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Origin and Acceleration of Suprathermal Ions

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1 Origin and Acceleration of Suprathermal Ions
PSP-SWG Meeting October 2-6, 2017 Mihir I. Desai Southwest Research Institute San Antonio, Texas

2 Outline What are suprathermal particles? Why are they important?
Spectral Properties Composition and Sources Major theoretical concepts Summary PSP/SoLO Opportunities Biggest Explosions (in tons of TNT equivalent) Conventional TNT 3.8x103 Atomic bomb (Hiroshima) 1.3x104 Hydrogen bomb 2x107 Tunguska event (1908) 1x107 Mount Pinatubo (1991) 7x107 Largest earthquake (Chile 1960) 3x109 Asteroid that wiped out dinosaurs 1014 Comet Shoemaker-Levy 9 on Jupiter 1014 Largest solar flare 1016 Top right: Flare/CME eruption on July 11, Angstrom 500,000 to 2,000,000 K. This sequence of extreme ultraviolet images shows brightening and expansion of coronal loops accompanied by a violent ejection of material away from the Sun's surface. A bubble of hot, ionized gas or plasma as well as cooler, dark filamentary material, erupts from the solar corona and travels through space at a high speed. The cross-shaped pattern at the peak of the loop brightening is an artifact of the instrument response rather than a feature on the Sun. Bottom left: Flare/CME eruption on July 11, Angstrom 4,000 to 10,000 K. This sequence of ultraviolet images shows the the same CME/flare event as seen in the chromosphere. The dark region at the center of the activity is a sunspot. Image Credits: NASA/TRACE:

3 What are Suprathermal Ions?
Solar wind Ions, Pickup ions, and suprathermal ion tails SW ions: high density, Maxwellian, bulk SW speed PUIs; ~0-2 Vsw; ring distributions ST Ions speeds > times bulk SW speed Energy range: ~2-100 keV/nuc. Fisk & Gloeckler, PNAS 2007;104:

4 Why are suprathermal particles important?
Biggest Explosions (in tons of TNT equivalent) Conventional TNT 3.8x103 Atomic bomb (Hiroshima) 1.3x104 Hydrogen bomb 2x107 Tunguska event (1908) 1x107 Mount Pinatubo (1991) 7x107 Largest earthquake (Chile 1960) 3x109 Asteroid that wiped out dinosaurs 1014 Comet Shoemaker-Levy 9 on Jupiter 1014 Largest solar flare 1016 Top right: Flare/CME eruption on July 11, Angstrom 500,000 to 2,000,000 K. This sequence of extreme ultraviolet images shows brightening and expansion of coronal loops accompanied by a violent ejection of material away from the Sun's surface. A bubble of hot, ionized gas or plasma as well as cooler, dark filamentary material, erupts from the solar corona and travels through space at a high speed. The cross-shaped pattern at the peak of the loop brightening is an artifact of the instrument response rather than a feature on the Sun. Bottom left: Flare/CME eruption on July 11, Angstrom 4,000 to 10,000 K. This sequence of ultraviolet images shows the the same CME/flare event as seen in the chromosphere. The dark region at the center of the activity is a sunspot. Image Credits: NASA/TRACE:

5 CME Shocks: SEPs and ESPs
CMEs drive shocks in the corona and the interplanetary medium Accel. Near-SunSEPs Accel. Near-EarthESPs ESP SEP Reames.SSR, 1999

6 Seed Particles for CME shocks
486 CMEs drive shocks in the corona and IP medium Shocks accelerate particles out of the ambient corona or the solar wind Gosling et al., 1981 Continuous distribution from solar wind to MeV energy  SW or quiet SW tail as seed population

7 CME shocks 3He and He+ in ESP events points to multiple suprathermal sources Desai et al., 2001; Kucharek et al., 2003; Allegrini et al. 2008 ULEIS MeV/n. SEPICA MeV/n.

8 He+ & 3He in CIRs Gloeckler et al., 1996 Möbius et al. 2000 Chottoo et al., 2000 Kucharek et al., 2003 Popecki et al., 2012 Mason et al. 2012 He+ 3He PUIs and 3He-rich SEPs are important sources for CIRs

9 Density Variations and SEPs
Large SEP events have higher fluences if the suprathermal ion densities are elevated one day before the SEP event. How does ST variability influence shock acceleration? Mewaldt et al., (2012) Mason et al., 2005 How do you determine the energy release mechanism(s) in solar flares? Observe emissions from the heated plasma Traditional H-alpha, UV, EUV (SOHO, TRACE), soft X-rays (Yohkoh) Reveals magnetic field morphology All energy release processes produce heat. Observe the accelerated particles in space ACE, WIND, SOHO, etc. Many particles do not escape from the Sun Transportation effects modify the information Observe the emissions from the accelerated particles Hard X-rays from electrons, gamma-rays from ions Provides the most direct signature of the energy release mechanism(s) Only stochastic acceleration mechanisms have been able to account for 3He, but they cannot account for the simultaneous enrichments in the heavy and ultra-heavy nuclei.

