The Occurrence and Speed of CMEs Related to The Occurrence and Speed of CMEs Related to Magnetic Helicity Injection in Their Source RegionsMagnetic Helicity Injection in Their Source Regions

Sung-Hong ParkSung-Hong Park

Solar and Space Weather Research GroupSolar and Space Weather Research Group

Korea Astronomy and Space Science InstituteKorea Astronomy and Space Science Institute

2011 12011 1stst APSP Meeting APSP Meeting

# Major Results

1. Importance of long-term evolution of magnetic helicity injection in source regions prior to CMEs

2. Two groups of CMEs classified by two characteristic helicity evolution patterns

3. Fairly good correlation between CME speed and helicity injection rate

2011-03-24 1st APSPM

1. Introduction

- Coronal Mass Ejections (CMEs) are the transient ejections into interplanetary space of as much as a few billion tons of plasma and embedded magnetic fields from the solar corona.

- Most of CMEs occur in active regions where intense magnetic fields exist in the solar atmosphere, from the photosphere to the corona. In addition, it is generally thought that CME-productive active regions have complex and non-potential magnetic structures.

1.1 CMEs in Solar Active Regions

Hinode/FG/Stokes-VSOHO/LASCO+EIT

Active Region NOAA 10930

2006-12-13 Halo CME Line-of-sight Magnetic Field

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1.2 Why Study Magnetic Helicity?

- Magnetic helicity is a useful parameter to represent the non-potentiality of a magnetic field system.

- Many of observations and simulations of solar eruptions indicate that the eruptions are associated with twisted magnetic field configuration.

- Therefore, magnetic helicity can be considered as a parameter to study the energy buildup and instability leading to solar eruptions.

An eruptive prominence on 2010 March 30 (courtesy of SDO Team).

1.3 Main Objective of This Study

- Magnetic helicity injected through the photospheric surface of CME-productive active regions is studied to find its relationship with (1) the gradual inflation of an active region coronal arcade building up to a CME and (2) the occurrence and speed of CMEs, which not only help to understand physical processes of energy build-up and onset of CMEs, but also provide a useful tool to carry out CME predictions.

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2.1 Magnetic Helicity

- Magnetic helicity is a measure of how much magnetic field lines in a flux tube are twisted around the tube axis (twists), how much the tube axis is kinked (kinks), and how much flux tubes are interlinked with each other in a magnetic field system (inter-linkages).

- Mathematically, magnetic helicity, H, inside a volume, V, of a magnetic field system is defined by:

where A is the vector potential of magnetic field, B (i.e., B=▽×A).

2. Calculation of Magnetic Helicity in Active Regions

P : potential field having the same normal component as B on Scor

Ap : vector potential for P

- Relative magnetic helicity in a coronal volume Vcor (Berger & Field 1984; Finn & Antonsen 1985): a gauge-invariant formula

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2.2 Magnetic Helicity Injection through a Photospheric Surface

where v represents the plasma velocity, and subscripts n and t denote the normal component and the transverse component to S, respectively. Ap is a specific vector potential satisfying:

- Berger & Field (1984) derived the change rate of magnetic helicity, Hr , in an open volume through a boundary surface, S :

∙

- Démoulin & Berger (2003):

Field line footpoint velocity

: Potential Field

: Coulomb Gauge

: Vanishing Normal Component

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2.3 Practical Method for Calculating

- Chae (2001) developed a practically useful method for calculating using vLCT, the velocity of the apparent motion of field lines determined by the technique of local correlation tracking (LCT), instead of using u:

Hr∙

with the integrand called magnetic helicity flux density (magnetic helicity per unit area per unit time).

where t0 and t are the start and end time of the magnetogram data set under investigation, respectively.

- After is determined as a function of time, the amount of helicity accumulation, ΔHr , is calculated by integrating with respect to time:

Hr∙

Hr∙

Hr

∙

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3.1 Gradual Inflation of a Coronal Arcade Building up to a CME (Liu, R., Liu, C., Park, S., Wang, H. 2010, ApJ, 723, 229)

3. Results

Slow Rising of Coronal Arcade on 2006 July 4

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-The time-height profile of the coronal arcade is similar to the short-term (several hours) profile of helicity injection in the active region where the coronal arcade is anchored.

-One remarkable thing is that there was a significant and continuous helicity injection for 2 days before the measurement time of the gradual inflation of the arcade, but magnetic flux changes very little in the active region.

Slow Rising of Coronal Arcade on 2006 July 4

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3.2 Two CME Groups by Helicity Injection Patterns

By calculating helicity injection rate in 28 active regions producing 46 CMEs, it is found that 46 CMEs can be categorized into two different groups by the two characteristic evolution patterns of helicity injection in their source regions.

※ Group A

- 30 CMEs - a pattern of continuous helicity injection followed by no (or a little) injection for a while

※ Group B

- 16 CMEs - a pattern of significant helicity injection followed by its sign reversal

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3.2.1 Monotonically Increasing Phase of Helicity in Group A

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3.2.1 Monotonically Increasing Phase of Helicity in Group A (Cont.)

