Questions about updating initial and boundary conditions in WRF-VPRM

[sushx]

Dear Mike:

I saw your reply to Pwang about CO2_bio being all positive (WRF_VPRM have no negative value in CO2_BIO and CO2_OCE). I had the same problem, I updated the initial and boundary conditions with CT2022, but since I didn't know which variable to update, I only updated the variable CO2_BCK. In this way the simulated CO2_bio were all positive.

Does updating the initial and boundary conditions mean updating all three variables, CO2_ANT, CO2_BCK and CO2_BIO, at the same time? In your previous reply you said that the initial and boundary conditions can be set to 400 ppm. Is this referring to the CO2_BCK variable?

In addition, I see that the CO2 background in CT2022 is about 400 ppm, biogenic CO2 is about -37 to 20 ppm, and anthropogenic CO2 is about 69 ppm. Should I update the initial and boundary conditions of the variables corresponding to them (CO2_BCK, CO2_BIO and CO2_ANT,) based on the values of these variables of CT2022? I am confused about how to correctly update the initial and boundary conditions to simulate CO2.

I apologize for asking so many questions at once. I appreciate it and look forward to your reply.

Best regards,
Shixiang Su

 

[michal_galkowski]

Hi Su,

Initial and boundary condition in the chem_opt = 16/17 need to be set for two tracers:

CO2_BIO
CO2_BCK

1. CO2_BIO is the tracer with which VPRM module interacts with, i.e. the GEE and respiration CO2 fluxes are added / subtracted in the model at every time step. If you initialize the field with 0 (and/or provide the boundary conditions equal to 0 via wrfbdy file), you might run into a problem if you simultaneously use positive tracer valuies in the namelist.input. Thus, the recommended initial and boundary value of CO2_BIO is constant and equal to 400 ppm. This value needs to be subtracted in post-processing. Please note that the usual care should be taken close to the boundaries of the domain, as the mole fractions will be unrealistic in case boundary is immediately upwind.

Typical CO2_BIO values are expected to vary be within -20 and +20 ppm, following photosynthetic and respiraction activity of the simulated biosphere. Thus. I am fairly convinced that your positive-only values are because you've run with forced-positive tracer option. This cannot be fixed and I'm afraid you'll need to rerun your simulations.

2. CO2_BCK, simply is meant to provide the realistic boundary conditions, usually from a coarse resolution global model. In studies over Europe and South America, we saw excellent performance using CO2 fields from optimized Jena CarboScope system (link here), but CT2022 will likely also work. Just FYI and for the record, one can run the model without providing CO2_BCK tracer, but this will make it extremely difficult to compare against in situ observations, as the other tracers only represent additions in your model from inside your d01 at most.

Other tracers (CO2_ANT, CO2_TST, CO2_BBU, CO2_OCE) available in the GHG module require no initial nor boundary condition, although some spinup period for the model is recommended (lenght should be established based on the domain size).

Hope this helps. Kind regards,

Mike Galkowski

 

[sushx]

Dear Mike,

Thank you very much for your patient and helpful reply! Now I understand why CO2_BIO is positive in my simulation and how to solve this problem.

Best regards,
Shixiang Su

 

[Ming]

Dear Mike:

I saw your reply to Pwang about CO2_bio being all positive (WRF_VPRM have no negative value in CO2_BIO and CO2_OCE). I had the same problem, I updated the initial and boundary conditions with CT2022, but since I didn't know which variable to update, I only updated the variable CO2_BCK. In this way the simulated CO2_bio were all positive.

Does updating the initial and boundary conditions mean updating all three variables, CO2_ANT, CO2_BCK and CO2_BIO, at the same time? In your previous reply you said that the initial and boundary conditions can be set to 400 ppm. Is this referring to the CO2_BCK variable?

In addition, I see that the CO2 background in CT2022 is about 400 ppm, biogenic CO2 is about -37 to 20 ppm, and anthropogenic CO2 is about 69 ppm. Should I update the initial and boundary conditions of the variables corresponding to them (CO2_BCK, CO2_BIO and CO2_ANT,) based on the values of these variables of CT2022? I am confused about how to correctly update the initial and boundary conditions to simulate CO2.

I apologize for asking so many questions at once. I appreciate it and look forward to your reply.

Best regards,
Shixiang Su

Hi Su,

Initial and boundary condition in the chem_opt = 16/17 need to be set for two tracers:

CO2_BIO
CO2_BCK

1. CO2_BIO is the tracer with which VPRM module interacts with, i.e. the GEE and respiration CO2 fluxes are added / subtracted in the model at every time step. If you initialize the field with 0 (and/or provide the boundary conditions equal to 0 via wrfbdy file), you might run into a problem if you simultaneously use positive tracer valuies in the namelist.input. Thus, the recommended initial and boundary value of CO2_BIO is constant and equal to 400 ppm. This value needs to be subtracted in post-processing. Please note that the usual care should be taken close to the boundaries of the domain, as the mole fractions will be unrealistic in case boundary is immediately upwind.

Typical CO2_BIO values are expected to vary be within -20 and +20 ppm, following photosynthetic and respiraction activity of the simulated biosphere. Thus. I am fairly convinced that your positive-only values are because you've run with forced-positive tracer option. This cannot be fixed and I'm afraid you'll need to rerun your simulations.

2. CO2_BCK, simply is meant to provide the realistic boundary conditions, usually from a coarse resolution global model. In studies over Europe and South America, we saw excellent performance using CO2 fields from optimized Jena CarboScope system (link here), but CT2022 will likely also work. Just FYI and for the record, one can run the model without providing CO2_BCK tracer, but this will make it extremely difficult to compare against in situ observations, as the other tracers only represent additions in your model from inside your d01 at most.

Other tracers (CO2_ANT, CO2_TST, CO2_BBU, CO2_OCE) available in the GHG module require no initial nor boundary condition, although some spinup period for the model is recommended (lenght should be established based on the domain size).

Hope this helps. Kind regards,

Mike Galkowski

Dear Mike and Su,

I added 400 ppm for CO2_BIO in the initial and boundary value as suggested. However, the simulated results still show values greater than 400 ppm, with no instances below 400 ppm. This implies that the vegetation's respiratory action is consistently stronger than the photosynthetic action, even in seasons when vegetation is growing vigorously (like in July and August). I am not sure what could be causing this issue and would appreciate your guidance.

Best regards,
Ming

 

[michal_galkowski]

Hello Ming.

This doesn't sound right. It could mean that the VPRM input files are somehow at fault, but the fact that you see respiration signal (? -- I assume they make sense?) suggests that the module functions. Could you provide a CO2_BIO plot for the second model level 2 at the centre of your domain, let's say from for a selected week in the middle of summer?

MG