Abstract
Abstract. We present observations of Almost Monoenergetic Ion (AMI) events in the energy range of 100–1200 keV detected with the Solar Electron and Proton Telescope (SEPT) onboard both STEREO spacecraft. The energy spectrum of AMI events contain 1, 2, or 3 narrow peaks with the relative width at half maximum of 0.1–0.7 and their energy maxima varies for different events from 120 to 1200 keV. These events were detected close to the bow-shock (STEREO-A&B) and to the magnetopause at STEREO-B as well as unexpectedly far upstream of the bow-shock and far away from the magnetotail at distances up to 1100 RE (STEREO-B) and 1900 RE (STEREO-A). We discuss the origin of AMI events, the connection to the Earth's bow-shock and to the magnetosphere, and the conditions of the interplanetary medium and magnetosphere under which these AMI bursts occur. Evidence that the detected spectral peaks were caused by quasi-monoenergetic beams of protons, helium, and heavier ions are given. Furthermore, we present the spatial distribution of all AMI events from December 2006 until August 2007.
Highlights
The presence of energetic ions (
Two Almost Monoenergetic Ion (AMI) events streaming from the Sun/antiEarth direction were detected with Solar Electron and Proton Telescope (SEPT)-A at distances 0.27 AU from the Earth and both were associated with the passage of a forward CIR shock
We have presented observations of Almost Monoenergetic Ion (AMI) events containing 1–3 narrow peaks in their energy spectra
Summary
1978), at the libration point (L1) at ∼240 RE (Balogh et al, 1978; Scholer et al, 1981; Klassen et al, 2008), and using STEREO observations far away from the bow-shock at the distances up to 1100 RE (Muller-Mellin et al, 2008a; Desai et al, 2008). Lutsenko and Kudela (1999) first reported observations of 1, 2 or 3 narrow peaks ( E/Emax 0.15÷0.30) in spectra of upstream ion events using observations with the DOK-2 instrument onboard the Interball-1 spacecraft (Lutsenko et al, 1998). The AMI event was detected during 4 successive accumulation craft was not connected to the magnetosphere or to the the bow-shock, but rather to the upstream region (red arrow intimes (4 min) and shows a narrow peak with a maximum at dicates the ecliptic magnetic field component). For comparison the following “normal” ion bursts show a simple power-law spectrum and three-peak events (Fig. 3b and a) on 2 April and 6 March 2007, the distances between STEREO-B and the Earth were 656 RE and 270 RE, respectively and the magnetic field vecwithout the peak structure. This supports the observations of Lutsenko and Kudela (1999) reporting a total absence of energetic electron fluxes exceeding background levels during AMI events
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