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Orientations of Halo CMEs and Magnetic Clouds

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Presentation on theme: "Orientations of Halo CMEs and Magnetic Clouds"— Presentation transcript:

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 36th COSPAR, 17-22 July 2006, Beijing, CHINA
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 9/18/2018 36th COSPAR, 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) 9/18/2018 36th COSPAR, 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 9/18/2018 36th COSPAR, 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 9/18/2018 36th COSPAR, 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. 9/18/2018 36th COSPAR, July 2006, Beijing, CHINA

7 36th COSPAR, 17-22 July 2006, Beijing, CHINA
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) 9/18/2018 36th COSPAR, 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) 9/18/2018 36th COSPAR, July 2006, Beijing, CHINA

9 36th COSPAR, 17-22 July 2006, Beijing, CHINA
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) 9/18/2018 36th COSPAR, July 2006, Beijing, CHINA

10 Halo CMEs and Erupting Flux Rope Modeling
In this study we assume that halo elongation indicates the orientation of an erupting flux rope sun Solid – ACE Dashed – Model Model halo CME top view earth 9/18/2018 36th COSPAR, July 2006, Beijing, CHINA

11 36th COSPAR, 17-22 July 2006, Beijing, CHINA
Oct 28 and Nov Events Nov Elongation of a halo CME closely matches the orientation of the erupting flux rope Oct 9/18/2018 36th COSPAR, July 2006, Beijing, CHINA

12 36th COSPAR, 17-22 July 2006, Beijing, CHINA
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) 9/18/2018 36th COSPAR, July 2006, Beijing, CHINA

13 Orientation of 25 halo CMEs
9/18/2018 36th COSPAR, July 2006, Beijing, CHINA

14 36th COSPAR, 17-22 July 2006, Beijing, CHINA
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%)  ? 9/18/2018 36th COSPAR, 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? 9/18/2018 36th COSPAR, 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? 9/18/2018 36th COSPAR, July 2006, Beijing, CHINA

17 Comparison between CMEs, HCS and MCs
Wilcox Solar Observatory Coronal Field Map at 2.5R 9/18/2018 36th COSPAR, 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 9/18/2018 36th COSPAR, July 2006, Beijing, CHINA

19 Orientations of CMEs, HCS and MCs are similar
9/18/2018 36th COSPAR, July 2006, Beijing, CHINA

20 Do CMEs rotate to align w/HCS?
9/18/2018 36th COSPAR, July 2006, Beijing, CHINA

21 Are Fast CMEs not affected by HCS?
9/18/2018 36th COSPAR, July 2006, Beijing, CHINA

22 36th COSPAR, 17-22 July 2006, Beijing, CHINA
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 9/18/2018 36th COSPAR, July 2006, Beijing, CHINA

23 36th COSPAR, 17-22 July 2006, Beijing, CHINA
Conclusions The data seem to support original assumption that the CME elongation represent the axis of an erupting flux rope 9/18/2018 36th COSPAR, July 2006, Beijing, CHINA

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