As suggested by the 15-day forecast from early August (discussed in the August Outlook report), the weather pattern for August completely changed from the pattern of June and July, decreasing the chance of a record September sea ice loss for 2009. The September minimum is likely to be around 5.0 million square kilometers, compared to around 4.5 million square kilometers for 2008 and 4.1 million square kilometers for 2007. It should be noted that this 2009 extent would still be well below the average for 1979–2000 of 6.7 million square kilometers. See the NSIDC Arctic Sea Ice News & Analysis website for daily updates.
Figure 1 (below) is the sea level pressure field for June and July 2009, showing the Dipole/negative Arctic Oscillation pattern with high pressure on the North American side of the Arctic. This pattern is favorable for sea ice loss as the winds, which roughly follow the contour lines, blow from the Bering Strait region across the entire Central Arctic. In contrast, Figure 2 (August) shows a localized low pressure region over the Central Arctic with higher pressure on the Atlantic side of the Arctic. This August pattern appears unfavorable to sea ice loss. These wind patterns would tend to keep polar air over the Arctic. Observations from the North Pole Environmental Observatory indicate that freeze-up started in late August (almost a week earlier than in other recent years), surface ocean temperatures are at the freezing point, and a near lack of snow cover will promote rapid ice growth.
Two interesting notes from the news. 2009 is the fourth time in five years that the Northeast Passage has been opened. Polar bears had more sea ice cover and better hunting this year in Hudson’s Bay than in other recent years.
At this point, the regional outlook on ice conditions indicates that the large-scale weather patterns, which dominated in August with cooler conditions and advection of ice into the eastern North American Arctic, can also help explain much of the observed ice distribution at the local level.
The prognosis for the Parry Channel of the Northwest Passage not opening up due to presence of multiyear ice and near-normal ice break-up patterns appears to have been correct. In the first week of September, the coverage of multiyear ice in the western Parry Channel region was comparable to 2008, with roughly half the extent of what is normal for the 1968–2000 time period. Ensemble model simulations suggested that the Northwest Passage would open up in this region. While a detailed evaluation will be forthcoming, the lack of high-resolution ice thickness fields in this topographically complicated region hampers such simulations.
In the Beaufort and Chukchi seas, ice distribution mimicks the Beaufort Gyre circulation pattern with advection of ice from the high Canadian Arctic into the Beaufort Sea and export of ice northward in the Chukchi Sea. The slowdown of the melt season starting in mid-June may have allowed more and thinner ice to survive melt than in either 2008 or 2007. Only a detailed analysis of buoy data and field observations will help resolve this question, but an ice mass balance buoy placed on 1.4 meter thick first-year ice north of Barrow in April has managed to survive into the late melt season, drifting 1,000 kilometers to the North over the course of the summer. It is currently shown to be in very low ice concentration in a large embayment formed in the central arctic ice pack. Only after freeze-up will we be able to assess whether ice extent in this region may have been underestimated due to the highly ponded nature of remaining ice (see also discussion of comparable conditions in 2008 Outlook Summary). As anticipated, traces of ice lingered in northern Chukchi coastal waters into early August.