Acceleration of Energetic Ions in Corotating Interaction Region near 1.5 au: Evidence from MAVEN

Abstract

The dearth of observations between 1 AU and 3 AU limits our understanding of energetic particle acceleration processes in interplanetary space. We present the first-of-their-kind observations of the energetic particle acceleration in a Corotating Interaction Region (CIR) using data from two vantage points, 1 AU (near Earth) and 1.5 AU (near Mars). The CIR event of June 2015 was observed by the particle detectors aboard the Advanced Composition Explorer (ACE) satellite as well as the SEP (Solar Energetic Particle) instrument aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft situated near 1.5 AU. We find that a CIR shock can accelerate a significant number of particles even at 1.5 AU. During this event the acceleration by the shocks associated with the CIR could cause an enhancement of around two orders of magnitude in the SEP energetic ion fluxes in the ∼500 keV to 2 MeV range when the observations near 1 and 1.5 AU are compared. To demonstrate the differences between SEP acceleration in CIR and other impulsive events, we show the energetic ion flux observations during an intense CME period in March 2015, in which case the enhanced SEP fluxes are seen even at 1 AU. These observations provide evidence that CIR shock can accelerate particles in the region between Earth and Mars, that is, only within the short heliocentric distance of 0.5 AU, in interplanetary space.

On the response of Martian Ionosphere to the Passage of a Corotating Interaction Region: MAVEN Observations

“…The CIR shock accelerated a significant number of particles at 1.5 AU, which are detected as enhanced flux of SEP ions [Thampi et al, 2019]. These enhanced energetic particles and CIR-associated magnetic field compressions could significantly affect the topside ionosphere of Mars, and the topology of Mars-solar wind interaction.…”

“…The images of coronal hole in May, June, and July are shown in Figure 7 of Lee et al (2017). The CIR associated with the coronal hole triggered a moderate geomagnetic storm on 7 June 2015, and a minor geomagnetic storm on 4 July 2015 at Earth (Lee et al, 2017) see Figure 4d of Lee et al, 2017 and Figure 6 of Thampi et al, 2019). Figures 1a-1d shows the solar wind density, dynamic pressure, velocity, and IMF (|B|, B x , B y , and B z ) conditions during 16 to 24 June 2015.…”

“…Also the magnetic sector switches from (−B x , +B y ) to (+B x , −B y ), and B z oscillates from positive to negative to positive (Figure 1d). The SEP ion enhancement is studied in detail in comparison with the observations at 1 au to understand the acceleration of particles associated with CIR events (Thampi et al, 2019). The peak enhancements in upstream solar wind parameters was observed on 22 June 2015, 16:45 UTC when the compression region (peak density, dynamic pressure, and magnetic field) arrived at ∼1.5 au.…”

“…The CIR event was associated with enhanced solar energetic particle (SEP) fluxes, with the arrival of SEP ions from 22 June 2015, 18:00 UTC (Figure 2c) and SEP electrons from 21 June 2015, 14:00 UTC (Figure 2d). The SEP ion enhancement is studied in detail in comparison with the observations at 1 AU to understand the acceleration of particles associated with CIR events (Thampi et al [2019], manuscript submitted to ApJL). The SEP electron flux increased from ∼ 10 2 to > 10 3 keV/[keV cm 2 sr s] with a corresponding order of magnitude increase in energy.…”

Recurrent Solar Energetic Particle Flux Enhancements Observed near Earth and Mars

“…It is interesting to see that a very weak CME could enhance SEPs to a significant level. The peak of these enhancements are only approximately an order of magnitude lower than the SEP event during March 2015 which is considered to be a major CME event observed at Mars by MAVEN (Jakosky et al 2015;Thampi et al 2019). Other minor enhancements in solar wind parameters and energetic particle flux during the period could be due to the transient fast solar wind and accelerated population of interplanetary/solar wind particles (Prinsloo et al 2019).…”