Orientations of Halo CMEs and Magnetic Clouds

Orientations of Halo Orientations of Halo CMEs and Magnetic CMEs and Magnetic

CloudsClouds

V. Yurchyshyn in collaboration with Q. Hu, R.P. Lepping, B. Lynch, J. KrallBBSO, UC Riverside, GSFC, Univ. Mich., NRL

04/22/23 36th COSPAR, 17-22 July 2006, Beijing, CHINA

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

CME

solar eruptions

earthearthsunsun

magnetic cloud,a flux rope

reconnection occurs whenCME’s MF and Earth’s MF have opposite components

OvervieOvervieww


The MC’s Bz - Dst Index The MC’s Bz - Dst Index RelationshipRelationship

Dst index is directly related to the strength of the Bz (Wu & Lepping 2004; Cane et al. 2001)

Yurchyshyn, Hu, Abramenko, 2005, Yurchyshyn, Hu, Abramenko, 2005, Space Weather, 3, #8, S08C02Space Weather, 3, #8, S08C02


CME Speed vs MC’s BzCME Speed vs MC’s Bz

Fast CMEs have a greater potential to cause a significant storm



Speed of CMEs vs Magnetic Speed of CMEs vs Magnetic FluxFlux

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

Qiu & Yurchyshyn, 2005, ApJLQiu & Yurchyshyn, 2005, ApJL



Summary of the Summary of the Introduction 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.


Halo CMEsHalo 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)


White Light Structure of White Light Structure of CMEsCMEs

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)


Halo CMEs are … 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)


Halo CMEs and Erupting Flux Rope Halo CMEs and Erupting Flux Rope ModelingModeling

In this study we assume that halo

elongation indicates the

orientation of an erupting flux ropesunsun

earthearth

Model Model halo CMEhalo CME

Solid – ACESolid – ACEDashed – ModelDashed – Model

top view


Oct 28 and Nov 18 2003 Oct 28 and Nov 18 2003 EventsEventsNov 18 2003

Oct 28 2003Elongation of a halo CME closely matches the orientation of the erupting flux rope


Data & AnalysisData & 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)


Orientation of 25 halo Orientation of 25 halo CMEsCMEs


ResultsResultsOvals – 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%) ?


• 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?

What Does This Result What Does This Result Mean? Mean?


CMEs & Heliospheric Current CMEs & Heliospheric Current SheetSheet

• 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?


Comparison between CMEs, Comparison between CMEs, HCS and MCsHCS and MCs

CME

Wilcox Solar Observatory Coronal Field Map at 2.5R


Results of the ComparisonResults 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


Orientations of CMEs, HCS Orientations of CMEs, HCS and MCs are similarand MCs are similar


Do CMEs rotate to align Do CMEs rotate to align w/HCS?w/HCS?


Are Fast CMEs not affected by Are Fast CMEs not affected by HCS?HCS?


ConclusionsConclusions• 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


ConclusionsConclusionsThe data seem to support original assumption that the CME elongation represent the axis of an erupting flux rope

Orientations of Halo CMEs and Magnetic Clouds

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