Evolution of the Earth's Ring Current during Geomagnetic Storms
Type of Degreethesis
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We examine the evolution of the ring current during the main and early recovery phases of five geomagnetic storms, three driven by co-rotating interaction regions (CIRs) in the solar wind and two driven by interplanetary coronal mass ejections (ICMEs), also known as solar flares. The equatorial energy density profiles of 5–65 keV ions are calculated from deconvolved energetic neutral atom (ENA) images from the Two Wide-Angle Imaging Neutral-Atom Spectrometers mission. The energy density in the ring current is enhanced by almost a factor of 2 and stretches from post-midnight to dusk immediately following injections identified by in situ measurements and increases in the auroral electrojet index. The energy density then drops back to pre-injection levels within 1–2 h. We also find that, for CIR-driven storms, there are often two peaks in the energy density following the injection, one at midnight and one close to dusk. We present the spectra for these peaks to show they contain different ion populations. For the ICME-driven storms, only one peak is observed in the energy density near midnight. For all storms in this thesis, the equatorial peak in energy density is thought to be mostly observed through low altitude emissions, owing to the higher geocoronal density at lower altitude. To better quantify where the peak in the ion distribution is being observed in the ENA images, we also show the equatorial pitch angle anisotropy in the ions for the ICME-driven storms. For both the CIR and ICME-driven storms, the asymmetry of the ring current observed is found to agree with previous in situ and simulation studies.