Acoustic thermometry time series in the North Pacific

Acoustic measurements of large-scale, depth-averaged temperature continue in the North Pacific as a follow on to the Acoustic Thermometry of Ocean Climate (ATOC) project. An acoustic source located just north of Kauai transmits six times per day at four-day intervals to six receivers to the east at 1-4 Mm ranges and one receiver to the northwest at about 4 Mm range. The time series run from 1997-1999 and from 2002 to the present, and are expected to continue for at least another five years. The paths to the east show cooling in the last year relative to the earlier data. The path to the northwest shows a modest warming, though a sudden cooling event appears to be just starting. The temperatures measured acoustically are compared with those inferred from TOPEX altimetry, Argo float data, and with ECCO (estimating the circulation and climate of the ocean) model output. This on-going data collection effort, to be augmented over the next years with a more complete observing array, contributes to the CLIVAR effort and can be used, for example, to separate whole-basin climate change from low-mode spatial variability such as the pacific decadal oscillation (PDO).