The Hotspot in the North Pacific

I received a couple of emails over the weekend about a news article that mentioned sea surface temperature anomalies as high as 7 deg F in the North Pacific. I took a quick look for the article but wasn’t been able to find it, so I can’t provide a link.  There was a pocket of high sea surface temperature anomalies in the northeast North Pacific last week. See the sea surface temperature anomaly map for the week centered on Wednesday January 29th, Figure 1.

Figure 1

Sea surface temperatures for the extratropical North Pacific were unusually warm last year, and now they’re still above their typical seasonal levels.  See Figure 2, which presents the (volatile) weekly sea surface temperature anomaly data for the extratropical North Pacific.

Figure 2

The hotspot has been in the northeastern North Pacific for a couple of months and appears to have migrated east from the Kuroshio-Oyashio Extension (east of Japan). See Animation 1, which is available from Unisys here.  Three weeks ago, sea surface temperature anomalies were close to 7 deg F (3.9 deg C) above normal for the primary hotspot.  But sea surface temperatures there have dropped since then.

Animation 1

Weather events are not limited to the surface of the continental land masses.

Back in August, we discussed the unusual warming event in the extratropical North Pacific sea surface temperature anomalies.  Then I stated:

It will probably be a year or so before someone publishes a paper about it, but I suspect the sudden upward spike in extratropical North Pacific sea surface temperatures was caused by a shift in wind patterns, related to a change in sea level pressure. In other words, it’s likely weather related.

WHAT CAUSED IT?

I don’t know for sure.  I suspect there are a number of causes for the unusual warming in the extratropical North Pacific.  Here are a few things to consider.

A blocking high?  There was a period of high sea level pressure at the high latitudes of the North Pacific last summer, Figure 3, which likely interrupted the normal poleward transport of heat to the Arctic (thus explaining part of the “rebound” of Arctic sea ice).

Figure 3

As you can see there have been other spikes in sea level pressure at the high latitudes of the North Pacific.  Now consider that there were also unusual conditions in the tropical Pacific in 2013, with ENSO neutral conditions in the central equatorial Pacific (NINO3.4 region), but strong La Niña-like conditions in the far eastern equatorial Pacific (NINO1+2) for much of last year, especially during the boreal summer.  See the weekly NINO3.4 and NINO1+2 data toward the end of the December 2013 Sea Surface Temperature (SST) Anomaly Update.  So I suspect, if there’s a paper that tries to explain the warming in the extratropical North Pacific this past year, there will be a number of influences, so that it turns out to be nothing more than a weather event.

And for those interested, Figure 4 is a graph of the ARGO-era NODC ocean heat content data for the extratropical North Pacific. There was no unusual warming (or cooling) event for the top 700 meters, so the warming event appears to be surface related.

Figure 4

DATA SOURCES

The weekly sea surface temperature data and map are available through the NOAA NOMADS website here.

The ICOADS sea level pressure and NODC ocean heat content data are available through the KNMI Climate Explorer.