Arnold Sullivan

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.

Asymmetry in ENSO Teleconnection with Regional Rainfall, Its Multidecadal Variability, and Impact

Abstract An asymmetry, and its multidecadal variability, in a rainfall teleconnection with the El Nino–Southern Oscillation (ENSO) are described. Further, the breakdown of this relationship since 1980 is offered as a cause for a rainfall reduction in an ENSO-affected region, southeast Queensland (SEQ). There, austral summer rainfall has been declining since around the 1980s, but the associated process is not understood. It is demonstrated that the rainfall reduction is not simulated by the majority of current climate models forced with anthropogenic forcing factors. Examination shows that ENSO is a rainfall-generating mechanism for the region because of an asymmetry in its impact: the La Nina–rainfall relationship is statistically significant, as SEQ summer rainfall increases with La Nina amplitude; by contrast, the El Nino–induced rainfall reductions do not have a statistically significant relationship with El Nino amplitude. Since 1980, this asymmetry no longer operates, and La Nina events no longer ind...

Rainfall teleconnections with Indo-Pacific variability in the WCRP CMIP3 models.

Abstract The present study assesses the ability of climate models to simulate rainfall teleconnections with the El Nino–Southern Oscillation (ENSO) and the Indian Ocean dipole (IOD). An assessment is provided on 24 climate models that constitute phase 3 of the World Climate Research Programme’s Coupled Model Intercomparison Project (WCRP CMIP3), used in the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC). The strength of the ENSO–rainfall teleconnection, defined as the correlation between rainfall and Nino-3.4, is overwhelmingly controlled by the amplitude of ENSO signals relative to stochastic noise, highlighting the importance of realistically simulating this parameter. Because ENSO influences arise from the movement of convergence zones from their mean positions, the well-known equatorial Pacific climatological sea surface temperature (SST) and ENSO cold tongue anomaly biases lead to systematic errors. The climatological SSTs, which are far too cold along the Paci...

Interactions of ENSO, the IOD, and the SAM in CMIP3 Models

Abstract Simulations of individual global climate drivers using models from the Coupled Model Intercomparison Project phase 3(CMIP3) have been examined; however, the relationship among them has not been assessed. This is carried out to address several important issues, including the likelihood of the southern annular mode (SAM) forcing Indian Ocean dipole (IOD) events and the possible impact of the IOD on El Nino–Southern Oscillation (ENSO) events. Several conclusions emerge from statistics based on multimodel outputs. First, ENSO signals project strongly onto the SAM, although ENSO-forced signals tend to peak before ENSO. This feature is similar to the situation associated with the IOD. The IOD-induced signal over southern Australia, through stationary equivalent Rossby barotropic wave trains, peak before the IOD itself. Second, there is no control by the SAM on the IOD, in contrast to what has been suggested previously. Indeed, no model produces a SAM–IOD relationship that supports a positive (negative)...

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

Fate of the Atlantic Meridional Overturning Circulation: Strong decline under continued warming and Greenland melting

National Oceanographic and Atmospheric Administration [NA15OAR4310239]; Netherlands Earth System Science Center (NESSC); Polar Program of the Netherlands Organization for Scientific Research (NWO); Regional and Global Climate Modelling Program (RGCM) of the U.S. Department of Energys Office of Science (BER) [DE-FC02-97ER62402]; Office of Science of the U.S. Department of Energy; ArCS; ICA-RUS; Natural Environment Research Council

Shoaling of the off‐equatorial south Indian Ocean thermocline: Is it driven by anthropogenic forcing?

[1]xa0Surface warming since 1950 in the off-equatorial south Indian Ocean (IO) occurs without a consistent surface heat flux trend, and is accompanied by a shoaling thermocline. The associated dynamics have not been fully explored. Using 20th century climate model experiments, we test if the shoaling thermocline is attributable to a transmission from the Pacific, where a similar shoaling occurs, and whether it is climate change-induced. A 22-model average produces no such signal. An average of a subset of models that better simulate El Nino-Southern Oscillation (ENSO) and its transmission produces the right direction of the IO thermocline trends. The shoaling in this subset average, taken as anthropogenically induced, is far weaker than the observed, suggesting a significant multidecadal variability component in the observed changes. The Pacific contribution increases with a stronger model ENSO amplitude and broader meridional structure, highlighting the importance of realistic ENSO simulations in modelling long-term change in the IO.

