(back to up to ScienceWorkRobin)
CO2 coupling in FAMOUS
normal release versions of FAMOUS use a specified, spatially constant atmospheric CO2 concentration that is unaffected by carbon exchange with the ocean or land. This is specified in Atmosphere→Science→General Physics. In releases using the a2o_specifiedCO2.mod the ocean biogeochemistry (HadOCC) sees this specified CO2 - for older releases without this mod, the CO2 concentration seen by HadOCC has to be separately specified in Ocean→Science→Carbon Cycle.
For a more coupled carbon cycle, there are two basic options:
- The MOSES1 land scheme cannot do carbon, but it is possible to have coupled ocean/atmosphere CO2, with spatially varying CO2 concentrations dependent on air-sea exchange. This can be seen in PUMA job xcvic. Fluxes of CO2 from the land could be specified using the CO2 emissions ancil. There are a couple of code mods, two post-processing scripts and the UMUI options required to enable CO2 as an atmospheric tracer
- alternatively, I’ve written a hack mod that keeps track of the integrated ocean-atmosphere CO2 fluxes and updates CO2 as seen by the ocean accordingly. This allows you to separate the radiative and biogeochemical effects of CO2 in the system and look at ocean uptake/outgassing issues whilst specifiying the background climate as you please. It’s a hack - most annoyingly, it doesn’t recall the new surface CO2 value for the ocean when the model stops, so you have to look back through stdout and put the new value back into the handedit manually when you restart a job. Email me if you’d really like it.
- MOSES2.2 land can do carbon, coupling the vegetation and soil into the carbon cycle properly. This can be seen in job XFHCY. This is pretty much just a proof-of-concept, due to the issues with the rest of the climate with MOSES2.2 enabled (see CurrentWorkMOSES2)
as usual, email me if you’d like more details
(the following notes are copied across from the old muddle)
conservative coupling of CO2 fields
CO2 coupling has previously only happened in HadCM3LC, where the ocean and atmosphere grids were congruent. Coupling just involved copying an array. FAMOUS needs the same grid interpolation for CO2 as it has for all the other coupling fields.
spinup/drift of biogeochemical tracers
Spinning up the ocean properly takes a few thousand years for the biogeochemistry, even without sediments. Even with iceberg calving to approximately balance the ocean water budget, there’s still some water flux, so some drift. The vflux_drift correction calculation, normally used to match the global tracer drift to the global water drift, is being used to artificially zero the drift of all ocean tracers (regardless of the actual water flux) whilst spinup is going on. Using UTOPIA advection for the biogeochemical tracers greatly improves
Had OCC’s surface pCO2, and hence carbon fluxes for the spun up state - this is important.
inland seas and surface carbon fluxes
the lack of communication between the inland seas and the rest of the ocean mean that, over time, small imbalances in their local P-E+R can blow up to give huge positive or negative tracer concentrations. Whilst this is inconvenient for, say, salinity, it’s even less helpful for TCO2, where fluxes are exchanged with the atmosphere based on the tracer concentration. For this reason, all biogeochemical tracers and the surface carbon fluxes for these inland seas have been masked out using the same mask employed in the vflux drift calculation. I’ve expanded it to include the (also “inland”) Baltic and Hudson Bay regions, which are capped so they can’t fall below 0 in salinity and which see some pretty high CO2 uptake. I guess they’d sort themselves out w.r.t TCO2 due to this feedback, but it would be inconsistent with salinity, Alk and the water budget in general. I think
- The Climate (May ‘08)
The actual code running at this point (the QUEST job, at least) is in much better shape than it was over the winter. It’s now properly reproduceable over restarts and configs with different numbers of processors, a couple of bugs have been caught and the whole thing is generally tidier. We’re not totally free of bugs, however: all MOSES2.2 runs still hit occasional NaNs in the 10m wind diagnostics (see
CurrentWorkMOSES Nov07) and the fully coupled CO2 run just segfaults after ~200 years (see Sep08 above), although a quick look shows nothing unusual. There’re also some legacy STASH options with MOSES1 diagnostics still left in that fill up with junk which can upset xconv/ff2pp.
notes for Fixed CO2 MOSES2.2 vs MOSES1
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the really glaring issue is the warming of most land surface areas by a few degrees. The warm bias extends higher into the atmosphere. The valnote suggests it’s a summer (JJA) problem, even in South America and Africa. In DJF, only Canada sees anomalous warming, and Asia is cooler. North America, Asia and Australia show an increase in net downward SW in JJA, but this doesn’t seem to apply to Africa and South America. The only thing that correlates well with all the warming is a reduction in net downward LW during JJA, which is a reflection of the higher surface temperatures. The switch to MOSES2 does mean some quite large changes in soil moisture, which I think are probably significant (NB the soil moisture plots in the valnote aren’t directly comparable due to changes in this diagnostic between the versions of MOSES)