P. F. Vohralik

The ACCESS coupled model: description, control climate and evaluation

4OASIS3.2–5 coupling framework. The primary goal of the ACCESS-CM development is to provide the Australian climate community with a new generation fully coupled climate model for climate research, and to participate in phase five of the Coupled Model Inter-comparison Project (CMIP5). This paper describes the ACCESS-CM framework and components, and presents the control climates from two versions of the ACCESS-CM, ACCESS1.0 and ACCESS1.3, together with some fields from the 20 th century historical experiments, as part of model evaluation. While sharing the same ocean sea-ice model (except different setups for a few parameters), ACCESS1.0 and ACCESS1.3 differ from each other in their atmospheric and land surface components: the former is configured with the UK Met Office HadGEM2 (r1.1) atmospheric physics and the Met Office Surface Exchange Scheme land surface model version 2, and the latter with atmospheric physics similar to the UK Met Office Global Atmosphere 1.0 includ ing modifications performed at CAWCR and the CSIRO Community Atmosphere Biosphere Land Exchange land surface model version 1.8. The global average annual mean surface air temperature across the 500-year preindustrial control integrations show a warming drift of 0.35 °C in ACCESS1.0 and 0.04 °C in ACCESS1.3. The overall skills of ACCESS-CM in simulating a set of key climatic fields both globally and over Australia significantly surpass those from the preceding CSIRO Mk3.5 model delivered to the previous coupled model inter-comparison. However, ACCESS-CM, like other CMIP5 models, has deficiencies in various as pects, and these are also discussed.

The ACCESS coupled model: documentation of core CMIP5 simulations and initial results

Martin Dix1, Peter Vohralik2, Daohua Bi1, Harun Rashid1, Simon Marsland1, Siobhan O’Farrell1, Petteri Uotila1, Tony Hirst1, Eva Kowalczyk1, Arnold Sullivan1, Hailin Yan1, Charmaine Franklin1, Zhian Sun3, Ian Watterson1, Mark Collier1, Julie Noonan1, Leon Rotstayn1, Lauren Stevens1, Peter Uhe1 and Kamal Puri3 1Centre for Australian Weather and Climate Research (CAWCR), a partnership between CSIRO and the Bureau of Meteorology, CSIRO Marine and Atmospheric Research, Australia 2CSIRO Materials Science and Engineering, Australia 3CAWCR/Bureau of Meteorology, Australia

Heterogeneous BrONO2 hydrolysis: Effect on NO2 columns and ozone at high latitudes in summer

The heterogeneous reaction, N 2 O 5 + H 2 O aerosol → 2HNO 3 , is responsible for increasing [HO x ] and repartitioning of active NO x into HNO 3 . Throughout much of the atmosphere, N 2 O 5 is formed predominantly at night owing to the rapid photolysis of its precursor, NO 3 , in sunlit hours. Laboratory measurements have shown that BrONO 2 + H 2 O aerosol → HOBr + HNO 3 (reaction (3)) also has the potential to cause repartitioning of ozone-depleting species, although better determination of γ, the reaction probability, is still required for some stratospheric conditions. The diurnal behavior of N 2 O 5 and BrONO 2 are entirely different. In contrast to N 2 O 5 , BrONO 2 is formed predominantly during the daytime. The result of (3) is to increase [HOBr] at the expense of [BrONO 2 ). Photolysis of HOBr then leads to increased [OH] and increased O 3 loss. In this work two-dimensional calculations show clearly that the impact of (3) is greatest for high aerosol levels and for high latitudes in summer. The calculations have been used to determine the effects of increased aerosol loading on calculated NO 2 columns in the Antarctic during summer and autumn of 1990, 1991, 1992 and 1993. It is shown that (3) could be responsible for reductions in NO 2 columns during polar day comparable to those measured in 1992 and 1993 following the eruption of Mount Pinatubo. Reaction (3) results in only marginal changes to ozone catalytic loss cycles in 1990. However, for the high aerosol levels of 1992, the inclusion of this reaction results in up to 50% higher ozone loss rates in the 12 to 20 km range. This is caused predominantly by a large increase in [HO x ] tempered by a reduction in loss due to NO x . Calculations in which transport terms were switched off showed that, between 12 and 20 km at 77.5°N, local chemistry removes about 30% of the ozone between April and September compared with 20% when the effects of (3) are not included.

