School of Earth Sciences - Research Publications
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ItemA transport model study of the breakup of the Antarctic ozone hole in November 2000(American Geophysical Union, 2003)A 3-D off-line transport model is used to examine the breakup of the Antarctic ozone hole in late November and early December 2000. The use of a transport model enables an analysis of the vortex breakup that is not possible from the use of ozonesonde observations alone. By initializing ozone mixing ratio on 1 September 2000, and using parameterized ozone production and loss rates, the evolution of the Antarctic ozone hole is simulated. The model simulation shows that during late November and early December 2000, the Antarctic ozone hole splits into two sections, with low-ozone air subsequently transported over New Zealand and south-eastern Australia. Modeled ozone values agree well with ozonesonde profiles, confirming the role of horizontal transport in the dilution of mid-latitude ozone.
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ItemTransport out of the Antarctic polar vortex from a three-dimensional transport model(AMER GEOPHYSICAL UNION, 2002-06)A three‐dimensional chemical transport model is utilized to study the transport out of the Antarctic polar vortex during the southern hemisphere spring. On average, over five consecutive years between 1993 and 1997, horizontal transport out of the vortex into the midlatitude stratosphere is smaller than vertical transport into the troposphere. However, there is significant interannual variability in the magnitude of mass exchange, which is related to year‐to‐year fluctuations in planetary wave activity. In 1994 the net loss of the vortex tracer mass in September is similar to that in October. However, the relative mass flux entering the midlatitude stratosphere and the troposphere differ between the two months. The ratio of horizontal transport out of the vortex to vertical transport into the troposphere is about 3:7 in September and 5:5 in October, indicating the higher permeability of the vortex in October compared to September. The September mass flux into the troposphere is larger than in October, consistent with the fact that stronger diabatic cooling occurs in September than October over Antarctica. The estimated ozone change at southern midlatitudes due to the intrusion of ozone‐depleted air from high latitudes during September–October 1994 is about −0.44% per decade, which could contribute up to 10% of observed ozone decline at southern midlatitudes in spring. This amount is an underestimate of the dilution effect from high latitudes during the spring season, as it does not include the vortex breakup in late spring.
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ItemDiurnal temperature range as an index of global climate change during the twentieth century(American Geophysical Union, 2004)The usefulness of global-average diurnal temperature range (DTR) as an index of climate change and variability is evaluated using observations and climate model simulations representing unforced climate variability and anthropogenic climate change. On decadal timescales, modelled and observed intrinsic variability of DTR compare well and are independent of variations in global mean temperature. Observed reductions in DTR over the last century are large and unlikely to be due to natural variability alone. Comparison of observed and anthropogenic-forced model changes in DTR over the last 50 years show much less reduction in DTR in the model simulations due to greater warming of maximum temperatures in the models than observed. This difference is likely attributed to increases in cloud cover that are observed over the same period and are absent in model simulations.
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ItemComparison of glacier-inferred temperatures with observations and climate model simulations(American Geophysical Union, 2006)A reconstructed temperature history for different regions of the globe was prepared by Oerlemans (2005) from length changes of 169 glaciers. In this study, we compare the glacier-inferred temperature variations over 1900–1990 with observed and climate model simulated temperatures for the global average and for five regions: Southern Hemisphere, northwest America, Atlantic, Asia, and the Alps. There is reasonable agreement between the glacier-inferred temperature trends and the observed temperature trends for the globe and in four of the five regions (except northwest America, NWAme). The trends for the globe and in these regions are significantly different from zero, cannot be explained by natural variability (again except for NWAme), and are consistent with the model-simulated response to anthropogenic forcing in all regions. Hence, it is likely that the glacier length reductions are outside the range of natural variations and due in part to regional warming associated with increasing concentrations of greenhouse gases in the atmosphere.
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ItemGravity waves observed in temperature, wind and ozone data over Macquarie Island(Australian Meteorological and Oceanographic Society, 2003)Characteristics of inertia-gravity waves are analysed in high-resolution vertical profiles of temperature, winds and ozone collected at Macquarie Island (54°S, 159°E) during the Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/MAESA) observation programme in 1994. Two particular techniques are outlined to identify gravity-wave modes. The first is based on the continuous wavelet transform and seeks altitudes where the atmospheric fluctuations satisfy the gravity-wave polarisation relations in the temperature and wind soundings. The second analyses the phase and amplitude relationship of small-scale wavelike signatures seen in temperature and ozone profiles. The wavelet method identified gravity-wave modes with vertical wavelengths of 1-10 km, horizontal wavelengths of 50-1000 km and intrinsic frequencies of 1-2 f. Both methods reveal the presence of dominant modes with vertical wavelength <4 km in the upper troposphere and lower stratosphere over Macquarie Island. The energy activity of observed modes agrees well with the seasonal cycle of the upper level jet at 10 km height. These techniques together with classical spectral methods are applied to the case study of 25 October 1994 for which three quasi-monochromatic coherent modes with upwardly propagating wave energy are detected in the lower stratosphere.
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ItemThree-dimensional simulations of springtime dissipation of the Antarctic ozone hole(AUSTRALIAN GOVT PUBL SERV, 2003-03)