A Separation of Ionospheric and Oceanic Tidal Components in Magnetic Fluctuation Data

Abstract

Signals at tidal frequencies are observed in magnetic fluctuations recorded along a line of sites spanning the region from inland Australia to the floor of the central Tasman Sea. Assuming the site furthest inland to be free from oceanic tidal effects, the M2 signal at 1.93 cycle. day-1 at each other site along the line is separated into a part due to a tidally-driven ionospheric dynamo, and a part due to a tidallydriven oceanic dynamo. Two factors are crucial to the separation method: the recognition that the ionospheric dynamo produces frequencies (known as the partial tides, and the phase-law tides), not associated with the oceanic dynamo; and the construction and use of an ionospheric induction transfer function, taken to be constant from continent to ocean. The separations thus carried out show that for the deep-ocean sites in the Tasman Sea, the ionospheric dynamo and the oceanic dynamo make comparable contributions to the horizontal fluctuations observed at the frequency of the M2 tide. The vertical fluctuation component at this frequency is almost entirely due to the oceanic dynamo. There is agreement with some features predicted by theoretical models. © 1988, Society of Geomagnetism and Earth, Planetary and Space Sciences. All rights reserved.