This parameter allows extra line broadening to be introduced into the
calculation of the synthetic spectrum. The value is in km s.
This quantity enters into the calculation of the line profile function,
which is used by the line opacity and emissivity. The line profile
function is a Voigt profile, which resembles a Gaussian in the Doppler core.
The turbulent velocity then enters into the `sigma' of the Gaussian.
The Gaussian 'sigma' in velocity units is
where
is the ion thermal speed.