COMPARISON OF BASIN-SCALE ACOUSTIC TRANSMISSIONS WITH RAYS AND FURTHER EVIDENCE FOR A STRUCTURED THERMAL FIELD IN THE NORTHEAST PACIFIC

From May to September of 1987, 250-Hz, 16-ms resolution acoustic signa ls were transmitted between four sources and nine receivers in the nor theast Pacific. This paper examines the acoustic transmissions across nine of the sections within this group, with path lengths ranging from approximately 1700 to 3300 km. Acoustic multipaths are tracked in the data, and ray theory is successfully used to identify the multipaths, where the spring and summer Levitus' climatological databases are use d to determine the sound speeds. The observed multipaths arrive on the order of 1 s later than the predicted rays. Travel time differences g reater than 0.15 s are due to temperature errors in Levitus' climatolo gy within the ocean's upper 1 km. The resulting corrections to Levitus ' spring and summer oceans are -0.2 and -0.3 degrees C, respectively. The upper turning depths for all rays an found to vary by less than 50 m from spring to summer. Variations in the measured travel times over the four month period are about 0.5 s. Some sections warm between the spring and summer seasons, while other sections cool. This variabilit y is inconsistent with a temperature field dominated by seasonal effec ts. The spatial and temporal scales of the heat content are qualitativ ely similar to those found from other basin-scale acoustic sections in the northeast Pacific [J. L. Spiesberger et al., J. Acoust. Sec. Am. 92, 384-396 (1992)]. (C) 1998 Acoustical Society of America.