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Nov 2011
I’ve briefly written up the (minor) changes to xfxwb, and the top-level friction variation (xfhcc) for Geoscientific Model Development:
XFXWB and XFHCC update paper
so it’s now available to all as a discussion paper.
Also following on from Till’s analysis, it seems that the diagnostics for d(tracer)/dt due to advection are rather misleading/wrong in FAMOUS - they’re a bit muddy in all UM4.5 code actually. There’s code for diagnosing both U.grad(T) and div(UT) in there, with the default giving U.grad(T), for some reason - the source field is actually updated using div(UT), so U.grad(T) will not show how the model field has really evolved. HadCM3 had a rather blunt override mod to put div(UT) into the diagnostic again which was not carried across to the newer UM4.5 advection mods used in FAMOUS. It’s pretty straightforward to edit the advect.f file to show div(UT) in FAMOUS, or ask me for a “fixed” mod you can use.
Sep 2011
Till Kuhlbrodt has been looking at the Southern Ocean under climate change across a range of models, and noted that xfxwb FAMOUS was alone in not showing a strengthening of the SO westerlies under CO2 forcing. A quick bit of analysis shows that the (zonal, at least) wind changes everywhere in FAMOUS are generally inconsistent with CO2-forced HadCM3, and seem to all be linked to the unrealistic top layer. Introducing just the simple top-level friction into xfxwb seems to solve this: CO2-forced changes in the vertical wind structure look much more like other models, and surface wind changes poleward of 40degrees, especially in the Southern Ocean, look like HadCM3. (Sub)Tropical wind changes are still inconsistent (but smaller), and there are knock-on effects on the control climate in this model: the seasonal cycle of temperatures in the northern hemisphere is improved, the ACC is slowed even more than before, the AMOC weakens by a few Sv and deepens. I’m conflicted whether to make this a standard version, or stick to the original plan and wait for all the bells and whistles of xfhcy to be tuned and released.
Aug 2011
There’s some significant FAMOUS development going on (alebit slowly), so I’ll go back to trying to keep these pages up-to-date with things as they occurr. I guess there’s four things that ought to be flagged up: