Acoustic thermometry data compared with ocean models: The importance of ENSO in modifying the ocean interior

Abstract

The difficulties in detecting anthropogenic changes in ocean temperature due to the industrial revolution are discussed using acoustic thermometry data taken between Oahu and seven SOSUS receivers at distances of 3000–4000 km. Measurements were made in late 1983, and over two 5-month intervals between 1987 and 1989. The travel times are dominated by interannual fluctuations. Two hydrodynamic ocean models are used to identify plausible oceanic features that could cause these variations. Modeled El Niños and La Niñas exhibit oceanic teleconnections between the Equator and mid-latitudes that lead to Rossby waves that propagate westward at mid−latitudes. Rossby waves are the dominant model features which affect the modeled acoustic travel times, and hence section-averaged temperatures in the eastern North Pacific. Modeled predictions of the travel times are significantly different than some of the data. The magnitude and rates of changes of the data are the same as those which result from the effects of the Rossby waves. The largely unknown large−scale variability of the ocean at interannual and decadal scales is a principal problem for detecting possible changes in temperature due to human activity. Effects from eddies, seasonal cycles, and internal waves are of second order.