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Influence of Time-dependent Processes and Background Magnetic Field on Shock Properties

Influence of Time-dependent Processes and Background Magnetic Field on Shock Properties. N. Lugaz, I. Roussev and C. Downs Institute for Astronomy Igor Sokolov University of Michigan Carla Jacobs KU Leuven. SHINE workshop , August 7, 2009. What do we know about shocks? (1). Observations

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Influence of Time-dependent Processes and Background Magnetic Field on Shock Properties

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  1. Influence of Time-dependent Processes and Background Magnetic Field on Shock Properties N. Lugaz, I. Roussev and C. Downs Institute for Astronomy Igor Sokolov University of Michigan Carla Jacobs KU Leuven SHINE workshop, August 7, 2009

  2. What do we know about shocks? (1) • Observations • In situ: some Helios data, otherwise above 0.6 AU only. Only single point (two-three points at best) • From coronagraphs: directly and through streamers’ deflection. Ontiveros & Vourlidas, ApJ, 2009 Shocks observed at 3-5 RSun Vourlidas et al., ApJ, 2003

  3. What do we know about shocks? (2) • Observations • From radio emissions: Type II (metric, decamteric (DH)) • From energetic protons/ions: SEP/GLE • Simulations are useful tools (e.g. Evans et al & Liu et al., ApJ, 2008), but corona is not the place best reproduced by MHD. • There might be a energy dependency regarding the release time of particles (GLE). • There might be important effects associated with the shock geometry (quasi-perp. vs. quasi parallel). Gopalswamy et al., Sol. Phys., 2009 Shock may form as low as 1.5 Rsun (also from Reiner et al. 2001)

  4. What don’t we know about shocks? • Simulations show the existence of a Alfvén “hump” around 3-4 Rs. Is this really important? • Presence of previous ejections is important for transport but also for seed particle energy and composition. Tan et al., 2008/2009, ApJ

  5. More we don’t know • The pre-event magnetic topology is important to determine the shock geometry and the connectivity (different from simple Parker spiral). • CMEs can get deflected in the corona, how is this important for SEP acceleration? • Reconnection during an eruption can result in a change of the magnetic topology and different connectivity with Earth. Ippolito, A&A, 2005

  6. Importance of pre-eruption topology Beyond Parker spiral • August 24, 2002 CME: AR is W 81, so we don’t expect it to be connected to Earth before the eruption. • However, field lines connected to the vicinity of Earth (within 10o) have footprints between S15W10 and N20W70.

  7. SEP (2): Shock formation • Field lines connecting to the vicinity of Earth: some of them reconnect through the null point at the end of the shearing phase, connecting Earth and AR 69. Possible consequences for SEP seed particles. • The shock can clearly form by 1 hour around 6 Rsun. Isosurface of Aflven Mach > 1 after 1 hour This shows the maximum extent of the shock Field lines connecting 10o around Earth

  8. Pre-condition of the magnetic field • Ejection in August 22, 2002 about 900 km s-1 48 hours before main eruption. • Same active region but possibly different topology (SE null). Flare: S07W62 • We want to study • how the topology and the magnetic connectivity with Earth changed. • The possible influence of this ejection on the propagation of the 08/24 CME. • The difference in SEP acceleration/shock formation

  9. 08/22/2002: Coronal deflection and reconnection (@ 1hr) reconnection Field line connecting the erupting active region with Earth through reconnection at the null point.

  10. Evolution of the Sun-Earth magnetic connectivity

  11. Heliospheric evolution: which shock was observed at Earth? August 22 CME? August 24 CME? • Requirement to associate shock with these CMEs: • Large deflection • Large (>130 deg) angular extent • Large deceleration (to 400 km/s) • For 08/22, 4.5 day transit. • For 08/24, 2.5 day transit. Shock reaches Earth but 2 days too early. 08/26 @1UT: shock only reaches 35 o west from Earth. • Solution: partial halo CME on 08/23 near 15 UT. Filament near disk center? • This would explain why the shock arrival at 1 AU is not associated with any particle flux enhancement.

  12. Some things I should know about shocks but don’t • What proportion of iCMEs are associated with shock? • 66% at 1 AU from Jian et al. (2007, 2008) • 46% at 0.72 AU from Jian et al. 2008 • 0% below 0.5 AU from Jian et al. poster at this SHINE • Around 30% below .8 AU from the same poster • No more than 30% from the top of my head (LASCO CDAW catalog) • 25% of CMEs faster than 550 km/s. • Remember slow CMEs may form shock when faster ones don’t (Shen et al., 2008, ApJ) • There were about 300-400 DH Type II bursts during last solar cycle (~12000 CMEs)

  13. from Manchester et al., 2004, JGR Alfvénic speed evolution in the heliosphere • Alfven/Fast speeds decrease fast at first then slower. • But CMEs also decelerate fast at first then slower. • Jian et al. (2008) paper: • Fast @0.72AU is 79 km/s Fast @1AU is 72 km/s • Cohen et al. (2008) solar wind model • Fast @0.72AU is 64 km/s Fast @1AU is 53 km/s • Fast @0.1AU is 270 km/s • Where do interplanetary CME-driven shocks form? • My guess is a large majority (80-90%) within 15-20 Rsun • Medium-speed CMEs (400-600 km/s) may sometimes drive a shock at larger distances. • Shock formation at larger distances might be associated with change of background properties.

  14. April 26, 2008 CME Best example yet of a CME observed by the two spacecraft. Followed until 1 AU in HIs (A). In-situ measurements by STEREO-B and ACE. How can we use STEREO to learn more about CME Heliospheric evolution?

  15. Determining position from elongation angle in SECCHI/HIs • Two main methods have strong assumptions: • Point-P: spherically symmetric, centered at the Sun. • Fixed-Phi: narrow, fixed radial trajectory. • Improvement for wide CMEs: assumes self-similar expansion of spherical CME • Resulting distance is the harmonic mean of P-P and F-Phi • Same general procedure as that presented by Ying Liu. Multi-spacecraft measurements can give us the radial and angular position. From COR-2 data: Phi = -21 (Thernisien) or Phi = -48 (Colaninno)

  16. Conclusions • Lots we don’t know about shocks. • Some indications they may form as low as 1.5 Rsun (see Carla Jacobs talk). • Recently people have focused on shock geometry mostly, and presence/absence of a magnetic barrier (previous iCME) to understand SEP events. • Previous CMEs are also important to change the background alfvenic speed, length of the field lines and connectivity. • CME deflection is something to consider. • I don’t believe: • Alfvén speed hump plays an important role for SEP production. • More than a very few CMEs have a shock forming beyond 0.2 AU.

  17. Advertisement • SH 03 session Fall AGU: CME heliospheric properties (beyond 0.1 AU) • Deflection • Rotation • Acceleration/deceleration/drag force • Deformation (pancake, indentation, etc…) • Expansion • Multi-spacecraft, SECCHI, SMEI, IPS observations • Simulations • Invited speakers: Odstrcil (Colorado), Liu (Berkeley), Rouillard (NRL), • Deadline: September 3, midnight ET • Conveners: Lugaz, Vourlidas & Webb

  18. Thank you! These studies have been made possible by the following grants: NSF-CAREER ATM0639335, NSF-NSWP ATM0819653 and NASA-LWS NNX08AQ16G.

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