I’ve moved to WordPress: http://bobtisdale.wordpress.com/

Thursday, June 19, 2008

Arctic SST

The monthly Arctic Sea Surface Temperature (SST) Anomaly from January 1854 to April 2008 (raw and smoothed with a 37-month filter) is illustrated in Figure 1. The first thing that stands out is the change that occurs after the 1920s to 1940s, when the positive spikes in temperature became more frequent and SST began to modulate more. It is impossible to tell if this is a result of better sampling in later years or if this is caused by a particular SST threshold being reached, above which annual and multiannual variations became greater.

Figure 1

The second thing that stands out is that Arctic SSTs were higher in earlier years than they are today. Did earlier high temperatures reduce Arctic sea ice thickness, while causing only minor variations in ice concentration? That would give the appearance of a recent runaway loss of sea ice, when, in fact, there was a greater reduction in total ice mass during earlier periods of elevated temperatures.

The third noteworthy item is the oscillation visible in the smoothed data that begins about 1940. It decreases in frequency but increases in amplitude as time progresses. Did something happen to disrupt it around 2000, or is the frequency decreasing more, heralding a further increase in amplitude?

Figure 2 illustrates the Arctic SST Anomaly from January 1979 to April 2008. The saw-tooth annual cycle after 2000 appears to illustrate the impact of annual variations in Arctic ice concentration.

Figure 2

The monthly Arctic SST from January 1854 to April 2008 is shown in Figure 3. It’s tough to pick out much of value with the data presented this way, other than the 2.5 to 3 degree C amplitude in annual variations.

Figure 3

In Figure 4, the time span has been shortened to 29+ years, from January 1979 to April 2008. The larger changes in Maximum Arctic SST, versus the changes in Minimum, become apparent.

Figure 4

I prepared Figure 5, a monthly comparison of the last 2+ years, to see if the recent global cooling has had any effect on the Arctic SSTs. Just the opposite. Arctic SSTs have risen.

Figure 5

To reduce the mass of data in Figure 3, I used EXCEL to pluck out the annual high and lows in Arctic SST. Refer to Figure 6.
Figure 6

The span between the two data sets still impairs the ability to view anything useful, so in Figure 7, I’ve zeroed both curves at 1854 values. If the change in amplitude of the variations in annual maximum temperatures is not the result of better sampling, it appears that a change in minimum Arctic SST results in an amplified variation in maximum, especially when changes are positive. It makes sense. Above a certain temperature, the freezing point of sea water, ice melts and the albedo changes, causing further melting.

Figure 7

Whenever I see spikes like those in the maximum Arctic SST in Figure 7, I compare NINO3.4 SST data to determine if there might be cause and effect. Refer to Figure 8. To my eye, Arctic SST reacts to changes in NINO3.4 SST, but it would take statistical tools to pull out the relationship, tools that I don’t use.

Figure 8


Sea Surface Temperature Data is Smith and Reynolds Extended Reconstructed SST (ERSST.v2) available through the NOAA National Operational Model Archive & Distribution System (NOMADS).

No comments:


Tips are now being accepted.

Comment Policy, SST Posts, and Notes

Comments that are political in nature or that have nothing to do with the post will be deleted.
The Smith and Reynolds SST Posts DOES NOT LIST ALL SST POSTS. I stopped using ERSST.v2 data for SST when NOAA deleted it from NOMADS early in 2009.

Please use the search feature in the upper left-hand corner of the page for posts on specific subjects.
NOTE: I’ve discovered that some of the links to older posts provide blank pages. While it’s possible to access that post by scrolling through the history, that’s time consuming. There’s a quick fix for the problem, so if you run into an absent post, please advise me. Thanks.
If you use the graphs, please cite or link to the address of the blog post or this website.