Global Warming or Arctic Oscillation
SEARCH BLOG: GLOBAL WARMING
After two fairly cold winters in a row, 2011-12 has started out very mild over a large part of the U.S. Here in SE Michigan, there is no snow and the lake ice, if present, is exceedingly thin. Last year, there were ice fisherman on our lake in early December and fairly deep snow from then through most of the winter. Obviously, the change is much too fast for a climate change... although as pleasant as this winter has been so far, we wouldn't object to a more permanent change in that direction. Of course, if you are a ski bum or can't wait to get out on the snowmobile, this is not change for the better.
What happened? From the National Snow and Ice Data Center [NSIDC]:
This graph shows daily Arctic Oscillation Index values from the NOAA Climate Prediction Center for early September 2011 to early January 2012. The index is a normalized (unitless) index of relative pressure anomalies between polar and mid-latitude regions.
Credit: NSIDC courtesy NOAA NWS Climate Prediction Center
High Resolution Image
Credit: NSIDC courtesy NOAA NWS Climate Prediction Center
High Resolution Image
Positive phase of the Arctic Oscillation
The past two Arctic winters were dominated by a negative phase of the Arctic Oscillation, a large-scale weather pattern that brings generally warm conditions to the Arctic and colder conditions to Europe and North America. In contrast, the winter of 2011 has so far seen a mostly positive phase of the Arctic Oscillation. While temperatures were above normal in the Kara and Barents seas, the positive phase of the Arctic Oscillation tends to keep the coldest winter air locked up in the Arctic, which keeps the middle latitudes free of frigid Arctic temperatures and strong snowstorms. This weather pattern helps to explain the low snow cover and warm conditions over much of the United States and Eastern Europe so far this winter.
Yeah, me too. I read it, but don't get it. What's an oscillation? And what's the "positive phase?" Well, it's a weather pattern... got that.The past two Arctic winters were dominated by a negative phase of the Arctic Oscillation, a large-scale weather pattern that brings generally warm conditions to the Arctic and colder conditions to Europe and North America. In contrast, the winter of 2011 has so far seen a mostly positive phase of the Arctic Oscillation. While temperatures were above normal in the Kara and Barents seas, the positive phase of the Arctic Oscillation tends to keep the coldest winter air locked up in the Arctic, which keeps the middle latitudes free of frigid Arctic temperatures and strong snowstorms. This weather pattern helps to explain the low snow cover and warm conditions over much of the United States and Eastern Europe so far this winter.
Separately, the NSIDC explains the phenomenon this way:
The Arctic Oscillation
The Arctic Oscillation refers to opposing atmospheric pressure patterns in northern middle and high latitudes.
The oscillation exhibits a "negative phase" with relatively high pressure over the polar region and low pressure at midlatitudes (about 45 degrees North), and a "positive phase" in which the pattern is reversed. In the positive phase, higher pressure at midlatitudes drives ocean storms farther north, and changes in the circulation pattern bring wetter weather to Alaska, Scotland and Scandinavia, as well as drier conditions to the western United States and the Mediterranean. In the positive phase, frigid winter air does not extend as far into the middle of North America as it would during the negative phase of the oscillation. This keeps much of the United States east of the Rocky Mountains warmer than normal, but leaves Greenland and Newfoundland colder than usual. Weather patterns in the negative phase are in general "opposite" to those of the positive phase, as illustrated below.
Over most of the past century, the Arctic Oscillation alternated between its positive and negative phases. Starting in the 1970s, however, the oscillation has tended to stay in the positive phase, causing lower than normal arctic air pressure and higher than normal temperatures in much of the United States and northern Eurasia.
of the Arctic Oscillation of the Arctic Oscillation
Okay, sort of like an atmospheric "fence" that, when positive, is strong enough to keep the cold air in the Arctic, but when negative, allows the cold air to push southward into the U.S. and northern Europe and Asia. These patterns are not related to CO2 or who is in the White House.
Well, I'm all for remaining positive, but it looks as if things could be changing toward the negative around here:
Wed
46° | 34°
Partly Sunny
Thu
39° | 19°
Chance Rain/Snow
Fri
26° | 16°
Chance Snow
From 
