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Solar Energetic Particle Events of July 2017: Multi-spacecraft Observations near 1 and 1.5 AU
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  • C Krishnaprasad,
  • Smitha V Thampi,
  • Christina O. Lee,
  • Srikar P. Tadepalli,
  • K. Sankarasubramanian,
  • Tarun Kumar Pant
C Krishnaprasad
Space Physics Laboratory, Space Physics Laboratory

Corresponding Author:[email protected]

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Smitha V Thampi
Space Physics Laboratory, Space Physics Laboratory
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Christina O. Lee
University of California, Berkeley, University of California, Berkeley
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Srikar P. Tadepalli
URSC, ISRO, URSC, ISRO
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K. Sankarasubramanian
URSC, ISRO, URSC, ISRO
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Tarun Kumar Pant
Vikram Sarabhai Space Centre, Vikram Sarabhai Space Centre
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Abstract

We investigate the solar 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 a Stream Interaction Region (SIR) event in July 2017, which is a period during the deep descending phase of the historically weak solar cycle 24. The 16 July CME was Earth directed and the 24 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 24 July event was stronger and wider in heliolongitude. This CME-driven 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 at the remote location of ACE was found to be similar. The 16 July SIR event was observed by both MAVEN and STEREO-A. Higher particle intensities (a factor of 6 enhancement for 1 MeV protons) 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 proton acceleration at the SIR forward shock during the radial propagation of 0.62 AU in the interplanetary space.