The driving mechanisms of particle precipitation during the moderate geomagnetic storm of 7 January 2005

Abstract

Abstract. The arrival of an interplanetary coronal mass ejection (ICME) triggered a sudden storm commencement (SSC) at ∼09:22 UT on the 7 January 2005. The ICME followed a quiet period in the solar wind and interplanetary magnetic field (IMF). We present global scale observations of energetic electron precipitation during the moderate geomagnetic storm driven by the ICME. Energetic electron precipitation is inferred from increases in cosmic noise absorption (CNA) recorded by stations in the Global Riometer Array (GLO-RIA). No evidence of CNA was observed during the first four hours of passage of the ICME or following the sudden commencement (SC) of the storm. This is consistent with the findings of Osepian and Kirkwood (2004) that SCs will only trigger precipitation during periods of geomagnetic activity or when the magnetic perturbation in the magnetosphere is substantial. CNA was only observed following enhanced coupling between the IMF and the magnetosphere, resulting from southward oriented IMF. Precipitation was observed due to substorm activity, as a result of the initial injection and particles drifting from the injection region. During the recovery phase of the storm, when substorm activity diminished, precipitation due to density driven increases in the solar wind dynamic pressure (P dyn ) were identified. A number of increases in P dyn were shown to drive sudden impulses (SIs) in the geomagnetic field. While many of these SIs appear coincident with CNA, SIs without CNA were also observed. During this period, the threshold of geomagnetic activity required for SC driven precipitation was exceeded. This implies that solar wind density driven SIs occurring during storm recovery can drive a different response in particle precipitation to typical SCs.

Pc5 geomagnetic pulsations, pulsating particle precipitation, and VLF chorus: Case study on 24 November 2006

“…[25] The mechanism for the enhancement and modulation of particle precipitation by the variations of the SW dynamic pressure was recently discussed by Longden et al [2007] applying to the variations of the riometer absorption during moderate magnetic storm. Moreover, the statistical results, obtained by Spanswick et al [2005], suggest there is a localized region in the pre-noon magnetosphere where Pc5 band ULF activity can modulate high-energy electron precipitation, and a necessary condition for the pulsations observed by riometer is magnetic pulsations.…”

Analysis of NOAA particle data and correlations to seismic activity

“…On 27 December 2004, at 21:30:26.5 UT, a giant hard X-ray/g ray flare, near the solar zenith, ionized the exposed part of Earths dayside ionosphere (Inan et al, 2007c). We stopped at the end of December 2004, since the month of January 2005 was perturbed by several ionospheric phenomena (Longden et al, 2007) which were associated with at least seven moderate or weak storms (Tverskaya et al, 2006). Days with high solar activity were excluded when we searched for any possible connection with seismic events and were labeled in grey in all the figures here.…”

Dropouts of the outer electron radiation belt in response to solar wind stream interfaces: global positioning system observations

“…The SGO network comprises a latitudinal chain of riometers in Finland (e.g. Aminaei et al 2006;Longden et al 2007) with additional instruments in Norway and Svalbard, thus providing good latitudinal coverage with limited longitudinal coverage. We used these data for a superposed epoch analysis of riometer absorption using the timings of SI presented in table 2.…”