Cross Sections in the Herzberg Continuum

Abztract. We propose that a significant overestimate of the molecular oxygen absorption cross sections in the important spectral window from 2200-22220 nm is in large part responsible for the discrepancy between observed and modeled vertical profiles of some halocarbons (CFCls in particular), as well as for the long-standing problem of simultaneously fitting NsO, CH4, CF•CI• and CFCls profiles with a single eddy diffusion model. Recent measurements of the direct solar fiux in the stratosphere by J.R. Herman and co-workers seem to support this idea. Replacing our current Os cross sections in t. he 200-220 nm range by values in better agreement with the results of the above group leads to a reduction in N•O, CF•CI• and CFCI.• concentrations (by factors of 0.70, 0.62 and 0.19, respectively, at 30 km), while CH4, Ha and CO profiles are essen+.ially unchanged. Moreover, the predicted concentration of HNOs above 30 km is reduced by --60%, yielding better agreement with observations. The reduction in Os cross sections produces a 10-20% decrease in ozone above about 36 kin, but a fairly large increase (~ 30%) near the peak around 220-225 km. The changes in other stratospheric species are also briefly discussed.