Computing and sending MEGAN VOC's from CTSM to CAM

[mvertens]

The following is a summary of how MEGAN VOC's are sent from CTSM to CAM

---

shr_megan_mod

• reads the megan_emis_nl namelist in the drv_flds_in file and makes the relavent
  information available to CAM and CTSM
  • CTSM needs to know what specific VOC fluxes need to be passed to the mediator and how to assemble the fluxes.
  • CAM needs to know what specific VOC fluxes to expect from CTSM.

~/$SRCROOT/components/cmeps/cesm/nuopc_cap_share/shr_megan_mod.F90

• shr_megan_mod.F90 reads in from the file drv_flds_in the namelist group dry_dep_inparm - which for the n1850 case is

&megan_emis_nl
 megan_factors_file = '/cluster/shared/noresm/inputdata/atm/cam/chem/trop_mozart/emis/megan21_emis_factors_78pft_c20161108.nc'
 megan_specifier = 'isoprene = isoprene',
     'monoterp = myrcene + sabinene + limonene+ carene_3 + ocimene_t_b + pinene_b + pinene_a'
/

• megan_specifier is a series of strings where each string contains one
  CAM chemistry constituent name (left of = sign) and one or more MEGAN
  compound (separated by + sign if more than one). Each MEGAN compound
  can be proceeded by a multiplication factor (separated by *). The
  specification of the MEGAN compounds to the right of the = signs tells
  the MEGAN VOC model within CLM how to construct the VOC fluxes using
  the factors in megan_factors_file and land surface state.

• megan_factors_file read by CLM contains valid MEGAN compound names,
  MEGAN class groupings and scalar emission factors

The contents of the megan_factors_file is the following:

netcdf megan21_emis_factors_78pft_c20161108 {
dimensions:
	Class_Num = 20 ;
	PFT_Num = 78 ;
	char = 40 ;
	Comp_Num = 150 ;
variables:
	float Agro(Class_Num) ;
		Agro:long_name = "growing leaf age factor" ;
	float Amat(Class_Num) ;
		Amat:long_name = "mature leaf age factor" ;
	float Anew(Class_Num) ;
		Anew:long_name = "new leaf age factor" ;
	float Aold(Class_Num) ;
		Aold:long_name = "old leaf age factor" ;
	float Ceo(Class_Num) ;
		Ceo:long_name = "emission optimum coefficient" ;
	float Class_EF(PFT_Num, Class_Num) ;
		Class_EF:long_name = "Emission factors at standard conditions for each class" ;
		Class_EF:units = "ug/m2/h" ;
	char Class_Name(Class_Num, char) ;
		Class_Name:long_name = "Classes" ;
	short Class_Num(Comp_Num) ;
		Class_Num:long_name = "Class Number for each Compound" ;
	float Comp_EF(PFT_Num, Comp_Num) ;
		Comp_EF:long_name = "Scale factors for calculating emission factors for each compound" ;
		Comp_EF:units = "fraction" ;
	float Comp_MW(Comp_Num) ;
		Comp_MW:long_name = "Molecular Weight for each Compound" ;
		Comp_MW:units = "g/mole" ;
	char Comp_Name(Comp_Num, char) ;
		Comp_Name:long_name = "Compounds" ;
	float LDF(Class_Num) ;
		LDF:long_name = "light dependent fraction" ;
	char PFT_Name(PFT_Num, char) ;
		PFT_Name:long_name = "Plant Functional Types" ;
	short PFT_Num(PFT_Num) ;
		PFT_Num:long_name = "PFT Number" `;`
	float betaT(Class_Num) ;
		betaT:long_name = "temperature factor" ;
	float ct1(Class_Num) ;
		ct1:long_name = "temperature coefficient 1" ;
	float ct2(Class_Num) ;
		ct2:long_name = "temperature coefficient 2" ;

in shr_megan_mod.F90, shr_megan_megcomps_n

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CTSM VOCEmissionsMod.F90 and MEGANFactorsMod.F90

• VOCEmissionsMod.F90 outputs
• vocflx_patch(:,1:shr_megan_mechcomps_n)
• shr_megan_mechcomps_n = 7 (based on the number of elements in myrcene + sabinene + limonene+ carene_3 + ocimene_t_b + pinene_b + pinene_a)
• subroutine VOCEmission computes the patch level vocflx (volatile organic compound emission)
  • E= epsilon * gamma * rho
  • VOC flux (E) [ug m-2 h-1] is calculated from baseline emission
  • emission factor epsilon [ug m-2 h-1] is specified for each of the PFT patches in the input file
    OR in the case of isoprene, from mapped EFs for each PATCH
  • emission activity factor (gamma) [unitless] includes! dependence on PPFT, temperature, LAI, leaf age and soil moisture.
    • gamma = gamma_l * gamma_sm * gamma_a * gamma_p * gamma_T * gamma_c