I often mention the Pacific Decadal Oscillation and Interior Alaska climate, and I've written about it before, but it's so important to understanding climate variability for most of Alaska (except the North Slope), that it's worth updating.
To start with, below is the classic PDO anomaly diagram from the University of Washington
. The color field is the sea surface temperature anomalies and the arrows are the surface wind anomalies. On the left is the positive phase of the PDO and the right is the negative phase. Note that from the North Pacific-wide perspective the phases are misnamed: the positive phase features a huge area of cooler than normal temperatures from Asia to about 155W, and the negative phase a similarly place warm anomaly. The surface wind anomalies are southerly into mainland Alaska during the positive phase and northerly during the negative phase.
|Courtesy of the U. of Washington|
Next is an updated plot of the PDO Index. I constructed this by taking the monthly PDO index page at the UW website and constructed four non-overlapping seasonal means per year (effectively a course low pass filter). The heavy black line is the ten year (40 season) centered
running mean. Using a centered mean preserves the timing of the phase transitions.
The phase changes in 1946 and 1976 are pretty clear in the ten year mean, while the early 20th and 21st century transitions are less obvious. At least the 21st century transitions is a little clearer in the even smoother annual averages (note I've used a July to June year in order to capture as a unit the Northern Hemisphere winter):
Since the 2005-06 year, only once (2009-10) has the annual mean PDO been above zero, and even that just barely, and the negative values have been repeatedly lower than any time since the 1976 transition. This is why I place the positive to negative phase PDO transition at 2007.
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More better of the above:ReplyDelete
One more Rick and I quit...are we in for another spell like '46-76?ReplyDelete
If so, why? PDO?
My sense is that we have stepped down from the warm winters of the positive phase of the PDO but will not be as cold as the 1946-76 negative phase mostly due to lack of extreme lows. Duration we're getting (e.g. 2008-09, Jan 2012) but the super cold temperatures are just not occurring. This is not merely an urban effect. Same story at. e.g. Northway, Tanana and Bettles, place with no urban impacts then or now. Nor a "thermometer effect" as some have suggested. This is the result of larger scale warming.Delete
Yes it would seem that's the case...some prolonged cold spells, but not to the extreme.Delete
I wonder how the Chukchi and Bering Sea ice is faring during the recent winter periods, i.e. thickness, extent, and duration for example. Other than watching the crab reality series, I know little about that aspect of our winter environment.
I should read up on what's happened to sea ice over periods paralleling the phases of the PDO. And inland freshwater thickness in monitored locations as well.
After I find the Borough's webcam.
Winter/early Spring ice coverage in the Bering Sea mostly depends on wind direction. So last winter (2011-12), with northerly winds the vast majority of the season, the Bering Sea maximum ice coverage was the greatest of the satellite era (since 1979). In the Chukchi the issue is more the lack of any multi-year ice.Delete
Here's one recent (2012) summary of estimated climate trends, indices, and projections for Alaska:ReplyDelete
And another (2010) from Dr. Akasofu regarding climate trends and possible contributing factors. Click on the DOI for a read: