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The December 2006 SEP Events: Unusual Signatures Within an ICME

The December 2006 SEP Events: Unusual Signatures Within an ICME. T. Mulligan, J. B. Blake The Aerospace Corporation, Los Angeles, CA D. Shaul and J. Quenby Imperial College, London, UK R. A. Leske and R. A. Mewaldt California Institute of Technology, Pasadena, CA, USA

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The December 2006 SEP Events: Unusual Signatures Within an ICME

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  1. The December 2006 SEP Events: Unusual Signatures Within an ICME T. Mulligan, J. B. Blake The Aerospace Corporation, Los Angeles, CA D. Shaul and J. Quenby Imperial College, London, UK R. A. Leske and R. A. Mewaldt California Institute of Technology, Pasadena, CA, USA Acknowledgements: E. Roeloff and J. Mazur

  2. Introduction • Brief review of the X-class flares and series of SEPs from AR #930 as it rotated across the solar disk from ~12/4 through 12/16 • C. Cohen’s talk yesterday concentrated on the main two SEPs in the series (thank you) • This “active” sun presented opportunity to exploit the large-geometric factor of Polar HIST scintillator & calibrate a high-statistics mode enabling high-count rate energetic particle studies to determine if (and how) local IP structures affect particle distributions • Fortuitous we noticed the unusual modulation in the third SEP in the series on 12/14 observed while inside an ICME • Observations from STEREO, ACE, Wind, Polar, GOES • Discussion of possible mechanisms causing modulation • Conclusions

  3. ~3 (LET) ~11 (SIS) 30 (SIS) Overview of December SEP Series Very quiet sun: No flares above B class for most of November In December 2006 AR#930: produced 4 X-class, 5 M-class, numerous C-class and several CMEs First was an X9 solar flare from longitude E71 X6.5 flare (at E57) apparently added to the SEP population, which peaked in intensity at the end of December 7th at W23 AR#930 released another X-class flare (X3.4) and fast coronal mass ejection (CME), which initiated yet another large SEP event One final flare (X1.5) at end of 12/14 http://www.srl.caltech.edu/ACE/ACENews/ACENews101.html

  4. Overview of December SEP Series Cont’d Spectra for He, O, and Fe obtained during the two SEP events Plots show combined data from ULEIS and SIS on ACE and LET on STEREO B STEREO A did not observe both events Relative amplitudes of the O and Fe spectra indicate the SEP event on 12/13 was significantly more Fe-rich than its counterpart from the east (on 12/6) Fe-richness in 12/13 SEP appears to increase with increasing energy (especially >12 MeV/n) Fe /O ratio increases to above 10 MeV/n, comparable to richest Fe events observed http://www.srl.caltech.edu/ACE/ACENews/ACENews101.html

  5. Polar High Sensitivity Telescope HIST HIST contains a ~3.5 x 5 cm plastic scintillator (large omni-directional geometric factor for penetrating particles) Designed for relativistic electron radiation-belt studies Large omni-directional geometric factor is well suited for studying short-period variations Observe GCR statistics of up to 1000 counts per 6-sec spin at energies >10 MeV In the December 13, 2006 SEP count rates exceeded 105 during a six-second rotation of the Polar satellite

  6. Polar HIST in High-Statistics (HS) Mode HIST HS mode has 256 digitized bins (0-255) Bins 0-254 range from threshold of noise up to ~10 MeV All pulses >10 MeV appear in the “overflow” bin 255 (magenta trace). As expected, most counts are in overflow bin December 13-15 2006 SEPs data are shown divided into four sums of 64 bins plus the overflow bin 255

  7. Opportunity in SEP Event of 12/13 12/13 SEP observed at Wind, ACE, STEREO B, GOES, and Polar Satellites in magnetosphere see similar signatures as s/c in solar wind Long SEP decay time allows intercalibration of HS mode Ensuing days bring IP shock and ICME with rise in energetic particles Note unusual SEP signature on 12/14 with dispersion only at GOES

  8. 100 MeV proton gyroradius 100 MeV proton gyroradius 40 MeV proton gyroradius 40 MeV proton gyroradius Y Wind X ACE STEREO Z Wind ACE Y STEREO Spacecraft Orbit Geometries Movie of orbit tracks for the spacecraft during the interval from 12/13 to 12/16 (same interval as the time series plot) Top panel is GSE ecliptic plane; bottom panel is plane of sky as viewed from Sun Top(bottom) tick marks every 20(15)Re; grid lines every 40(30)Re Wind and ACE are on opposite sides of the Earth-Sun line and above the neutral sheet; Wind is ~250 Re sunward. Gyroradii of 40 MeV proton (8 Re) and 100 MeV proton (16 Re) shown for leading edge ICME field ACE and Wind separated azimuthally by 6x-12x proton gyroradii in energies of interest

  9. SEP Protons Within an ICME on 12/15 IP shock on 12/14 driven by ICME on 12/15 Classic particle decrease in ICME magnetosheath same at all s/c Just inside ICME leading edge another SEP is observed Polar is enters northern auroral oval on 12/15 just after SEP onset Wind, ACE, STEREO, and Polar observe short-scale modulation of particle signature within the ICME injection is dispersionless

  10. Electron Observations on 12/15 SEP on 12/13 is also clearly seen in ACE EPAM electrons 12/14 SEP just inside ICME leading edge is also observed with strong modulation e- pitch angle anisotropies (especially at higher energies) do not clearly show this injection– signatures are bidirectional (E. Roeloff communication) Question of whether shock acceleration may be overwhelming flare acceleration signatures Could this be just a drastic modulation of decaying intensities from the previous SEP?

