Monday, September 23, 2013

3 Reasons Why the Arctic Oscillation Will be Negative This Winter

As we approach winter, we begin to look at how certain atmospheric patterns will turn out for the season. I have found three reasons why the Arctic Oscillation should turn out negative this winter.

1. Positive Atlantic Multidecadal Oscillation (AMO)

Weekly sea temperature anomalies and monthly AMO data indicate we are in a moderate positive AMO. The AMO is shown by positive or negative sea temperature anomalies in the upper Atlantic and Arctic oceans. Taking a glance around the waters east of Canada and around Greenland, we find widespread positive temperature anomalies. While the strength of these anomalies varies, it is apparent that we are in a positive AMO scenario. Because it is called the Atlantic Multidecadal Oscillation, it would not be unreasonable to predict we see a positive AMO this winter. With the presence of warmer than normal waters around Greenland and in the Arctic, the polar vortex is weakened, leading to a negative Arctic Oscillation.

2. Warming Arctic Temperatures

Observed Arctic temperature across this year are shown above in red, with the average Arctic temperature pictured in green. The horizontal blue line depicts the freezing temperature, to identify times when ice coverage may grow or shrink, among other uses. Taking a look at the latest Arctic temperatures, we find that temperature anomalies have trended warmer since the below-normal temperatures experienced this past summer. The latest temperatures are on the drop from already-definitive above normal temperatures. The presence of warmer than normal Arctic temperatures, should they persist into the winter, will hamper development of the polar vortex and enable a negative Arctic Oscillation. Additionally, these warm Arctic temperatures may be able to enhance the positive AMO by warming up already-warm waters in the upper latitudes.

3. Low Solar Activity

This chart above shows observed sunspot values on a monthly basis, with the average trend line shown in blue. The forecast line is in red, but since it obviously has not verified and will not verify in the future, we will disregard the forecast. Notice how low we are in terms of sunspot activity now when compared to the beginning of this century, on the far left of this graph. Did you notice that the winter of 2011-2012 was warmer than normal? Take a look at the trend line for the area right above the number '12' and you can see a bump up in sunspot activity right as it crosses that '12' line. There's no coincidence here; the spike in sunspot activity did affect the winter of 2011-2012. Did you feel colder than normal for the winter of 2009-2010? The sunspot graph agrees- we saw a cold United States in that winter, as well as a minimum in the sunspot count. Now, as we progress towards the winter of 2013-2014, sunspot numbers will begin to fall off again. Chances are elevated that we see a cooler winter than those in the last few years due to, among other things, a weakening sun. With a weaker sun comes a weaker polar vortex and jet stream, helping lead to not only a negative AO, but a cooler winter.