Monday, September 24, 2012

Positive AMO Should Enhance Negative NAO This Winter

The presence of a strengthening positive-phase AMO, or Atlantic Multidecadal Oscillation, indicates that the Atlantic is warming up, enhancing prospects for a negative NAO this winter.

The Atlantic Multidecadal Oscillation is an index used for measuring water temperatures in the Atlantic. This AMO can be measured using a sea surface temperature chart like the one above. The chart above is the weekly SST anomaly. You can clearly see the warmer than normal temperatures across waters to the south of Greenland and in the Atlantic Canadian regions.

The NAO, or North Atlantic Oscillation, has a positive and negative state. In the positive, a high pressure forms over a portion of Greenland and blocks the atmospheric flow. This blockage releases cold air south into the US.

The AMO is related to the NAO in how the AMO affects the NAO's stage. Right now, the AMO is positive, providing warm waters to the north Atlantic. However, with these warm waters comes the increased likelihood of a negative NAO. A negative NAO can also be characterized by warm waters in the North Atlantic, and this correlation between the two may help explain the recent streak of negative NAO values.

So, the positive AMO appears to be on the East Coast's good side at the moment. Should this positive AMO continue into the winter, I have no doubt that the probability of a negative phase of the NAO would greatly increase.

It should be noted that last winter, the AMO was mainly neutral, explaining a part of the lack of a negative NAO.


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