Evaluation of ACCESS climate model ocean diagnostics in CMIP5 simulations

Global and regional diagnostics are used to evaluate the ocean performance of the Australian Community Climate and Earth System Simulator coupled model (ACCESS-CM) contributions to the Climate Model Intercomparison Project phase 5 (CMIP5). Two versions of ACCESS-CM have been submitted to CMIP; namely CSIRO-BOM ACCESS1.0 and CSIRO-BOM ACCESS1.3. Results from six of the core CMIP5 experiments (piControl, historical, rcp45, rcp85, 1pctCO2, and abrupt4xCO2) are evaluated for each of the two ACCESS-CM model versions. Overall, both model versions exhibit a reasonable and stable representation of key diagnostics of ocean climate performance in the pre-industrial control simulations, including a meridional overturning circulation with North Atlantic Deep Water maxima in the range 22–24 Sv, and a poleward heat transport maximum of around 1.5 PW. For the projected climate change scenarios considered the ACCESS-CM results are in reasonable agreement with responses found in other CMIP models, with the familiar ocean warming, and reduction in strength of meridional overturning and poleward heat transport. Drifts in the control simulations of both global ocean salinity and global sea-level are opposite in sign for ACCESS1.0 and ACCESS1.3, suggesting problems exist in the closure of the hydrological cycle. The simulation of ocean climate change over the historical period shows a weak response compared to observations, which manifests as a late response of ocean warming and sea level rise starting around 1990 in the model, compared to the mid 1960s in observations. Further historical simulations are underway to ascertain if this late response in ACCESS is a robust model feature, or just low frequency variability. If the weak response over the historical period proves robust, the likely cause is a too strong cooling from atmospheric aerosols. Broadening the set of experiments to further investigate the relative warming response of the ACCESS-CM to greenhouse gases compared to the cooling response to aerosols is underway, and preliminary results do suggest that the cooling due to aerosols is strong in the historical simulations.

ACCESS-OM: the Ocean and Sea ice Core of the ACCESS Coupled Model

Daohua Bi1, Simon J. Marsland1, Petteri Uotila1, Siobhan O’Farrell1, Russell Fiedler2, Arnold Sullivan1, Stephen M. Griffies3, Xiaobing Zhou4, and Anthony C. Hirst1 1 CAWCR/CSIRO Marine and Atmospheric Research, Aspendale, Australia 2 CAWCR/CSIRO Marine and Atmospheric Research, Hobart, Australia 3 NOAA/Geophysical Fluid Dynamics Laboratory, Princeton, NJ, USA 4 CAWCR/Bureau of Meteorology, Melbourne, Australia

Are Anthropogenic Aerosols Responsible for the Northwest Australia Summer Rainfall Increase? A CMIP3 Perspective and Implications

AbstractSevere rainfall deficiencies have plagued southern and eastern Australian regions over the past decades, where the long-term rainfall is projected to decrease. By contrast, there has been an increase over northwest Australia (NWA) in austral summer, which, if it continues, could be an important future water resource. If increasing anthropogenic aerosols contribute to the observed increase in summer rainfall, then, as anthropogenic aerosols are projected to decrease, what will the likely impact over NWA be? This study uses output from 24 climate models submitted to phase 3 of the Coupled Model Intercomparison Project (CMIP3) with a total of 75 experiments to provide a multimodel perspective. The authors find that none of the ensemble averages, either with both the direct and indirect anthropogenic aerosol effect (10 models, 32 experiments) or with the direct effect only (14 models, 43 experiments), simulate the observed NWA rainfall increase. Given this, it follows that a projected rainfall reducti...