Variability of heat content in the Northcentral Pacific in summer 1987 determined from long-range acoustic transmissions

The evolution of the depth integrated heat content in the Northeast Pacific during summer 1987 has been measured using long-range acoustic transmissions between transceivers deployed in a triangle approximately 1000 km on a side. Transmissions at 4-day intervals gave travel times that were inverted to obtain estimates of the range-average sound-speed fields along the sides of the triangle. The estimated sound-speed fields are converted to temperature fields and integrated to obtain depth and range averaged heat content. The acoustically determined sound-speed and temperature fields agree with conventional CTD and XBT data. The accuracy of acoustical measurements of heat content are comparable to estimates from CTD and XBT data and can be made much more frequently. The acoustically measured variability of heat content at short-time time scales limits the accuracy of studies using infrequent XBT sections. Ocean/atmosphere heat exchange from bulk formulas cannot fully explain the observed heat content change; the excess heat change is calculated to be of order 50–150 W m−2. [Work supported by NSF and ONR.]