Remarkable Similarity Between the Propagation of Whistlers and the Bow Wave of aShip

摘要

It is well known that lightning-generated whistlers propagate along the Earth'smagnetic field lines within a cone that at low frequencies makes an angle of 19 deg 28 min with respect to the local magnetic field. This angle turns out to be exactly the same as the half-angle of the bow wave of a ship in deep water. Both problems are complicated by the fact that the wave propagation is dispersive. In this paper we show that these two seemingly unrelated problems can be understood using the same basic approach, which is to analyze the group velocity direction as a function of the wave normal angle. This approach may have applications to other problems of geophysical interest, such as the bow wave generated by the interaction of an asteroid with the solar wind.