The Power Stroke

Guest Post by Willis Eschenbach

I got to thinking about the well-known correlation of El Ninos and global temperature. I knew that the Pacific temperatures lead the global temperatures, and the tropics lead the Pacific, but I’d never looked at the actual physical distribution of the correlation. So I went to the CERES dataset, and Figure 1 shows the result.

Figure 1. Correlation of detrended gridcell temperatures with the global temperature two months later. Blue square shows the extent of the 3D section shown in Figure 2. Gray lines show the zero value.

The joy of science to me is wondering what the final map will look like. This map made me laugh when it came up on the silver screen. I laughed because it’s a very good map of the path of the warm water pumped from the equator to the poles by the magnificent El Nino pump. I didn’t expect that at all.

To understand why a map showing each gridcell’s correlation with the planetary temperature two months later should also be a great map of the path of the water pumped by the El Nino pump, let’s consider the action of the pump in detail. Figure 2 shows a 3D section of the Pacific showing the ocean before and after the power stroke of the El Nino pump.

Figure 2. 3D section of the Pacific Ocean looking westward along the equator. The area covered is the blue box at the equator in Figure 1. Click on image for larger size. ORIGINAL CAPTION: This is a view of the current El Nino / La Nina evolving in the tropical Pacific Ocean. You are looking westward, across the equator in the Pacific Ocean, from a vantage point somewhere in the Andes Mountains in South America. The colored surfaces show TAO/TRITON ocean temperatures. The top surface is the sea-surface, from 8°N to 8°S and from 137°E to 95°W. The shape of the sea surface is determined by TAO/TRITON Dynamic Height data. The wide vertical surface is at 8°S and extends to 500 meters depth. The narrower vertical surface is at 95°W. SOURCE: click on “Animation”.

Now, every intermittent pump has a “power stroke” when it does the actual pumping. For example, the power stroke of your heart is marked by the “beat” of your heartbeat. (The heart has two pumping chambers, so there are two power strokes, with their timing signified by the “lub-dub” of your heartbeat.) The power stroke is the time when the work is done—it is the portion of the cycle where the water is moved by the pump. Figure 2 shows the situation before and after the power stroke of the El Nino pump.

On the left of Figure 2, we have the condition prior to the power stroke of the El Nino pump. In this condition, there is a build-up of warm water on the surface. As you might imagine, this also warms the atmosphere above it, and a few months later the warmth spreads to the planet as well.

However, when the amount of this warm water reaches a critical point, the El Nino phenomenon emerges. The wind that powers the El Nino pump arises, and it begins to blow. This wind blows the warm surface water strongly westwards. Essentially, the wind skims off the warm surface layer and pushes it all along the equator until it meets up with continental arc. This movement of untold cubic kilometres of water is the result of the power stroke of the El Nino pump.

On the right of Figure 2, we have the condition after the power stroke, when the wind has  already blown the warm surface water westwards. Note that the cooler subsurface layers have been exposed. These layers are up to as much as 10°C cooler than the surface was  before the power stroke. Naturally, the exposure of this huge area of cool water cools the atmosphere and thus the planet.

So with that as prologue, why does the correlation map of Figure 1 show the track taken by the warm water? It’s all a matter of timing.

Consider what happens when the El Nino pump skims off the warm surface of the equatorial Pacific waters. When the cool subsurface water is exposed all across that huge tropical area, first the Pacific atmosphere and then the whole planet starts to cool.

But actually, that’s not quite true. The whole planet doesn’t cool … because the warm surface water moved by the El Nino pump has to go somewhere. This means that the previously cooler areas to which the warm tropical water has been pumped are warming, while the rest of the planet is cooling … and as a result, we get the lovely blue and green areas of negative correlation shown in the western Pacific in Figure 1.

These areas demonstrate that when the warm Equatorial water hits the Asian continent and the shallow-water arc connecting Asia to Australia, the water pumped by the El Nino splits into two parts. One part of the warm water goes north, and one goes south.

And of course, like the other emergent climate phenomena, the El Nino pump functions to keep the Pacific from overheating. When there is a buildup of warm water, the El Nino pump emerges, pumps the warm water to the poles along the path shown in Figure 1, and then disappears until it is needed once again.

I can only stand in awe. This is a most ingenious method for temperature regulation. When the warm Pacific tropical surface waters get overheated, an emergent pumping system arises, which pumps the warm water polewards and exposes the cooler water underneath, and the cooler ocean waters in turn bring down the temperature of the whole planet … brilliant.

My regards to everyone,

w.

AS ALWAYS: If you disagree with something I’ve said, please quote the exact words you disagree with. That way all of us can understand exactly what you object to.

PS—It does strike me that with both a positively correlated and a negatively correlated area regarding the global temperature two months later, we should at least be able to forecast a few key climate parameters for a couple of months ahead …