The role of interplanetary shocks in the longitude distribution of solar energetic particles

Abstract

A study of solar proton events with well‐identified sources has been carried out using data from Goddard particle experiments on IMPs 4, 5, 7, and 8 and ISEE 3. The experiments cover the energy range from about 1 to 300 MeV. The 235 events of our study represent approximately 70% of all increases above 10−3 particles cm−2 sr−1 s−1 MeVminus;1 at energies > 20 MeV detected in a 19.7‐year period commencing mid‐May 1967. It is shown that intensity‐time profiles of solar proton events display an organization with respect to heliolongitude. Whilst it has been known for many years that the profile of a proton event depends on the longitude of the solar event relative to the observer, we suggest that the major controlling agent is the existence of an interplanetary (IP) shock. Furthermore, we explain the change in shape as a function of heliolongitude within the framework of a recently derived model for the large‐scale structure of IP shocks. In particular, the long delay to maximum intensity for far eastern events (a property previously ascribed to coronal processes) and the overall extended duration can be accounted for by IP shock acceleration and continued magnetic connection to the shock even after it has propagated beyond 1 AU.

The Acceleration of High-energy Protons at Coronal Shocks: The Effect of Large-scale Streamer-like Magnetic Field Structures

“…A key issue that is not well known is the primary acceleration region along the CME shock where most of highenergy particles are produced. While several studies have shown that the large gradual SEP events can be understood under the assumption that the shock nose is the main source of energetic particles (e.g., Cane et al 1988;Reames et al 1997;Reames 1999), some other studies have suggested that the shock flank can provide the majority of energetic particles (e.g., Kahler 2016). We note here that the role of magnetic field configuration is of great importance for determining the primary acceleration region.…”

Solar Energetic Particles (SEP) and Galactic Cosmic Rays (GCR) as tracers of solar wind conditions near Saturn: Event lists and applications

“…This time delay (∆ t) can be up to about 127 5 days at 1 AU (Cane et al, 1988). The SEP intensity peaks impulsively 128 soon after the onset since connection to the shock region has a short duration 129 and/or because the observer gets gradually connected to weaker parts of the 130 shock.…”

“…and Cane et al (1988), provides useful insights on the different ways SEPs 120 may reach an observer, despite being based on observations at 1 AU.…”

“…The schematic is based on Reames (1999) and Cane et al (1988) from observations in the inner heliosphere. The dotted vertical line indicates when the ICME shock passes the observer.…”

Probing the magnetic topology of coronal mass ejections by means of Ulysses/HI-SCALE energetic particle observations

“…According to Cane et al (1988), an abrupt decrease in the particle¯uxes is expected to be observed as the spacecraft enters the CME. However, on the contrary, in March 1991, an enhancement is observed at the onset of the ®rst CME and no variation in the particle¯ux is observed for the second CME.…”