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Simultaneous ALMA-Hinode-IRIS observations on footpoint signatures of a soft X-ray loop-like microflare  

Toshifumi Shimizu   Submitted: 2021-09-30 18:35

Microflares have been considered to be among the major energy input sources to form active solar corona. To investigate the response of the low atmosphere to events, we conducted an ALMA observation at 3 mm coordinated with IRIS and Hinode observations, on March 19, 2017. During the observations, a soft X-ray loop-type microflare (active-region transient brightening) was captured using Hinode X-ray telescope in high temporal cadence. A brightening loop footpoint is located within narrow field of views ALMA, IRIS slit-jaw imager, and Hinode spectro-polarimeter. Counterparts of the microflare at the footpoint were detected in Si IV and ALMA images, while the counterparts were less apparent in C II and Mg II k images. Their impulsive time profiles exhibit the Neupert effect pertaining to soft X-ray intensity evolution. The magnitude of thermal energy measured using ALMA was approximately 100 times smaller than that measured in the corona. These results suggest that impulsive counterparts can be detected in the transition region and upper chromosphere where the plasma is thermally heated via impinging non-thermal particles. Our energy evaluation indicates a deficit of accelerated particles that impinge the footpoints for a small class of soft X-ray microflares. The footpoint counterparts consist of several brightening kernels, all of which are located in weak (void) magnetic areas formed in patchy distribution of strong magnetic flux at the photospheric level. The kernels provide a conceptual image in which the transient energy release occurs at multiple locations on the sheaths of magnetic flux bundles in the corona.

Authors: Shimizu, T., Shimojo, M., and Abe, M.
Projects: ALMA,Hinode/SOT,Hinode/XRT,IRIS

Publication Status: Accepted for publication in ApJ
Last Modified: 2021-10-01 15:11
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3D magnetic field configuration of small-scale reconnection events in the solar plasma atmosphere  

Toshifumi Shimizu   Submitted: 2015-08-24 18:43

The outer solar atmosphere, i.e., the corona and the chromosphere, is replete with small energy-release events, which are accompanied by transient brightening and jet-like ejections. These events are considered to be magnetic reconnection events in the solar plasma, and their dynamics have been studied using recent advanced observations from the Hinode spacecraft and other observatories in space and on the ground. These events occur at different locations in the solar atmosphere, and vary in their morphology and amount of the released energy. The magnetic field configurations of these reconnection events are inferred based on observations of magnetic fields at the photospheric level. Observations suggest that these magnetic configurations can be classified into two groups. In the first group, two anti-parallel magnetic fields reconnect to each other, yielding a 2D emerging flux configuration. In the second group, helical or twisted magnetic flux tubes are parallel or at a relative angle to each other. Reconnection can occur only between anti-parallel components of the magnetic flux tubes and may be referred to as component reconnection. The latter configuration type may be more important for the larger class of small-scale reconnection events. The two types of magnetic configurations can be compared to counter-helicity and co-helicity configurations, respectively, in laboratory plasma collision experiments.

Authors: T. Shimizu
Projects: Hinode/SOT

Publication Status: Accepted for publications in Physics of Plasmas
Last Modified: 2015-08-25 16:48
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High speed photospheric material flow observed at the polarity inversion line of a delta-type sunspot producing an X5.4 flare on 7 March 2012  

Toshifumi Shimizu   Submitted: 2014-06-08 18:30

Solar flares abruptly release the free energy stored as a non-potential magnetic field in the corona and may be accompanied by eruptions of the coronal plasma. Formation of a non-potential magnetic field and the mechanisms for triggering the onset of flares are still poorly understood. In particular, photospheric dynamics observed near those polarity inversion lines that are sites of major flare production have not been well observed with high spatial resolution spectro-polarimetry. This paper reports on a remarkable high-speed material flow observed along the polarity inversion line located between flare ribbons at the main energy release side of an X5.4 flare on 7 March 2012. Observations were carried out by the spectro-polarimeter of the Solar Optical Telescope onboard Hinode. The high-speed material flow was observed in the horizontally-oriented magnetic field formed nearly parallel to the polarity inversion line. This flow persisted from at least 6 hours before the onset of the flare, and continued for at least several hours after the onset of the flare. Observations suggest that the observed material flow represents neither the emergence nor convergence of the magnetic flux. Rather, it may be considered to be material flow working both to increase the magnetic shear along the polarity inversion line and to develop magnetic structures favorable for the onset of the eruptive flare.

Authors: Shimizu, T., Lites, B.W., and Bamba, Y.
Projects: Hinode/SOT

Publication Status: Accepted to PASJ, Hinode special issue
Last Modified: 2014-06-09 06:57
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Abstracts by Author
Simultaneous ALMA-Hinode-IRIS observations on footpoint signatures of a soft X-ray loop-like microflare
3D magnetic field configuration of small-scale reconnection events in the solar plasma atmosphere
High speed photospheric material flow observed at the polarity inversion line of a delta-type sunspot producing an X5.4 flare on 7 March 2012

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