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derbOaclast Friday at 11:41 PM1 replyview on HN

The press statement is full of stuff like this:

"Area for future improvement: developers continue to improve the ensemble’s ability to create a range of forecast outcomes."

Someone else noted the models are fairly simple.

My question is "what happens if you scale up to attain the same levels of accuracy throughout? Will it still be as efficient?"

My reading is that these models work well in other regions but I reserve a certain skepticism because I think it's healthy in science, and also because I think those ultimately in charge have yet to prove reliable judges of anything scientific.


Replies

Majromaxyesterday at 12:56 AM

> My question is "what happens if you scale up to attain the same levels of accuracy throughout? Will it still be as efficient?"

I've done some work in this area, and the answer is probably 'more efficient, but not quite as spectacularly efficient.'

In a crude, back-of-the-envelope sense, AI-NWP models run about three orders of magnitude faster than notionally equivalent physics based NWP models. Those three orders of magnitude divide approximately evenly between three factors:

1. AI-NWP models produce much sparser outputs compared to physics-based models. That means fewer variables and levels, but also coarser timesteps. If a model needs to run 10x as often to produce an output every 30m rather than every 6h, that's an order of magnitude right there.

2. AI-NWP models are "GPU native," while physics-based models emphatically aren't. Hypothetically running physics-based models on GPUs would gain most of an order of magnitude back.

3. AI-NWP models have fantastic levels of numerical intensity compared to physics-based NWP models since the former are "matrix-matrix multiplications all the way down." Traditional NWP models perform relatively little work per grid point in comparison, which puts them on the wrong (badly memory-bandwidth limited) side of the roofline plots.

I'd expect a full-throated AI-NWP model to give up most of the gains from #1 (to have dense outputs), and dedicated work on physics-based NWP might close the gap on #2. However, that last point seems much more durable to me.