Abstract
Using two heliospheric vantage points, we study 22 solar energetic particle (SEP) events, 14 of which were detected at both locations. SEP proton events were detected during the declining phase of solar cycle 23 (November 2003–December 2006) by means of two nearly identical Standard Radiation Environment Monitor (SREM) units in energies ranging between 12.6 MeV and 166.3 MeV. In this work we combine SREM data with diverse solar and interplanetary measurements, aiming to backtrace solar eruptions from their impact in geospace (i.e., from L1 Lagrangian point to Earth’s magnetosphere) to their parent eruptions at the Sun’s low atmosphere. Our SREM SEP data support and complement a consistent inner-heliospheric description of solar eruptions (solar flares and coronal mass ejections [CMEs]) and their magnetospheric impact. In addition, they provide useful information on the understanding of the origin, acceleration, and propagation of SEP events at multi-spacecraft settings. All SEP events in our sample originate from major eruptions consisting of major (>M-class) solar flares and fast (>1800 km/s, on average), overwhelmingly (>78%) halo, CMEs. All but one SEP event studied are unambiguously associated with shock-fronted CMEs, suggesting a CME-driven shock acceleration mechanism. Moreover, a significant correlation is found between the SEP event peak and the onset of the storm sudden commencement, that might help improve prediction of magnetospheric disturbances. In general, SEP events correlate better with interplanetary (i.e., in-situ; L1-based) than with solar eruption features. Our findings support (a) the routine use of cost-effective SREM units, or future improvements thereof, for the detection of SEP events and (b) their implementation in multi-spacecraft settings as a means to improve both the physical understanding of SEP events and their forecasting.
Highlights
The physical processes resulting in solar energetic particle (SEP) events remain controversial to this day
Composition measurements of SEP events are essential to distinguishing impulsive from gradual SEP events (Desai and Burgess 2008, and references therein). Even with such observational evidence at hand, it is often complicated to identify ‘‘flare’’ material in gradual SEP events. This is either because remnant suprathermal particles from previous impulsive events appear as seed particles (Tylka et al, 2005; Klecker, 2013) or because flare accelerated particles get direct access to open magnetic field lines with low-energy particles accelerated by the coronal mass ejection (CME) and high-energy particles originating from the flare location
As we show in this work, this has proved useful in interpreting each event separately
Summary
The physical processes resulting in solar energetic particle (SEP) events remain controversial to this day. Even with such observational evidence at hand, it is often complicated to identify ‘‘flare’’ material in gradual SEP events This is either because remnant suprathermal particles from previous impulsive events appear as seed particles (Tylka et al, 2005; Klecker, 2013) or because flare accelerated particles get direct access to open magnetic field lines with low-energy particles accelerated by the CME and high-energy particles originating from the flare location (for details, see Klecker, 2013, and references therein). Identical instruments at different heliospheric vantage points offer simultaneous measurements of single SEP events, providing us with an important tool for understanding the SEP origin, propagation, and acceleration (Agueda et al, 2012; Lario et al, 2013; Dresing et al, 2014; Lario et al, 2016) In this respect, the European Space Agency’s (ESA) Standard Radiation Environment Monitor (SREM; Bühler et al, 1996; Mohammadzadeh et al, 2003), a heritage instrument with proven, tractable technology, was mounted on several ESA space missions situated in different orbits. The study and findings and offers an outlook on the future utilization of SREM measurements
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