Ultrafast Kelvin wave variations in the surface magnetic field

The simulated daytime UFKW-driven meridional magnetic perturbations dBn (similar to +/- 5 nT) (or zonal currents) between about 5 degrees and 20 degrees magnetic latitude in each hemisphere are opposite in sign to those equatorward of +/- 5 degrees and produced by the equatorial electrojet (EEJ), with the directions on any given day determined by the phase of the UFKW as it propagates eastward with respect to the sunlit ionosphere.

Since the nominal daytime Sq zonal current between similar to +/- 30 degrees is uniformly eastward flowing, the present results are consistent with the hypothesis that the EEJ is part of a local current vortex with oppositely directed currents near the equator versus those between 5 degrees and 20 degrees at low latitudes. UFKWs are a special wave type wherein meridional winds are relatively small, which leads to our finding that the EEJ dBn constitutes a simple quantitative proxy for E-region UFKW neutral winds near the 107-km peak height of the Hall conductivity, including the variable wave period of the UFKW packet.