CHI Flag

RFM Flags: Apply Chi-Factor to CO2 Lineshape


Set default lineshape for CO2 to Voigt × Chi-factor (a scaling factor to allow for the observed sub-Lorentzian dependence of CO2 lines on pressure-broadening).

Set default lineshape for CO2 to Voigt (ie same as for other molecules)


  1. The RFM uses the chi-factor model of Cousin et al (1985).
  2. This flag represents a quick way of applying the chi-factor to CO2 lines (compared to using the SHP flag + *SHP section). It is similar to the MIX flag (for CO2 line-mixing) in having no associated driver table sections.
  3. The effect of this flag is to change the default lineshape for any CO2 lines from Voigt to Voigt × chi-factor, so it can still be over-ridden by the *SHP section.
  4. It is not necessary to include CO2 as an absorber if this flag is enabled, but a warning message will result if it is not included:
    W-INPGAS: CHI flag selected but CO2 not used
  5. Although in principle including the chi-factor gives a more accurate representation of pressure-broadened CO2 lines, it is computationally quite expensive and probably makes little difference at higher altitude where Doppler broadening starts to dominate.

[none reported]