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QUASI-PERIODIC OSCILLATIONS IN FLARES AND CORONAL MASS EJECTIONS ASSOCIATED WITH MAGNETIC RECONNECTION  

Takuya Takahashi   Submitted: 2017-09-17 19:22

We propose a mechanism for quasi-periodic oscillations of both coronal mass ejections (CMEs) and flare loops as related to magnetic reconnection in eruptive solar flares. We perform two-dimensional numerical MHD simulations of magnetic flux rope eruption, with three different values of the global Lundquist number. In the low Lundquist number run, no oscillatory behavior is found. In the moderate Lunquist number run, on the other hand, quasi-periodic oscillations are excited both at the bottom of the flux rope and at the flare loop-top. In the high Lundquist number run, quasi- periodic oscillations are also excited; in the meanwhile, the dynamics become turbulent due to the formation of multiple plasmoids in the reconnection current sheet. In high and moderate Lundquist number runs, thin reconnection jet collide with the flux rope bottom or flare loop-top and dig them deeply. Steep oblique shocks are formed as termination shocks where reconnection jet is bent (rather than decelerated) in horizontal direction, resulting in supersonic back-flows. The structure becomes unstable, and quasi-periodic oscillation of supersonic back-flows appear at locally confined high-beta region at both the flux rope bottom and flare loop-top. We compare the observational characteristics of quasi-periodic oscillations in erupting flux ropes, post-CME current sheets, flare ribbons and light curves, with corresponding dynamical structures found in our simulation.

Authors: Takuya Takahashi, Jiong Qiu and Kazunari Shibata
Projects: GOES X-rays

Publication Status: accepted for publication in ApJ
Last Modified: 2017-09-20 09:04
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Sheath-Accumulating Propagation of Interplanetary Coronal Mass Ejection  

Takuya Takahashi   Submitted: 2017-02-27 06:51

Fast interplanetary coronal mass ejections (interplanetary CMEs, or ICMEs) are the drivers of strongest space weather storms such as solar energetic particle events and geomagnetic storms. The connection between space weather impacting solar wind disturbances associated with fast ICMEs at Earth and the characteristics of causative energetic CMEs observed near the Sun is a key question in the study of space weather storms as well as in the development of practical space weather prediction. Such shock-driving fast ICMEs usually expand at supersonic speed during the propagation, resulting in the continuous accumulation of shocked sheath plasma ahead. In this paper, we propose the "sheath-accumulating propagation" (SAP) model that describe the coevolution of the interplanetary sheath and decelerating ICME ejecta by taking into account the process of upstream solar wind plasma accumulation within the sheath region. Based on the SAP model, we discussed (1) ICME deceleration characteristics, (2) the fundamental condition for fast ICME at Earth, (3) thickness of interplanetary sheath, (4) arrival time prediction and (5) the super-intense geomagnetic storms associated with huge solar flares. We quantitatively show that not only speed but also mass of the CME are crucial in discussing the above five points. The similarities and differences among the SAP model, the drag-based model and the`snow-plough' model proposed by tappin2006 are also discussed.

Authors: Takuya Takahashi, Kazunari Shibata
Projects: None

Publication Status: accepted for publication in ApJL
Last Modified: 2017-03-01 12:20
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Shock-Cloud Interaction in the Solar Corona  

Takuya Takahashi   Submitted: 2017-01-29 17:58

Flare associated coronal shock waves sometimes interact with solar prominences leading to large amplitude prominence oscillations. Such prominence activation gives us unique opportunity to track time evolution of shock-cloud interaction in cosmic plasmas. Although the dynamics of interstellar shock-cloud interaction is extensively studied, coronal shock-solar prominence interaction is rarely studied in the context of shock-cloud interaction. Associated with X5.4 class solar flare occurred on 7 March, 2012, a globally propagated coronal shock wave interacted with a polar prominence leading to large amplitude prominence oscillation. In this paper, we studied bulk acceleration and excitation of internal flow of the shocked prominence using three-dimensional MHD simulations. We studied eight magnetohydrodynamic (MHD) simulation runs with different mass density structure of the prominence, and one hydrodynamic simulation run, and compared the result. In order to compare observed motion of activated prominence with corresponding simulation, we also studied prominence activation by injection of triangular shaped coronal shock. We found that magnetic tension force mainly accelerate (and then decelerate) the prominence. The internal flow, on the other hand, is excited during the shock front sweeps through the the prominence and damps almost exponentially. We construct phenomenological model of bulk momentum transfer from shock to the prominence, which agreed quantitatively with all the simulation results. Based on the phenomenological prominence-activation model, we diagnosed physical parameters of coronal shock wave. The estimated energy of the coronal shock is several percent of total energy released during the X5.4 flare.

