Spatial Evolution of 20 MeV Solar Energetic Proton Events

Kahler, S. W.; Ling, A. G.; Reames, D. V.

doi:10.3847/1538-4357/aca7c0

Cited by 4 publications

(5 citation statements)

References 62 publications

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“…( 2) with σ FL = 35 • , this corresponds to κ φ ∼ (6 • ) 2 /h. Similar values can be obtained from the analysis of four SEP events by Kahler et al (2023) whose linear change rate of ∼10 • /day is equivalent to diffusive rates ∼(5 • ) 2 /h. These values are slightly higher than our results; however, they are of the same order, indicating that turbulence-induced diffusion of SEPs across the mean field, as seen in our simulations, is a possible explanation for the observed evolution of the cross-field extent of SEPs during solar events.…”

Section: Discussionsupporting

confidence: 80%

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Solar energetic particle event onsets at different heliolongitudes: The effect of turbulence in Parker spiral geometry

Laitinen¹,

Dalla²,

Waterfall³

et al. 2023

A&A

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Context. Solar energetic particles (SEPs), accelerated during solar eruptions, are observed to rapidly reach a wide heliolongitudinal range in the interplanetary space. Turbulence-associated SEP propagation across the mean Parker spiral direction has been suggested to contribute to this phenomenon. Aims. We study SEP propagation in turbulent magnetic fields to evaluate SEP spatial distribution in the heliosphere, their path lengths, and the overall evolution of SEP intensities at 1 au. Methods. We use full-orbit test particle simulations of 100-MeV protons in a novel analytic model of the turbulent heliospheric magnetic field, where the turbulence is dominated by modes that are transverse and 2D with respect to the Parker spiral direction. Results. We find that by propagating along meandering field lines, SEPs reach a 60°-wide heliolongitudinal range at 1 au within an hour of their injection for the turbulence parameters considered. The SEP onset times are asymmetric with respect to the location connected to the source along the Parker spiral, with the earliest arrival times being 15° westwards from the well-connected Parker spiral longitude. The inferred path length of the first arriving particles is 1.5−1.8 au within 30° of the well-connected longitude; 20−30% longer than the length of the random-walking field lines, increasing monotonously at longitudes further away; and 30−50% longer than the Parker spiral. The global maximum intensity is reached 15° west from the well-connected longitude an hour after the SEP injection. Subsequently, the SEP distribution broadens, consistent with diffusive spreading of SEPs across the field lines. Conclusions. Our results indicate that magnetic field line meandering can explain rapid access of SEPs to wide longitudinal ranges, as well as several other features of SEP event intensity evolution.

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Section: Discussionsupporting

confidence: 80%

“…This does not preclude that a wide CME source may also be contributing to wide SEP events (e.g. Reames 1999), as well as to shifting the SEP peak intensity (Lario et al 2013;Kahler et al 2023), and to temporally increasing the heliolongitudinal extent of an SEP event (e.g. Kouloumvakos et al 2016).…”

Section: Discussionmentioning

confidence: 99%

Solar energetic particle event onsets at different heliolongitudes: The effect of turbulence in Parker spiral geometry

Laitinen¹,

Dalla²,

Waterfall³

et al. 2023

A&A

View full text Add to dashboard Cite

show abstract

“…For the evolution of the longitudinal standard deviation that follows the form given by Equation ( 2) with σ FL = 35 • , this corresponds to κ φ ∼ (6 • ) 2 /hr. Similar values can be obtained from the analysis of four SEP events by Kahler et al (2023) whose linear change rate of ∼ 10 • /day are equivalent of diffusive rates ∼ (5 • ) 2 /hr. These values are slightly higher than our results, however they are of the same order, indicating that turbulence-induced diffusion of SEPs across the mean field, as seen in our simulations, is a possible explanation for the observed evolution of the crossfield extent of SEPs during solar events.…”

Section: Discussionsupporting

confidence: 80%

“…This does not preclude other suggested mechanisms, such as wide CME source (e.g. Reames 1999) which has been suggested to be the reason for wide SEP events, as well as to shift the SEP peak intensity (Lario et al 2013;Kahler et al 2023), and to temporally increase the heliolongitudinal extent of an SEP event (e.g. Kouloumvakos et al 2016).…”

