Internal Waves in the SESAME II Experiment: Speed, Direction, and Effect on Acoustic Transmission
Abstract
The SESAME II experiment was conducted off the northwestern coast of Scotland in July-August 1996. Three vertical arrays (named 'the deep array,' the shallow array,' and 'the temperature array') containing thermal sensors and hydrophones were deployed. An analysis of temperature and sound speed data from the experiment over a 5 days span reveals that the relatively long period variations can be identified with the M2 tidal cycles (principal lunar tides with period 12.42 h). Short period events (of about 10 min duration) on the shallow array are usually accompanied by similar, though not identical, events on the temperature array, delayed by 2-10 min. Such correspondence was found to be rare between the deep array and the shallow array. The time delays correspond to a range of internal wave (IW) speeds of 0.15-0.35 m/s. During the 5 days period, a search for prominent short-period events (soliton-like events) in which the isospeed contour dips from a depth of about 50 m to a depth of over 120 m on both arrays, reveals several candidates at days 215.35, 217.6, 218.65, 218.97, 219.48, 219.6, and 219.74. Among these, the event at day 217.6 seems closest to being soliton-like because it retained its shape more perfectly than others while traveling from the shallow array to the temperature array. Assuming its direction (the wave vector direction) to be approximately toward southeast with compass angle 105 deg (the average value obtained from analysis of current-meter data), its speed would be 0.3 m/s, in excellent agreement with the value of 0.35 m/s, also obtained from current-meter data. During the middle period of this soliton-like event, the sound speed profile has been found to possess approximately constant gradient. According to a well known theorem, such a constant gradient sound speed profile should cause refraction of the sound energy passing through the IW.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 02, 1998
- Accession Number
- ADA342889
Entities
People
- Jacob A George
- Robert L. Field
Organizations
- United States Naval Research Laboratory