Opened 4 years ago
Last modified 2 years ago
#641 accepted defect
Change in downregulation parametrization
| Reported by: | cpipsl | Owned by: | cpipsl |
|---|---|---|---|
| Priority: | major | Milestone: | Not scheduled yet |
| Component: | Biogeochemical processes | Version: | orchidee_2_0 |
| Keywords: | Cc: |
Description
Downregulation is a "technique" which enables, even in the absence of an explicit nitrogen cycle representation, to account for the impact of nitrogen limitation on the CO2 fertilization effect.
In ORCHIDEE, until 6.1.10 included (FLAG: downregulation_co2), downregulation is modeled as a logarithmic function of the increase of CO2 concentration relatively to 380ppm. This allows to simulate biogeochemical processes in line with observation data. However, at high atmospheric CO2 concentration values (700ppm and above) the nitrogen limitation effect may be overestimated. This in turn reduces too much the carbon assimilation by vegetation, in face of respiration processes.
In ORCHIDEE, 6.1.11 onwards (FLAG: downregulation_co2_new), to address this issue the downregulation parametrization has changed and is now an hyperbolic function of the increase of CO2 concentration relatively to 380ppm. For low CO2 concentration values (under 280ppm) the parametrization allows for the processes to behave in the same way as over the historical period.
Note: Downregulation is not available in ORCHIDEE trunk. Also, since ORCHIDEE trunk includes the nitrogen cycle, specific adaptation will be needed to support downregulation in that context.
Key people: Vlad Vladislav, Philippe Peylin, Nicolas Vuichard, Nicolas Viovy, Josefine Ghattas and Patricia Cadule
Change History (5)
comment:1 Changed 4 years ago by jgipsl
comment:2 Changed 4 years ago by jgipsl
- Same changset now done as well in ORCHIDEE_2_2 [6393].
- In configurations IPSLCM6 and LMDZOR_v6: comment is set in orchidee.def_CWRR to make it easier to activate it. Can be activated for CMIP6 configurations v6.1.11 and later. See commit here: https://forge.ipsl.jussieu.fr/igcmg/changeset/4860
- In configurations IPSLCM6.2 and LMDZOR_v6.2: the new downregulation parametrization has been activated in orchidee.def, see commit here: https://forge.ipsl.jussieu.fr/igcmg/changeset/4861
comment:3 Changed 4 years ago by cpipsl
- Owner changed from somebody to cpipsl
- Status changed from new to accepted
comment:4 Changed 4 years ago by luyssaert
- Milestone set to Not scheduled yet
comment:5 Changed 2 years ago by jgipsl
Can this ticket be closed?
Done in tag ORCHIDEE_2_0 [6392]. To activate, set DOWNREGULATION_CO2_NEW=y in run.def or orchidee.def.