Here's a try at an explanation of why it was so cold in April in Fairbanks and much of Alaska.
First, here's the mean 500 mb heights and anomalies:
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| Courtesy of NCEP.NCAR Reanalysis |
The most notable features are the big high over the northwest Bering Sea, with a mean height anomaly for the month of over 200 gpm. The other feature is the trough from the western Canadian Arctic across mainland Alaska, though the heights are not especially low, with the 50 gpm anomaly just reaching Alaska near Eagle. The weakness in the contours over Interior Alaska reflect the frequent closed low that was found over the area, especially early in the month.
This pattern is reflected in the April anomaly of the meridional (north-south) component of the 700 mb (roughly 10,000ft) wind flow:
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| Courtesy of NCEP.NCAR Reanalysis |
The blues and purples show more northerly wind component in the 700 mb wind than is usual in April over nearly all of mainland Alaska, with more southerly than average flow over Kamchatka, the Sea of
Okhotsk and most of eastern Siberia.
Finally, the mean April near surface (1000mb) temperature anomalies are about what you'd expect with this transport pattern:
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| Courtesy of NCEP.NCAR Reanalysis |
April was extremely warm over the East Siberian Sea and quite warm over all over eastern Siberia and Chukotka, with the cold over most Alaska (extending southeast thru the Canadian Praise Provinces and into the upper Midwest). The northwest North Slope and Bering Straits region were not so nearly so cold, being closer to the high aloft and, for the Slope, getting occasional warm pushes from the west.
I'll anticipate regular reader Gary and suggest the following to the question "why this particular pattern at this time?" The high aloft over the Bering sea and anomalous northerly flow are signature features of the negative PDO phase of North Pacific sea surface temperatures, which as been the case since 2010. This was amplified by only limited deep tropical convection in the western Pacific (in jargon, a not especially active MJO). This allowed a favored negative PDO pattern to persist.
Limited Madden-Julian Oscillation...good obs Rick. Not mine but available elsewhere. Soon we'll be discussing Kelvin Waves and their effect.
ReplyDeleteMy next question...does the Jetstream aloft drive the anomalies you described very well above, and very clearly BTW, or do the anomalies alter or otherwise modify the Jet? And if so, at what heights? Who in the end wags the weather tail or has the hammer?
Gary
The above is beyond good...it's excellent. I wish I had the ability.
Thank you.
Gary
Late night confused comment above...I meant to refer to the Atmospheric Rossby Waves, not the reference to oceanic Kelvin Waves.
DeleteGary
Gary, atmospheric Kelvin waves propagate through the equatorial atmosphere much faster than MJO but impact development of convection. They can produce a more smeared out looking tropical convection pattern than a simple MJO would imply.
ReplyDeleteHi Rick, I was tending towards cross referencing the Rossby Waves (Jetstream) and the effects of Arctic Amplification aspect in my late night foggy comment. Imagine a hive full of bees settling down before bed.
DeleteI'd been reading and watching on YouTube some of Dr. Jennifer Francis' recent analyses, and was comparing that climate theory to your Alaskan anomalies noted above.
I'd come across the Jet path amplification, fragmentation, and stagnation last Fall, but hadn't really connected the Jet to the theory of formation and sustenance of pressure cells.
More to learn as always. Now snowing in town again so here we go.
Gary