Dueling ITCZs

Guest Post by Willis Eschenbach

Inspired by a comment about modeled rainfall by Dr. Richard Betts over in the Twitterverse, I decided today to look at how well the climate models are able to hindcast historical rainfall amounts and patterns.

I already had the satellite rainfall data from the Tropical Rainfall Measuring Mission. So I went over to KNMI and got the Climate Model Intercomparison Project 6 (CMIP6) climate model rainfall results of the 38 different models in their database.

Let me start with a look at the TRMM satellite data. It extends from 40°N to 40°S. The two graphs below are the same, but the left one is Pacific centered and the right is Atlantic centered.

Figure 1. 18-year average, TRMM annual rainfall, Dec. 1997 – Mar 2015

Of interest in this is the line of rain just north of the Equator in both the Pacific and the Atlantic Oceans. This marks the average location of the Inter-Tropical Convergence Zone (ITCZ). It is a line of semi-permanent thunderstorms located where the northern and southern halves of the atmosphere come together. It forms the ascending part of the great Hadley cell circulation, which rises just north of the equator, moves polewards on both sides, descends over the 30° N/S desert belts, and returns to the ITCZ just north of the Equator. Here’s a cross-section of the Hadley cell circulation.

Figure 2. Cross-section of the ITCZ and the northern and southern Hadley cells.

With that as a prologue, consider the following Pacific-centered maps of some of the model results.

Figure 3. Rainfall model output, CMIP6 models

I’m sure you can see the problem. There are two ITCZs in the model output, one above and one below the Equator.

Now, this is not something that’s only found in the modern models. It’s been a problem since there have been climate models. It even has its own name. Here is a comment from 2013 in PNAS:

The double-Intertropical Convergence Zone (ITCZ) problem, in which excessive precipitation is produced in the Southern Hemisphere tropics, which resembles a Southern Hemisphere counterpart to the strong Northern Hemisphere ITCZ, is perhaps the most significant and most persistent bias of global climate models.

That was ten years ago, the problem was old and well-recognized back then, and they still haven’t been able to fix it.

And we’re supposed to totally destroy our current energy source and power the world on unicorn methane based on these garbage Tinkertoy™ climate models? Really? They can’t even hindcast the past!

More to the point, they can’t replicate the Hadley cells, a most basic feature of the global circulation, but they are supposed to be able to predict the future a hundred years out?

Laughable, but also tragic in that governments are passing laws and shafting the poor based on this nonsense.

The problems continue. Here are the monthly rainfall observations from the TRMM, along with the modeled monthly rainfall, for the area 40°N to 40°S.

Figure 4. TRMM (red) and modeled (colored) monthly rainfall values, 40°N/S, Dec 1997 – Mar 2015

Again, you can see the problems. Not only is there no overlap between models and observations, but the models are far from agreeing with each other.

Well, how about the trends? There’s a slight upwards trend in the TRMM data, but what about the models? Here’s a “violin plot” of the model trends per decade, along with the TRMM trend over the period.

Figure 5. Violin plot of the model trends in millimeters per decade, along with a yellow/black line representing the TRMM trend. The width of the violet area at any point represents the number of models with trends of the value shown on the vertical (Y) axis. For those familiar with a “density plot”, a violin plot is just two of them back to back.

Again, problems. Not only are the various model trends quite different from each other, but they also don’t even agree as to sign. 17% of them are less than zero. Also, the TRMM trend is larger than all but two of the model trends.


Anyone who seriously believes one word that the models say about rainfall is either a climate alarmist or a fool … but I repeat myself.

My best to all,


As Always: I ask that when you comment, you quote the exact words you are referring to so we can all be clear about your subject and who said it.

via Watts Up With That?


April 18, 2023 at 01:00PM

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