MODEL CALCULATIONS ON SEA TIDAL GENERATION OF ELECTRIC CURRENTS AND MAGNETIC FIELDS

Abstract

Electric currents generated by sea tidal induction flow mainly within the sea, whose electrical conductivity much exceeds that of the land; but the electric potential is not constant over the sea bed, and part of the sea electric current completes its circuit through the land. This paper gives model calculations of the magnetic field of currents in both sea and land, induced by a sea wave system of lunar semidiurnal period in an infinitely long channel with parallel sides whose depth is very small compared with its width. A quarter wave of this motion gives a crude analogy of the English Channel, between Dover-Calais and the Isle of Wight-Cherbourg. The model represents the land by a thin conductor. It appears that, no matter how small the electric currents in the land may be, the presence of the land causes the sign of the vertical component of magnetic field to reverse far inland from the coast. This result is borne out also by calculations for a model with land electric currents in three dimensions. Numerical illustrations are given for parameters corresponding to the English Channel. The case of a blocked channel is also discussed.