Small scale interactions in the near surface ocean

Abstract

Experiments were conducted at the NURDC oceanographic tower off San Diego, California to describe the small scale physical properties in the upper ocean and to determine their temporal and spatial interrelationships. The measured parameters included water particle velocities, temperatures, salinity, sound speed, sound speed (phase) modulation, sound amplitude modulation and surface waves. Simultaneous time series measurements are analyzed for a twenty minute record taken at a depth of 7.3 m. The spatial correlation distance for temperature was found to be about 25 cm. Sound modulation of a 60 kHz sound beam underwent a mean attenuation of about 5%. The correlation distance of an effective inhomogeniety due to the combined temperature, salinity, and bubble effects was found to be 8.8 cm. The change in the index of refraction of the speed of sound at 60 kHz (a bubble resonant region) was found to be 99% induced by bubbles . The energy density spectra were dominated by wave induced motion. First order wave theory accurately predicts orbital water particle motion and its irrotationality. High coherence is found between wave-induced water particle motion and sound modulation and decreasing coherence between water particle motion and salinity, sound velocity, and temperature.