The same helicity variation pattern is shown in the other cases of Group A.

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- Fan & Gibson (2004)

Hood & Priest (1981) studied the stability of line-tied, uniformly twisted, force-free cylindrical flux tubes and found that the tubes become kink-unstable when the number of rotations that each field line winds about the axis between the line-tied ends exceeds 1.25.

Fan & Gibson (2004) performed isothermal MHD simulations of the three-dimensional evolution of the coronal magnetic field as an arched, twisted magnetic flux tube emerges gradually into a pre-existing coronal arcade, under the condition of low β-plasma and high electric conductivity.

3.2.1 Monotonically Increasing Phase of Helicity in Group A (Cont.)

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3.2.2 Helicity Reversal Phase of 16 CMEs in Group B

A trigger by reconnection-favorable emerging flux (Chen & Shibata 2000)

- CMEs are triggered by the localized reconnection between the reconnection-favorable emerging flux and pre-existing coronal field.

- Observational supports (Feymann & Martin 1995; Wang et al. 2004; Jing et al. 2004)

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3.2.3 Comparison Between Group A and Group B

- The CME speed of Group B is much faster than that of Group A. There is also a significant difference in the CME acceleration between Group A and Group B.

- Furthermore, the CMEs in Group A tend to be single events, while those in Group B mainly consist of successive events.

- These differences may indicate different pre-CME conditions and trigger mechanisms for the two groups. CMEs in Group A seem to be associated with the kink instability. CMEs in Group B might be involved with the emergence of opposite sense of helicity into an existing helicity system, and perhaps an interaction between two helicity systems may be responsible for the CMEs in Group B.

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3.3 Correlation of Helicity Injection Rate with the Speed of CMEs

- The 30 CMEs in Group A were used for the study of helicity injection related to the CME speed.

- The solid line indicates the least-squares linear fits to the data points. The correlation coefficient (CC) of the linear fits is also given in the panel.

- There is a fairly good correlation (CC=0.71) between |< Hr >| and the CME speed. .

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- A coronal arcade in AR 10898 is examined. The gradual inflation of the arcade sustains for hours at ~5 km/s, and it is temporally associated with helicity injection.

- The CMEs under investigation can be categorized into two different groups by the two characteristic evolution patterns: (1) a monotonically increasing phase with one sign of helicity (Group A, 30 CMEs in 23 active regions) and (2) a phase of significant helicity injection followed by its sign reversal (Group B, 16 CMEs in 5 active regions).

- It is suspected that these two groups may have different preconditions and trigger mechanisms. CMEs in Group A seem to be associated with kink instability. CMEs in Group B seem to be involved with emergence of the helicity in the opposite sign into an existing helicity system.

- A fairly good correlation (CC=0.71) between the average helicity injection rate and the speed of 30 CMEs in Group A is found.

4. Summary and Conclusion

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References

Berger, M. A. and Field, G. B.: 1984, Journal of Fluid Mechanics 147, 133Chae, J.: 2001, Astrophys. J. Lett. 560, L95Chen, P. F. and Shibata, K.: 2000, Astrophys. J. 545, 524Démoulin, P. and Berger, M. A.: 2003, Sol. Phys. 215, 203Fan, Y. and Gibson, S. E.: 2004, Astrophys. J. 609, 1123Feynman, J. & Martin, S. F. 1995, J. Geophys. Res., 100, 3355.Finn, J. M. and Antonsen, T. M.: 1985, Comments Plasma Phys. Controlled Fusion 9, 111Hood, A. W. and Priest, E. R.: 1981, Geophysical and Astrophysical Fluid Dynamics 17, 297Jing, J., Yurchyshyn, V. B., Yang, G., Xu, Y., & Wang, H. 2004, Astrophys. J., 614, 1054.Wang, J., Zhou, G., & Zhang, J. 2004, Astrophys. J., 615, 1021

Acknowledgments

New Jersey Institute of Technology Seoul National University Dr. Haimin Wang Dr. Jongchul Chae Dr. Jeongwoo Lee Dr. Rui Liu

KASI/Solar and Space Weather Research Group Dr. Young-Deuk Park Dr. Kyung-Suk Cho Dr. Yeon-Han Kim Dr. Su-Chan Bong

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is the heliocentric angle of the point of interest

2006-12-10 04:51:30 UT

2006-12-10 06:27:30 UT

2006-12-10 08:03:30 UT

2006-12-10 05:39:30 UT

2006-12-10 07:15:30 UT

Averaged

Averaged

Local Correlation Tacking (LCT)

-Window size = 10”

-Window function: top-hat profile

-Correlation criterion: above 0.9

-Bz criterion: above 5 G

Fast Fourier Transform

GA

× (-2Bn)

vLCT

Ap

×

Bn

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※ List of CMEs in Group A

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※ Parameterization of the long-term evolution of helicity injection rate

a, b, c, d, & e = constants

1. CME speed 2. CME occurrence time

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