Opened 11 months ago

Last modified 7 months 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 (4)

comment:1 Changed 10 months ago by jgipsl

Done in tag ORCHIDEE_2_0 [6392]. To activate, set DOWNREGULATION_CO2_NEW=y in run.def or orchidee.def.

comment:2 Changed 10 months ago by jgipsl

Last edited 9 months ago by jgipsl (previous) (diff)

comment:3 Changed 10 months ago by cpipsl

  • Owner changed from somebody to cpipsl
  • Status changed from new to accepted

comment:4 Changed 7 months ago by luyssaert

  • Milestone set to Not scheduled yet
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