Conveners: M. A. Dayeh (SwRI), R. Bucik (MPS/UG), and C. Salem (UCB) Session # 14 Suprathermal ions and electrons in interplanetary space: Properties and Roles Conveners: M. A. Dayeh (SwRI), R. Bucik (MPS/UG), and C. Salem (UCB)

Science Questions: What are the properties of ST ions and electrons across the heliosphere? 2. What are the observational tracers that enable the identification of ST sources and acceleration processes? 3. How can our understanding of ST population in different space environments help us develop theoretical models to describe ST acceleration? 4. Are there systematic behaviors that characterize ST population? (e.g., function of solar activity; location in the IP medium; trends for particular events). 5. Is there a link between ST ions and ST electrons properties? 6. What is different about the ST population in 3He- and Fe-rich events? 7. What are the implications of understanding the ST population on space weather forecasting?

Suprathermal electrons Session focus Suprathermal ions Suprathermal electrons The goal of our session is to join forces and introduce the ST electron and ion communities. Mewaldt 2001

Scene-setting speakers Mihir Desai (SwRI): Suprathermal ion observations across the heliosphere Linghua Wang (Peking University): Suprathermal electrons in IP space

M. Desai; ST ions = multiple origins What is the suprathermal tail and why it is important Ions at several times the solar wind speed, thought to form the seed material for accelerating shocks Compelling evidence that they come from different sources of different acceleration mechanisms Spectral and abundance properties show trends with the solar cycle Theoretical concepts (i) Continuous acceleration in the corona or IP space, producing ubiquitous power-law tails (ii) Low energy portion of material accelerated in shocks, CIRs, etc. Conclusion: Composition and spectral measurements at several times the SW speed are scarce and much needed  Future upcoming missions likely advance our current understanding

L. Wang; ST electrons = Complex structure What are the properties of ST electrons? Omnipresent Solar wind ST electrons: beaming strahl + isotropic halo + isotropic superhalo. strahl/halo: Kappa distribution, κ Teff ; superhalo : J E-2.4 Solar energetic electrons: closely associated with 3He-rich events Where and how are these ST electrons formed? Solar wind ST electrons: strahl: acceleration by interaction with whistler waves in the corona halo: scattering of strahl electrons by interactions with waves superhalo: escaping nonthermal electrons related to the source region of solar wind, or from stochastic acceleration in the IP medium Solar energetic electrons: -accelerated in smaller flares, or narrow CMEs/jets originating from interchange reconnection; they generate waves that selectively accelerate 3He and heavy ions.

D. Lario; Suprathermal Proton Populations at Shocks The evolution of the suprathermal populations upstream of shocks depends on the shock geometry. Observation capabilities are essential to properly identify the evolution of such particles. The observation of suprathermal particles far upstream occurs in parallel shocks, when the particles can easily escape from the shock vicinity. Suprathermal enhancements upstream of perpendicular shocks are limited to a few minutes prior to the shock arrival or completely absent. Lario et al. [2018] 7

Suggestions based on live discussions: Determining uncertainties is very important when ST spectral indices are presented, because of the low-statistics that pose a serious concern. A suggestion came along for revisiting the ULYSSES/SWICS data. This would enable studying ST population during pure fast SW times at high latitudes. The upstream spectrum of a shock is not always representative of the seed population, velocity dispersion and elimination of the foreshock particles is important before calculating such spectrum.

What are the properties of ST ions and electrons across the heliosphere? Spectral indices do not exhibit v-5 behavior on shorter (~hr) timescales and above ~6*Vsw 2. What are the observational tracers that enable the identification of ST sources and acceleration? Composition >6*Vsw reflects CIRs or SEPsOrigin is low-energy portion of accelerated particles 3. How can our understanding of ST population in different space environments help us develop theoretical models to describe ST acceleration? Need two-step processes; Step 1: inject and accelerate ST ions above Vsw into the ST regime and then into diffusive shock acceleration processes Factors: higher speed ST ions can cross the shock; ST distributions are nearly isotropic 4. Are there systematic behaviors that characterize ST population? (e.g., function of solar activity; location in the IP medium; trends for particular events). Composition >6*Vsw is CIR-like during solar minimum and SEP-like during solar maximum 5. Is there a link between ST ions and ST electrons properties? Needs further investigation 6. What is different about the ST population in 3He- and Fe-rich events? The seed population is most likely enriched in 3He and heavy ions (Mason & Klecker 2018) 7. What are the implications of understanding the ST population on space weather forecasting? Incorrect seed populations likely leads to unreliable predictions of SEP occurrence and intensity