10 Variability in SEPs Kahler (2001) Mewaldt et al., (2006) CME speed (km/s) Peak intensities and SEP kinetic energies vary by ~3-4 orders of magnitude for a given CME speed and kinetic energy

11 Suprathermal Seed Particles
Rare (tracer) species like flare-accelerated 3He and PU He+ found in ESPs, CIRs, large SEPs, and upstream events CME & CIR shocks accelerate suprathermal (ST) ions with energies >1.5-2 keV/n. Suprathermal origin for 3He, He+, C-Fe in CIRs, CME shocks & large SEPs Mewaldt et al., 2001

12 Spectral Properties of Suprathermal Ions
Biggest Explosions (in tons of TNT equivalent) Conventional TNT 3.8x103 Atomic bomb (Hiroshima) 1.3x104 Hydrogen bomb 2x107 Tunguska event (1908) 1x107 Mount Pinatubo (1991) 7x107 Largest earthquake (Chile 1960) 3x109 Asteroid that wiped out dinosaurs 1014 Comet Shoemaker-Levy 9 on Jupiter 1014 Largest solar flare 1016 Top right: Flare/CME eruption on July 11, Angstrom 500,000 to 2,000,000 K. This sequence of extreme ultraviolet images shows brightening and expansion of coronal loops accompanied by a violent ejection of material away from the Sun's surface. A bubble of hot, ionized gas or plasma as well as cooler, dark filamentary material, erupts from the solar corona and travels through space at a high speed. The cross-shaped pattern at the peak of the loop brightening is an artifact of the instrument response rather than a feature on the Sun. Bottom left: Flare/CME eruption on July 11, Angstrom 4,000 to 10,000 K. This sequence of ultraviolet images shows the the same CME/flare event as seen in the chromosphere. The dark region at the center of the activity is a sunspot. Image Credits: NASA/TRACE:

13 ST tails v-5 spectra ~4-40 VSW in all periodsE-1.5 in diff. intensity
Roll-over above ~40 VSW Gloeckler & Fisk ApJ (2008)

14 1-hr Averages Ions with speeds between ~2-8 Vsw exhibit power-laws with v-3-v-7 Fisk & Gloeckler (2012) SSR.

15 Spectral Indices Time-series of spectral indices Ions with speeds between ~2-8 Vsw exhibit power-laws with v-3-v-7 Fisk & Gloeckler (2012) SSR.

16 Histograms Power-laws with mean v-4.5
Index shows a broad distribution with ~1-9 Fisk & Gloeckler (2012) SSR.

17 Quiet-times Desai et al., 2006; Dayeh et al., ApJ (2009; 2017)
“Quiet-times” identified using low levels in hourly averaged C-Fe intensities between MeV/n; Dayeh et al 2017; Desai et al., 2006; Dayeh et al., ApJ (2009; 2017)

18 Spectral Properties Fe and O spectra have similar indices at MeV/n Fe spectra are somewhat steeper than O spectra at MeV/n Dayeh et al., (2017);

19 Spectral Indices vs Solar cycle
No clear SC dependence; Fe spectra in SC24 somewhat steeper than SC23 Dayeh et al., (ApJ 2017)

20 Composition and Sources of Suprathermal Ions
Biggest Explosions (in tons of TNT equivalent) Conventional TNT 3.8x103 Atomic bomb (Hiroshima) 1.3x104 Hydrogen bomb 2x107 Tunguska event (1908) 1x107 Mount Pinatubo (1991) 7x107 Largest earthquake (Chile 1960) 3x109 Asteroid that wiped out dinosaurs 1014 Comet Shoemaker-Levy 9 on Jupiter 1014 Largest solar flare 1016 Top right: Flare/CME eruption on July 11, Angstrom 500,000 to 2,000,000 K. This sequence of extreme ultraviolet images shows brightening and expansion of coronal loops accompanied by a violent ejection of material away from the Sun's surface. A bubble of hot, ionized gas or plasma as well as cooler, dark filamentary material, erupts from the solar corona and travels through space at a high speed. The cross-shaped pattern at the peak of the loop brightening is an artifact of the instrument response rather than a feature on the Sun. Bottom left: Flare/CME eruption on July 11, Angstrom 4,000 to 10,000 K. This sequence of ultraviolet images shows the the same CME/flare event as seen in the chromosphere. The dark region at the center of the activity is a sunspot. Image Credits: NASA/TRACE:

21 3He from flares Wiedenbeck et al., 2005 Fraction of time 3He present varies with solar activity Constant abundance till 2004 Drops by an order of magnitude in Solar Max Solar Min Desai et al. (2006) Dayeh et al. (2009)

22 Composition vs. Solar Cycle
Desai et al., 2006; Dayeh et al., ApJ (2009; 2017)

23 Summary of key ST properties
Speed Range Spectral Forms Composition ~1-5 Vsw ∝v-5; but 1-hr averages show variability, roll-over at higher speeds N/A ~6-20 Vsw v-4.4-v-6.6, rolls-over at higher speeds: NB: roll-over could affect spectral index at lower energy 3He enhanced in solar max. drops during solar min C/O & Fe/O: CIR/SW-like in solar minimum, SEP-like in solar maximum

