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Telescoping in on the Microscopic Origins of the Fast Solar Wind

Telescoping in on the Microscopic Origins of the Fast Solar Wind. Steven R. Cranmer & Adriaan van Ballegooijen Harvard-Smithsonian Center for Astrophysics. Magnetic connectivity of the open field. Cranmer & van Ballegooijen (2005). Fisk (2005). Tu et al. (2005).

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Telescoping in on the Microscopic Origins of the Fast Solar Wind

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  1. Telescoping in on theMicroscopic Origins of theFast Solar Wind Steven R. Cranmer & Adriaan van Ballegooijen Harvard-Smithsonian Center for Astrophysics

  2. Magnetic connectivity of the open field Cranmer & van Ballegooijen (2005) Fisk (2005) Tu et al. (2005)

  3. Is a time-steady approach doomed? • Open-field regions show frequent jet-like events. • Evidence of magnetic reconnectionbetween open and closed fields? • How much of the solar wind is ejected like this? Hinode/SOT: Nishizuka et al. (2008) Antiochos et al. (2011) • Is there enough mass & energy released to heat/accelerate the entire solar wind?

  4. What processes drive solar wind acceleration? • No matter the relative importance of reconnection events, we do know that waves and turbulent motions are present everywhere... from photosphere to heliosphere. • How much can be accomplished by only these processes? (Occam’s razor?) Hinode/SOT SUMER/SOHO G-band bright points UVCS/SOHO Helios & Ulysses Undamped (WKB) waves Damped (non-WKB) waves

  5. Turbulence-driven solar wind models • A likely scenario is that the Sun produces MHD waves that propagate up open flux tubes, partially reflect back down, and undergo a turbulent cascade until they are damped at small scales, causing heating. Z– Z+ Z– (e.g., Matthaeus et al. 1999) • Cranmer et al. (2007) explored the wave/turbulence paradigm with self-consistent 1D models, and found a wide range of agreement with observations (including composition!) Ulysses 1994-1995 (see also, e.g., Suzuki & Inutsuka 2006; Verdini et al. 2010; Usmanov et al. 2011; Matsumoto & Suzuki 2011; Chandran et al. 2012)

  6. Turbulent heating scales with field strength • Mean field strength in low corona: • If the regions below the merging height can be treated with approximations from “thin flux tube theory,” then: • Thus, . . .and the turbulent heating in the low corona scales directly with the mean magnetic flux density there (e.g., Pevtsovet al. 2003; Schwadron et al. 2006; Kojima et al. 2007; Schwadron & McComas 2008).

  7. Increase the complexity of the field . . . • Existing models used low-resolution magnetic fields. What will happen when we solve for the time-steady plasma conditions along higher-resolution field structures (with higher rates of shear, more QSLs, etc.)? 8727 field lines: Δt = 1 min. Δφ = 0.01o Δx on surface = 100 km 1 SOLIS pixel ≈ 800 km Overkill? \Maybe not... SOLIS Vector SpectroMagnetograph on KittPeak + PFSS (Borovsky 2008)

  8. Expectations from flux-tube expansion Wang & Sheeley (1990) found an anticorrelation between flux tube expansion and wind speed at 1 AU . . . low f FAST high f SLOW

  9. Adjusting the field strength Unmodified SOLIS potential fields: Add photospheric component... is it enough? Black curves: Cranmer et al. (2007)

  10. Extremely preliminary results Cranmer et al. (2007) ZEPHYR output ~WS90 scaling ACE SOLIS B-field insufficient coronal heating!?

  11. Do the “flux tubes” survive to 1 AU? • Fast/slow wind stream structure leads to corotating interaction regions (CIRs) and shocks in the heliosphere. • We applied the upwind differencing method of Riley & Lionello (2011) to the empirical u–f relationship. • The finest-scale flux tube variations may be swept away at 1 AU, but SPP & Orbitermay see much higher variances in plasma parameters in the inner heliosphere! r = 20 Rs r = 40 Rs r = 1 AU

  12. Conclusions • There is still a lot that can be done with “time-steady” wave/turbulence models. • Some “spaghetti-like” time variability may be generated from high-resolution lower boundary structure in the magnetic field. (more expected closer to Sun) AIA/SDO • Magnetically complex regions may generate more waves. (ZEPHYR models used identical wave boundary conditions.) • Take into account how turbulence “shreds” flux tubes. • Collisionlesskinetic physics (Tp ≠ Te ≠ Tion) • Confront models with actual data! (present & future) Next steps . . .