Use of correlations between long‐lived atmospheric species in assessment studies

The results of airborne measurement campaigns and two-dimensional (2-D) model calculations show compact relationships between certain pairs of long-lived species. Such correlations have been used in the present study to reduce the number of transported species used in the Commonwealth Scientific and Industrial Research Organisation (CSIRO) two-dimensional chemical transport model (2-D CTM) when calculating ozone changes from proposed fleets of supersonic aircraft or changing halocarbon concentrations. Differences to both the composition of the background atmosphere and to the predicted ozone changes are examined. It is shown that the use of correlations has only a small effect on the predicted ozone changes. Larger differences are found for the changing halocarbon scenario than for the supersonic aircraft scenario. These differences are due to difficulties associated with correctly accounting for the time variation of the source gas mixing ratios. Further work is required to reduce this source of error. The results of these studies should be applicable to 3-D CTMs, where large savings in computational time can be achieved through the reduction in the number of transported species.

Normalization of correlations for atmospheric species with chemical loss

In order both to measure and to model the time dependence of atmospheric trace species, it is possible to make use of the correlations that occur between the stratospheric mixing ratios for a range of atmospheric constituents. If the correlation is to have any generality, it is necessary to take into account the time dependence of the release rate from the surface of the Earth. Previous studies have done this by using the age of the air Γ. For compounds with stratospheric loss processes and rapidly changing tropospheric mixing ratios, the use of Γ when normalizing correlations is inappropriate. The correlation derived in this way may be time-dependent and therefore of limited usefulness. In the work described here a two-dimensional (2-D) chemical transport model has been used to calculate Γ*, the mean arrival time for a pulsed emission of a chemically active species released from the surface of the Earth. Because chemical reactions preferentially remove molecules from the tail of the distribution, Γ* is always shorter than Γ. The tropospheric concentrations of both CH3CCl3 (methylchloroform) and CH3CFCl2 (HCFC-141b) are currently undergoing rapid change. The results of time-dependent 2-D model calculations show that the use of Γ* results in unique correlations for CH3CCl3 with CFCl3 and for CH3CFCl2 with N2O. Furthermore, empirical methods are described which allow Γ* to be estimated if Γ and the mean stratospheric lifetime of the species are known. This permits the methods described here to be applied to the measurements of atmospheric constituents taken at different times if estimates of the age of the air are available.

Impact of heterogeneous BrONO2 hydrolysis on ozone trends and transient ozone loss during volcanic periods

The hydrolysis of BrONO2 on sulphate aerosols has been included in a 2-D model calculation of ozone changes over the period 1980–1995. Inclusion of this reaction has only a marginal impact on the calculated ozone trends between 1980 and 1990. The effect of the reaction on an atmosphere which has been heavily perturbed by sulphate aerosols for the period June 1991–1995 has been examined by using the idealised WMO 1995 scenario. The results show that the addition of this reaction has a major impact on the calculated transient ozone loss under enhanced aerosol conditions and approximately doubles the calculated ozone loss between 60°S and 60°N in 1992 (when maximum loss of ozone occurs). In contrast to the effects of the hydrolysis of N2O5, the effects of the hydrolysis of BrONO2 are most marked at high latitudes in summer.

Impact of the heterogeneous hydrolysis of BrONO2 on calculated ozone changes due to HSCT aircraft and increased sulphate aerosol levels

The heterogeneous hydrolysis of BrONO2 via sulphate aerosols has been included in 2-D model calculations of the impact of projected fleets of supersonic aircraft on atmospheric ozone. Calculations have been performed for aerosol levels ranging from zero to 16× the lower limit in WMO [1992]. The results show that the addition of this reaction has a major effect when the heterogeneous hydrolysis of N2O5 has reached saturation in regions where the night length is short. At 4× the lower limit of aerosols, the additional calculated change in aircraft impact due to the inclusion of BrONO2 hydrolysis is of the same order as the impact calculated when this reaction is not included. Calculations for background atmospheres at high aerosol levels show that the inclusion of this reaction significantly increases the predicted ozone depletion resulting from volcanically-enhanced aerosol levels.

Charge transport in Fe2O3 films deposited on nanowire arrays

The short diffusion length of photo-excited charge carriers in Fe2O3 is one of the factors limiting the water splitting efficiency of iron oxide based materials. To overcome this problem we are engineering transparent arrays of nanowires to act as conducting substrates for the Fe2O3. To help understand the charge transport characteristics of the Fe2O3 component we report transient photocurrent measurements performed on an absorbing thin film of Fe2O3 deposited by filtered arc deposition on conducting glass with a semi-transparent silver Schottky top contact. Ultraviolet laser pulses were used to generate charge carriers near the surface and the resulting current transients were measured. A simulation of this charge transport has also been developed. The sign of the observed transients was independent of applied bias, consistent with a fully depleted film. The measurements also suggest that recombination may play a significant factor in determining the transient shape. Further investigation is required to confidently predict mobilities.