Magnetic Field Strength in the Solar Corona from Type II Band Splitting

Cho, K. S.; Lee, J.; Gary, Dale E.; Moon, Yong‐Jae; Park, Y. D.

doi:10.1086/519160

Cited by 79 publications

(64 citation statements)

References 18 publications

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“…However, it would not significantly affect the height variation of B. On the other hand, since almost all of the direct (Lin et al 2000;Lin et al 2004) or indirect (Cho et al 2007;Ramesh et al 2010;West et al 2011) measurements of coronal fields strength in previous studies are mainly focused on the stronger fields above or at least emanate from major active regions, our results could offer helpful information about the magnetic field structures above mini active region newly-emerged in coronal hole.…”

Section: Discussionmentioning

confidence: 84%

The kinematics of an untwisting solar jet in a polar coronal hole observed bySDO/AIA

Chen¹,

Zhang²,

Ma³

2012

Res. Astron. Astrophys.

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Using the multi-wavelength data from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) spacecraft, we study a jet occurred in coronal hole near the northern pole of the Sun. The jet presented distinct helical upward motion during ejection. By tracking six identified moving features (MFs) in the jet, we found that the plasma moved at an approximately constant speed along the jet's axis, meanwhile, they made a circular motion in the plane transverse to the axis. Inferred from linear and trigonometric fittings to the axial and transverse heights of the six tracks, the mean values of axial velocities, transverse velocities, angular speeds, rotation periods, and rotation radiuses of the jet are 114 km s −1 , 136 km s −1 , 0.81 • s −1 , 452 s, and 9.8 × 10 3 km respectively. As the MFs rose, the jet width at the corresponding height increased. For the first time, we derived the height variation of the longitudinal magnetic field strength in the jet from the assumption of magnetic flux conservation. Our results indicate that, at the heights of 1 × 10 4 ∼ 7 × 10 4 km from jet base, the flux density in the jet decreased from about 15 to 3 G as a function of B=0.5(R/R ⊙ -1) −0.84 (G). A comparison was made with the other results in previous studies.

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Section: Discussionmentioning

confidence: 84%

The kinematics of an untwisting solar jet in a polar coronal hole observed bySDO/AIA

Chen¹,

Zhang²,

Ma³

2012

Res. Astron. Astrophys.

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“…There are still some disputes on the exact mechanisms responsible for the band-splitting (e.g., Treumann & Labelle 1992;Du et al 2015). The interpretation proposed by Smerd et al (1975) is preferred in many recent papers (Cho et al 2007a;Ma et al 2011;Gopalswamy et al 2012;Zimovets et al 2012). Vršnak et al (2002) proposed a method to obtain the compression ratio of the shock from the bandsplitting of a type II radio burst.…”

Section: Parameters Derived From Radio Spectrummentioning

confidence: 99%

Investigating the Conditions of the Formation of a Type Ii Radio Burst on 2014 January 8

Cheng

Ding

et al. 2016

ApJ

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It is believed that type II radio bursts are generated by shock waves. In order to understand the generation conditions of type II radio bursts, in this paper, we analyze the physical parameters of a shock front. The type II radio burst we selected was observed by Siberian Solar Radio Telescope (SSRT) and Learmonth radio station and was associated with a limb CME occurring on 2014 January 8 observed by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). The evolution of the CME in the inner corona presents a doublelayered structure that propagates outward. We fit the outer layer of the structure with a partial circle and divide it into 7 directions from -45• to 45• with an angular separation of 15• . We measure the outer layer speed along the 7 directions, and find that the speed in the direction of -15• with respect to the central direction is the fastest. We use the differential emission measure (DEM) method to calculate the physical parameters at the outer layer at the moment when the type II radio burst was initiated, including the temperature (T ), emission measure (EM ), temperature ratio (T d /T u ), compression ratio (X), and Alfvén Mach number (M A ). We compare the quantities X and M A to that obtained from band-splitting in the radio spectrum, and find that this type II radio burst is generated at a small region of the outer layer that is located at the sector in 45• direction. The results suggest that the generation of type II radio bursts (shock) requires larger values of X and M A rather than simply a higher speed of the disturbance.

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“…Many recent works have suggested that the interaction region between CME shocks and streamers could possibly be an important source of both metric and interplanetary type IIs (e.g., Reiner et al 2003;Mancuso & Raymond 2004;Cho et al 2007Cho et al , 2008Feng et al 2012Feng et al , 2013Kong et al 2012Kong et al , 2015Shen et al 2013;Chen et al 2014;Magdalenić et al 2014;Eselevich et al 2015). Possible explanations for these results are twofold.…”

Section: Introductionmentioning

confidence: 99%

Electron Acceleration at a Coronal Shock Propagating Through a Large-Scale Streamer-Like Magnetic Field

Kong

Chen

Guo

et al. 2016

ApJ

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Using a test-particle simulation, we investigate the effect of large-scale coronal magnetic fields on electron acceleration at an outward-propagating coronal shock with a circular front. The coronal field is approximated by an analytical solution with a streamer-like magnetic field featuring a partially open magnetic field and a current sheet at the equator atop the closed region. We show that the large-scale shock-field configuration, especially the relative curvature of the shock and the magnetic field line across which the shock is sweeping, plays an important role in the efficiency of electron acceleration. At low shock altitudes, when the shock curvature is larger than that of the magnetic field lines, the electrons are mainly accelerated at the shock flanks; at higher altitudes, when the shock curvature is smaller, the electrons are mainly accelerated at the shock nose around the top of closed field lines. The above process reveals the shift of the efficient electron acceleration region along the shock front during its propagation. We also find that, in general, the electron acceleration at the shock flank is not as efficient as that at the top of the closed field because a collapsing magnetic trap can be formed at the top. In addition, we find that the energy spectra of electrons are power-law-like, first hardening then softening with the spectral index varying in a range of −3 to −6. Physical interpretations of the results and implications for the study of solar radio bursts are discussed.

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Magnetic Field Strength in the Solar Corona from Type II Band Splitting

Cited by 79 publications

References 18 publications

The kinematics of an untwisting solar jet in a polar coronal hole observed bySDO/AIA

The kinematics of an untwisting solar jet in a polar coronal hole observed bySDO/AIA

Investigating the Conditions of the Formation of a Type Ii Radio Burst on 2014 January 8

Electron Acceleration at a Coronal Shock Propagating Through a Large-Scale Streamer-Like Magnetic Field

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