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Investigation of Southern Ocean sea ice response in ensemble CMIP5 historical and ozone perturbation simulations

Investigation of Southern Ocean sea ice response in ensemble CMIP5 historical and ozone perturbation simulations
Siobhan O'Farrell


Siobhan O’Farrell
CSIRO Marine and Atmospheric Research


The sea ice covered area in the Southern ocean has a small significant positive trend in recent decades in contrast to the decay in the Arctic sea ice cover. There have been a number of theories suggesting that it is driven by strengthening of SAM as a result of ozone depletion; increasing stratification of the ocean from sea ice melt and/or ice shelf melting, increased divergence of the ice pack or could be part of natural variability of the climate system.

The CMIP5 models provide a data set to investigate several of these theories; in particular the CSIRO Mk3.6 model has a 10 member historical ensemble in which the sea ice concentration has individual members that show ice advance and others that show ice retreat trends over the recent period (1976-2005). By studying the atmospheric drivers on the sea ice, air temperature, large scale circulation, surface, wind stress, the sea ice transport and sea ice divergence of individual ensemble members at monthly/seasonal timescale we hope to understand why the differences arise. We also investigate the changes in ocean temperature salinity and the ocean stratification in the individual members.

As part of CMIP5, many of the modelling groups undertook ozone only historical runs or all forcing historical runs that omitted the recent ozone perturbations. CSIRO Mk3.6 did the latter (with a 10 member ensemble); these runs are close to the present day signal so can be compared to the existing historical runs and observations. These data will be investigated to ascertain if the ozone signal in this model impacts on the ensemble spread of the results and how individual members of the ensemble respond compared to the all forcing case.

There are now similar experiments underway for the ACCESS 1.0 and ACCESS 1.3 model with the ozone distribution at high southern latitudes remaining held at 1960 values until 2012. The ensemble size will be smaller at only 3 members which is the same size as the existing all forcing historical ACCESS 1.3 ensemble but we hope sufficient to detect a signal if it is present in either of the ACCESS model configurations.

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Key dates

  • 11th June 2013
    Registrations close
  • 21st June 2013
    Registrations at the AAD open for staff
  • 24th June 2013
    Registrations at the venue open
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    Conference commences
  • 26th June 2013
    Conference concludes

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This page was last modified on 2 September 2013.