Australia State of the Environment Report 2001 (Theme Report)
Lead Author: Dr Peter Manins, Environmental Consulting and Research Unit, CSIRO Atmospheric Research, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06746 9
Stratospheric Ozone (continued)
Stratospheric ozone over Australia and New Zealand [A Indicator 2.2]
The total amount of ozone in a column of air from the earth's surface to the top of the atmosphere can be measured remotely, using a ground-based Dobson UV spectrophotometer. The Australian ozone observing network, operated by the Bureau of Meteorology, uses Dobson spectrophotometers at Macquarie Island (55S), Melbourne (38S), Perth (32S), Brisbane (28S) and Darwin (12S).
Data were obtained during summer from the Australian Dobson network at Macquarie Island (1956, 1963-1999), Melbourne (1956-1999), Perth (1977-1998), Brisbane (1956-1999) and Darwin (1990-1999), and from the New Zealand Dobson spectrophotometer at Lauder, New Zealand (45S, 1978-1999) (Figure 71). Since the late 1970s, data from Macquarie Island, Lauder, Melbourne and Perth all show statistically significant ozone decreases during summer of about 4% per decade, whereas Brisbane and Darwin show ozone losses of about 1% per decade (not statistically significant). The southern Australian and New Zealand data show that the rate of ozone depletion slowed in the 1990s compared to the 1980s, and ozone levels may not decline much further.
Figure 71: Summer (Dec.-Feb. mean) total column ozone.
Dobson units, (1 DU = 10-3 cm column of pure ozone at standard temperature and pressure) from the Australian and New Zealand network of Dobson spectrophotometers. Mean includes Macquarie Island, Lauder, Melbourne and Perth; shaded area 1 s.d.
Source: Bureau of Meteorology; NIWA, NZ; McKenzie et al. (1999, 2000)
The 4% per decade decreases in ozone derived from Australian-New Zealand Dobson data for 32S to 55S in summer from the late 1970s to the late 1990s are similar to those derived from satellite data (3% per decade) for the same season and latitudes, averaged over all longitudes. Small differences may arise between these ground-based and zonally averaged satellite data due to real variations with longitude and unresolved differences between ozone data sets obtained via similar instruments on different satellites (Bojkov & Hudson 1999).
Ozone losses of this magnitude at mid-latitudes from the 1980s to 2000 have been ascribed to growing levels of stratospheric chlorine and bromine. Stratospheric ozone losses were expected to reach a maximum when stratospheric chlorine reached a maximum in the late 1990s. However, stratospheric ozone levels exhibit large natural variability so that it may take most of the years 2000 to 2010 to deduce when ozone depletion reached a maximum and when ozone recovery commenced.
The Australian-New Zealand Dobson network is a vital component of the global ozone observing system. It accounts for about half of the Dobson network in the Southern Hemisphere, in a region where the first signs of ozone recovery are expected to be detected, possibly as early as 2010-2015 (Weatherhead et al . 2000).
Vertical profiles of ozone in the troposphere and stratosphere can be measured directly using balloon-borne ozone sondes. Vertical ozone profiles from Macquarie Island have changed from 1970 to the late 1990s during winter (Figure 72). Peak ozone levels in the stratosphere at 20 km have declined by about 20 to 25%; the major loss is occurring at the altitude of the ozone maximum.
Figure 72: Mean ozone profiles at Macquarie Island (55S) in August (top) and launching an ozone sonde at Macquarie Island.
Profiles are from 1999-2000 (left) compared with mean profile for August 1970 (right).
Southern Australia and New Zealand will experience minimum ozone levels for the next five to 15 years before ozone recovery is detected. The Australian-New Zealand Dobson network is a vital component of the global ozone observing network; it accounts for about half of the Dobson network in the Southern Hemisphere, in a region where the first signs of ozone recovery are expected to be detected, possibly by 2010 to 2015, and if complete ozone recovery is to be observed (possibly by 2050).