A correlation of the ionospheric electric field and the time derivative of the magnetic field was noticed over thirty years ago and has yet to be explained. Here we report on another set of examples during the superstorm of November 2004. The electric field in the equatorial ionosphere, measured with the Jicamarca incoherent scatter radar, exhibited a 3？mV/m electric field pulse that was not seen in the interplanetary medium. It was, however, accompanied by a correlation with the time derivative of the magnetic field measured at two points in Peru. Our inclination was to assume that the field was inductive. However, the time scale of the pulse was too short for the magnetic field to penetrate the crust of the Earth. This means that the area threaded by was too small to create the observed electric field by induction. We suggest that the effect was caused by a modulation of the ring current location relative to the Earth due to the electric field. This electric field is required, as the magnetic field lines are considered frozen into the plasma in the magnetosphere. The closer location of the ring current to the Earth in turn increased the magnetic field at the surface. 1. Introduction In his Ph.D. thesis, Gonzales [1] published Figure 1 using interplanetary and auroral indices, electric field measurements using the incoherent scatter radar (ISR) technique at Chatanika (Alaska) and Jicamarca (Peru), and measured on the ground at San Juan, Puerto Rico. The correlation between the latter three parameters was excellent. The ratio was 50 million meters. Here we report on an extensive set of observations we believe to be of the same type obtained during the superstorm of November 2004 (see [2], and companion papers). Figure 1: From top to bottom: The AU, AL indices; five superposed midlatitude magnetograms (Kakioka, Tashkent, Tangerang, San Juan, Honolulu) with the arrow pointing to the San Juan magnetogram; the zonal electric field at the equator (Jicamarca, Peru); the auroral zonal electric field at College, Alaska; the time derivative of the horizontal component of the magnetic field at San Juan, Puerto Rico. In the last three panels, the dots indicate local magnetic midnight. (After [ 5]. Reproduced with permission of the American Geophysical Union). 2. Data Presentation Various unusual phenomena that occurred in the November 2004 magnetic storm are documented in a series of papers, the first of which summarizes many of the observations from the interplanetary medium to the equatorial ionosphere [2]. The second part of the two-phase storm was monitored by
References
[1]
C. A. Gonzales, Electric fields in the low latitude ionosphere and their relationship to magnetospheric and interplanetary phenomena, Ph.D. thesis, Cornell University, Ithaca, NY, USA, 1979.
[2]
M. C. Kelley, R. R. Ilma, M. Nicolls et al., “Spectacular low- and mid-latitude electrical fields and neutral winds during a superstorm,” Journal of Atmospheric and Solar-Terrestrial Physics, vol. 72, no. 4, pp. 285–291, 2010.
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M. C. Kelley, B. G. Fejer, and C. A. Gonzales, “An explanation for anomalous equatorial ionospheric electric fields associated with a northward turning of the interplanetary magnetic field,” Geophysical Research Letters, vol. 6, pp. 301–304, 1979.
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C. A. Gonzales, M. C. Kelley, R. A. Behnke, J. F. Vickrey, R. Wand, and J. Holt, “On the longitudinal variations of the ionospheric electric field during magnetospheric disturbances,” Journal of Geophysical Research, vol. 88, pp. 9135–9144, 1983.
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