Figure 2. Acoustic arrival patterns for receivers k and v1 at approximate ranges of 5000 and 3000km, respectively. Arrival patterns are presented as “dot plots” where the dot size is proportional to the signal-to-noise ratio. Predicted ray arrivals (open circles) were generated from climatology15 and then shifted in time to optimize the comparison. Only the early arrivals, corresponding to steep rays, are tracked (solid lines). Rays propagating at shallow angles arrive in quick succession and are more difficlult to resolve. Receiver v1, a 40-element vertical line array, permits a cleaner reception than receiver k, a horizontal array mounted on the sea floor.
Other data, such as acoustic or expendable temperature profiler (XBT) data, and theory (including GCMs) are used to separate the various components by geography and by space-time scales.
Direct Temperature Measurements. XBT surveys from ships were conducted adjacent to section v1 (Fig. 3). Such surveys provide a direct measure of heat content of the upper ocean (＜800m).
Repetition of the surveys is, however, difficult to arrange. Climatologies15 (multidecadal averages of historical data) are able to provide rough estimates of the mean seasonal cycle of heat and salinty changes.
Modeling Component. Ocean GCMs are a representation of Newton's laws of motion and thermodynamics for the fluid ocean driven at the sea surface through exchanges with the atmosphere of stress (winds) and buoyancy fluxes (heat and fresh water). We used a GCM constructed for ATOC16 that “predicts” the fields observed by acoustic tomography and altimetry.
