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Global climate change

The Blob off the West Coast of North America

4/10/2015, 11:09:53 AM

For the past 18 months or so there has been an unusually large, circular area (blob) of unusually warm (relative to normal) Pacific surface water off the west coast of North America.

Latest weekly sea surface temperature anomalies (March 29 to April 4, 2015)

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Sea surface temperatures in this region of the eastern Pacific have been averaging anywhere from 1 to 4 deg. C. (2 to 7 deg F.) above normal.

New research out of the University of Washington suggests that this blob of warmer water may be caused by a persistent high pressure ridge in the northeast Pacific, which has led to calmer ocean conditions over the past two winters.

The calmer ocean conditions allowed more heat to remain near the ocean surface instead of normally getting mixed out under stormier and windier conditions during the winter.

Basically what the study is saying is that these warmer sea surface temperatures are not caused by more heating, but by less winter cooling, according to the University of Washington News Today report.

This area of warmer, Pacific water has likely had a significant impact on the western U.S/Canada winter weather over the past two seasons by bringing in more heat and less snow to the region.

Actual temperature anomalies (deg C.) for this past winter in North America.

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Dennis Hartmann, A University of Washington professor of atmospheric science and lead author of the study points out that we need to look beyond the popular 'polar vortex' term as a reason for the recent cold winters in the midwest and eastern U.S.

Possible culprit is the 'North Pacific mode'

His (Hartmann's) study shows a decadal-scale pattern in the tropical Pacific Ocean linked with changes in the North Pacific, called the North Pacific mode, that sent atmospheric waves snaking along the globe to bring warm and dry air to the West Coast and very cold, wet air to the central and eastern states. (via the UW News)

“Lately this mode seems to have emerged as second to the El Niño Southern Oscillation in terms of driving the long-term variability, especially over North America,” Hartmann said. (via the UW News)

The North Pacific mode has apparently become stronger since 1980 and has overtaken the Pacific Decadal Oscillation (PDO) for second behind El Nino in it's influence on global weather patterns, according to the study.

Hartmann also notes that this blob of warm water is unlikely to be caused by climate change, but that some of it's impacts on the West Coast weather are similar (drought for instance).

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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Global climate change