  13. extra slides . . .

  14. Cranmer et al. (2007): other results Wang & Sheeley (1990) ACE/SWEPAM ACE/SWEPAM Ulysses SWICS Ulysses SWICS Helios (0.3-0.5 AU)

  15. What is the source of solar wind mass? • Until relatively recently, the dominant idea was that a steady rate of “evaporation” is set by a balance between downward conduction, upward enthalpy flux, and local radiative cooling (Hammer 1982; Withbroe 1988). heat conduction radiation losses • On the other hand, new observations of spiculesand jets (e.g., Aschwanden et al. 2007; De Pontieu et al. 2011; McIntosh et al. 2011) fuel the idea that a lot of the corona’s mass is injected impulsively from below. 5 2 — ρvkT Schrijver (2001)

  16. Controversies about waves & turbulence • Where does the turbulent cascade begin?Chromosphere? Low corona? Some say it doesn’t become “fully developed” turbulence until < 1 AU. ~ In simulations that include flux-tube expansion, complex turbulent motions are induced, even down in the middle chromosphere! (van Ballegooijen et al. 2011) Simple motions input at photospheric lower boundary.

  17. Other questions to address • Coronal heating from MHD turbulence: • Does damping of turbulence produce the right mixture of collisionless kinetic effects? • How can we better constrain the frequency spectrum of waves/turbulence in the corona? (crucial for non-WKB reflection) • Origin of lowest-frequency (1/f) waves seen at 1 AU: • The self-consistent product of a turbulent cascade? • Spacecraft passage through “spaghetti-like” flux tubes rooted on the solar surface? (Borovsky 2008) • Do reconnection/loop-opening events generate enough mass, momentum, & energy to power the solar wind?

  18. How are ions preferentially heated? UVCS results (mainly in coronal holes) have spurred a lot of theoretical work . . . but observations still haven’t allowed the exact mechanisms to be pinned down! • MHD turbulence may have some kind of “parallel cascade” that gradually produces ion cyclotron waves in the corona and solar wind. • When MHD turbulence cascades to small perpendicular scales, the small-scale shearing motions may be unstable to generation of cyclotron waves (Markovskii et al. 2006). • Dissipation-scale current sheets may preferentially spin up ions (Dmitruk et al. 2004). • If MHD turbulence exists for both Alfvén and fast-mode waves, the two types of waves can nonlinearly couple with one another to produce high-frequency ion cyclotron waves (Chandran 2005). • If nanoflare-like reconnection events in the low corona are frequent enough, they may fill the extended corona with electron beams that would become unstable and produce ion cyclotron waves (Markovskii 2007). • If kinetic Alfvén waves reach large enough amplitudes, they can damp via wave-particle interactions and heat ions (Voitenko & Goossens 2006; Wu & Yang 2007). • Kinetic Alfvén wave damping in the extended corona could lead to electron beams, Langmuir turbulence, and Debye-scale electron phase space holes which could heat ions perpendicularly (Matthaeus et al. 2003; Cranmer & van Ballegooijen 2003).

  19. CPI is a large-aperture ultraviolet coronagraph spectrometer that has been proposed to be deployed on the International Space Station (ISS). • The primary goal of CPI is to identify and characterize the physical processes that heat and accelerate the plasma in the fast and slow solar wind. • CPI follows on from the discoveries of UVCS/SOHO, and has unprecedented sensitivity, a wavelength range extending from 25.7 to 126 nm, higher temporal resolution, and the capability to measure line profiles of He II, N V, Ne VII, Ne VIII, Si VIII, S IX, Ar VIII, Ca IX, and Fe X, never before seen in coronal holes above 1.3 solar radii. • 2011 September 29: NASA selected CPI as an Explorer Mission of Opportunity project to undergo an 11-month Phase A concept study.

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