Authors: Takuya Takahashi
Projects: SDO-AIA

Publication Status: accepted for publication in ApJ
Last Modified: 2017-01-31 11:46
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Scaling Relations in Coronal Mass Ejections and Energetic Proton Events associated with Solar Superflares  

Takuya Takahashi   Submitted: 2016-11-20 22:19

In order to discuss the potential impact of solar 'superflares' on space weather, we investigated statistical relations among energetic proton peak flux with energy higher than 10 MeV (Fp), CME speed near the Sun (VCME) obtained by SOHO/LASCO coronagraph and flare soft X-ray peak flux in 1-8Å band (FSXR) during 110 major solar proton events (SPEs) recorded from 1996 to 2014. The linear regression fit results in the scaling relations VCME ∝ FSXR^ α , F_p∝ FSXR^?\eta and F_p∝ VCME^\gamma with α = 0.30± 0.04, β = 1.19 ± 0.08 and \gamma = 4.35 ± 0.50, respectively. On the basis of simple physical assumptions, on the other hand, we derive scaling relations expressing CME mass (MCME), CME speed and energetic proton flux in terms of total flare energy (Eflare) as, MCME∝ Eflare2/3, VCME∝ Eflare1/6 and Fp∝ Eflare5/6∝ VCME^5, respectively. We then combine the derived scaling relations with observation, and estimated the upper limit of VCME and Fp to be associated with possible solar superflares.

Authors: Takuya Takahashi, Yoshiyuki Mizuno, Kazunari Shibata
Projects: SoHO-LASCO

Publication Status: Accepted for publication in ApjL
Last Modified: 2016-11-21 12:29
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Prominence Activation by Coronal Fast Mode Shock  

Takuya Takahashi   Submitted: 2015-01-07 23:46

An X5.4 class flare occurred in active region (AR) NOAA11429 on 2012 March 7. The flare was associated with very fast coronal mass ejection (CME) with its velocity of over 2500 km s-1. In the images taken with STEREO-B/COR1, a dome-like disturbance was seen to detach from expanding CME bubble and propagated further. A Type-II radio burst was also observed at the same time. On the other hand, in EUV images obtained by SDO/AIA, expanding dome-like structure and its foot print propagating to the north were observed. The foot print propagated with its average speed of about 670 km s-1 and hit a prominence located at the north pole and activated it. While the activation, the prominence was strongly brightened. On the basis of some observational evidence, we concluded that the foot print in AIA images and the ones in COR1 images are the same, that is MHD fast mode shock front. With the help of a linear theory, the fast mode mach number of the coronal shock is estimated to be between 1.11 and 1.29 using the initial velocity of the activated prominence. Also, the plasma compression ratio of the shock is enhanced to be between 1.18 and 2.11 in the prominence material, which we consider to be the reason of the strong brightening of the activated prominence. The applicability of linear theory to the shock problem is tested with nonlinear MHD simulation.

Authors: Takuya Takahashi, Ayumi Asai, Kazunari Shibata
Projects: SDO-AIA

Publication Status: accepted
Last Modified: 2015-01-09 12:49
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Abstracts by Author
QUASI-PERIODIC OSCILLATIONS IN FLARES AND CORONAL MASS EJECTIONS ASSOCIATED WITH MAGNETIC RECONNECTION
Sheath-Accumulating Propagation of Interplanetary Coronal Mass Ejection
Shock-Cloud Interaction in the Solar Corona
Scaling Relations in Coronal Mass Ejections and Energetic Proton Events associated with Solar Superflares
Prominence Activation by Coronal Fast Mode Shock

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