#699 closed task (fixed)

Check NPP/GPP ratio

Reported by: luyssaert Owned by: luyssaert
Priority: critical Milestone: ORCHIDEE 4.1
Component: Biogeochemical processes Version: trunc
Keywords: Cc:


Check NPP/GPP ratio at the end of FG2 following the default spinup and transient simulation. The NPP/GPP ratio should be between 0.4 and 0.6 with a global mean around 0.5

Change History (2)

comment:1 Changed 12 months ago by luyssaert

  • Owner changed from somebody to luyssaert
  • Status changed from new to assigned

In r6913 a second option to calculate Rm was added (the parameters were committed in r6955). The option is set with the flag ok_control_maint_resp and can be set to 'nitrogen' and 'cn'. The first option is what was developed in CAN and moved into the trunk during th emerge. The 'cn' option is the default for ORCHIDEE 3.0. This should become the trunk default.

In r6956 a reasonable parameter set for 'nitrogen' was committed because this approach is straightforward to parameterize (= tune coeff_maint_init). The challenge is now is to match the model performance of r6947 by using the 'cn' option. In doing so a small numerical and scientific bug were fixed in r6961. Matching parameters were committed in r6962.

The 'cn' option made use of carbohydrates. Common thinking is that the carbohydrates come with little or no maintenance respiration but the labile pool comes with respiration. This was implemented in r6963.

The gpp written to the history files only accounts for the gpp calculated in diffuco but ignores the carbon flux that enters the system through processes which are difficult to model. In ORCHIDEE these processes are quantified through the variable atm_to_bm. This encompasses the gpp needed to grow from a seed to a small seedling (ORCHIDEE starts with the small seedling not the seed). Omitting this bypass of gpp in the gpp calculation will result in too high NPP/GPP ratios. gpp is the stomate history files now accounts for this bypass. This fix has been committed in r6977. But see ticket #748 for a similar issue with gpp in the ipcc history file.

Last edited 12 months ago by luyssaert (previous) (diff)

comment:2 Changed 12 months ago by luyssaert

  • Resolution set to fixed
  • Status changed from assigned to closed
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