While working on an El Nino story to be published soon, I happen to talk Monday morning to Ed Olenic, who forecasts seasonal climate for NOAA's Climate Prediction Center.
I know nothing about the Arctic Oscillation, but Mr. Olenic walked me through the basics of the extraordinary extent of the phenomenon, which I may as well do for those of you curious about the incredible cold gripping much of the nation.
I confess we in Southern California -- the fortunate or the doomed, depending on your outlook -- are enjoying a balmy New Year's week here in the opening days of 2010.
But that's not true in most of the nation. It's been extraordinarily cold.
Tthat doesn't mean global warming is over, unfortunately.
To make that point, and to introduce a major paper to come, Gerald Meehl of the National Center for Atmospheric Research explained this unfortunate reality with an eloquent graph he published today:
(Meehl is one of four climate scientists who testified on climate change to Congress, after the Democratic wins in 2008, by the way.)
In his words, the data this graph represents:
If temperatures were not warming, the number of record daily highs and lows being set each year would be approximately even. Instead, for the period from January 1, 2000, to September 30, 2009, the continental United States set 291,237 record highs and 142,420 record lows, as the country experienced unusually mild winter weather and intense summer heat waves.
A record daily high means that temperatures were warmer on a given day than on that same date throughout a weather station's history. The authors used a quality control process to ensure the reliability of data from thousands of weather stations across the country, while looking at data over the past six decades to capture longer-term trends.
What does this have to do with the Arctic Oscillation?
We don't know. So I am told.
So let's turn back to how the Arctic Oscillation works.
What we know, said Olenic, is that the AO is about as low -- negative -- as it's ever been.
He then directed me to this graph on the Climate Prediction Center's vastly deep website:
Which gives us a notion as to how deep this dip into negativity is.
[Note: the black line is the instrumental record; the red lines represent a suite of models' speculation on how the AO will wax or wane in the next couple of weeks.]
Then he took me to another graph, showing what the Arctic Oscillation looks like in temperatures on a map of the world, seen from above:
Or, in the words of the caption:
Since the AO has the largest variability during the cold season, the loading pattern primarily captures characteristics of the cold season AO pattern.
Huh? I asked him, does the blue represent a negative condition that drives cold into most of the U.S.?
He said yes.
Here's a graph of the positive (left) and negative (right) phases of the Arctic Oscillation that I found helpful, from the National Snow and Ice Data Center:
The figure on the right represents the Arctic Oscillation in its negative phase, which is where we are now, bigtime. You can see above what this means for the cold and storm tracks, and explains why much of the U.S. and the U.K. is absolutely freezing.
(Or so I see on Flickr...here from Birmingham in the UK, in a picture taken today)
UPDATE: Weather writer John Cox adds a helpful description of how the AO works in its positive phase and negative phases:
When the pattern is positive, the winds are strong, and the power of the vortex holds the storms in its embrace. When the pattern is negative, the winds are weak, winter storms slide farther south and their sub-freezing temperatures grip much deeper into the Northern Hemisphere. As Andrew Revkin at the New York Times has pointed out recently, the Arctic Oscillation is more deeply negative this year than it has been since the 1980s.
In 2001, after analyzing its impact on Northern Hemisphere winters, University of Washington researchers suggested that effects of the Arctic Oscillation on weather patterns "appear to be as far-reaching as those triggered by El Niño in the South Pacific."
