Abstract:
The purpose of ATOC is to study climate variability in the oceans using three related techniques: (i) satellite altimetry, (ii) acoustic thermometry, and (iii) climate modeling. Satellite altimetry is related to ocean temperature by thermal expansion (melting glaciers are a secondary factor) with each mm of sea level rise corresponding to 15 to 30 mJ/m[sup 2] of stored thermal energy. Acoustic thermometry is associated with the temperature dependence of the speed of sound, and relates changes in the interior heat storage with small changes in acoustic travel times (10 ms at 5000 km, say). The THETIS experiment (Send, 1995; Menemenlis and Wunsch, 1996) in the western Mediterranean gives consistent results for the seasonal heat storage when all three techniques are combined; model prediction alone does not account for the observed changes. Fu and associates at JPL have reported on the changes in sea level measured by TOPEX-POSEIDON for the period 1992--5. For a global spatial average they obtain an astounding (but preliminary) 6 mm/year, but with regional departures by an order of magnitude. Some of the departures can be related to decadal variability. A comparison between the satellite and acoustic measurements is needed for interpretation. [Work supported by SERDP/ARPA.]