Extremely Fast Coronal Mass Ejection on 23 July 2012

1. ST21-A011 Extremely Fast Coronal Mass Ejection on 23 July 2012 K. Liou1, M. Dryer2, C.-C. Wu3, S. T. Wu4, N. Rich3, S. Plunkett3, L. Simpson3, C. D. Fry5, and K. Schenk6 1 Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland,20723, USA 2 NOAA Space Weather Prediction Center (Ret.), Boulder, CO, 80305, USA 3Naval Research Laboratory, Washington, DC, 20375, USA 4 CSPAR, University of Alabama, Huntsville, Alabama, 35899, USA 5 Exploration Physics International, Inc., Huntsville, Alabama,35806, USA 6 NASA/GSFC, Greenbelt, MD, USA AOGS-AGU(WPGM), Singapore, August 13-17, 2012

2. The July 23, 2012 CME Event: Why It's Important? 1) The Sun has been active for a few years; however, the Earth is still “quiet” geomagnetically 2) This CME Initiated on the Sun's back side: no warning sign (no flare observed at the Earth); can pose danger to spacecraft 3) Extremely fast: CME-driven shock arrived at STEREO-A in ~20 h (typical 2-3 days, ~19h for the Halloween 2003 event) 4) Extremely large magnetic cloud field

3. Positions of STEREO A & B on 2012-07-23 STEREO-B Earth STEREO-A Heliographic (HEEQ) longitude -114.819 0.000 121.246 Heliographic (HEEQ) latitude -6.979 5.088 1.750 From NASA STEREO SCIENCE CENTER

4. STEREO OBSERVATIONS Halo CME STEREO-A COR2 STEREO-B COR2

5. OBSERVATION

6. Global Three-dimensional MHD simulation Simulation model: HAF+3DMHD (H3DMHD)[Wu et al., JGR, 112,A09104, 2007; Adv. Space Rev., 40, 1827, 2007] • Hakamada-Akasofu-Fry code (HAFv.2) [Fry et al., 2001] : simulating data from the Sun (2.5 solar radii, Rs) to 0.08 AU (18 Rs). • A fully three-dimensional (3D), time-dependent magnetohydrodynamic (MHD) simulation code [Han et al., 1988; Detman et al., 1991, 2006] : simulating data from 0.08 AU (18 Rs) to > 1 AU 6

7. Simulation Domain Coordinates - Sun-centered spherical coordinate system (r, θ, φ) -87.5° ≤ θ ≤ 87.5° 0° ≤ ϕ ≤ 360° 2.5 Rs ≤ r ≤ 18 Rs(HAF) & 18 Rs ≤ r ≤ 345 Rs (MHD) Earth at (r, θ, ϕ) = (215 Rs, 0°, 0°) in the ecliptic plane Uniform grids and open boundary condition > Uniform grid step size∆r = 3 Rs, ∆θ = 5° and ∆ϕ = 5° > θ = ±87.5°(no reflective disturbances) Simulation procedure > Pre-event steady state solar wind based on solar magnetic maps > Apply a Gaussian velocity pulse at the flare site at r = 2.5 RSUN to drive the > CME (free parameters: the peak and the width of the pulse) 7

8. Governing Equations Conservation of mass Conservation of momentum Conservation of energy* Induction equation In the equations, D/Dt denotes the total derivative, ρ is the mass density, V is the velocity of the flow, p is the gas pressure, B is the magnetic field, e is the internal energy per unit mass (e = p/(γ-1)ρ), GM(r) is solar gravitational force, and γ is the specific heat ratio. For this research, we applied an adiabatic gas assumption (i.e.,γ =5/3). In conservation of energy: we ignored the Coriolis force, Joule heating, thermal conduction, and viscous items.

