Solar Energetic Particle Events of July 2017: Multi-spacecraft
Observations near 1 and 1.5 au
Abstract
We investigate the space weather events of late solar cycle 24 in July
2017 observed by a number of spacecraft in the inner heliosphere widely
separated in heliolongitude and radial distance. These include
spacecraft at L1 point, STEREO-A, near Earth satellites, and MAVEN (near
Mars). The GRASP payload onboard Indian GSAT-19 satellite provides a new
vantage point for Solar Energetic Particle (SEP) observations near
Earth. There were two major Coronal Mass Ejections (CMEs) and one Stream
Interaction Region (SIR) event in July 2017. The 16 July CME was Earth
directed and the 25 July CME was STEREO-A and Mars directed. Earth and
Mars were on the opposite sides of the solar disk, while Mars and
STEREO-A were aligned with respect to the nominal Parker spiral field.
The 25 July event was more stronger and wider in heliolongitude. This
CME shock had magnetic connectivity to Earth, which produced an SEP
event at Earth ~two days later. The spectral indices of
the event observed directly at STEREO-A and remotely at ACE was found to
be similar. The 17 July SIR event was observed by both MAVEN and
STEREO-A. Higher particle intensities (a factor of 6 enhancement for 1
MeV ions) are observed by MAVEN (at 1.58 au) compared to STEREO-A (at
0.96 au). Also a spectral hardening is observed while comparing the
spectral indices at these two locations, indicating an acceleration of
energetic ions in SIR shock during the radial propagation of 0.62 au in
the interplanetary space.