Auad, G., A. J. Miller and W. B. White, 1998:
Simulation of heat storages and associated heat budgets in the Pacific Ocean
2. Interdecadal timescale
Journal of Geophysical Research,
103, 27,621-27,635.
Abstract.
We use a primitive equation isopycnal model of the Pacific Ocean to simulate and diagnose the anomalous heat balance
on interdecadal timescales associated with heat storage changes observed from 1970-1988 in the expendable
bathythermograph (XBT) data set. Given the smallness of the interdecadal signals compared to the El Nino-Southern Oscillation
(ENSO) signal, the agreement between model and observations is remarkably good. The total
anomalous heat balance is made up of two parts, the diabatic part (from the model temperature equation) and the
adiabatic part (from the model mass conservation equation) due to thermocline heave. We therefore describe our
analysis of both the total and diabatic anomalous heat balances in four areas of the tropical and subtropical North
Pacific Ocean in the upper 400 m. The interdecadal total (diabatic plus adiabatic) heat balance in the North Pacific
Ocean is characterized by a complicated interplay of different physical processes, especially revealed in basin-scale
averages of the heat budget components that have comparable amounts of variance. In smaller subregions, simpler
balances hold. For example, in the western equatorial Pacific (area 1) the total heat content tendency term is nearly
zero, so that a simple balance exists between surface heat flux, vertical heat transport, and horizontal mixing. In the
western subtropical Pacific the total heat content tendency balances the three-dimensional divergence of the heat flux.
We speculate that this complexity is indicative of multiple physical mechanisms involved in the generation of North
Pacific interdecadal variability. The diabatic heat balance north of 24 degrees N, a region of special interest to The
World Ocean Circulation Experiment (WOCE), can be simplified to a balance between the tendency term, surface heat
flux, and meridional advection, the last term dominated by anomalous advection of mean temperature gradients. For
the western equatorial region the diabatic heat content tendency is nearly zero and the steady balance involves simply
horizontal advection and the surface heat flux, which at these latitudes has a damping role in the model, hn important
finding of this study is the identification of two interdecadal timescales, roughly 10 and 20 years, both similar to those
reported by other investigators in recent years. [Tourre et al., 1998; Latif and Barnett, 1994; Robertson, 1995; White et
al., 1997; Gu and Philander, 1997; Jacobs et al., 1994]. The 20-year timescale is only present in diabatic heat budget
components, while the 10-year timescale is present in both diabatic and adiabatic components. The 10-year timescale
can also be seen in the surface heat flux time series, but it occurs in the ocean adiabatic components which
demonstrates the importance of oceanic adjustment through Rossby wave dynamics on decadal timescales.
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