The remarkable growth of Arctic ice extent continues with a new development yesterday, as shown by the graph below.
Note that as of day 330, Nov. 26, 2018, Arctic ice extent exceeds the 11 year average reached at month end. At 11.08M km2, it is 400k km2 above the average for day 330. It also matches 2013 (not shown) with only 2014 slightly higher in the last decade.
Dr. Judah Cohen at AER posted yesterday on the difficulties forecasting this winter’s coming months. Excerpts in italics with my bolds.
In my opinion troposphere-stratosphere coupling is now in full gear and is having a significant impact on the large-scale circulation of the atmosphere. The relatively active vertical transfer of energy from the troposphere to the stratosphere is repeatedly perturbing the stratospheric PV though it is not of sufficient magnitude to force a significant PV disruption but only minor disruptions. Still the stratospheric PV is predicted to be continuously displaced from the North Pole towards northwest Eurasia. The displacement of the stratospheric PV south of its normal position is allowing the stratospheric PV to grab milder temperatures from more southern latitudes and sling shot it from across Asia towards Eastern Siberia and Alaska, where the warming temperatures are building ridging/positive geopotential height anomalies in the stratosphere centered near Alaska. This is resulting in northerly flow between the Alaskan ridge and stratospheric PV on the North Atlantic side of the Arctic from central Siberia to eastern North America. We have seen the same flow already mimicked or repeated in the troposphere during the month of November contributing to an overall cold month of November in the Eastern US.
As far as the winter as a whole, I believe that the behavior of the stratospheric PV is critical. The vertical atmospheric energy transfer looks active to me for the foreseeable future. This could lead to a significant or major stratospheric PV as early as the second half of December and extending into early January. If a large stratospheric PV disruption were to occur in the late December and early January timeframe this would be almost ideal in contributing to an overall cold winter for the usual favored regions across the NH mid-latitudes, but each event is unique. Any delay in a significant stratospheric PV disruption would lead to an extended period of volatile weather and increase the odds for an overall mild winter especially if the stratospheric PV strengthens and becomes circular in shape. There is the scenario where the vertical energy transfer remains active, the stratospheric PV is perturbed but no significant disruptions occur and the Eastern US still experiences a cold winter ala winter 2013/14 and is described in our new paper: Kretschmer et al. 2018, but more on the paper in a future blog.
Meanwhile, in Nunavut, it is a great time to be a polar bear, even more of them than people want.
via Science Matters
November 27, 2018 at 09:33AM