Jason and the Argo Notes

Guest Post by Willis Eschenbach

Like Jason, I proceed into the unknown with my look at the Argo data, and will post random notes as I voyage.

Come, my friends,

'Tis not too late to seek a newer world.

Push off, and sitting well in order smite

The sounding furrows; for my purpose holds

To sail beyond the sunset, and the baths

Of all the western stars, until I die.

I have no great insights at this point, just some interesting results. Thanks to a commenter who pointed me to where to get the Argo data in one block. It’s at the Asia-Pacific Data-Research Center.

I downloaded it, and I’ve looked first at the file containing the surface data. It’s where I swim, so it’s the most interesting data to me. Figure 1 shows all Argo measurements of the ocean surface temperature taken to date.

Figure 1. All Argo ocean surface temperature data. There have been 696,872 Argo measurements to date of the ocean surface temperature. 

So far, so good. The results look real, which is always good to see, it means I’ve graphed them up properly. You can see the warm ocean along the coast of Europe, for example. But there is one curiosity about the Argo data.

Here’s the oddity. I took the data arranged by latitude as shown in Figure 2. I averaged it by 1° latitude bands, and then took an area adjusted average to give a global mean. The mean is 19.7°C ± 0.02 (95% CI).

Figure 2. All Argo ocean temperatures, sorted by latitude. NOTE: several people commented correctly below that I had not included the variation in ocean area by latitude band in the calculations. They are correct, I was wrong, and the actual corrected 60N-60S average is slightly higher, at 19.9°C.

Note that there is an obvious upper limit to the ocean temperatures, the “flat-top” on the graph at just above 30°C. No matter how much incoming solar there is, the ocean doesn’t get any warmer than that. This provides a “cap” on how hot the ocean can get. Above that temperature, any extra incoming energy is converted to latent and sensible heat, rather than warming the surface.

But I digress, that part’s just interesting. It’s not the curiosity.

The curiosity is the other ocean data sets give the following values for the average ocean surface temperature 2000-2011:

Hadley Center HadISST1 60N – 60S: 20.5°C ± 0.02°C (95%CI)

Reynolds Optimally Interpolated SST 60N – 60S: 20.4°C ± 0.02°C (95%CI)

NCDC Extended SST 60N – 60S: 20.3°C ± 0.02°C (95%CI)

The curiosity is that the Argo average ocean surface temperature data is significantly cooler than the other datasets, half to three-quarters of a degree …

Always more to learn. I do love real data. Look how much colder and more uniform the Southern Ocean is than the northern oceans, for example. Fascinating stuff.

Best to everyone,

[UPDATE]

The data I used is available at the website listed above, identified as “Near-real time Argo profile data interpolated on standard levels”. It’s the largest file on this page, 895 Mb, titled “Argo_TS.tar”.

The info sheet detailing the arrangement of the data is here.

It’s a tarball containing all of the depth files, one for each layer. The one I used was the zero depth file, “Argo_TS_0000.dat”. I downloaded them all, because I wanted the full set. If you only want surface temps you can download just that one file.

To read it in once it was downloaded (in the “R” computer language), I used:

depthcolumns=c("Longitude", "Latitude", "Level", "Depth", "Julian", "Temperature", "Salinity", "Potential Temperature", "Potential Density", "Dynamic Depth Anomaly", "Spiciness", "Extrapolation", "Error Temperature", "Error Salinity", "Error Potential Temperature", "Error Potential Density", "Error Dynamic Depth Anomaly", "Error Spiciness", "Ocean Code", "Region Code", "Argo Float ID", "Cycle Number", "Dynamic Depth", "Dynamic Depth-2")

depthwidths=c(9, 9, 3, 7, 10, 9, 9, 9, 9, 9, 9, 2, 11, 11, 11, 11, 11, 11, 2, 3, 8, 4, 9, 9)

depthinfo0=read.fwf("/Users/willis/Argo_TS/Argo_TS_0000.dat",depthwidths, col.names=depthcolumns)

You’ll need to change the filepath in the final line to wherever you have put the “Argo_TS_0000.dat” file.

w.