Corresponding author email: M.Tully@bom.gov.au Comparison of ozone profiles from Broadmeadows and Macquarie Island,1999-2016. M.B.Tully 1 & A.R. Klekociuk 2 1 Bureau of Meteorology, Melbourne Victoria, Australia. 2 Australian Antarctic Division, Kingston, Tasmania, Australia Corresponding author email: M.Tully@bom.gov.au ABSTRACT The Australian Bureau of Meteorology maintains two long-standing programs of weekly ozonesonde flights in southern hemisphere mid-latitudes, at Macquarie Island (55°S 159°E) and Broadmeadows (38°S 145°E). Ozonesonde flights at Macquarie Island began in 1993, while Broadmeadows, a suburb of the city of Melbourne, continues a program dating back to 1965 originally located in Aspendale, and later relocating to Laverton, before moving again to Broadmeadows. Here, however, only the period from 1999 to 2016 is considered, during which time changes have been minimal, in particular the same type of ozonesonde (Science Pump Corporation ECC6A) has been in continuous use, with only the model of radiosonde flown being upgraded from the Vaisala RS80 to the RS92 in 2006. We compare the annual cycle at different heights between the two sites and the interannual variability in different seasons. In particular, the variations in winter and spring build up in ozone around the partial pressure peak in the profile (approximately 20 km) from year to year are very consistent between the two sites, despite their geographical separation. At altitudes above 30 km, the time-series at both locations shows some suggestion of a step-change corresponding to the time of the transition in radiosonde. MIXING RATIO CLIMATOLOGY The ozone mixing ratio climatology is very similar at the two locations in both magnitude and annual cycle. For higher altitudes dominated by photochemical control of ozone Broadmeadows has higher concentration in summer being closer to the equator, whereas Macquarie has a higher maximum in the lower stratosphere with greater transport build-up of ozone in spring. The summer minimum in the boundary layer is only discernible at Macquarie. Macquarie Island Macquarie Island INTERANNUAL VARIABILITY The 12 month running mean shows remarkable agreement around the altitude of the maximum ozone partial pressure in the lower stratosphere. The annual mean at this height is determined mainly by the strength of the transport build-up in spring for which the two sites show almost exact correlation. This demonstrates the major influence of large-scale circulation effects. Broadmeadows Broadmeadows UPPER LEVEL TREND Above 30 km there is a pronounced negative trend over the study period at both sites in all months. There is some appearance of a step change having taken place, marked in orange. The dashed vertical lines give approximate indication of the period in which the running mean was influenced by the transition between the RS80 and RS92 radiosodes. Broadmeadows Broadmeadows Macquarie Island Macquarie Island BOUNDARY LAYER ANNUAL CYCLE The natural annual cycle in boundary layer ozone is very clearly resolved at Macquarie Island due to its pristine oceanic environment. At Broadmeadows, the cycle is disturbed by different air-mass origins (maritime versus continental) and considerable anthropogenic influences.