Megan ouputs dependence on meteorological conditions

Hello there.

Im running Meganv3.2 for most of Argentina. I was able to successfully ran the Fortran Preprocessor that generated the CT3.csv, grid_ecotype.csv and grid_growth_form.csv files.

I did this for two periods of one week each: One in spring and one in winter. I noticed that the three files generated for each week (CT3.csv, grid_ecotype.csv and grid_growth_form.csv) are exactly the same.

Am I doing something wrong here? Of course I changed the wrfout file and the start_lai_mnth and end_lai_mnth variables for each week in prepmegan4cmaq.growthform.inp, prepmegan4cmaq.cantype.inp and prepmegan4cmaq.ecotype.inp.

Am I missing something here? Is there somewhere else where I should change my wrf inputs?

Thank you for your help

That’s correct. These files are time independent. The only time dependency for BVOC is from meteorology and LAI change. If you’re using MEGAN 3.2 with CMAQ then all of that will be taken care of as the model runs (the MCIP files)

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Thank you so much for your answer.

Yes, Im using CMAQ…

Ok, I think now I understand.

When using CMAQ the only part of MEGAN that needs to be ran (after the Fortran and python pre processors) is TXT2IOAPI. This generates the inputs files for CMAQ (CT3.ncf, LDF.ncf and EFMAP.ncf) and are the same for any time period considered and then CMAQ is in charge of taking into account meteorological conditions.

On the other hand, if using other models that are not CMAQ, MET2MGN, DAYMET, MEGCAN, MEGSEA and MEGVEA are the ones responsible for considering meteorological conditions.

Is this correct?

Again, thank you very much for your answers!

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That’s exactly right.

The only thing I’d add is you need more files if you want to use BDSNP soil NO. It’s reasonable to expect the default option to underestimate soil NO, while BDSNP will often overestimate it. Looking forward to your results.


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Hello, Jeff.

Im sorry to bother you again, but you always provide such clear and useful answers!

I succesfully ran CMAQ with MEGAN biogenic emissions. As results didnt differ that much from other simulations runs without biogenic emissions I was curious to see how these biogenic emissions calculated inline by CMAQ were.

The thing is the only output file generated related to MEGAN that I see is “”. It is my understanding that this file contains temperature, rainfall and radiation data that CMAQ uses to actually compute the biogenic emissions.

What I dont see is a file that contains the actual biogenic emissions calculated by CMAQ. Is this file somewhere? How can I check the biogenic emissions calculated by CMAQ?

Thank you very much!


You can add a rule to your CMAQ_Control_DESID.nml file to get any emission stream’s contribution to CMAQ:

   Desid_N_Diag_Rules = 1    ! Exact Number of Diagnostic Rules Below
  Desid_Max_Diag_Streams=20 ! Maximum number of species variables on all rules
                            ! below (do not count expansions)
  Desid_Max_Diag_Spec = 80  ! Maximum number of species variables on all rules
                        ! below (do not count expansions)


Desid_Diag_Streams_Nml(1,:)= 'MIOG'
Desid_Diag_Fmt_Nml(1)      = 'COLSUM'    ! Options: LAYER1, COLSUM, 3D
Desid_Diag_Spec_Nml(1,:)   = 'ALL'

And this will output a file along the lines of CCTM_DESID1_MIOG* that has the emissions.


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