This post is a follow-up on discussions at the 2025 ACCESS-NRI workshop with @Matt_Woodhouse and @rmholmes . One of the long-running challenges of interpreting experiments using an ocean-sea ice model is the over-strong constraint that the surface boundary conditions place on surface variability, es…

Thanks @willrhobbs . I think this would be a cool thing to do. Besides sea ice, there are applications in the tropics in terms of freeing up intrinsic ocean variability (e.g. I used an atmospheric boundary layer model to free-up intrinsic ocean variability for an ENSO study in this paper ). That said,…

Hi All, I agree this is a nice idea. The one catch with using atmospheric nudging is that it would come with a significant computational cost - because I think you would have to run the whole UM. And it might have to be at high resolution if you want decent coupling to a high-res ocean … An alterna…

ooo, yes I’d be interested. Were you thinking of restoring heat and winds etc, or just winds? I suspect we might need to run a few short runs with nudging at different heights to see how strongly they constrain the ocean (which could be interesting in itself, really) to pick a good level for a long…

@AndyHoggANU in the paper I linked above I built an updated version of CheapAML and added it to ROMS. I agree this alternative approach of running a full coupled model would be more expensive, but the advantage is it requires no coding to get going…which lowers the bar to actually doing something (a…

Echoing what @rmholmes stated, I agree that an ‘emulated’ boundary layer is probably the long-term solution, but this is a nice stop-gap and we can perhaps use it to estimate just how ‘bad’ the surface air temperature constraint is. With NCMAS grants coming I’m minded to put in for an allocation fro…

U, V and potential temperature are the typically nudged parameters, though potential temperature is optional. I don’t know of any facility to nudge clouds and radiation - that’s the domain of full data assimilation and well beyond what nudging is intended to do

Re ocean/atmosphere cost: CM3 is 30 kSU/year for the 25 km version. I remember OM3 being twenty-something kSU/year? But I’ve been kicked out of the NRI internal chat so I can’t verify the second one :frowning: CM2 is 12.5 kSU/yr, OM2 is 7.2 kSU/yr if both at quarter degree ocean and CM uses an N96…

[image] rmholmes: Also - it sounds like for your application (zonal winds responding to the ocean) - you just want to run the full coupled model with no nudging? It sounds like I shouldn’t reply to exciting hive posts while still in holiday-brain-mode :rofl: I don’t think glueing on an atmos…

[image] jemmajeffree: I don’t think glueing on an atmospheric mixed layer would produce an ENSO? Or am I misunderstanding? Nope it won’t. There were two parts to the atmosphere in my Climate Dynamics study; 1) an ABLM which removes some of the damping of intrinsic ocean variability by the fix…

Freely-evolving boundary layer; 'Nudged' atmosphere run in ACCESS-CM

COSIMA

dougiesquire (Dougie Squire, ACCESS-NRI Ocean/Sea-Ice Modelling Team) 24 September 2025 04:43 10

The released OM3 25km_jra_ryf-1.0-beta configuration requires ~15.5kSU/year with diagnostics on density coords, or ~14kSU/year without - see here.

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Freely-evolving boundary layer; 'Nudged' atmosphere run in ACCESS-CM

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