SOUTHERN-HEMISPHERE MIDLATITUDE SEASONAL CYCLE IN TOTAL COLUMN NITRIC-ACID

Total column ground based HNO3 measurements were made at Lauder, New Zealand (45.0-degrees-S, 169.7-degrees-E). Approximately 760 infra-red spectra were recorded over the period from October 1990 to October of 1993. Two microwindows, near 870 cm-1, were analyzed using a non-linear least squares spectral fitting technique. A seasonal cycle has been established with an amplitude of 27%, a minimum in February, and an annual mean of 1.2 x 10(16) molecules cm-2. The seasonal phase, amplitude and absolute amounts of HNO3 were found to be consistent with similar high resolution studies from Northern Hemisphere sites and with satellite measurements. Sensitivity tests indicated that the retrieved column in the stratosphere is generally insensitive to the temperature and assumed HNO3 vertical profile.