Dependence of the structure of the shallow convergence zone on deep ocean bathymetry.

During an experiment in the northern Philippine Sea in 2009, low-frequency tones were transmitted from a shallow (15- and 60-m) source deployed from R/V Melville keeping station to a shallow (250-m) horizontal receiver array towed by R/V Kilo Moana approximately one convergence zone (CZ) away. Recordings were made during events in which the receiver ship maintained constant range in the convergence zone and during events in which the receiver ship transited radially through the CZ. The shallow CZ exhibits strong dependence on the bathymetry mid-way between the source and receiver array. In fact, the variability of the structure of the first CZ in this environment is significantly more strongly affected by the heterogeneous character of the bottom than water column fluctuations. Numerical modeling with a parabolic equation code is used to support the conclusions from the data analysis.