Predicting acoustic effects of internal waves from the basic climatology of the world ocean

Abstract

Internal waves of a given strength will produce acoustic effects that vary from water mass to water mass. Presented here is a means of predicting the strength of acoustic fluctuations due to internal waves, given the basic climatology, that is, measurements of depth, temperature, and salinity of an oceanic region. An acoustic fluctuation strength parameter F is defined as the ratio of the fractional potential sound-speed change to the fractional potential-density change. Here F is calculated at three depth levels (275, 550, and 850 m), on a one-degree grid of latitude and longitude, using NODC/OCL's World Ocean Atlas 1994. Representative values of F are presented for 15 upper water masses that range from F = 5 in the North Pacific to F = 34 in the North Atlantic, with a typical value for most of the upper waters being F = 15. Results for two depth levels within 12 intermediate water masses range from F = 7 in the North Pacific to F = 62 in the North Atlantic, with a typical value of F = 20, although there is considerable variation. In general, F exhibits higher values in the Atlantic Basin than in the Indian or Pacific, and has a maximum at 550 m. The main use of F will be the prediction of travel-time fluctuations in acoustic propagation experiments, which will be proportional to the value of F, given a universal strength of internal waves.