RRTMGP: gas concentrations

Class ty_gas_concs from module mo_gas_concentrations in the RRTMGP library is the means for specifying gas concentrations to ty_gas_optics%gas_optics. The class has four user-facing procedures. The following examples assume the declaration type(ty_gas_concs) :: gas_concs

Initialization

  function init(gas_names) result(error_msg)
    character(len=*), dimension(:), intent(in   ) :: gas_names
    character(len=128)                            :: error_msg

takes a vector of strings specifying the names of the gases that will be provided. Gas names are normally the chemical formula. Note that some compilers expect each string to be the same length, so shorter names have to be padded with trailing spaces.

Specifying gas concentrations

  function set_vmr(name, value) result(error_msg)
    character(len=*),    intent(in   ) :: name
    real(wp), ...        intent(in   ) :: value
    character(len=128)                 :: error_msg

specifies the absolute volume mixing ratio for the named gas. The routine is invoked as e.g.err_msg = gas_concs%set_vmr("co2", 280._wpE-6). Gas names are normally the chemical formula.

Values may be specified as scalars, one-dimensional profiles assumed to apply layer-by-layer to all columns, or as a 2D field dimensioned (columns, layers). The number of columns is set the first time a 1D or 2D field is supplied; the number columns is determined from the first 2D field.

Specifying a concentration for a gas not provided during initialization is an error.

Extracting a subset of columns

  function get_subset(start, n, subset) result(error_msg)
    integer,                  intent(in   ) :: start, n
    class(ty_gas_concs),      intent(inout) :: subset
    character(len=128)                      :: error_msg

extracts columns start to start+n-1 from the class. Example: err_msg = gas_concs%get_subset(2, n, gas_conc_subset)

Misc.

call gas_concs%reset() will return variable gas_concs to an un-initialized state. This is useful if, for example, the problem size has changed since concentrations were last specified.

gas_concs%get_vmr() is used within ty_gas_optics%gas_optics() to extract the gas concentrations. Asking for the vmr of a gas that wasn't provided during init() or hasn't been set through a call to set_vmr() is an error.