LASCO C2 Jan 24, 2006, www image Future progress understanding Solar Energetic Particles Glenn Mason, JHU/APL 10th RHESSI Workshop Annapolis, MD August 5, 2010

work cited here from: Spiro Antiochos Hilary Cane Eileen Chollet Christina Cohen Mihir Desai Richard DeVoreJ Jim Drake Joe Giacalone George Gloeckler Dennis Haggerty Steve Kahler Judy Karpen Säm Krucker Gang Li Bob Lin Joe Mazur Dick Mewaldt Nariaki Nitta Chee Ng Vahé Petrosian Monique Pick Don Reames Ed Stone Alan Tylka Linghua Wang Y. -M. Wang Mark Wiedenbeck

SEPs - scientific importance: Solar energetic particle studies are: of broad interest due to their relevance to the question, “how are charged particles accelerated and transported?” of particular interest due to their impact on Earth and space systems This priority consistently reflected in Heliophysics community planning: 2003 Decadal survey: Solar Probe, multispacecraft Heliospheric Mission, Sentinels, L1 Monitor, and Solar Orbiter 2009 Heliophysics Roadmap: SEPAT notional mission (STP #6)

Examples of recent progress: Large, shock associated SEP events: 1) role of suprathermal seed population suprathermal tail continuously present contains SEP 3 He most of the time 3He is often reaccelerated in IP shocks

Examples of recent progress: Large, shock associated SEP events: 2) role of shock acceleration 10,000  particle intensities correlate with CME speed but with huge spread observed spectral index not well fitted by shock compression parameters but particle spectra DO correlate with upstream ambient suprathermals ! correlation with source longitude

Examples of recent progress: Large, shock associated SEP events: 3) spectral “breaks” as clues to acceleration process in large SEP events spectra typically roll over between 1-10 MeV/n for different species such as C and Fe, this usually leads to changes in relative abundance these changes may be clues to the geometry of the accelerating shock

Examples of recent progress: Large, shock associated SEP events: 4) untangling transport from acceleration Different SEP species show diferent time- intensity profiles leading to abundance variations during the event Comparing species such as Fe and O at different energies often organizes the data by removing most abundance variations same en/nuc O at 2x Fe en/nuc changing this factor ~8 variation to this:

Examples of recent progress: 3 He-rich SEP events: 1) extremely common! Coordinated measurements link the energetic particles to type III bursts and jets at the Sun good correlation between 3He-rich events and impulsive electron events, both correlate with solar activity cycle; microflares? role in coronal heating?

Examples of recent progress: 3 He-rich SEP events: 2) onset timing of events -- delays from type III burst velocity dispersion in electron onsets allows timing comparison with type III bursts some electron releases coincide with type III burst some electron releases delayed up to ~1/2 hour ion release may also be delayed compared to electron release

Examples of recent progress: 3 He-rich SEP events: 3) unique 3 He spectra; presence of UH nuclei to 220 amu 3 He spectral form is often different from other species below ~1 MeV/nuc, leading to large energy dependence on the 3 He/ 4 He ratio; consistent with resonant acceleration of 3He due to unique M/Q ratio UH nuclei are present in these events with enrichments of ~several hundred to thousands; sometimes enrichment is greater than 3 He; continuous range of UH M/Q ratios argues against resonance mechanism in acceleration

Examples of recent progress: 3 He-rich SEP events: 4) associated coronal activity: these injections of SEP 3 He were associated with western hemisphere jets however, most 3 He-rich SEP events cannot be associated with any event on the Sun; in He events were observed during periods when there were no sunspots in the western hemisphere

Examples of recent progress: advanced theory and more complete models are critical for interpretation and handling of sparse data sampling: CME liftoff resonant acceleration fully 3D SEP transport anisotropy modeling acceleration by magnetic reconnection can enhance heavy ion abundances

Key reasons for advances in experimental SEP studies: high resolution, high sensitivity measurements open new areas measurement of spectra over a broad energy range to allow discrimination of shapes; sensitive probing of suprathermal ion pool heavy ions coverage of multiple ion species to test M/Q dependence SEP ionization state measurements to high energies availability of key supporting data -- plasma and field data, including SW composition & charge states remote sensing data: SOHO, RHESSI, TRACE, SDO multipoint viewing: STEREO (full potential not realized) availability of key data sets on www facilitates interdisciplinary work availability of advanced theory & models to capture more of the physics

Example questions for this science target are: How is variability in the intensity, spectrum, and composition of the suprathermal seed population reflected in high-energy SEPs? How do solar energetic particles reach a wide range of heliospheric longitudes and latitudes and what are the time scales involved? How does the three-dimensional distribution of energetic electrons, various elements, and their ionic charge states evolve in the heliosphere? Do multiple acceleration mechanisms, including shock acceleration associated with fast CMEs and stochastic acceleration in flares, contribute to large SEP events seen at 1 AU? What is the importance of diffusive shock acceleration? Where are particles accelerated and released from solar flares? What are the roles of waves, turbulence, and electric fields for particle acceleration? from 2009 Heliophysics roadmap

Typical measurements: Measurements over a range of spatial and temporal scales could include: Energetic particle intensity, anisotropy, composition, and charge state. Solar radio observations. Solar wind and interplanetary magnetic field. Coronal x-ray imaging/timing. Note that this is not a prioritized or complete list from 2009 Heliophysics roadmap

Assets available: first half of Decadal Study period ( ): STEREO, SDO, ACE (?), Wind (?) SMEX missions? second half of Decadal Survey period ( ): Solar Orbiter Solar Probe STEREO? SDO? new L1 mission with high quality instruments? other SMEX or STP missions?

Earth

Solar Orbiter Solar Probe radial distances of the inner heliosphere missions Solar Orbiter will eventually survey up to ~35° solar latitude

Solar Orbiter & Solar Probe will carry out joint observations from complementary vantage points

By going close to the Sun with a full complement of modern instruments, SO and SPP will explore the inner heliosphere to: sample large SEP events timing 10-20x better accuracy than possible at 1 AU, allowing precise correlation with solar activity and testing of M/Q dependence of acceleration mechanisms probe shock acceleration processes close to the Sun, and possibly sample the SEP shock acceleration region itself probe acceleration at the Sun with gamma-ray and neutron measurements measure hundreds - thousands of impulsive 3 He-rich events including UH nuclei, to probe acceleration mechanism low in the corona survey the inner heliospheric suprathermal ion pool, the likely source for many SEPs probe scattering and transport properties close to the Sun where particle transport is likely to be nearly scatter-free, and decisive tests for motion across field lines are possible

What new investigations could greatly improve the science return during the SO and SPP era? “Imagine trying to monitor Earth’s oceans with a small number of buoys. You’d miss a lot. That’s the situation we’re in now with the ‘ocean of space.’ ” --- Lika Guhathakurta, quoted in Space News, July 24, 2010

Capable measurements from L1 are a must for SEP studies, as well as magnetospheric studies; including fields, particles, radio, EUV, x-rays, etc. In the inner solar system, we need to survey large scale features with multiple spacecraft, either: medium mission (Sentinels), or Explorer mission (e.g. Helix)