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CSIRO Marine and Atmospheric Research
Past Seminars

Seminar Abstract

Improving the simulation of tropical Pacific climate: the impacts of
biology and a more accurate surface stress calculation

The elusiveness to many coupled general circulation models (CGCMs) of a realistic simulation of the mean state of the tropical Pacific has led to the speculation of missing physics. In this study, the effects of two traditionally neglected processors on the simulation of tropical Pacific climate, both of the mean and variations about it, are investigated using the Max-Planck-Institute's climate model.

First, the impact of neglecting surface ocean currents in the calculation of surface stress is assessed by conducting an experiment in which they are taken into account. Compared to a control experiment, without the shear correction, there are several significant improvements: the model's equatorial SST cold bias is reduced by over 1 degree Celsius in the western central Pacific; there is a reduction of equatorial interannual variability of up to 30% to more realistic levels; the dominant period also increases to around 4 years; and the propagation characteristics of SST anomalies change from westward to an almost standing pattern.

Second, the impact of neglecting temporal and spatial variations in optical penetration depth due to ocean biological processes is assessed by performing an experiment in which the HAMOCC5 biogeochemistry model is used in the climate model to estimate these variations. Compared to the simulation with wind shear correction there are several further improvements: the equatorial cold bias in the eastern Pacific is reduced by Upton 0.5 degree Celsius. The phase of the simulated annual cycle is shifted earlier by about two weeks, improving the simulation. Interannual SST variability weakens by a further 15-20%, to even more realistic levels. The dominant period is lengthened further to around 5 years.

In both cases, the reasons for changes in ENSO characteristics are due to both changes in the mean state and to changes in the relevant feedbacks. These shall also be discussed.

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CSIRO = Marine Laboratories Auditorium, Castray Esplanade, Hobart

For further information, or to schedule a seminar, contact:
Peter Oke, (Oceanographic seminars) CSIRO Marine Research (03) 6232 5387
Piers Dunstan, (Biological seminars) CSIRO Marine Research (03) 6232 5382
Katrina Nitschke, Antarctic Climate and Ecosystems CRC (03) 6226 2265 & IASOS, University of Tasmania (03) 6226 2509