Analysis of record-low ozone values during the 1997 winter over Lauder, New Zealand

Abstract

Record-low ozone (O3) column densities (with a minimum of 222 DU) were observed over the Lauder NDSC (Network for the Detection of Stratospheric Change) station (45°S, 170°E) in August 1997. Possible causes are examined using height-resolved O3 measurements over Lauder, and high-resolution reverse trajectory maps of O3 (initialised with Microwave Limb Sounder measurements) and of potential vorticity. The analysis shows that O3 poor air originated from two regions: Below the 550 K isentrope (~22 km) subtropical air was observed, while between 600 and 1000 K (~25 - 33.5 km) the polar vortex tilted over Lauder for several days. A rapid recovery of the O3 column density was observed later, due to an O3 rich polar vortex filament moving over Lauder between 18 and 24 km, while simultaneously the O3 poor higher vortex moved away.