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Orientations of Halo CMEs and Magnetic Clouds

Orientations of Halo CMEs and Magnetic Clouds. V. Yurchyshyn in collaboration with Q. Hu, R.P. Lepping, B. Lynch, J. Krall BBSO, UC Riverside, GSFC, Univ. Mich., NRL. Overview. reconnection occurs when CME’s MF and Earth’s MF have opposite components. solar eruptions. magnetic cloud,

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Orientations of Halo CMEs and Magnetic Clouds

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  1. Orientations of Halo CMEs and Magnetic Clouds V. Yurchyshyn in collaboration with Q. Hu, R.P. Lepping, B. Lynch, J. Krall BBSO, UC Riverside, GSFC, Univ. Mich., NRL

  2. Overview reconnection occurs when CME’s MF and Earth’s MF have opposite components solar eruptions magnetic cloud, a flux rope CME sun earth Geo. storm is response of the magnetosphere on southwardly directed IMF • Geoeffectiveness of a halo CME depends on • the field strength in it and • the orientation of the mag. field 36th COSPAR, 17-22 July 2006, Beijing, CHINA

  3. The MC’s Bz - Dst Index Relationship Yurchyshyn, Hu, Abramenko, 2005, Space Weather, 3, #8, S08C02 Dst index is directly related to the strength of the Bz (Wu & Lepping 2004; Cane et al. 2001) 36th COSPAR, 17-22 July 2006, Beijing, CHINA

  4. CME Speed vs MC’s Bz Yurchyshyn, Hu, Abramenko, 2005, Space Weather, 3, #8, S08C02 Fast CMEs have a greater potential to cause a significant storm 36th COSPAR, 17-22 July 2006, Beijing, CHINA

  5. Speed of CMEs vs Magnetic Flux Qiu & Yurchyshyn, 2005, ApJL Yurchyshyn, Hu, Abramenko, 2005, Space Weather, 3, #8, S08C02 High speed CMEs are associated with those flares where a large amount of the magnetic flux reconnected. Agrees w/ previous conclusion that CME speed is related to the Bz 36th COSPAR, 17-22 July 2006, Beijing, CHINA

  6. Summary of the Introduction • Thus, the intensity of Bz component can be predicted based on solar data (magnetograms, Halpha, TRACE and/or LASCO images) What about the orientation? • Many (mainly case) studies argue that the orientation and helicity of the magnetic field of CME source regions (mainly ARs) agree very well with those of the corresponding MCs. 36th COSPAR, 17-22 July 2006, Beijing, CHINA

  7. Halo CMEs • CMEs observed near the earth often exhibit a magnetic structure that can be described as complex ejecta, magnetic clouds, plasmoids or shocks. Well defined MCs are associated with 30-50% of CMEs • MC, in turn, have magnetically organized geometry that is thought to correspond to a curved flux rope (Burlaga 1981; Bothemer & Schwenn 1998) 36th COSPAR, 17-22 July 2006, Beijing, CHINA

  8. White Light Structure of CMEs White light morphology of CMEs seems to bear information on their magnetic structure: they are organized in the axial direction, which corresponds to the axis of the underlying erupting flux rope (Cremades & Bothmer, 2004) 36th COSPAR, 17-22 July 2006, Beijing, CHINA

  9. Halo CMEs are … 2D projection of a 3D structure and they often exhibit various sizes and shapes. Many of them can be enveloped by an ellipse and fitted with a cone model (Zhao, Plunkett & Liu 2002, Xie Ofman & Lawrence 2004; Zhao 2005) 36th COSPAR, 17-22 July 2006, Beijing, CHINA

  10. Solid – ACE Dashed – Model Halo CMEs and Erupting Flux Rope Modeling In this study we assume that halo elongation indicates the orientation of an erupting flux rope sun Model halo CME top view earth 36th COSPAR, 17-22 July 2006, Beijing, CHINA

