (SOS)]. Over the North Slope and Kotzebue Sound, no clear difference exists between the tracks of ROS-producing and SOS-producing storms. However, in the interior, southwest, and Anchorage, tracks of ROS-producing storms tend to be farther north and west than for SOS-producing storms. The northwest shift of ROS-producing storms is linked to the position of upper-tropospheric anticyclones in the eastern Gulf of Alaska during ROS events. ROS-producing storms are no more intense than SOS-producing storms, but their association with atmospheric blocking leads to stronger pressure gradients on the east side of storms and thereby stronger advection of positive anomalies in temperature and precipitable water. For several sites, sea level pressure in the eastern Gulf of Alaska is also significantly higher a few days prior to ROS events than prior to SOS events, further implicating atmospheric blocking as a facilitator and potential predictor of ROS events.more » « less
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