9. Initial speed of Shock/CME from COR2-A (STEREO-A) Center: 2964 km/s Averages: ~3285 km/s Bottom: 3606 km/s This simulation: Vpeak = 3100 km/s Δτ = 3.5 hours

10. H3DMHD Simulation Results ~ 1000UT on 2012-07-24 SHOCK arrived at STEREO-B ~2300UT on 2012-07-25 SHOCK arrived at ACE ~2300UT on 2012-07-23 SHOCK arrived at STEREO-A

12. Results of H3DMHD in situ solar wind at 1 AU It takes ~18 hours for Shock propagating from Sun to STEREO-A It takes ~42 hours for shock propagating from the Sun to the Earth It takes ~29 hours for shock propagating from the Sun to STEREO-B ~2300UT on 2012-07-23 SHOCK arrived at STEREO-A ~1000UT on 2012-07-24 SHOCK arrived at STEREO-B ~2300UT on 2012-07-25 SHOCK arrived at ACE

13. H3DMHD STEREO-B in situ solar wind at 1 AU STEREO-A in situ solar wind at 1 AU

14. STEREO-B in situ solar wind at 1 AU Density

15. Discussion • The CME on July 23 2012 is extremely fast, the fastest CME in cycle 24 so far • The initial speed of the CME (at 2.5 solar radii) could exceed 3000 km/s > Magnetic field at 1 AU (STEREO-A) is largest (~100 nT) |B| ~80 nT for the Halloween event. > What would be the storm size if the CME hit the Earth head on? For this event Bzmin ~ -50 nT (Dst)p = 0.83 + 7.85×Bzmin (nT) ~ -392 nT [Wu & Lepping, 2005] (Dst)p= 31.9 + 6.67×Bs (nT) ~ -365 nT[Bakare & Chukwuma, 2010] For the Halloween event: Dstmin = -383 nT 15

16. 04 UT 00 UT ~06 UT CNO 7-10 MeV/n Fe 0.64-0.91 MeV/n 07/16 07/18 07/20 07/22 07/24 07/26

17. Some possibilities: 1) SEP source (shock)-STEREO connection 2) Shock strength weaken away from the CME nose 3) Efficiency of shock type (parallel and perpendicular)

18. SEP Source ConnectionAssume Parker Spiral • At 04 UT, the CME was inside of 20 Rs • 5 hours after the onset (03 UT), the CME had expanded radially and azimuthally and covered ~120° E and W of the CME onset • At 08 UT, the CME had expanded over the Earth's solar foot point, consistent with the SEP observations at ACE • At 12 UT, the CME and the STEREO-B are well connected but no SEP was observed until 12 hours later

19. Shock Strength 06 UT 23/07 • Fast shock Mach no. is larger at the shock nose (9-12) than at the shock flank (5-9) • No information about the shock within 18 Rs because of the limitation of the HAF code (no Temperature) • Beyond 18 RSUN, shock Mach number decreases with the distance from the Sun, implying that the shock reached its maximum strength with 18 RSUN. Shock nose Fast shock Mach no. 50° E of shock Distance from Sun (RSUN)

20. Comparison with the Halloween CME The July 23 CME event produced a large SEP event with MeV Helium flux 30 times larger than those associated with the Halloween 2003 epoch

21. Conclusions • We have demonstrated that H3DMHD is capable of simulating extremely fast CMEs with speed > 3000 km/s > Good timing and magnitude match in total B and V but not n > Lack of solar wind density jump at STEREO-A at shock? • The CME-associated magnetic field at 1 AU is the largest (|B| ~100 nT) in record Our preliminary and qualitative study of the SEP events at multiple spacecraft locations suggests: • Largest SEP fluxes are magnetically connected to the nose of the CME-driven shock • Azimuthal expansion of the CME caney to understand the SEP onset • Large solar events do exist when no one is looking; Initiation location of CMEs is an important factor that determines geomagnetic activity • Dstmin vs. Longitude has a few source on backside. Required high model velocity input suggests the need for flare energy output evaluation for SWx objectives 21

22. THE END

23. Background speed is faster in the west than in the nose 45º West of source location 2º West of source location 50º East of source location

24. STEREO-B Earth STEREO-A CME Background speed is faster in the west than in the nose of source region

26. Wave Tracing Method (Wu et al., 1996) t = t2 t = t1 r = r2 Cfast = Speed of Fast Wave Δt = t2 - t1 Δr = r2 - r1 Vshock = Δr/Δt Mfast-shock = |Vshock-Vsolar-wind|/Cfast r = r1 Shock front Shock front

27. 45º West of source location 2º West of source location 50º East of source location

28. Comparison with the Halloween CME The July 23 CME event produced a large SEP event with MeV helium fluxes 30 times larger than those associated with the Halloween epoch Peak ~30 298 300 302 304 DOY of 2003