Relating the interplanetary-induced electric fields with the low-latitude zonal electric fields under geomagnetically disturbed conditions

Abstract

The overall ionospheric variability with periods ranging from long-term, secular changes to days, hours, and even minutes and seconds, is influenced by the solar activity, geomagnetic activity, and processes originating in the lower atmospheric layers. Using a wavelet transform approach, in this paper, we study the short-term (minutes to hours) and day-to-day variability of the ionospheric low-latitude zonal electric fields (LLZEF) at three longitude sectors, Peruvian, Philippine, and Indian, during time intervals of increased geomagnetic activity and relate the LLZEF variability to changes in the dawn-to-dusk component of the interplanetary electric field (IEF). Continuous Morlet wavelet and cross-wavelet amplitude spectra with reduced and increased frequency resolutions were obtained to analyze and compare the oscillation activity in the LLZEF and IEF spectra, in the 10-min to 10-h and 1.25- to 12-d period ranges. For the 1.25- to 12-d period range, periodicities in the LLZEF spectrum were compared with similar periodicities in the IEF spectrum over 9 February to 9 June 2001, with our wavelet results indicating the geomagnetic activity as an important driver of LLZEF variability in this period range. For the 10-min to 10-h period range, four case studies were examined when concurrent observations of Jicamarca incoherent scatter radar zonal electric field and IEF, as calculated from the ACE satellite solar wind velocity and interplanetary magnetic field data, were available. We show that the wavelet transform represents a powerful tool to study the frequency dependence of the two specific mechanisms of ionospheric electric field variability, which are dominant during geomagnetic storms, namely penetration and disturbance dynamo.