Showing papers by "G. M. Simnett published in 2005"
TL;DR: In this paper, the authors present serendipitous observations of a visual phenomenon detected at high altitudes (≥840 km) over the auroral zones and polar caps, which they interpret as localized filamentary structures, viewed from a distance, possibly extending to visible altitudes of 2000 km or higher.
Abstract: [1] The Solar Mass Ejection Imager (SMEI) is a sensitive scanning instrument mounted on the Coriolis satellite that assembles an approximately all-sky image of the heliosphere in red-biased visible light once per orbit. Its lines of sight pass obliquely through the topside ionosphere and magnetosphere. We present serendipitous observations of a visual phenomenon detected at high altitudes (≥840 km) over the auroral zones and polar caps. The phenomenon is observed in two basic forms. The first, and more common, are periods of brief (1–3 min), nearly uniform illumination of the imager's field of view, which we interpret as transits of the satellite through a luminous medium. The second appear as localized filamentary structures, which we interpret as columns of luminous material, viewed from a distance, possibly extending to visible altitudes of 2000 km or higher. More than 1000 occurrences of these phenomena were recorded during the first full year of operations. These observations are well correlated in brightness and frequency with periods of enhanced geomagnetic activity.
31 citations
TL;DR: In this article, the authors measured the energy spectrum of the ambient ions associated with the passage of a fast magnetosonic quasi-perpendicular shock driven by a coronal mass ejection (CME).
Abstract: Recent observations from the $\it Ulysses$ spacecraft (Simnett 2003, Sol. Phys., 213, 387) have measured the energy spectrum of the ambient ions associated with the passage of a fast magnetosonic quasi-perpendicular shock driven by a coronal mass ejection (CME). Near the shock front the energy spectrum of the accelerated ions, which are predominantly protons, exhibits features (maxima) at about 250 keV-1.5 MeV. We show that these are the right order of magnitude for protons which have been accelerated by the surfatron mechanism at a fast magnetosonic shock wave propagating perpendicular to the ambient magnetic field. The in situ measurements therefore illustrate directly that this mechanism could possibly be responsible for interplanetary particle acceleration. The shock is also accompanied by an increase in the near-relativistic electron intensity of almost two orders of magnitude. We present a similar event observed by the ACE spacecraft.
23 citations
TL;DR: The 28 October 2003 solar flare event was one of the largest electron events above 50 keV of the current solar cycle as discussed by the authors, which was associated with a major flare, at least one fast coronal mass ejection (CME), and a prominence eruption.
Abstract: [1] The 28 October 2003 solar flare event was one of the largest electron events above 50 keV of the current solar cycle. The event was associated with a major flare, at least one fast coronal mass ejection (CME), and a prominence eruption. The evolution of the electron spectrum for this event enables us to resolve three, or possibly four, separate electron sources. The source associated with the passage of a fast CME through the corona lasts about half an hour, has a very soft spectrum, and appears at 1 AU as a highly anisotropic beam. The most intense source has a weak outward anisotropy, lasts 2 days before starting a slow decay, and has a hard spectrum. The event is at its most intense around the arrival of the shock which is ahead of the CME, and this is also when the electron spectrum is hardest. One possible interpretation to explain the spectral and angular distribution properties of the electrons from this event is discussed.
15 citations
TL;DR: In this article, a series of nine impulsive, highly collimated beams of nearrelativistic electrons seen by ACE/EPAM on 26 and 27 June 2004 occurred at a quiet time with respect to solar flare and CME production.
Abstract: The series of nine impulsive, highly collimated beams of near-relativistic electrons seen by ACE/EPAM on 26 and 27 June 2004 occurred at a quiet time with respect to solar flare and CME production. However, they were accompanied by decametric type III radio bursts observed by WIND/WAVES, which had progressively higher starting frequencies, suggestive of coronal acceleration. There were no CMEs seen by SOHO/LASCO in association with any of the type III bursts except possibly the first. The energy spectrum of the electrons was soft, typically E−4.5 but extended up to at least ∼200 keV. We suggest that the source region for these events is in the high corona. We discuss this result in the context of solar electron acceleration at other times.
11 citations