  11. Oct 28 and Nov 18 2003 Events Nov 18 2003 Elongation of a halo CME closely matches the orientation of the erupting flux rope Oct 28 2003 36th COSPAR, 17-22 July 2006, Beijing, CHINA

  12. Data & Analysis • Selected 25 halo CME -- MC events • Determined the orientation of CMEs • Determined the clock angle of MCs: • Grad-Shafranov MC reconstruction by Q. Hu • MC fitting by Lepping et al. (2006) • MC fitting by Lynch et al. (2005) • MC fitting with the EFR model (J. Krall & V. Yurchyshyn) 36th COSPAR, 17-22 July 2006, Beijing, CHINA

  13. Orientation of 25 halo CMEs 36th COSPAR, 17-22 July 2006, Beijing, CHINA

  14. Results Ovals – CMEs, lines – MCs. Short lines are used when the difference between CME and MC orientations, , exceeds 45 deg. Black dotted line – mean MC orientation angle Green boxes: 15 events (60%)  < 45 deg Red boxes: 8 events (32%)  > 45 deg Blue boxes: 2 events (8%)  ? 36th COSPAR, 17-22 July 2006, Beijing, CHINA

  15. What Does This Result Mean? • For 60% of events (“green”) CME elongation agrees with MC orientations • What about the “red” events? Was our initial assumption wrong? Or is there something that affects a coronal ejecta? Is there any systematic difference between the CMEs and MCs? • Can MCs be deflected and their orientation changed during the propagation toward the Earth? 36th COSPAR, 17-22 July 2006, Beijing, CHINA

  16. CMEs & Heliospheric Current Sheet • CMEs disrupt heliospheric magnetic fields (Zhao & Hoeksema 1996) • Fast moving CMEs interact w/ upstream plasma, shock formation (Gosling et al., 1994; Howard & Tappin 2006, Liu & Hayashi 2006) • CMEs may “displace” and “push” the heliospheric magnetic fields (Smith 2001) • Most CMEs may be associated with HCS, which is considered to be a conduit for CMEs (Crooker et al., 1993) • Does the heliosphere affects CMEs? 36th COSPAR, 17-22 July 2006, Beijing, CHINA

  17. Comparison between CMEs, HCS and MCs CME Wilcox Solar Observatory Coronal Field Map at 2.5R 36th COSPAR, 17-22 July 2006, Beijing, CHINA

  18. Results of the Comparison • 13 events CME,MC<45 deg and MC agrees w/HCS • 7 events CME,MC>45 deg, while MC agrees w/HCS • 2 events CME,MC<45 deg, however MC  HCS (V>2000km/s) • 1 event CME,MC>45 deg, MC is  to HCS • 2 events – uncertain 36th COSPAR, 17-22 July 2006, Beijing, CHINA

  19. Orientations of CMEs, HCS and MCs are similar 36th COSPAR, 17-22 July 2006, Beijing, CHINA

  20. Do CMEs rotate to align w/HCS? 36th COSPAR, 17-22 July 2006, Beijing, CHINA

  21. Are Fast CMEs not affected by HCS? 36th COSPAR, 17-22 July 2006, Beijing, CHINA

  22. Conclusions • For about 60% of events the halo elongation and the MC orientation correspond to the local tilt of the HCS • For majority of solar ejecta (80%), the underlying erupting flux rope at 1AU (i.e. MC) aligns itself with the HCS • It seem that very fast (V>2000km/s, 2 events) CMEs maintain their orientation constant • There is an indication that the degree of CME rotation , if indeed occurs, might depend on the speed of a CME: faster CMEs are less affected by the HCS (shorter interaction time? stronger CMEs?) • The data seem to support our initial assumption although the results should be tested on a larger data set 36th COSPAR, 17-22 July 2006, Beijing, CHINA

  23. Conclusions The data seem to support original assumption that the CME elongation represent the axis of an erupting flux rope 36th COSPAR, 17-22 July 2006, Beijing, CHINA

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