FY 1996

Characteristics of a 4-day oscillation trapped by the Juan de Fuca Ridge

Cannon, G.A., and R.E. Thomson

Geophys. Res. Lett., 23, 1613–1616, doi: 10.1029/96GL01370 (1996)

Current meter observations from different studies along the crest of the Juan de Fuca Ridge have been combined to show new features of the relatively large, broad spectral peak centered near a period of about 4 days. The coherence range of the 4-day oscillations has been extended to the extreme ends of the ridge, and the trapped waves appear to propagate northward along the entire length of the ridge at about 1 m/s. Spectral amplitudes are about double on the south end compared to the north end, and a recent model for bottom-trapped subinertial waves over topography shows this may be due to variations in ridge width [Allen and Thomson, 1993]. New observations show coherence between temperatures and currents near the South Cleft vent field and suggest 4-day oscillations can play a major role in the local advection of hydrothermal plumes. These observations combined with earlier results demonstrate that 4-day oscillations are a significant ridge-trapped feature, and they suggest that other ridges may be important in transmitting energy over much longer distances.