Statistical and dynamical analysis of internal waves on the continental shelf of the Middle Atlantic Bight from space shuttle photographs

Abstract

By interpreting two space shuttle photographs taken with a Linhof camera on June 8, 1991, a total of 34 internal soliton packets on the continental shelf of the Middle Atlantic Bight are recognized. The internal soliton field has a three‐level structure: packet groups with average wavelength of 17.5 km, packets with average wavelength of 7.9 km, and solitons with average wavelength of 0.6 km. Using the finite‐depth theory we derive that the maximum amplitude of solitons is 5.6 m, the phase speed is 0.42 m/s, and the period is 23.8 min. The frequency distribution of solitons is triple‐peaked at 1.9 × 10 −4 Hz, 3.0 × 10 −4 , and 6.9 × 10 −4 Hz. Substituting statistical results of number of solitons in a packet into the fission law, we find that the upper and the lower edges of the shelf break are the primary and the secondary generation sources of internal solitons, respectively. This reveals that the sharp change in the bottom topography is a key condition for the soliton fission or disintegration. Calculations show that the group period of solitons is 12.5 hours coinciding with that of local semidiurnal tides. This fact confirms that the tides are a dominant generation force for internal solitons on the continental shelf.