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North Slope snow season shortening
Alan Bailey Petroleum News
The duration of the annual period when snow covers the North Slope of Alaska has been becoming progressively shorter, according to a paper published by a group of scientists in the Bulletin of the American Meteorological Society. The length of the snow season is important both for local North Slope residents and for the oil industry, which depends on the snow cover protecting the Arctic tundra when conducting off-road exploration and development. The findings come mainly from observations made near Utqiagvik (formerly Barrow). Began in 1970s A trend towards the earlier melting of the winter snowpack began in the mid-1970s, with the date of the disappearance of the snow cover receding at an average rate of 2.86 days per decade between 1975 and
2016, the paper says. The date on which snow begins to accumulate at the beginning of the winter has become later at an average rate of 4.6 days per decade over the same time period. On the other hand, exceptionally short snow seasons in 2015 and 2016 dominate the average trend for the shrinking season length since 1975, a factor that suggests the need for some caution in interpreting the data.
It appears that the timing of the snow melt is particularly related to the flow of relatively warm air northward from the North Pacific Ocean. The timing of the fall freezeup seems related to warm air in the lower atmosphere, with sea-ice conditions appearing to strongly influence temperature patterns at Utqiagvik. There is no obvious correlation between the depth of the snow cover and the timing of the snow melt, the paper says.
The authors of the paper suggest that temperature and atmospheric circulation anomalies in the North Pacific may help with the statistical forecasting of the spring snow melt, while variations in the summer sea ice melt may help anticipate the timing of the arrival of the winter snowpack. Lengthened snow-free season Taken together, the earlier snow melt and later freezeup have combined to cause a dramatic increase in the length of the snowfree season. This phenomenon proved particularly notable in 2016, in which year the duration of the snow-free period was 45 percent longer than the 1975 to 2015 average, the paper says.
A key tool that the scientists are using to monitor the timing of the North Slope snow cover is the measurement of electromagnetic radiation - snow on the ground reflects radiation, while uncovered tundra tends to absorb the radiation. In addition to using this technique near Utqiagvik, a mobile observatory near Oliktok Point on the coast of the central North Slope has demonstrated a similar snowmelt pattern to that at Utqiagvik since 2013. Moreover, correlations with radiometric data collected at Sagwon and Franklin Bluffs, inland to the south of Prudhoe Bay, support the likelihood that data collected at Utqiagvik is representative of regional conditions, the paper says. Natural variation There has, however, been significant natural variation in the snow season timing across the years: The third earliest snow melt date on record happened as long ago as 1902, although 2016 holds the record for
the earliest melt date. But eight of the 10 earliest melt dates have occurred since 1990, the paper says.
Curiously, the egg-laying habits of a species of cormorant found near Utqiagvik correlate statistically with the snow melt timing determined from radiometric measurements - egg laying has trended earlier, in near lockstep with the snow melt, the paper says.
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