So I’m sitting in the sun on my patio, dogs snoozing on the lawn, contemplating the Winter Weather Alert for California mountains from now to next weekend and pondering Climate Models. Wondering about things like how to have the land contour handled, how to compute winds upslope and downslope, how to compute damp valley warm air turning into cold mountain snow with no change of external heating or loss. Just what’s happening now.
Then it occurs to me two things:
1) I could look in the model code I have and see how they do it.
2) I don’t remember seeing anything like ground contours in the GCM code I’ve got (Model II).
Now this matters rather a lot. Much of weather comes directly from valleys and mountains interacting. Everything from all those loverly named downslope winds (like the Santa Anna’s that can make L.A. hot and miserable) to massive ridge lift snow levels.
After all, if climate, as the Warmers claim, is the “long term average of weather” and if weather depends a lot on ground texture and contours (which it clearly does), what is the long term average of model weather if it does NOT have ground contours and mountains in it? Seems to me it will be rather, um, “bogus” from the get go.
So I went off to my postings about GCMs. Did some simple word searches. Does “altitude” or “alt” appear? How about Mountain? Nope. Only in one comment by me about the layers processing.
Now I need to get back on my Climate Model Workstation and go back thorough all that model code in more detail. A simple word search on a write up / description of it with a few quotes is NOT enough. What if the programmer called it ‘mntn’ as a variable name and hid it in the “surface layer” handling somewhere? It could still be in there.
I’m pretty sure it isn’t. I read all this once and usually my brain hangs onto that kind of thing and reminds me later when I ask a question about it. Furthermore, there’s the issue of “scale”. Most models from that era run at about 8,000 cells. Only recently did GIStemp move to 16,000 cells. So how big is a cell?
Pondering this on the lawn chair, I used a simplification. The Earth is about 8,000 miles diameter, about 24,000 to 25,000 miles circumference (Wiki says 24,901 but I didn’t have it on the lawn chair). Say we have the Earth divided into 100 x 100 grid, that gives 10,000 grid cells (so more than the usual 8k as a safety margin). What is 1/100 of 25,000 miles? 250 miles. IF you start at sea level and proceed into the Sierra Nevada Mountains, you are well past the peaks at 250 miles inland. Nevada is wider than California and it is only 322 miles wide. Google Maps says it’s 228 miles by car from San Francisco airport to Reno Nevada on the backside of the peaks. That’s by car, so shorter by air.
Basically the resolution of the models is too course to contain the Sierra Nevada Mountains. One cell spans from sea level to the peaks and down to the valley beyond with Reno in it (and then some).
IMHO, that explains why they just use a few “layers” of atmosphere. Often as few as single digits. IIRC 7 was available if you turned it on in one model. Sometimes only surface, troposphere, and stratosphere look to be referenced. How do you model the changes from moist warm sea level air as it rises 7000 feet up the mountains and becomes a Winter Storm dumping lots of snow, if you don’t have mountains and you divide 70,000 feet of air into at most 10,000 foot layers?
Simply put, GCMs like Model II can not correctly model real topography, so can not get weather right, so their time-averages of it to give hypothetical climate can not be right, so their conclusions are garbage. That’s what it looks like to me. How can you get the monsoons in India without the Himalaya ridge lift wringing the water from the clouds? Or the desert in China behind them?
I need to look at some bigger, newer, finer grain climate model codes. In particular, those that try to be good weather models first. Like the MPAS code or maybe Model E and see if they have this same spectacular failure mode.
I suspect they will. As a first approximation, I think it would need at most a 25 mile wide swath to capture topography from major mountains such as the Sierra Nevada, and likely a 2.5 mile cell side length to get accuracy. that would require roughly a 25,000 / 1000 or 25,000 / 10,000 scale. Or a 1,000,000 (million) grid cell model to a 100,000,000 (one hundred million) grid cell model. Near as I can find out, nobody is even running things at a faction of that grid detail.
All of which leaves me wondering:
Without mountains, how can you get any climate model right?