Under The Equator

Guest Post by Willis Eschenbach

Inspired by my previous posts, Boy Child Girl Child and Sea Levels in the Nino-Nina Cycle, I decided to take a look at what is happening below the sea surface along the Equator. A commenter pointed me to an Australian archive of past sub-surface analyses, with an unfortunate URL that includes “oceantemp/pastanal/” … but I digress.

These analyses show the longitude on the horizontal axis and the depth on the vertical axis. Here’s their view of the peak of the El Nino in November 1997. The black area on the right is South America, and the black area on the left is Africa. The shallow zone between 90°E—120°E is Indonesia and Borneo.

Figure 1. Equatorial Pacific Ocean vertical section temperature analysis for the peak El Nino, November 1997. Date is shown in the center. Top panel shows the “climatology”, a term of art meaning the long-term average for the climate variable for the month. In this case the variable is the temperature distribution. Middle panel shows the actual temperatures for the month. And the final panel shows the “anomaly”, which is the actual temperature less the climatology. This is how much hotter or cooler than average the ocean is in that location that month.

In Figure 1 you can see how the anomalous heat in the eastern Pacific just off of South America extends from the surface down deep, a couple hundred meters. The “H” note shows it peaked at over eight degrees warmer than average. There’s also a corresponding subsurface cool spot to the west of that, which the “L” note says is some six degrees cooler than average. Big swings.

Compare that with the situation one year later, November 1998 at the peak of the corresponding La Nina.

Figure 2. Equatorial Pacific Ocean vertical section temperature analysis for the peak La Nina, November 1998.

Here we can see that the warm water has been moved out and has been replaced by the colder subsurface waters, which have now come to the surface..

And to give myself a larger understanding of the undersea world, here’s a movie I made of the month-by-month situation from 1995 to 2008, when they changed the format. See the Endnote for details on how I made the movie.

Figure 3. Monthly changes in the vertical section temperature analysis.

Always more to learn … please quote whatever you are commenting on, avoids misunderstandings.

Half-moon tonight, crisp and cold. The deer came by again today. Hummingbirds were drinking from the flowers. Life in the forest doesn’t care about politics, which seems like a brilliant plan to me these days. The silence of the woods is my balm and my refuge.

My best regards to all,

w.

Endnote: To make the movie, first I had to download the .GIF files. I do most of my work in the computer program R. If you program, you should learn R. Free, cross-platform, free killer user interface called RStudio, interpreted. But I digress. I first needed to create the year/month number combinations used by the Aussies in the URLs of the graphics. Here’s that code. Everything on a line after a hashmark “#” is a comment.

allyears=paste0(rep(1995:2020,each=12),twodigit(rep(1:12,26))) # repeats the numbers from 1995 to 2020 twelve times each, and pastes the two-digit representations of the months onto each one
head(allyears) #shows the first few data points of the variable
[1] "199501" "199502" "199503" "199504" "199505" "199506"

(“twodigit” is a function I wrote because I couldn’t remember the actual code to format a number with two digits.)

twodigit=function(x) {
    if(is.numeric(x)){
        sprintf("%02d",x) # formats numbers
    } else {
        format(x,digits = 2) # formats text
    }
}

Then I created a folder (directory) to store the .GIF images, and put the path to the folder into a variable.

dir.create("Aussie Underwater All")
pathname="Aussie Underwater All/"

Then I wrote a loop to read each .GIF and write it to the folder. Comments after the “#” in each line.

for (i in 1:length(allyears)){ # cycle through all the years

print(paste0(allyears[i])) # prints progress

aurl=paste0("http://www.bom.gov.au/archive/oceanography/ocean_anals/IDYOC002/IDYOC002.",allyears[i],".gif") #paste together the URL

mygif=image_read(aurl) # read the gif image file at that URL

image_write(mygif,paste0(pathname,basename(aurl))) # write the image file to the folder created above.
}

Once I had the images, the rest I did online. Upload the images to the Animated GIF Maker, and make an animated GIF. Upload the animated GIF to CloudConvert, and convert it to MP4. Whole thing took me a couple hours.

w.