Atmospheric river · Greenland ice sheet
Rain on the summit of Greenland
Summit Station sits at the highest point of the Greenland ice sheet, 3,216 metres above the sea, where even in August the air is usually around −15 °C. On 14 August 2021 the temperature rose above freezing and rain fell for several hours, freezing into a glaze on the snow. It was the first rain seen there since continuous observations began in 2008, and ice cores drilled at the site suggest there had been none for at least the whole twentieth century before 1995. [N1]
13–15 August 2021 · Central Greenland · ERA5
3,216m
Summit Station
The highest point of the Greenland ice sheet, where rain had never been observed.N1
3rd
Year above freezing at Summit since 2008
After 2012 and 2019: three such years in less than a decade.N1
−0.3°C
ERA5's high at Summit, 14 August
Against an August normal of −15.9 °C; the station itself went above 0 °C.
20mm
ERA5's precipitation at Summit, 13–15 August
More than a whole normal August (18 mm) in three days.
What happened
In mid-August 2021 an atmospheric river, a long, narrow plume of moist air from the subtropical Atlantic, was steered north between a trough over Baffin Island and a ridge over southern Greenland. The air rose over the ice sheet, cooled and dropped its water. On 14 August the temperature at Summit passed 0 °C and rain fell on the snow.N1S1
Across the ice sheet the warm air and the rain melted the surface over a wide area in mid-August. The rain also darkened the snow: wet snow and the glaze of ice it left absorb more sunlight than fresh snow, and so melted faster for days afterwards.S1
12–13 Aug
Moist air streams north over Baffin Bay and western Greenland.
14 Aug
Above-freezing temperatures and rain at Summit; melt over a large part of the ice sheet.N1
15–16 Aug
The air cools again; Summit returns to around −10 °C.
The river of moisture
On ERA5's map of water vapour, the river shows as a tongue of moist air up Davis Strait and over western Greenland, with more water in the column than anywhere else in the region. Aloft, the 500 hPa map shows the pattern that steered it: high heights over southern Greenland, a trough to the west, and the flow between them running north.
At the top of the ice
−0.3°C
ERA5's highest temperature at Summit on 14 August, nearly 16 °C above the August normal. The station measured above 0 °C; ERA5's grid, which averages the cell and its snow surface, falls just short.
| Day | Lowest, °C | Highest, °C | Precipitation, mm |
|---|---|---|---|
| Aug 12 | -14.3 | -9.4 | 0.8 |
| Aug 13 | -14.4 | -6.7 | 8.0 |
| Aug 14 | -6.0 | -0.3 | 9.3 |
| Aug 15 | -8.3 | -3.9 | 3.1 |
| Aug 16 | -10.7 | -7.5 | 0.5 |
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References
News
- N1National Snow and Ice Data Center. Greenland surface melting 2021: rain at Summit. 2021.The rain at Summit, the station's records and the history of rain on the ice sheet.
Studies and guidelines
- S1Box, J. E., et al. (2022). Greenland ice sheet rainfall, heat and albedo feedback impacts from the mid-August 2021 atmospheric river. Geophysical Research Letters, 49, e2021GL097356.The atmospheric river, the rain and heat it brought, and the melt that followed.