Measuring heat storage changes in the equatorial Pacific: A comparison between TOPEX altimetry and Tropical Atmosphere-Ocean buoys

Heat storage variations in the equatorial Pacific have been studied from December 1992 through February 1997, using sea level data from the TOPEX altimeter and temperatures measured by 42 tethered buoys that are part of the Tropical Ocean-Atmosphere (TAO) array. The TOPEX measurements are converted to heat storage anomalies using a coefficient determined from mean climatological values. For 30-day averages the two measurements agree well over most of the region, except for the southwestern quadrant of the warm pool and a small region of the north-central equatorial Pacific. In the southwestern quadrant the TOPEX measurements indicate a smaller long-term heating rate than the TAO measurements, differing by as much as 30%. After examining conductivity-temperature-depth data in this region, it appears that the difference is due to a change in ocean salinity which is reflected in the TOPEX sea level measurements but not in the TAO heat measurements. The signal in the north-central region is predominately at an annual period, but there is not enough external measurements to determine what the source of the difference is. In the remainder of the equatorial Pacific, the agreement between the data suggests that the TOPEX measurements can be used to measure heat storage variations in the upper layer with reasonable accuracy. Thus TOPEX altimeter data can provide information about the heat budget of the equatorial Pacific in regions where there are few or no direct measurements.