Sensitivity of Global Circulation Response to a Southern Ocean Zonal Wind Stress Perturbation
Previous studies indicate that Southern Ocean wind stress may drive global oceanic overturning variability on decadal timescales. An experiment with a perturbation to a near-global ocean model with realistic topography and forcing (Klinger and Cruz, 2009) raises questions about the evolution of the...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.619.1742 http://mason.gmu.edu/~bklinger/cruzklinger09.pdf |
| Summary: | Previous studies indicate that Southern Ocean wind stress may drive global oceanic overturning variability on decadal timescales. An experiment with a perturbation to a near-global ocean model with realistic topography and forcing (Klinger and Cruz, 2009) raises questions about the evolution of the overturning anomaly. What determines the relative strength of the Atlantic and Pacific response? Is the model’s large Indo-Pacific response due to the great width of the Indo-Pacific basin? What is the relationship between the initial response and the final equilibrium? What determines the timescale of the response? These questions are addressed through experiments with a primitive equation model (MOM4) in which the sensitivity of the response to basin width and Atlantic-Pacific density differences are tested. Pacific overturning anomaly is very roughly proportional to basin width. The North Pacific stratification has little influence on the initial response but strongly affects the final equilibrium response. For strongly stratified North Pacific, the Pacific’s transient overturning anomaly is much stronger than its final value, implying a large decadal response. Response timescales are proportional to the global basin width, consistent with shallow water theory. Mass budgets indicate that cross-isopycnal flow anomalies can be ignored for the first few decades (as in the simplest shallow water models), but become increasingly im-portant afterwards. The response of a single-basin configuration is independent of horizontal resolution, horizontal viscosity, and the use of unequal tracer and momentum timesteps. This strengthens the conclusion that on decadal scales, the behavior is dominated by Rossby wave dynamics and is independent of the detailed behavior of the Kelvin waves. |
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