by Judith Curry
Arctic sea ice extent has been anomalously low this winter.
A time series plot from NSIDC:
The spatial distribution of the anomaly from NSIDC:
The greatest anomalies are in the European sector, specifically in the Barents Sea
To what extent are the anomalies associated with warm temperatures? From the DMI surface temperature plot, north of 80N (from ECMWF reanalysis):
So, what might be causing this particular anomaly? Some possibilities are:
- global warming (January 2016 was warmest Jan on record, according to the surface temperature analyses
- multidecadal oscillations (e.g. stadium wave) predicts ice recovery to be occurring in the same region (European Arctic) where we see the sea ice decline).
- seasonal weather circulation patterns – this has been a year with with unusual weather patterns, with both low temperature and high temperature records being set.
New paper by Goss et al.
A very interesting series of papers by a team at Penn State has come to my attention, here is the latest:
Stationary Wave Interference and Its Relation to Tropical Convection and Arctic Warming
Michael Goss, Stephen Feldstein, Sukyoung Lee
The interference between transient eddies and climatological stationary eddies in the Northern Hemisphere is investigated. The amplitude and sign of the interference is represented by the stationary wave index (SWI), which is calculated by projecting the daily 300-hPa streamfunction anomaly field onto the 300-hPa climatological stationary wave. ERA-Interim data for the years 1979 to 2013 are used. The amplitude of the interference peaks during boreal winter. The evolution of outgoing longwave radiation, Arctic temperature, 300-hPa streamfunction, 10-hPa zonal wind, Arctic sea ice concentration, and the Arctic Oscillation (AO) index are examined for days of large SWI values during the winter.
Constructive interference during winter tends to occur about one week after enhanced warm pool convection and is followed by an increase in Arctic surface air temperature along with a reduction of sea ice in the Barents and Kara Seas. The warming of the Arctic does occur without prior warm pool convection, but it is enhanced and prolonged when constructive interference occurs in concert with enhanced warm pool convection. This is followed two weeks later by a weakening of the stratospheric polar vortex and a decline of the AO. All of these associations are reversed in the case of destructive interference. Potential climate change implications are briefly discussed.
I didn’t do the data analysis to see if their ideas holds up for the current sea ice blip in the Arctic, but this is clearly an interesting idea that I haven’t come across before.
Here are several other relevant papers that I’ve spotted from this group:
Attribution of the recent winter sea ice decline over the Atlantic sector of the Arctic Ocean. Punchline: These findings suggest that most of the winter sea ice concentration trends can be attributed to changes in the large-scale atmospheric circulations.
A theory for polar amplification from a general circulation perspective. Punchline: this theory invokes that La-Niña-like tropical heating can help tap available potential energy and warm the Arctic by exciting poleward and upward propagating Rossby waves.
There are 3 factors in play regarding Arctic sea ice variations:
- secular global warming trend
- multidecadal variability associated with large-scale ocean oscillations
- subseasonal weather variations associated with with weather regimes such as the MJO, AO, etc.
The amplitude of the subseasonal variations in sea ice is greater than the amplitude associated with multidecadal ocean oscillations and secular warming trend, hence invariably it is weather that is responsible for an individual blip (that may contribute to a record in sea ice extent). The sea ice data set is inadequate for sorting out the secular global warming trend from the multi-decadal variability.
The Penn State team is making important contributions to unraveling this, in presenting some ideas that challenge ‘alarmist wisdom’ about the Arctic sea ice decline. I look forward to following their work.