Guest post by Bob Tisdale
The National Oceanographic Data Center’s Ocean Heat Content (OHC) data for the depths of 0-700 meters are available through the KNMI Climate Explorer Monthly observations webpage. The NODC OHC dataset is based on the Levitus et al (2009) paper “Global ocean heat content(1955-2008) in light of recent instrumentation problems”, Geophysical Research Letters. Refer to Manuscript. It was revised in 2010 as noted in the October 18, 2010 post Update And Changes To NODC Ocean Heat Content Data. As described in the NODC’s explanation of ocean heat content (OHC) data changes, the changes result from “data additions and data quality control,” from a switch in base climatology, and from revised Expendable Bathythermograph (XBT) bias calculations.
This update includes the data through the quarter of October to December 2010. There has been an upswing in the Indian Ocean OHC data. And in the tropical Pacific, there’s been a delayed response to ENSO or a downward shift. Other than those, there are no other major changes with the latest 3 months on which to report.
The Global OHC data through December 2010 is shown in Figure 1. It continues to be remarkably flat, considering the rise that took place during the 1980s and 1990s.
In an upcoming post, I’ll present only the post-2003 data, the era when ARGO floats dominated OHC data.
A CHANGE OF COORDINATES
I’ve changed the coordinates of the Indian Ocean and South Pacific data. The coordinates I was using for the Indian Ocean (60S-30N, 20E-145E) caused too much overlap with the North Pacific and Tropical Pacific data. So I’ve shifted the coordinates so that the Indian Ocean is now represented by 60S-30N, 20E-120E. This required that I shift the South Pacific; it’s coordinates are now 60S-0, 120E-90W.
Figure 2 illustrates the Tropical Pacific OHC data (24S-24N, 120E-90W). The major variations in tropical Pacific OHC are related to the El Niño-Southern Oscillation (ENSO). Tropical Pacific OHC drops during El Niño events and rises during La Niña events.
At least it should. Figure 3 compares tropical Pacific OHC to NINO3.4 SST anomalies (a commonly used ENSO proxy) where the NINO3.4 SST anomalies have been scaled and inverted (multiplied by a scaling factor of -0.15) to help show the relationship. The drop in the tropical Pacific OHC during 2010 is unusual. It should be rising (recharging) during this period. It’s impossible to tell at this time if this is a delayed response or a downward shift.
The equatorial Pacific, on the other hand, Figure 4, is responding as one would expect.
We’ll have to keep an eye on the tropical Pacific OHC data.
Figure 5 illustrates the Indian Ocean OHC data. Note the sudden upswing since 2006. It’s odd when we consider the trends for most of the other ocean basins since 2003 are flat or negative. (I’ll illustrate this in an upcoming post.)
The Tropical Pacific OHC dropped and the Indian Ocean OHC rose; one might think warm water has migrated from the Tropical Pacific to the Tropical Indian Ocean. If we combine the Tropical Indian and Pacific subsets and compare it to the Tropical Pacific, Figure 6, we can see the two datasets mimic one another and that the recent drop is suppressed. It’s possible (and likely) there has been some migration of warm water from one subset to the other (likely because the current known as the Indonesian Throughflow does flow between the tropical Pacific and Indian Oceans).
In fact, this transport appears to take place in the animation of NODC OHC from 2005 to 2010, Animation 1, which was taken from the video that’s included in the post The Electric Kool-Aid Ocean Heat Content Animation.
And here’s the YouTube video from that post. (The animation with music starts around the 2 minute mark, so check your volume setting if you’re at work.)
But the recent rise in Indian Ocean OHC is not limited to the tropics. Figure 7 compares Indian Ocean OHC to the OHC of the Indian Ocean South of 24S. The OHC of the mid-to-high latitudes also has the sudden surge.
And yes, that rise and fall in the OHC of the Indian Ocean South of 24S during the late 1990s does look odd. In fact, if we smooth those two datasets, Figure 8, we can see how unusual that spike appears.
THE HEMISPHERES AND THE REST OF THE BASINS
(9) Northern Hemisphere
(10) Southern Hemisphere
(11) North Atlantic (0 to 75N, 78W to 10E)
(12) South Atlantic (0 to 60S, 70W to 20E)
(13) North Pacific (0 to 65N, 100 to 270E, where 270E=90W)
(14) South Pacific (0 to 60S, 120E to 290E, where 290E=70W)
(15) Arctic Ocean (65 to 90N)
(16) Southern Ocean (60 to 90S)
All data used in this post is available through the KNMI Climate Explorer: