Abstract
Variability in snow melt onset (MO) on Arctic sea ice since 1979 is examined by determining the area of sea ice experiencing the onset of melting during the melt season on a daily basis. The daily MO area of the snow and ice surface is determined from passive microwave satellite-derived MO dates for the Arctic Ocean and sub-regions. Annual accumulations of MO area are determined by summing the time series of daily MO area through the melt season. Daily areas and annual accumulations of MO area highlight inter-annual and regional variability in the timing of MO area, which is sensitive to day-to-day variations in spring weather conditions. Two distinct spatial patterns in MO area accumulations including an intense, fast accumulating melt area pattern and a slow accumulating melt pattern are examined for two melting events in the Kara Sea. In comparing the 34 years of MO dates for the Arctic Ocean and sub-regions, melt accumulations have changed during the period. In the earlier years, 1979–1987, the MO generally was later in the year than the mean, while in more recent years, the MO accumulations have been occurring earlier in the melt season. The sub-regions of the Arctic Ocean also exhibit greater annual variability than the Arctic Ocean.
Highlights
Arctic sea ice is varying rapidly and is a sensitive indicator of climate change
The present study examines the variability in the timing of areal accumulations of melt onset (MO) on Arctic
The timing of MO in a particular location is tied to the atmospheric conditions present at the time of melting, resulting in air temperatures reaching the freezing point
Summary
Arctic sea ice is varying rapidly and is a sensitive indicator of climate change. Over the satellite record, Arctic sea ice thickness and annual extent minima have seen drastic reductions. Since solar radiation in the Arctic gradually tapers off through the summer months, the timing of freeze-up in the fall does not impact the year’s ice conditions to the same extreme that early melt onset can influence the annual September sea ice extent minimum for the current year [10,13]. We find that melt onset area is accumulating increasingly early in the year over much of the Arctic sea ice cover and the spatial and temporal patterns in daily melt onset area may give insight into changes in spring weather conditions occurring at the time of melt onset. The 10-day time series described above prevents the algorithm from assigning first year ice locations with a melt onset date that is too early, before air temperatures reach 0 °C. “Early melt” corresponds to the period of time during which maximum daily temperatures reach the freezing point, the snow and ice cover may continue to melt and refreeze as diurnal temperatures cycle above and below freezing
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