Unusual stratospheric ozone anomalies observed in 22 years of measurements from Lauder, New Zealand

Abstract. The Microwave Ozone Profiling Instrument (MOPI1) has provided ozone (O₃) profiles for the Network for the Detection of Atmospheric Composition Change (NDACC) at Lauder, New Zealand (45.0° S, 169.7° E), since 1992. We present the entire 22-year data set and compare with satellite O₃ observations. We study in detail two particularly interesting variations in O₃. The first is a large positive O₃ anomaly that occurs in the mid-stratosphere (~ 10–30 hPa) in June 2001, which is caused by an anticyclonic circulation that persists for several weeks over Lauder. This O₃ anomaly is associated with the most equatorward June average tracer equivalent latitude (TrEL) over the 36-year period (1979–2014) for which the Modern Era Retrospective-Analysis for Research and Applications (MERRA) reanalysis is available. A second, longer-lived feature, is a positive O₃ anomaly in the mid-stratosphere (~ 10 hPa) from mid-2009 until mid-2013. Coincident measurements from the Aura Microwave Limb Sounder (MLS) show that these high O₃ mixing ratios are well correlated with high nitrous oxide (N₂O) mixing ratios. This correlation suggests that the high O₃ over this 4-year period is driven by unusual dynamics. The beginning of the high O₃ and high N₂O period at Lauder (and throughout this latitude band) occurs nearly simultaneously with a sharp decrease in O₃ and N₂O at the equator, and the period ends nearly simultaneously with a sharp increase in O₃ and N₂O at the equator.