Abstract:
For the ATOC program two dense vertical-line arrays (VLA) centered on the sound-channel axis and located off of the islands of Hawaii and Christmas, and several bottom-mounted horizontal arrays located around the North Pacific have recorded basin-scale acoustic transmissions emminating from a bottom mounted source located on Pioneer Seamount since December 1995. Coherent ``raylike'' wavefronts with small travel-time fluctuations are observed at these stations ( ranges 1 to 5 Mm). The ``ray- like'' arrivals can be unambiguously identified with specific ray paths using standard climatologies so that travel times of these ray arrivals may be used to infer oceanic variability such as tidal current and average heat content. The ``raylike'' arrivals recorded on the bottom receivers appear to be associated with ray paths whose lower turning points are several hundred meters above the receiver. Vertical leakage of acoustic energy below the ray turning point from internal waves and/or diffraction effects are insufficient to explain these observations. At the VLAs, the ``raylike'' arrivals are followed by a complex ``modelike'' finale. Resolved modal arrivals show mode 1 to be fairly adiabatic, yet nonadiabaticity increases rapidly with increasing mode number. [Work supported by the Strategic Environmental Research and Development Program through ARPA.]