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

Total column ground based HNO3 measurements were made at Lauder, New Z ealand (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-linea r least squares spectral fitting technique. A seasonal cycle has been established with an amplitude of 27%, a minimum in February, and an an nual mean of 1.2 x 10(16) molecules cm-2. The seasonal phase, amplitud e and absolute amounts of HNO3 were found to be consistent with simila r high resolution studies from Northern Hemisphere sites and with sate llite measurements. Sensitivity tests indicated that the retrieved col umn in the stratosphere is generally insensitive to the temperature an d assumed HNO3 vertical profile.