PROPAGATION PARAMETERS OF SEA-SURFACE WAVES INFERRED FROM OBSERVATIONS FROM 2 CLOSELY SPACED VECTOR MAGNETOMETERS

The alternating magnetic dynamo field of sea surface waves, a conseque nce of their Lorentz electric field, has been observed with a pair of simultaneously operated, closely spaced tri-axial magnetometers. Measu rements from a magnetometer located in the centre of a tiny, uninhabit ed island served to compensate measurements from a near-shore magnetom eter for magnetic pulsations of ionospheric origin, leaving the water wave dynamo field, effective close to shore only, as the dominant resi dual magnetic field. Amplitude and frequency of waves and swell were r ecorded with a vertical accelerometer (wave rider buoy), floating on t he sea surface. The wave rider data are in good agreement with those o btained from the magnetometers. Amplitude and phase relations between the three vector components of the magnetic oscillations yield a sea s urface wave vector which is consistent with the swell propagation dire ction usually found in that area. The magnetic field data further demo nstrate that the water mass motion close to shore was not confined to a vertical plane (as would be the case for freely propagating gravity waves in the open ocean). The motion rather took place in a plane incl ined at about 40 degrees from the horizontal, which is roughly twice t he inclination of the island flanks. We conclude that the magnetometer measurements yield a reasonably accurate description of the surface w ave water motion within about one wavelength from shore.