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Large-scale ocean-atmosphere interactions and ocean circulation in the tropics

PI: Jaclyn Brown
Institution: Centre for Australian Weather and Climate Research (CAWCR), CSIRO
Additional Investigators: Alexey Fedorov
Abstract:
My main interests focus on large-scale ocean-atmosphere interactions and ocean circulation in the tropics. In particular, I study what factors and characteristics of the tropical ocean and the atmosphere affect the amplitude, frequency and other important properties of El Niño. One of those factors, which also influence stability properties of the coupled ocean-atmosphere system, is net energy dissipation rates in the ocean.

To quantify those dissipation rates, one can consider the damping (decay) timescale for the thermocline anomalies associated with the large-scale oceanic motion. Fedorov (2006) explored these ideas in an oceanic GCM using the analyses of the ocean energetics conducted by Goddard and Philander (2000). He found that the damping rate was dependent upon the frequency range. In the interannual frequency range, he found a damping of (2.3 years)-1, similar to the values used in the original Cane and Zebiak (1987) model. In the near annual frequency sub-range, the damping had larger values of about (7 months)-1.

Fedorov’s analysis was limited to an ocean-only model forced with observed monthly winds. The low temporal resolution of the windstress smoothed out the effect of important ENSO forcing features such as westerly wind bursts. We will firstly explore Fedorov’s analysis technique using coupled model data, to see if there is a difference between coupled models and ocean-only models, and also whether increased temporal resolution leads to significantly different outcomes. Having weekly data, as opposed to monthly, will also allow us to improve the resolution of the analysis for high frequency events. Further, we will explore this problem by comparing damping rates in different coupled models. We hypothesize that the damping scales will vary and that this may explain the differing ENSO properties simulated by different coupled GCMs, Guilyardi (2005).
Publications:
  • Brown, J.N. and A.V. Fedorov, 2008: Mean energy balance in the tropical Pacific Ocean. J. Marine Research, 66, 1-23. Abstract. Edit.
  • Brown, J.N. and A.V. Fedorov, How much energy is transferred from the winds to the thermocline on ENSO timescales?. J. Climate. Submitted. Abstract. Edit.

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