Magnetic Remote Sensing of Ocean Flow

It is known that ocean flow generates weak magnetic fields that are detected by land and satellite magnetic observatories, and that there is thereby a potentially important opportunity to develop a new method for the remote sensing of ocean/climate variability. Based on the physical relationship between the magnetic fields and flow sources, it could be argued that in principle this method could become the method of choice for inferring large-scale flow integrals. There are, however, substantial challenges in the practical implementation. We review both the opportunities and challenges in developing this new method of magnetic remote sensing of ocean flow in terrestrial and extra-terrestrial applications. We describe past examples of ocean flow generated magnetic signals associated with swell, ocean tides, tsunamis, and circulation. We discuss the spatio-temporal statistics of ocean flow generated signals and their overlap with other sources in an effort to explain how some oceanic signals are readily identified while others have been illusive. We also present an extraction of tidal magnetic signals using a recent version of the NASA-GSFC/DTU Comprehensive Model of the Earth's magnetic field, and we present an inversion of this signal to produce the global distribution (amplitude and phase) of the Earth's M2 ocean tide. This example of ocean flow (tides, in this case) obtained from magnetic data provides a proof in concept in the terrestrial application which shall be further developed. In extra-terrestrial applications of oceans on icy satellites in the Outer Solar System basic descriptions of the tides are still unavailable and the methods shown may be of more immediate practical application.