A comparison of acoustic thermometry, XBT, TOPEX, and HOT observations of ocean temperature in the northeast Pacific

Time series of temperature have been measured acoustically in the northeast Pacific as part of the Acoustic Thermometry of Ocean Climate (ATOC) project. These time series are compared with other available data types. The acoustic time series of transmissions from the California and Kauai acoustic sources were obtained during 1996–1999. As a result of marine mammal protocols, the time series are intermittent; the California source was turned off in Fall 1998. Assuming that variations in sea-surface height observed by TOPEX/POSEIDON are caused by thermal expansion, the amplitude of the annual cycle of heat content derived from altimetry is larger than that found by the acoustic data, Levitus climatology, and monthly maps of ocean temperature from XBTs of opportunity. The heat content ‘‘anomalies’’ determined by the XBT maps are comparable in size to the differences between the XBT and acoustically derived heat content. A variety of problems with the XBT sampling may account for these differences. The 12-year time series of temperature derived from the Hawaiian Ocean Time series (HOT) data highlights the mesoscale noise in single-point sampling. However, thermal variability at 100-day time scales is observed in the acoustic data obtained between Hawaii and California using the Kauai source. Acoustic thermometry is complementary to altimetry and hydrography.