How to spin up land for an emissions driven run

[aswann2]

I'm setting up an emissions-driven CESM2 run using a non-default parameter set for the land that will have a different photosynthesis rate. I'm working on spinning up the carbon pools for the coupled model and I could use some input!

My general goal is to:
1. spinup land to equilibrium with pre-industrial CO2
2. couple the newly spun up land to the already spun up ocean and set free in emissions-driven mode

It was a bit of meandering path to get here, but here is the progression:

• ran an emissions-driven (B case) pre-industrial run branched from an existing spun up emissions-driven run (flat10-esm run).
• branched a land-only run (I case) using existing coupler history output => ran this for 200 years with AD spinup mode on
• hybrid branch from the B case run using the I case land restart file as finidat for land, AD mode turned off => new B case with spun up land.

I ran the new B case with spun up land initial conditions for 60 years, but land still not in equilibrium in some places (mostly TOTVEGC, see plots below). TOTVEGC is drifting in opposite directions from how it was changing during spinup in the I case, so I think this must be because the climate of the coupled model is different.

Here are two maps showing changes over the spinup of the new B case, as well as time series plots for three regions showing big changes in TOTVEGC. I also plotted lower level global average CO2 which I converted to ppm, although the numbers seem slightly high and I'm not sure why.

Here are some options, I'd love input on what to try next:
a. continue the new B case in AD spinup mode to bring the land into equilibrium more quickly. I'm worried this might make atmospheric CO2 drift?
b. create new coupler history output (either from the original B case or the new B case, or an additional F case?) and run an I case with that atmospheric driver with AD mode on to bring land into equilibrium with the coupled climate.

Thoughts on what process to take for this spinup?

 

[slevis]

@klindsay @wwieder
This is a new forum in case you have not been notified. Feel free to ping additional interested forum members.

 

[aswann2]

@klindsay @wwieder
This is a new forum in case you have not been notified. Feel free to ping additional interested forum members.

Thanks @slevis! We agreed to make a new place for CO2 emissions-driven specific things so I figured I would start things off! I realize this question is mostly about land, but land in a coupled system context!