A Study of the Geomagnetic Disturbance Field Asymmetry


  • Nancy Uss Crooker,

  • George L. Siscoe


Hourly averages of the H component of the low-latitude geomagnetic disturbance field are Fourier analyzed to obtain the amplitude G and local-time phase ϕ of the first diurnal harmonic for the one and one-half years of the IGY. The amplitude G is found to correlate roughly with the AE index and, in particular, to exhibit the same storm-time behavior. For major storms, G can exceed 100γ and, in the example shown, exceeds 80γ for an interval of six hours. The phase ϕ tends to be located near 1800 LT, and this characteristic is nearly independent of AE. A comparison of the observed phase and that associated with the usual bay return current suggests a two-component model of the disturbance field asymmetry, with one component at a non-bay orientation. The non-bay component is discussed in terms of possible ionospheric and magnetospheric currents. The second possibility seems to require currents located on the plasmapause to sustain the large forces involved in the asymmetry.