A decade of acoustic thermometry in the North Pacific Ocean: Using long-range acoustic travel times to test gyre-scale temperature variability derived from other observations and ocean models

Abstract

Large-scale temperatures in the North Pacific were measured by long-range acoustic transmissions from 1996–2006. Acoustic sources off California and Kauai transmitted to receivers distributed throughout the North Pacific from 1996–1999. Kauai transmissions continued from 2002–2006. Acoustic travel-time data are inherently integrating. This averaging suppresses mesoscale variability and provides an accurate measure of large-scale temperature, subject to the limitations of the ray path sampling. At basin scales, the ocean is highly variable, with significant changes occurring at time scales from weeks to years. The interannual variability is large compared to trends in the data. Willis, et al. used objective mapping techniques applied to satellite altimetry and hydrography to derive 0–750 m temperature fields for the global ocean. Travel times equivalent to the measured travel times can be calculated using these fields. The measured and calculated travel times are similar, but also show significant differences. Similar comparisions using travel times derived from the ‘‘Estimating the Circulation and Climate of the Ocean’’ (ECCO) model and a high-resolution Parallel Ocean Program (POP) model also show similarities and differences. The ECCO model was constrained by altimetric and profile data by data assimilation, suggesting that the acoustic travel times provide meaningful additional constraints on model behavior.