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Rashid H.A.,CSIRO | Sullivan A.,CSIRO | Hirst A.C.,CSIRO | Bi D.,CSIRO | And 2 more authors.
Australian Meteorological and Oceanographic Journal | Year: 2013

One of the key performance measures for Coupled General Circulation Models (CGCMs) is their ability to realistically simulate the prominent modes of climate variability. Here, we investigate the realism of El Niño-Southern Oscillation (ENSO), the dominant mode of observed interannual climate variability, as simulated by the Australian Community Climate and Earth System Simulator (ACCESS). We examine the key ENSO properties calculated from observations and from the pre-industrial control and historical simulations performed by versions 1.0 and 1.3 of the ACCESS coupled model (ACCESS-CM), as part of the Coupled Model Intercomparison Project phase 5 (CMIP5). The ENSO properties examined are the spatial structure and timescales, phase locking to the annual cycle, growth and decay of Niño3 SST anomalies, and the coupled ENSO evolution, as well as the ENSO induced teleconnection patterns (as diagnosed by linear regressions of the three-dimensional atmospheric circulation field, rainfall, sea-level pressure, and the upper-tropospheric geopotential heights onto the Niño3 index). The coupled evolutions of SST, zonal wind stress, and the thermocline depth during a typical ENSO event are used to illustrate the essential features of ENSO dynamics. Our results show that both versions of the ACCESS-CM perform reasonably well in simulating the ENSO properties and teleconnections. In particular, the spatial structure, timescales, phase locking, and the growth and decay rates of ENSO are well simulated. The evolution of SST, zonal wind stress, and the thermocline depth during ENSO events is also reasonably well simulated, although the SST (zonal wind stress) response is found to be stronger (weaker) than observed. The simulated ENSO teleconnection patterns are also mostly realistic, despite some adverse impact of the equatorial Pacific cold SST bias on the local precipitation response. The present study shows that the ACCESS-CMs simulate the key ENSO properties (e.g. amplitude and spatial structure, timescales, and atmospheric teleconnections) better than most of the previous generations of CGCMs. Copyright © 2013, Common wealth of Australia. Source

Bi D.,CSIRO | Marsland S.J.,CSIRO | Uotila P.,CSIRO | O'Farrell S.,CSIRO | And 5 more authors.
Australian Meteorological and Oceanographic Journal | Year: 2013

The Australian Community Climate and Earth System Simulator Ocean Model (ACCESS-OM), a global coupled ocean and sea-ice model, has been developed at the Centre for Australian Weather and Climate Research1. It is aimed to serve the Australian climate sciences community, including the Bureau of Meteorology, CSIRO2 and Australian universities, for ocean climate research. ACCESS-OM comprises the NOAA/GFDL3 Modular Ocean Model version 4p1; the LANL4 Sea-ice Model version 4.1, a data atmospheric model; and the CERFACS5 OASIS3.25 coupler, which constrains data exchange between the sub-models. ACCESS-OM has been functioning as the ocean and sea-ice coupling core of the ACCESS coupled model, one of the Australian models participating in the Coupled Model Inter-comparison Project phase 5. This paper describes the ACCESS-OM sub-models, coupler, coupling strategy and framework. A selection of key metrics from an ACCESS-OM benchmark simulation, which has run for 500 years using the Coordinated Ocean-ice Reference Experiments normal year forcing, is presented and compared with observations to evaluate the model performance. It shows ACCESS-OM simulates the global ocean and sea-ice climate generally comparably to the results from other ocean sea-ice models of the same class (Griffies et al. 2009). For example, the global ocean volume-averaged temperature undergoes minor evolution. The maximum transport of North Atlantic overturning circulation is 18.5 Sv and the Antarctic Circumpolar Current transport through Drake Passage is 150 Sv, both in fair agreement with the observations; and the sea-ice coverage has reasonable distribution and annual cycle. Measured against other ocean sea-ice models and observations, ACCESS-OM is an appropriate tool for Australia's future ocean climate modelling efforts. Copyright © 2013, Common wealth of Australia. Source

Pook M.J.,CSIRO | Pook M.J.,Climate Adaptation National Research Flagship | Risbey J.S.,CSIRO | Mcintosh P.C.,CSIRO | And 4 more authors.
Monthly Weather Review | Year: 2013

The seasonal cycle of blocking in the Australian region is shown to be associated with major seasonal temperature changes over continental Antarctica (approximately 15°-35°C) and Australia (about 8°-17°C) and with minor changes over the surrounding oceans (below 5°C). These changes are superimposed on a favorable background state for blocking in the region resulting from a conjunction of physical influences. These include the geographical configuration and topography of the Australian and Antarctic continents and the positive west to east gradient of sea surface temperature in the Indo-Australian sector of the Southern Ocean. Blocking is represented by a blocking index (BI) developed by the Australian Bureau of Meteorology. The BI has a marked seasonal cycle that reflects seasonal changes in the strength of the westerly winds in the midtroposphere at selected latitudes. Significant correlations between the BI at Australian longitudes and rainfall have been demonstrated in southern and central Australia for the austral autumn, winter, and spring. Patchy positive correlations are evident in the south during summer but significant negative correlations are apparent in the central tropical north. By decomposing the rainfall into its contributions from identifiable synoptic types during the April-October growing season, it is shown that the high correlation between blocking and rainfall in southern Australia is explained by the component of rainfall associated with cutoff lows. These systems form the cyclonic components of blocking dipoles. In contrast, there is no significant correlation between the BI and rainfall from Southern Ocean fronts. © 2013 American Meteorological Society. Source

Bi D.,CSIRO | Dix M.,CSIRO | Marsland S.J.,CSIRO | O'Farrell S.,CSIRO | And 24 more authors.
Australian Meteorological and Oceanographic Journal | Year: 2013

The Australian Community Climate and Earth System Simulator coupled model (ACCESS-CM) has been developed at the Centre for Australian Weather and Climate Research (CAWCR), a partnership between CSIRO1 and the Bureau of Meteorology. It is built by coupling the UK Met Office atmospheric unified model (UM), and other sub-models as required, to the ACCESS ocean model, which consists of the NOAA/GFDL2 ocean model MOM4p1 and the LANL3 sea-ice model CICE4.1, under the CERFACS4 OASIS3.2-5 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 20th 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 including 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 aspects, and these are also discussed. Copyright © 2013, Common wealth of Australia. Source

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