Weakening Gulf Stream?

[Xnn]

http://www.noaanews.noaa.gov/stories2009/20090831_tides.html

Persistent winds and a weakened current in the Mid-Atlantic contributed to higher than normal sea levels along the Eastern Seaboard in June and July, according to a new NOAA technical report.

After observing water levels six inches to two feet higher than originally predicted, NOAA scientists began analyzing data from select tide stations and buoys from Maine to Florida and found that a weakening of the Florida Current Transport—an oceanic current that feeds into the Gulf Stream—in addition to steady and persistent Northeast winds, contributed to this anomaly.

There has been a fair amount of speculation concerning weakening of the Gulf Stream and it's implications for the climate. Most of this dealt with the climate of Europe, but this article points out that it has contributed to higher sea level along the Eastern US coast. This is a somewhat surprising result.

No word yet, if the weakening is only temporary or part of a longer term trend. "Further Analysis is needed..."

Global warming is generally thought to result in a weakening of the Gulf Stream because the stream is driven in part by the formation of ice in the North Atlantic. Less ice formation will ultimately mean less of a driving force. Its the timing, magnitude and implication of the weakening that is not as clear.

[Xnn]

Here is the latest image of Sea Surface Temperatures from NOAA.
Notice, that despite a weaking Gulf Stream, temperatures
in the North Atlantic are actually above average.
Southwest of England is another story.

http://www.physicsforums.com/attachment.php?attachmentid=20464&stc=1&d=1252368495

Also, El Nino is growing stronger in the Pacific.

http://www.ncdc.noaa.gov/oa/climate/research/sst/weekly-sst.php

[sylas]

http://www.noaanews.noaa.gov/stories2009/20090831_tides.html



There has been a fair amount of speculation concerning weakening of the Gulf Stream and it's implications for the climate. Most of this dealt with the climate of Europe, but this article points out that it has contributed to higher sea level along the Eastern US coast. This is a somewhat surprising result.

No word yet, if the weakening is only temporary or part of a longer term trend. "Further Analysis is needed..."


This article seems to be speaking of a transient "event". The associated report linked in the story (Elevated East Coast Sea Level Anomaly: June – July 2009 (http://tidesandcurrents.noaa.gov/publications/EastCoastSeaLevelAnomaly_2009.pdf), NOAA Technical Report NOS CO-OPS 051, W. Sweet et. al., August 2009) is 40 pages long, and gives more detail.

From the summary:
There are two probable mechanisms responsible for the June – July 2009 high SL residuals. The first is northeasterly (NE) wind forcing. In June 2009, winds over the entire geographic area from Cape Hatteras, NC to the Gulf of Maine had a moderate NE wind component, whose transport caused coastal SL to rise. South of Cape Hatteras, winds were primarily southwesterly (SW). The other mechanism is the changing transport of the Florida Current, which is measured in the Florida Straits before it supplies the Gulf Steam off of Cape Hatteras, NC. When the Florida Current / Gulf Stream transport is low, the eastward-rising cross-current slope relaxes and raises coastal SL. In June 2009, the SL residual rise was concurrent with a noted decrease in transport of the Florida Current.

The June – July 2009 SL event decays in mid-July 2009 as the SL residuals diminish. ...

So it is definitely not a long term trend; but a short term anomaly. The questions are what caused this anomaly. I don't think this report or the event has much to do with the speculations about long term changes in the North Atlantic Circulation, or Gulf Stream. It's all about short term variation, which can be both above and below predictions for any given month, thanks to normal natural short term variations in winds and currents.

Cheers -- sylas