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

Wednesday, July 22, 2009

Sea Level Data In Monthly Format

I’ve moved to WordPress.  This post can now be found at Sea Level Data In Monthly Format
As noted in prior Sea Level posts (Sea Level Update - Through March 2009 and Sea Level Data: Global and Indian, Atlantic, and Pacific Oceans), the sea level data available from the University of Colorado is not in monthly format. Some years there may be 38 readings, for example, while for others there may be 35. And to complicate matters, the total number of readings for the global dataset is different than the individual ocean subsets. For this post, I converted the Global Sea Level data and the Sea Level data for the Atlantic, Indian, and Pacific Oceans into monthly data.

I apportioned the data by sampling dates. For example, if the dates of the readings were greater than or equal to “1983.000” but less than “1983.083”, the data was considered January 1983 data and all readings for that month were averaged. And I repeated the process each month from December 1982 to March 2009.

In this post I have also provided comparisons to scaled NINO3.4 SST anomalies. As could be expected, some of the rises and falls are related to ENSO events. The step changes also appear to be direct responses to El Nino events. I am not, however, implying that Sea Level variability is only impacted by ENSO.


The monthly Global Sea Level data from December 1992 to March 2009 is illustrated in Figure 1. The late 1995 spike in the sea level data stands out similarly to the way the 1997/98 El Nino stands out in global temperature data.
Figure 1

Figure 2 compares Global Sea Level to scaled NINO3.4 SST anomalies. The peak in late 2005 is not directly related to an El Nino. The impacts of the 1997/98 and the 2002/03 El Nino events, however, can be seen in the Global Sea Level data.
Figure 2


As preliminary notes, the annual variability in the Atlantic and Indian Ocean Sea Level data can be clearly seen in the monthly data. The Pacific data is noisier, which masks an annual signal.

Note how the smoothed Atlantic Sea Level data, Figure 3, appears to rise in steps. The first step is in 1995. This should be a rebound from the Mount Pinatubo aerosol effects.
Figure 3

The scaled NINO3.4 SST anomaly data has been added in Figure 4. The smoothed Atlantic Sea Level data rises again in 1997, which should be a response to the 1997/98 El Nino. Are the rises in 2003 and 2005 also responses to the 2003/04 and 2004/05 El Nino events?
Figure 4

The raw and smoothed Indian Ocean Sea Level data, Figure 5, show a major step change in 1998 and a curious increase in trend in 2004.
Figure 5

The 1998 upward step in the smoothed Indian Ocean Sea Level data appears to be a lagged response to the 1997/98 El Nino. Refer to Figure 6. The 2004 change in trend does not appear to be ENSO related. Was there a shift in Indian Ocean cloud cover in 2004?
Figure 6

Following the significant increase from 1998 to 2002, the Pacific Ocean Sea Level, Figure 7, has been relatively flat since 2002. The rise in Pacific Sea Level slowed after 2002, and Pacific Sea Level has declined since 2006.
Figure 7

In the comparison with NINO3.4 SST anomalies, Figure 8, note how the Pacific Ocean Sea Level surged upward in mid-1996, one year before the 1997/98 El Nino. Does this indicate that there was a sudden rise in ocean heat content in the year leading up to that El Nino? Does this confirm the findings in my post “Did A Decrease In Total Cloud Amount Fuel The 1997/98 El Nino?” It does seem to show that the 1997/98 El Nino was fueled by a short-term change (one year) in the ocean heat content of the Pacific.
Figure 8


Figure 9 is a comparison of Sea Levels for the Atlantic, Indian, and Pacific Oceans. Note how one dataset always appears to be out of phase with the variations of the other two. Rarely do the sea levels of all three oceans rise or fall in unison.
Figure 9

The SST anomalies for the Atlantic, Indian, and Pacific Oceans are illustrated in Figure 10. There are significant differences between the SST and Sea Level curves. (I can’t see any reason to compare the individual ocean sea level and SST data.)
Figure 10


Sea Level data is available through the University of Colorado at Boulder webpage:http://sealevel.colorado.edu/index.php


Ken Gregory said...

The best fit linear trend of sea level rise from January 2004 through March 2009 of the Pacific, Atlantic and Indian oceans are 0.15 mm/yr, 0.35 mm/yr and 6.04 mm/yr, respectively. The global rate from January 2004 is 1.52 mm/yr.

Can you provide any comment on why the Indian ocean shows such a high rate of sea level rise in recent years compared to the other oceans?

Bob Tisdale said...

Ken Gregory: Give me a day or two to post a video of SSH Residuals that I threw together a couple of weeks ago. I animated weekly SSH maps (2002 to "present") that are available from JPL. The reason I haven't posted it sooner is that JPL unfortunately changed the scale in 2006.

jelsliger said...

Hi I am a university student from UBC, I have been analyzing the same data set. I notice a trend between the Pacific and Atlantic Oceans that I cannot account for. It appears as though there is a lag between sea level peaks. Specifically if you plot yearly averages it is easy to see. I was wondering if you have any idea what might be causing the shifting of sea level between the Pacific and the Atlantic?
I was thinking it may be the ocean circulation, but the only circulation i could think would cause a difference between the atlantic and pacific would be thermohaline. however this dooesn't make sense as the thermohaline is a slow moving current and would not affect the oceans annually. Any thoughts?

Bob Tisdale said...

jelsliger: The North Atlantic has the highest trend in sea level, SST, OHC, etc., since 1975 for a number of reasons. The North Atlantic warms in response to El Nino events and cools in response to La Nina events, obviously, and the ENSO-induced SST variations (positive and negative) linger in the North Atlantic. In effect, the North Atlantic integrates ENSO. And since the frequency and magnitude of El Nino events have exceeded La Nina events since the mid-1970s, the North Atlantic SST anomalies rise.

The South Atlantic is the only ocean basin where heat travels from the pole to the equator, traveling toward the North Atlantic. This contributes to it.


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.