I wasn't expecting another instalment in this year's series of blog posts on Winter Weirdness, extreme weather events that could be linked to the decline in Arctic sea ice. It's not even winter anymore officially. But as spring has been revoked in large parts of Europe, and the atmospheric blocking that is causing it is being linked to Arctic sea ice as a potential cause, I figure it's a fitting end for the series.
One of the first articles alluding to the link, appeared on the Guardian's website on Monday: Scientists link frozen spring to dramatic Arctic sea ice loss. Stefan Rahmstorf, professor of Physics of the Oceans at Potsdam University, went further, writing a blog post showing the similarities between the current event and modeled projections in recent research that investigated the influence of Arctic sea ice loss on atmospheric patterns. Lepus Universalis Eli Rabett was so kind as to translate Rahmstorf's blog post to English:
Melting Ice and Cold Weather
The media are debating if the decrease in Arctic ice is related to this winter's cold weather in Germany. This post discusses the most recent current research about this including the most important figures from relevant studies.
First, what does the unusual temperature distribution observed this March actually look like? Here is a map showing the data (up to and including March 25, NCEP / NCAR data plotted with KNMI Climate Explorer):
Freezing cold in Siberia, reaching across northwestern Europe, unusually mild temperatures over the Labrador Sea and parts of Greenland and a cold band diagonally across North America, from Alaska to Florida. Averaged over the northern hemisphere the anomaly disappears - the average is close to the long-term average. Of course, the distribution of hot and cold is related to atmospheric circulation, and thus the air pressure distribution. The air pressure anomaly looks like this:
There was unusually high air pressure between Scandinavia and Greenland. Since circulation around a high is clockwise [anticyclone], this explains the influx of arctic cold air in Europe and the warm Labrador Sea.
Arctic sea ice
Let us now discuss the Arctic sea ice. The summer minimum in September set a new record low, but also at the recent winter maximum there was unusually little ice (ranking 6th lowest - the ten years with the lowest ice extent were all in the last decade). The ice cover in the Barents sea was particularly low this winter. All in all until March the deficit was about the size of Germany compared to the long-term average.
Is there a connection with the winter weather? Does the shrinking ice cover influence the atmospheric circulation, because the open ocean strongly heats the Arctic atmosphere from below? (The water is much warmer than the overlying cold polar air.) Did the resulting evaporation of sea water moisten the air and thus lead to more snow? These questions have been investigated by several studies in recent years.
Update: Commenter R. Gates has a firm meteorological grasp of current events, which not only could be influenced by the state of the sea ice, but also have to do with the early breaking down of the Polar Vortex I alluded to in my latest blog post on the cracking event (Arctic freezing season ends with a loud crack). Here's his explanation in a comment below:
Regarding the easterly wind anomaly over higher latitudes of the NH that began as part of the January SSW event, this chart shows this quite clearly:
The easterly anomaly began with the SSW event and has brought colder Siberian and Arctic air masses consistently from the east over Europe since Janauary. The higher pressure over the polar regions also had its origins with the January SSW event:
If SSW's are not caused by lower sea ice, but their effects are potentially enhanced by them, then we would expect more extreme effects from SSW's in future NH winters as alterations in the jet stream and blocking effects from lower sea ice levels enhance SSW effects.
Finally, the very low AO, which coincided with the cracking of MYI as reported so well by A-team and others, may certainly be one example of the an enhancement of January's SSW effects. The descending air and higher pressure over the Arctic brought about a stronger anti-cyclonic rotation of that lasted over a longer period. This is the same easterly anomaly as discussed and linked to above. The ice may have been primed to crack by being thinner anyway, but the sustained high pressure and anticyclonic action worked over a long period and helped to enhance the cracking in my estimation.
The BBC put up a useful video at the beginning of the year to explain what SSWs are.