Use of hydromagnetic waves to map geomagnetic field lines

Abstract

Quasi‐periodic oscillations in magnetospheric electric and magnetic fields are communicated to the ionosphere via guided Alfvén waves, propagating along magnetic field lines. Thus, if one could identify ionospheric and magnetospheric regions showing highly correlated temporal variations, one would, in effect, have determined the region in the ionosphere conjugate to a given location in the magnetosphere. In this paper we present a cross correlation analysis of Pc 5 magnetic field oscillations observed by GEOS 2 with drift velocity oscillations (electric field) observed with the STARE radars in the ionosphere. GEOS 2 is in geostationary orbit with its conjugate point nominally located in the STARE field of view. Several comparisons were made over a one hour period in the early afternoon sector and correlation coefficients reaching 0.84 over a limited area in the ionosphere were obtained. Between the beginning and end of the hour, the measured footpoint was displaced by ∼ 1° in latitude and ∼2.5° in longitude. Neither of the two determinations agreed with the predictions of the Mead‐Fairfield or Olson‐Pfitzer models, although the difference at the end of the hour was of the same order as the dispersion between the two models.