Section: Discussionmentioning

confidence: 94%

Solar Energetic Particle event onsets at different heliolongitudes: The effect of turbulence in Parker Spiral Geometry

Laitinen¹,

Dalla²,

Waterfall³

et al. 2023

Preprint

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Context. Solar energetic particles (SEPs), accelerated during solar eruptions, are observed to rapidly reach a wide heliolongitudinal range in the interplanetary space. To access these locations, the particles must have either been accelerated at a wide particle source, or propagated across the mean Parker spiral magnetic field. Aims. We study the propagation of SEPs in a new model of heliospheric turbulence which takes the spiral geometry of the average magnetic field into account, to evaluate how this improved description affects the SEP path lengths and the overall evolution of SEP intensities at 1 au. Methods. We use full-orbit test particle simulations of 100-MeV protons in a novel analytic model for turbulent magnetic field in the Parker spiral geometry, where the turbulence is dominated by modes that are transverse and 2-dimensional with respect to the Parker spiral direction. Results. We find that the particles spread along the meandering field lines to arrive at a 60 • heliolongitudinal range at 1 au heliocentric distance within an hour of their injection at the Sun, consistent with the heliolongitudinal extent of the meandering field lines. The SEP onset times are asymmetric with respect to the location connected to the source along the Parker spiral, with westward locations seeing earlier arrival and higher peak intensity. The inferred path length of the first-arriving particles is 1.5-1.7 au, 30-50% longer than the Parker spiral, and 20% longer than the length of the random-walking field lines. Subsequently, the SEP distribution broadens, consistent with diffusive spreading of SEPs across the field lines. Conclusions. Our results indicate that due to the nature of interplanetary turbulence, SEPs can propagate rapidly across the mean Parker Spiral field to arrive at wide range of longitudes, even without a wide particle source. The modelled SEP onset times, the peak intensity and subsequent heliolongitudinal evolution replicate several observed SEP event features. Further studies are be required to investigate the relative importance of interplanetary transport and source size in different turbulence environments.

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“…This lack of dependence on A/Q seems to argue against lateral diffusive transport. Kahler et al (2023) fit the data on 20-MeV protons to hourly Gaussians, showing substantial broadening of the distribution with time, especially on the western flank where the shock expanded across new spiral field lines. However, all of these similar widths and parameters only apply to the largest ≈20% of events that span three spacecraft.…”

Section: Stereo With Wind Ace and Sohomentioning

confidence: 99%

Review and outlook of solar energetic particle measurements on multispacecraft missions

Reames

2023

Front. Astron. Space Sci.

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The earliest evidence of spatial distributions of solar energetic particles (SEPs) compared events from many different source longitudes on the Sun, but the early Pioneers provided the first evidence of the large areas of equal SEP intensities across the magnetically confined “reservoirs” late in the events. More detailed measurements of the importance of self-generated waves and trapping structures around the shock waves that accelerate SEPs were obtained from the Helios mission plus IMP 8, especially during the year when the two Voyager spacecraft also happened by. The extent of the dozen widest SEP events in a solar cycle, which effectively wrap around the Sun, was revealed by the widely separated STEREO spacecraft with three-point intensities fit to Gaussians. Element abundances of the broadest SEP events favor average coronal element abundances with little evidence of heavy-element-enhanced “impulsive suprathermal” ions that often dominate the seed population of the shocks, even in extremely energetic local events. However, it is hard to define a distribution with two or three points. Advancing the physics of SEPs may require a return to the closer spacing of the Helios era with coverage mapped by a half-dozen spacecraft to help disentangle the distribution of the SEPs from the underlying structure of the magnetic field and the accelerating shock.

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Spatial Evolution of 20 MeV Solar Energetic Proton Events

Cited by 4 publications

References 62 publications

Solar energetic particle event onsets at different heliolongitudes: The effect of turbulence in Parker spiral geometry

Solar energetic particle event onsets at different heliolongitudes: The effect of turbulence in Parker spiral geometry

Solar Energetic Particle event onsets at different heliolongitudes: The effect of turbulence in Parker Spiral Geometry

Review and outlook of solar energetic particle measurements on multispacecraft missions

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