Sunday, July 22, 2012

Sea Surface Temperatures Show Negative NAO; Will it Continue?

Weekly Sea Surface Temperatures
Courtesy Australian Government BOM
Weekly sea surface temperature (SST) anomalies indicate the continuing presence of a negative NAO, as shown by the positive SST anomalies currently residing over the waters surrounding Greenland.

As I mentioned in my most recent winter forecast update, the North Atlantic Oscillation/NAO can be influenced by the Quasi-Biennial Oscillation, or QBO. Looking at the latest QBO readings tells me that the monthly average for June was -21.39. That is a very strong negative QBO that is undoubtedly helping out the NAO. Let's look at the NAO and QBO to confirm that there is actually a correlation between the two indices and their actions.

Observed NAO (Per CPC)

Observed QBO (per ESRL)
In the observed NAO, we see a very sharp downturn of the NAO beginning roughly at the end of May and solidifying in the beginning of June. the NAO has not reached positive territory since that date. If we look to the QBO for help, we see a surge to strong negative QBO territory beginning in April/May and continuing through June that seems to have helped/influenced this prolonged negative NAO phase.
Of additional interest is the tanking of the SOI beginning in spring 2012 and continuing to this day, which may also hold a correlation with these two indices.

So, the big question now is 'Will the NAO stay negative through Fall?'

I did a little research and pulled up some stratospheric temperature maps. Because the positive NAO brings a stronger polar vortex, it can be expected that a positive NAO would bring cold temperatures to the stratosphere. Likewise, a negative NAO would warm up the stratosphere. Take a look at the observed 50mb temperatures.

Beginning in Spring, the 50mb temperatures had been fairly cool, even to near record low points. However, as seen in mid June, a warming trend began and has persisted to this day. This is a direct correlation to the change in the NAO: warmer stratosphere = negative NAO (usually).
That said, using the QBO and stratospheric temperatures, I would say that the atmosphere looks prepared to carry this negative NAO through summer and fall, and may even stick around for winter. However, I'm not too ready to go that far out, so I will just say a negative NAO in summer and fall looks like a realistic proposition.


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