The fair weather atmospheric electrical current (Jz) couples the ionosphere to the lower atmosphere and thus provides a route by which changes in solar activity can modify processes in the lower troposphere. This paper examines the temporal variations and spectral characteristics of continuous measurements of Jzconducted at the Wise Observatory in Mitzpe-Ramon, Israel (30°35′ N, 34°45′ E), during two large CMEs, and during periods of increased solar wind density. Evidence is presented for the effects of geomagnetic storms and sub-storms on low latitude Jzduring two coronal mass ejections (CMEs), on 24-25th October 2011 and 7-8th March 2012, when the variability in Jzincreased by an order of magnitude compared to normal fair weather conditions. The dynamic spectrum of the increased Jzfluctuations exhibit peaks in the Pc5 frequency range. Similar low frequency characteristics occur during periods of enhanced solar wind proton density. During the October 2011 event, the periods of increased fluctuations in Jzlasted for 7 h and coincided with fluctuations of the inter-planetary magnetic field (IMF) detected by the ACE satellite. We suggest downward mapping of ionospheric electric fields as a possible mechanism for the increased fluctuations.
Bibliographical noteFunding Information:
The authors would like to thank the Wise Observatory, and to Boris Shirman from Israel Survey for supplying Bar Giora magnetic DC data. ACE IMP, proton flux and solar wind proton density data was obtained from NOAA SWPC. KAN acknowledges an Early Career Fellowship from the Leverhulme Trust. This research was supported by the Israeli Science Foundation (Grant No. 423/14). The editor thanks Michael Rycroft and two anonymous referees for their assistance in evaluating this paper.
© G. Elhalel et al., Published by EDP Sciences 2014.