Great Arctic Cyclone of 2016
August 17, 2016
As of Tuesday, the deepest cyclone in the Northern Hemisphere wasn’t anywhere near the tropics–it was spinning in the central Arctic Ocean. A surface low located near 83°N, about 500 miles from the North Pole and about 1000 miles north of Barrow, Alaska, deepened to a central pressure of 968 mb at 2 am EDT Tuesday morning, August 16. This is on par with the central pressure you might find in a moderately-sized Category 2 hurricane. Such lows are a common feature of Arctic climate, but they rarely gain such intensity in the middle of summer. The only deeper Arctic cyclone on record in August is the Great Arctic Cyclone (GAC) of 2012, a low that bottomed out at 966 mb on August 6. This was the lowest pressure analyzed across more than 1600 August cyclones in the Arctic since 1979, according to a 2012 study by Ian Simmonds and Irina Rudeva (University of Melbourne).
The GAC of 2012 churned across the Arctic for ten days while its central pressure was below 1000 mb. The cyclone had major effects on the distribution of regional ice and appears to have played at least some role in that summer’s record depletion of Arctic sea ice. Normally, low pressure near the North Pole causes ice to spread out (as surface waters and sea ice move to the right of the surface wind). Yet the intensity and duration of the 2012 cyclone’s winds and waves appears to have more than compensated for that effect, leading to an overall loss of ice extent. The extent plummeted in August 2012 en route to a record-low extent in September.
A study in 2013 led by Jinlun Zhang (University of Washington) found that the GAC quadrupled the melting of sea ice from below by pushing warm surface water against the bottom of wind- and wave-tossed ice floes. However, because much of the Arctic ice was already thin and compromised, much of the extent loss that occurred in August and September was baked into the system when the cyclone came along. Zhang and colleagues estimated from a model simulation that the record September minimum was only about 4% lower as a result of the GAC of 2012.
It’s too soon to know exactly how this year’s storm–let’s call it the Great Arctic Cyclone of 2016 for now–will affect the Arctic. However, according to polar researcher James Screen (University of Exeter), “This certainly has the potential to be an interesting event and possibly have a big influence on whether or not we see a new record sea ice minimum next month.” As many reports have noted in the last few years, the Arctic’s summer ice pack is in the midst of a dramatic long-term decrease due to global and regional warming. However, there remains a good bit of year-to-year variation in the ice extent. Each summer’s ice pack has a different character in terms of the area it covers, its thickness, the extent and location of surface melt ponds, and so on. This means the impacts of a strong August cyclone in the high Arctic could be quite different from one year to the next. The current cyclone is located near a zone that separates relatively thick, dense ice to its east (north of the Canadian Archipelago) from thinner, more dispersed ice extending from the eastern coast of Siberia all the way up to near the North Pole.
As of early August, the Arctic’s sea ice extent was among the four lowest on record since satellite monitoring began in 1979. Temperatures across the Arctic for the year thus far have been far above record levels (see Figure 5), so there is concern that the ice pack may be weaker than satellite measurements and models imply. We can expect some dramatic changes over the next few days, as winds and waves break up ice and churn up relatively warm water from below. Much will depend on the exact track of this Arctic cyclone and how long it persists as an intense low.
Remarkably, the most recent runs of the ECMWF and GFS keep the current low and/or subsequent lows spinning across the Arctic Ocean for at least the next week–perhaps at pressures below 990 mb for much or most of the time. The models even flag the possibility of another unusually intense cyclone at some point next week. One caution from polar scientist Steven Cavallo (University of Oklahoma): “There is not really much skill in the forecast models accurately predicting the strength of an Arctic cyclone more than 3 days ahead of time.” However, if the model’s overall message of unusually persistent and strong low pressure in the central Arctic verifies, there could be very significant impacts to the sea ice pack extending through the rest of the melt season.