24 Major theoretical concepts
Biggest Explosions (in tons of TNT equivalent) Conventional TNT 3.8x103 Atomic bomb (Hiroshima) 1.3x104 Hydrogen bomb 2x107 Tunguska event (1908) 1x107 Mount Pinatubo (1991) 7x107 Largest earthquake (Chile 1960) 3x109 Asteroid that wiped out dinosaurs 1014 Comet Shoemaker-Levy 9 on Jupiter 1014 Largest solar flare 1016 Top right: Flare/CME eruption on July 11, Angstrom 500,000 to 2,000,000 K. This sequence of extreme ultraviolet images shows brightening and expansion of coronal loops accompanied by a violent ejection of material away from the Sun's surface. A bubble of hot, ionized gas or plasma as well as cooler, dark filamentary material, erupts from the solar corona and travels through space at a high speed. The cross-shaped pattern at the peak of the loop brightening is an artifact of the instrument response rather than a feature on the Sun. Bottom left: Flare/CME eruption on July 11, Angstrom 4,000 to 10,000 K. This sequence of ultraviolet images shows the the same CME/flare event as seen in the chromosphere. The dark region at the center of the activity is a sunspot. Image Credits: NASA/TRACE:

25 Two Basic Categories Continuous acceleration processes in IP space produce v-5 or E-1.5 power-law tails Lower-energy portion of material accelerated in multiple CME shocks, SEPs, CIRs etc.,

26 Desai & Giacalone (2016), Living Reviews in Solar and Space Physics

27 Desai & Giacalone (2016), Living Reviews in Solar and Space Physics

28 Summary ST ions above ~2 keV/nucleon are important sources for CME shocks, SEPs, CIRs  Effects on acceleration mechanisms are poorly understood Quiet-time ST ion composition and spectra above ~6xVsw suggest that ST tails are created from a mix of lower-energy material accelerated in CME shocks, SEPs, CIRs etc; Relation between ~v-5 tails between ~1.3-5 Vsw and variable spectra and composition >5 Vsw is unclear Theoretical concepts fall into two basic categories: Continuous acceleration in the corona or IP space could result in v-5 or E-1.5 power-law tails Superposition of lower-energy material accelerated in CME shocks, SEPs, CIRs etc SPP will determine relative contributions wrt distance

29 PSP/SoLO; courtesy, N. Savani
Unprecedented opportunity to distinguish between the two ST origin concepts Cross-calibrate sensors when s/c are close Study ST & SEP origin when s/c along same field lines Use radial alignment to differentiate between local vs. remote sources These new measurements are critical for validating and refining CME shock and SEP acceleration models Biggest Explosions (in tons of TNT equivalent) Conventional TNT 3.8x103 Atomic bomb (Hiroshima) 1.3x104 Hydrogen bomb 2x107 Tunguska event (1908) 1x107 Mount Pinatubo (1991) 7x107 Largest earthquake (Chile 1960) 3x109 Asteroid that wiped out dinosaurs 1014 Comet Shoemaker-Levy 9 on Jupiter 1014 Largest solar flare 1016 Top right: Flare/CME eruption on July 11, Angstrom 500,000 to 2,000,000 K. This sequence of extreme ultraviolet images shows brightening and expansion of coronal loops accompanied by a violent ejection of material away from the Sun's surface. A bubble of hot, ionized gas or plasma as well as cooler, dark filamentary material, erupts from the solar corona and travels through space at a high speed. The cross-shaped pattern at the peak of the loop brightening is an artifact of the instrument response rather than a feature on the Sun. Bottom left: Flare/CME eruption on July 11, Angstrom 4,000 to 10,000 K. This sequence of ultraviolet images shows the the same CME/flare event as seen in the chromosphere. The dark region at the center of the activity is a sunspot. Image Credits: NASA/TRACE:

30 Specific Opportunities: PSP/SoLO
Quiet-times during the early phase (solar minimum) of PSP are ideal for studying continuous acceleration in inner heliosphere and corona Differentiate between continuous vs. discrete sources by comparing with predictions of ST origin/acceleration models Currently very few models predict what PSP/SoLO should observe Need all contenders to provide specific predictions that can be tested using PSP/SoLO observations E.g., if STs are lower-energy populations from discrete events such as flares (e.g., impulsive SEP or nano/picoflares) or CME-driven shocks, then the ST density should increase as PSP/SoLO move inward – could apply Lario’s radial gradient

31 Thank You & Questions

32 Large Gadual SEP Events
3He-enrichments in many large SEPs 3He-enrichments in many large SEPs Large SEP events occur after a ~10 day period during which the suprathermal fluences are elevated Predicting particle properties such as peak intensities, energy spectra, maximum energy extent during the CME-driven shocks has proved to be difficult. One possible reason for this is that the particles available for acceleration - the seed population - by these CME shocks includes solar wind ions and other ions that may be present in the inner heliosphere; it may even include energized particles from earlier events. The range of speeds is larger for CME shocks than for any of the other heliospheric shocks, leading to a wide range of possible energies for the accelerated particles. Image Credit: Mason et al., 1999 Mewaldt et al.2005 AIP conf. proceedings, 525, L133

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