Glasgow, March 24, 2005 Large-scale coronal shock waves H.S. Hudson SSL/UCB

Glasgow, March 24, 2005 Outline How coronal imaging should help with understanding shock waves Origins of large-scale coronal waves Mach numbers

Glasgow, March 24, 2005 Conclusions Large-scale coronal waves originate in compact magnetic structures The Mach numbers in the corona are low We can’t yet image the CME flow field in the corona (ie, below coronagraph occulting edges)

Glasgow, March 24, 2005 What does “shock” mean in astrophysics? Adiabatic law P  -  = const Sound speed c s = (  P/  ) 1/2 Steepening and eventual discontinuity for sound waves in a fluid For most practical purposes, any thin layer with drastic variation is interpreted as a shock

Glasgow, March 24, 2005 Collisionless shocks Compressive wave modes still lead to steepening of wave fronts A discontinuity cannot occur because of finite interaction scales (no shock discontinuity can actually form!) Wave-particle effects of unknown nature structure the boundary between the flows But the Rankine-Hugoniot conditions still apply macroscopically

Glasgow, March 24, 2005 Rankine-Hugoniot conditions Upstream/downstream parameter jumps constrained by conservation laws in mass, energy, momentum, magnetic flux Simplest statement is T 2 /T 1 = (  +1) M /(  -1) M where M = c/c s

Glasgow, March 24, 2005 Rankine, a typical Weegie

Glasgow, March 24, 2005 What coronal shocks should look like… Korreck et al., 2004 Quasi-parallel,  ~ 0.1; M = 200?

Glasgow, March 24, 2005 Chandra E

Glasgow, March 24, 2005 Different possibilities for coronal shock structure Blast wave (simple wave) runs away from any disturbance Bow shock (driven wave) separates an obstacle from a flow

Glasgow, March 24, 2005 Type II burst

Glasgow, March 24, 2005 Inference of source motion in drifting radio bursts Assume a density model  (z) with height z, normally empirical (e.g. “fourfold Newkirk”) Determine the drift rate in MHz/s Convert to height from plasma-frequency assumption; f p = 9000 n e 0.5 Hz Typically, assume radial motion Probably there will be a good discussion of this sort of thing at the RHESSI-Nessie workshop

Glasgow, March 24, 2005 Type III (“fast drift”) Type II (“slow drift”), harmonic “Ignition”

Glasgow, March 24, 2005 Cartoon showing Earth’s bow shock (ex Birkeland?)

Glasgow, March 24, 2005

Imaging of coronal shocks: good news and bad news A shock wave should provide a sharp density gradient, easy to detect in images We can observe motions in two dimensions The medium is optically thin => confusion The wave may not be bright compared with other flare components The corona generally has low plasma beta, so the observed mass may not be structurally important

Glasgow, March 24, 2005 … Only imaging can properly characterize the large-scale structure The solar corona isn’t really accessible any other way

Glasgow, March 24, 2005 Imaging of coronal shocks Type II bursts (plasma radiation) Moreton waves (H  in the chromosphere) New modalities: EIT, X-rays 1, microwaves, He 10830, meter waves (thermal), meter waves (nonthermal) 1 Three events: Khan & Aurass (2002); Narukage et al. (2002); Hudson et al. (2003)

Glasgow, March 24, 2005 Moreton-Ramsey wave and EIT wave Thompson et al., 1998

Glasgow, March 24, 2005 G. A. Gary, Solar Phys. 203, 71 (2001) CH Mann et al., A&A 400, 329 (2003) Gopalswamy et al., JGR 106, (2001) (v A ~ 200  -1/2 km/s ?)

Glasgow, March 24, 2005 Direct X-ray observation Uchida 1968 Yohkoh 1998 EIT

Glasgow, March 24, 2005 Why X-ray waves are hard to observe directly Pre-flare transect Flare transect Ripple

Glasgow, March 24, 2005 Field and energy are concentrated in active regions Active-region magnetic fields via Roumeliotis-Wheatland technique (McTiernan) Mass loading via empirical law (Lundquist/Fisher)

Glasgow, March 24, 2005 Lundquist et al., SPD 2004

Glasgow, March 24, 2005 NOAA 10486, Haleakala IVM data,  cube Roumeliotis-Wheatland-McTiernan method pixel size ~3000 km ScaledNot scaled

Glasgow, March 24, 2005 Heliospheric shocks in images? Maia et al., ApJ 528, L49 (2000) Vourlidas et al., ApJ 598, 1392 (2003) SOHO/UVCS

Glasgow, March 24, 2005 Vourlidas et al., ApJ 598, 1392 (2003) Where is the bow shock ?

Glasgow, March 24, 2005 Inferring the Mach number Method: Estimate temperature jump from soft X-ray images and apply Rankine-Hugoniot condition

Glasgow, March 24, 2005 X-ray signal S ~ n e 2 f(T) f(T) ~ T 2  ln(S)/  ln(n) ~ 2  Mach number estimate for 6 May 1998 event

Glasgow, March 24, 2005 Movie of dimming (Aug 28, 1992) Coronal Dimming

Glasgow, March 24, 2005 Dimming observed spectroscopically Harra & Sterling, ApJ 561, L216, 2001

Glasgow, March 24, 2005 UVCS shock observations Raouafi et al., A&A 434, 1039, 2004 Mancuso et al., A&A 383, 267, 2002 Raymond et al., GRL 27, 1439, 2000

Glasgow, March 24, 2005 Cartoons illustrating wave origins? cf. There doesn’t seem to be a satisfactory cartoon! Sturrock CME Hudson flare

Glasgow, March 24, 2005 Coronal wave simulations Chen et al., ApJ in press (2005)

Glasgow, March 24, 2005 The CME-driven shock in the corona The CME involves outward plasma motions perpendicular to the field We see the result of these motions as dimmings, but the data are not good enough to follow the flows nor to see a bow wave There is an Alfven-speed “hole” in the middle corona in which Mach numbers could be larger

Glasgow, March 24, 2005 SUMMARY Coronal shock waves (metric type II) are blast waves (Uchida) launched by compact structures at flare onset. These propagate in an undisturbed corona The CME eruption restructures the corona and pushes a bow wave ahead of it into the solar wind. This creates a type II burst at long wavelengths

Glasgow, March 24, 2005 Where do “Solar cosmic rays” come from? Consensus holds that CME-driven shocks are responsible for most SEPs, but that something else is also happening Shock geometry and Mach numbers in the high corona are crucial factors: quasi-perpendicular fronts and large Mach numbers preferred The theory is incomplete but PIC simulations are appearing for the planetary bow shocks, at least

Glasgow, March 24, 2005 Conclusions Large-scale coronal waves originate in compact magnetic structures The Mach numbers in the corona are low We can’t yet image the CME flow field in the corona (ie, below coronagraph occulting edges)

Glasgow, March 24, 2005 END

Glasgow, March 24, 2005 Emslie et al., JGR (2004)

Glasgow, March 24, 2005 Flare and CME energy partition

Glasgow, March 24, 2005 Gosling et al., JGR 110, A01107, 2005