Seasonal variations in stratospheric NO2at 45°S

We present daily twilight measurements of stratospheric NO 2 at latitude 45°S for the period from December 1980 to May 1982. The technique used is ground based long path absorption spectroscopy. The deduced column abundances are in general agreement with comparable measurements in the Northern Hemisphere, with evening abundances exhibiting a seasonal variation from 3.2 × 10 15 mol.cm −2 to 6.4 × 10 15 mol.cm −2 in phase with the cycle of annual variation in length of day. The corresponding range in morning abundances is from 2 × 10 15 mol.cm −2 to 4.5 × 10 15 mol.cm −2 . The lower morning values are generally consistent with an overnight decay of NO 2 with a time constant of about a day.