  11. ACE Solar Wind and Flux Rope Fit Comet Mc Naught Axial field

  12. STEREO A IMF and Flux Rope Fit Sun Axial field

  13. Possible Mechanism: Scattering at ICME sheath Sheath tangential rotations and planar structures preferentially scatter particles away from flux rope guiding fields numerical particle tracing through relativistic EM fields shows scattering at the sheath boundary Sheath affects the particle trajectories similarly over the spectral range of 20-110 MeV Fields map into the GSE spatial domain using bulk plasma solar wind velocity Shock located very close at 1/12 AU beyond Earth at this snapshot Sheath region (MS) is highly unstructured Question of turbulence level?

  14. Possible Mechanism #2: Flux Dropout Impulsive flaring event signatures are susceptible to footpoint motion of solar wind convected flux tubes (Mazur et al., 2000) Flare populates flux tubes connected to the acceleration site while other, unconnected flux tubes remain empty Mixing occurs via solar wind convection to 1 AU causing “dropouts” ~ 0.01 AU in size (a) Energy of H-Fe ions vs. arrival time at 1 AU for the impulsive flare events of 1999 January 9. (b) H-Fe counts vs. time in ~14 minute bins. Vertical lines show subintervals with a peak-to-valley ratio criterion of ~1.3.

  15. Yet More Unusual Signatures: GOES Differential Proton Fluxes Differential proton flux data shown at ~1 MeV to 80 MeV energies for GOES 10, 11, and 12 GOES 10 and 11 show little if any short-scale modulation GOES 12 15-40 MeV and 40-80 MeV energy bands shows clear short-scale modulation Not clear this is data processing issue Is this a lack of connectivity at subsolar region?

  16. Geosynchronous Satellite Orbit Geometries Movie of orbit tracks during 12/14 1400 UT to 12/15 0600 UT (from the IP shock through the 1st half of the ICME) Top panel is GSE ecliptic plane; bottom panel is plane of sky as viewed from Sun (tick marks 1 Re apart; grid lines 2 Re apart) GOES 12 (red)leadsGOES 11 (yellow) by ~4 hrs MLT ; GOES 10 lags GOES 11 by same amount (not shown) When leading edge of ICME hits Earth, GOES 10 is pre-noon, GOES 11 is post-noon, and GOES 12 is near dusk; Polar (green) in northern auroral oval during this time The short-scale particle variation inside the ICME exists in the solar wind and at Polar so why not at GOES 11?

  17. Summary, but… • 4 X-class flares and a series of 3 SEPs originated from AR #930 as it rotated across the solar disk from 12/4 through 12/16 • First two SEPs (12/6 and 12/13) had very different signatures and different magnetic connectivity • Unusual modulation observed during third SEP on 12/14 inside an ICME at 1 AU • solar wind signature at Wind, ACE, and STEREO looks dispersionless • The modulation is observed at GOES 10 near dawn and GOES 12 near dusk, but no modulation is observed at GOES 11 • ACE EPAM electrons also have strong modulation, but e- pitch angle anisotropies (especially at higher energies) are bidirectional • Question of whether shock acceleration may be overwhelming the flare acceleration signature

  18. …no Conclusions yet Could this be just a drastic shock modulation of decaying intensities from the previous SEP? Dispersionless signature at multiple s/c consistent with ICME sheath causing particle scattering-- can tangential rotations and planar structures in ICME sheath preferentially scatter particles away from flux rope guiding fields as shown in particle tracing? Or might field line mixing at 1 AU be the cause of the flux “dropouts” (similar to Mazur et al., 2000)? What role does shock acceleration and pre-conditioning play? Study is ongoing– What role does ICME play in transport? The shock geometry? Did Comet McNaught have an effect?

  19. Supplemental Charts

  20. Additional Acknowledgements We thank the ACE SWEPAM instrument team and the ACE Science Center for providing the ACE particle data. We also thank N. Ness of Bartol Research Institute for providing ACE MAG data, and T. Von Rosenvinge for providing Wind Epact data.

  21. Versatility in Magnetic Flux Rope Modeling

  22. New Observational Constraints for ICME Models Solar Mass Ejection Imager (SMEI) white-light density reconstructions obtain the global 3-D geometry of CMEs/ICMEs Use these reconstructions in conjunction with in situ models of ICMEs to better determine flux rope topology Magnetic flux is frozen in to the plasma so the density should follow the global magnetic structure Multispacecraft observations allow large-scale reconstructions of ICME global 3-D geometry ACE and NEAR flux rope inversion shows axis of flux rope has a radius of curvature slightly larger than that of a dipole field

  23. Coupling MHD Simulations and ICME Models (Top) bent flux rope cylinder geometry of the Riley et al. (2003) MHD simulation rope ACE and Ulysses data inverted simultaneously Expected geometry as the rope transits 1 AU. The Earth's orbit is shown as a green ellipse. (Bottom) MHD simulation of ICME from various slices passing through Earth Flow velocity (color scale) and ICME boundaries (thick black lines) show 3-D ICME legs and morphology in realistic solar wind

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