UV Index values related to anomaly low Ozone events during summer over Australia

Strong decreases in the total ozone over Australia have been observed during summer 1997, 1998 and 1999 . These rapid decreases last from one day to a week, and have a relative small horizontal scale in comp arison to the Antarctic ozone hole. However in occasions they cover at least one third of the country. Here we analyse the record low ozone events over Australia during the period January to March. The corr esponding strong increases in surface UV during these ozone depletion events are calculated using the T OMS ozone data sets and the Australian UV Index system. These increases are important because is the ti me when most of the Australian population is exposed to a already high UV radiation. Usually short-term ozone variations have been observed in association with transient weather systems (Dobson et al 1929). While modeling studies (James et al, 1997) have demonstrated the correlation between column total ozon e and the tropopause height and show the important role played by horizontal advection and vertical air motions (Atkinson and Plumb, 1997). In general these studies have focussed on the period during the An tarctic ozone hole and the aftermath of the break up. Here we study record low ozone cases during summe r, well after the Antarctic ozone hole has closed. Using data from ozonesondes, TOMS, meteorological an alysis from the Weather forecast model of the Bureau of Meteorology, NCEP reanalysis and trajectory ana lysis we suggest that the low ozone events resulted from combination of an upward shift of the tropopau se with the horizontal transport playing a significant, but secondary role.