FAMOUS

(back up to Science Work Robin)

HadOCC Marine Biogeochemistry

FAMOUS comes with the HadOCC model of marine biogeochemistry. It’s an NPZD model, with phosphate as the nutrient. There’s no iron limitation or sedimentation, although light absorption in the mixed layer is dependent on the biology. HadOCC in FAMOUS uses a handful of extra tuning mods and a fix to enable the biology shading in the coupled model (see below). It’s been reported to add about 10% to the model runtime over the pure ocean-atmosphere model (Chris Jones)

HadOCC’s tracer fields are significantly improved by the use of the 3rd order flux-limited UTOPIA advection scheme, which is included in XDBUA (temperature and salinity are still advected using the model’s normal centred-differences). The XDBUA ocean dumps are reasonably well spun up for ocean-atmosphere CO2 exchange - earlier releases and dumps have rather a lot of CO2 outgassing when used with 1860 atmospheric CO2.

The original mixed-layer light absorption mod (self_shade.mod_4.5) is written in an unsafe way, such that disabling HadOCC leaves the absorption profile undefined. Without bounds-checking, the model runs and the spun-up climate seems fairly insensitive to this issue but it’s still not a good idea. If you have HadOCC disabled in any version of FAMOUS, remove the mod before compiling or use the “*_safe” version.

Standard release HadOCC appears to have the zooplankton production diagnostic “hijacked” to reflect export calcite flux instead. This issue affects all releases of FAMOUS so far - I have a mod.

As of Aug 2011, the UMUI has been modified to allow the specification of UTOPIA advection (QUICK with flux limiter) in the tracer advection panel, doing away with the requirement for a handedit. If you want to use the UMUI options, make sure to remove the previous handedit that overrode UMUI choices for the biogeochemistry advection and forced UTOPIA on.

(the following notes are copied across from the old muddle)

October ‘07

HadOCC includes dilution of surface tracers by freshwater fluxes, but ignores the freshwater flux adjustment field, if it exists. I’m not sure if this is deliberate or not, but it is inconsistent, especially when the adjustment is being used - as it is in FAMOUS - as a “real” flux of water due to iceberg calving. The version of vflux_drift.mod used in the Summer 07 release includes dilution of Alkalinity and TCO2 by surface freshwater flux adjustments too.
Spin-up runs for the Summer 07 release showed up an amusing little feature. The equations for gas exchange use the formula from Wanninkhof (1992) to compute the Schmidt number, whose square root is used in setting the piston velocity. This formula goes negative for SSTs over 41 degrees, at which point the piston velocity NaNs and the global TCO2 field does likewise after a few timesteps. The model appears to be able to cope with this just fine, and nothing else goes wrong - so if you happen not to look at TCO2 when checking your model climate nothing seems wrong. 41 degrees seems a lot for an SST, but odd spikes in the high 30s don’t seem that uncommon, especially with the small tropical warm bias from the new ozone. The problem area was off California, where FAMOUS amplifies other UM version’s warm bias, identified in other models as a serious lack of marine stratocumulus. Clearly, at least on one timestep, FAMOUS has managed to hit an SST>41 degrees. For the moment, a simple bound has been put on the Schmidt number to keep it above 0 (schmidt_bounds.mod)
self_shade.mod_4.5model modsimple self-shading mod to work with standard one-band radiation
alk_2.mod_4.7.mhmodel modchanges rain_ratio to improve spun-up alkalinity
tuning_2.mod_4.7.mf77model moduses a simple depth-dependent remineralisation rate below level 6; slightly reduces the CO2 piston velocity
adbipo@dam19c1ocean restartCJ’s restart containing ocean biogeo. fields
notes
turn ocean tracers on and request the ocean carbon cycle in the UMUI. And have a restart with biogeochem. fields in it!
Standard HadOCC needs the two-band radiation scheme to be enabled - at least, the UMUI tells you that biology won’t work without it, although this isn’t really true - but the coupled model cannot run like this. Ignore the UMUI, leave the radiation scheme as standard and use the self_shade mod detailed above (the complex self shading is what is actually turned off if two-band radiation is not used).
Page last modified on August 16, 2011, at 11:50 AM by robin