Keywords: atm-comparison

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### FORTRAN interface

The different subroutines, which interface both version of ATM, are extensively described in Appendix A. In short, the programmer first calls

    call atm_setup('1985',error)

or

    call atm_setup('2009',error)

to select the version of ATM to be used from this point on. If this call is missing, GILDAS assumes that it must use ATM 1985 (default behavior). ATM 2009 enables the fine tuning of the atmospheric profile. This is implemented in the GILDAS interface by the call of two subroutines

    call atm_atmosp_get(ctype_out,humidity_out,wvsh_out,tlr_out,top_out,  &
        p_step_out,p_step_factor_out,error)

which gets the default values and

    call atm_atmosp_set(ctype_in,humidity_in,wvsh_in,tlr_in,top_in,  &
        p_step_in,p_step_factor_in,error)

which sets the wanted values. `ctype_in` and `ctype_out` are the atmospheric types, which can be set to `tropical, midlatsummer, midlatwinter, subarcticsummer, subarcticwinter`.

The calls to the other ATM routines are unchanged compared to the historical behavior, i.e.

    call atm_atmosp(t0,p0,h0)

defines the atmosphere profiles,

    call atm_transm(water,airmass,freq,temi,tatm,tauox,tauw,taut,ier)

returns the atmospheric temperatures and opacities and

    call atm_path(water,airmass,freq,path,ier)

returns the integrated optical length of current atmosphere. Note that the support for the `atm_path` is not yet available with ATM 2009.