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Solar Longitude Distribution of High-energy Proton Flares : Fluences and Spectra

Cliver, E. W. ; Mekhaldi, F. LU and Muscheler, R. LU orcid (2020) In Astrophysical Journal Letters 900(1).
Abstract

The distribution of the longitudes of solar flares associated with the high-energy proton events called ground level events (GLEs) can be approximated by a Gaussian with a peak at ∼W60, with a full range from ∼E90 to ∼W150. The longitudes of flares associated with the top third (24 of 72) of GLEs in terms of their >430 MeV fluences (F 430) are primarily distributed over E20-W100 with a skew toward disk center. This 120 span in longitude is comparable to the latitudinal spans of powerful coronal mass ejections (CMEs) from limb flares. Only 5 of 24 strong GLEs are located within the W40-80 zone of good magnetic connection to Earth. GLEs with hard spectra, i.e., a spectral index SI30/200(= log(F 30/F 200)) < 1.5, also tend to avoid... (More)

The distribution of the longitudes of solar flares associated with the high-energy proton events called ground level events (GLEs) can be approximated by a Gaussian with a peak at ∼W60, with a full range from ∼E90 to ∼W150. The longitudes of flares associated with the top third (24 of 72) of GLEs in terms of their >430 MeV fluences (F 430) are primarily distributed over E20-W100 with a skew toward disk center. This 120 span in longitude is comparable to the latitudinal spans of powerful coronal mass ejections (CMEs) from limb flares. Only 5 of 24 strong GLEs are located within the W40-80 zone of good magnetic connection to Earth. GLEs with hard spectra, i.e., a spectral index SI30/200(= log(F 30/F 200)) < 1.5, also tend to avoid W40-80 source regions. Three-fourths of such events (16 of 21) arise in flares outside this range. The above tendencies favor a CME-driven shock source over a flare-resident acceleration process for high-energy solar protons. GLE spectra show a trend, with broad scatter, from hard spectra for events originating in eruptive flares beyond the west limb to soft spectra for GLEs with sources near central meridian. This behavior can be explained in terms of: (1) dominant near-Sun quasi-perpendicular shock acceleration of protons for far western (>W100) GLEs; (2) quasi-parallel shock acceleration for well-connected (W40-80) GLEs, and (3) proton acceleration/trapping at CME-driven bow shocks from central meridian (E20-W20) that strike the Earth.

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author
; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Astrophysical Journal Letters
volume
900
issue
1
article number
L11
publisher
IOP Publishing
external identifiers
  • scopus:85091102028
ISSN
2041-8205
DOI
10.3847/2041-8213/abad44
language
English
LU publication?
yes
id
7332bd3c-33f7-4f5f-9c0d-60d562945ed4
date added to LUP
2021-01-08 12:43:05
date last changed
2022-04-26 23:08:37
@article{7332bd3c-33f7-4f5f-9c0d-60d562945ed4,
  abstract     = {{<p>The distribution of the longitudes of solar flares associated with the high-energy proton events called ground level events (GLEs) can be approximated by a Gaussian with a peak at ∼W60, with a full range from ∼E90 to ∼W150. The longitudes of flares associated with the top third (24 of 72) of GLEs in terms of their &gt;430 MeV fluences (F 430) are primarily distributed over E20-W100 with a skew toward disk center. This 120 span in longitude is comparable to the latitudinal spans of powerful coronal mass ejections (CMEs) from limb flares. Only 5 of 24 strong GLEs are located within the W40-80 zone of good magnetic connection to Earth. GLEs with hard spectra, i.e., a spectral index SI30/200(= log(F 30/F 200)) &lt; 1.5, also tend to avoid W40-80 source regions. Three-fourths of such events (16 of 21) arise in flares outside this range. The above tendencies favor a CME-driven shock source over a flare-resident acceleration process for high-energy solar protons. GLE spectra show a trend, with broad scatter, from hard spectra for events originating in eruptive flares beyond the west limb to soft spectra for GLEs with sources near central meridian. This behavior can be explained in terms of: (1) dominant near-Sun quasi-perpendicular shock acceleration of protons for far western (&gt;W100) GLEs; (2) quasi-parallel shock acceleration for well-connected (W40-80) GLEs, and (3) proton acceleration/trapping at CME-driven bow shocks from central meridian (E20-W20) that strike the Earth. </p>}},
  author       = {{Cliver, E. W. and Mekhaldi, F. and Muscheler, R.}},
  issn         = {{2041-8205}},
  language     = {{eng}},
  number       = {{1}},
  publisher    = {{IOP Publishing}},
  series       = {{Astrophysical Journal Letters}},
  title        = {{Solar Longitude Distribution of High-energy Proton Flares : Fluences and Spectra}},
  url          = {{http://dx.doi.org/10.3847/2041-8213/abad44}},
  doi          = {{10.3847/2041-8213/abad44}},
  volume       = {{900}},
  year         = {{2020}},
}