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Probing the Puzzle of Behind-the-limb γ-Ray Flares: Data-driven Simulations of Magnetic Connectivity and CME-driven Shock Evolution  

Meng Jin   Submitted: 2018-11-06 17:24

Recent detections of high-energy γ-rays from behind-the-limb (BTL) solar flares by the Fermi Gamma-ray Space Telescope pose a puzzle and challenge on the particle acceleration and transport mechanisms. In such events, the γ-ray emission region is located away from the BTL flare site by up to tens of degrees in heliographic longitude. It is thus hypothesized that particles are accelerated at the shock driven by the coronal mass ejection (CME) and then travel from the shock downstream back to the front side of the Sun to produce the observed γ-rays. To test this scenario, we performed data-driven, global magnetohydrodynamics simulations of the CME associated with a well-observed BTL flare on 2014 September 1. We found that part of the CME-driven shock develops magnetic connectivity with the γ-ray emission region, facilitating transport of particles back to the Sun. Moreover, the observed increase in γ-ray flux is temporally correlated with (1) the increase of the shock compression ratio and (2) the presence of a quasi-perpendicular shock over the area that is magnetically connected to the γ-ray emitting region, both conditions favoring the diffusive shock acceleration (DSA) of particles. These results support the above hypothesis and can help resolve another puzzle, i.e., long-duration (up to 20 hr) γ-rays flares. We suggest that, in addition to DSA, stochastic acceleration by plasma turbulence may also play a role, especially in the shock downstream region and during the early stage when the shock Alfvén Mach number is small.

Authors: Meng Jin, Vahé Petrosian, Wei Liu, Nariaki V. Nitta, Nicola Omodei, Fatima Rubio da Costa, Frederic Effenberger, Gang Li, Melissa Pesce-Rollins, Alice Allafort, and Ward Manchester IV
Projects: Fermi/LAT,SDO-AIA,SDO-HMI

Publication Status: The Astrophysical Journal, Volume 867, Number 2
Last Modified: 2018-11-07 12:04
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Data Constrained Coronal Mass Ejections in A Global Magnetohydrodynamics Model  

Meng Jin   Submitted: 2017-01-12 15:19

We present a first-principles-based coronal mass ejection (CME) model suitable for both scientific and operational purposes by combining a global magnetohydrodynamics (MHD) solar wind model with a flux-rope-driven CME model. Realistic CME events are simulated self-consistently with high fidelity and forecasting capability by constraining initial flux rope parameters with observational data from GONG, SOHO/LASCO, and STEREO/ COR. We automate this process so that minimum manual intervention is required in specifying the CME initial state. With the newly developed data-driven Eruptive Event Generator using Gibson-Low configuration, we present a method to derive Gibson-Low flux rope parameters through a handful of observational quantities so that the modeled CMEs can propagate with the desired CME speeds near the Sun. A test result with CMEs launched with different Carrington rotation magnetograms is shown. Our study shows a promising result for using the firstprinciples-based MHD global model as a forecasting tool, which is capable of predicting the CME direction of propagation, arrival time, and ICME magnetic field at 1 au (see the companion paper by Jin et al. 2016a).

Authors: M. Jin, W. B. Manchester, B. van der Holst, I. Sokolov, G. Toth, R. E. Mullinix, A. Taktakishvili, A. Chulaki, and T. I. Gombosi
Projects: None

Publication Status: Published by ApJ
Last Modified: 2017-01-13 06:08
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Chromosphere to 1 AU Simulation of the 2011 March 7th Event: A Comprehensive Study of Coronal Mass Ejection Propagation  

Meng Jin   Submitted: 2017-01-12 15:16

We perform and analyze the results of a global magnetohydrodynamic simulation of the fast coronal mass ejection (CME) that occurred on 2011 March 7. The simulation is made using the newly developed Alfvén Wave Solar Model (AWSoM), which describes the background solar wind starting from the upper chromosphere and extends to 24 R ⊙. Coupling AWSoM to an inner heliosphere model with the Space Weather Modeling Framework extends the total domain beyond the orbit of Earth. Physical processes included in the model are multi-species thermodynamics, electron heat conduction (both collisional and collisionless formulations), optically thin radiative cooling, and Alfvén-wave turbulence that accelerates and heats the solar wind. The Alfvén-wave description is physically self-consistent, including non-Wentzel-Kramers-Brillouin reflection and physics-based apportioning of turbulent dissipative heating to both electrons and protons. Within this model, we initiate the CME by using the Gibson-Low analytical flux rope model and follow its evolution for days, in which time it propagates beyond STEREO A. A detailed comparison study is performed using remote as well as in situ observations. Although the flux rope structure is not compared directly due to lack of relevant ejecta observation at 1 au in this event, our results show that the new model can reproduce many of the observed features near the Sun (e.g., CME-driven extreme ultraviolet [EUV] waves, deflection of the flux rope from the coronal hole, "double-front" in the white light images) and in the heliosphere (e.g., shock propagation direction, shock properties at STEREO A).

Authors: M. Jin, W. B. Manchester, B. van der Holst, I. Sokolov, G. Toth, A. Vourlidas, C. A. de Koning, and T. I. Gombosi
Projects: None

Publication Status: Published by ApJ
Last Modified: 2017-01-13 06:08
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A Numerical Study of Long-Range Magnetic Impacts during Coronal Mass Ejections  

Meng Jin   Submitted: 2016-03-15 16:13

With the global view and high-cadence observations from SDO/AIA and STEREO, many spatially separated solar eruptive events appear to be coupled. However, the mechanisms for "sympathetic" events are still largely unknown. In this study, we investigate the impact of an erupting flux rope on surrounding solar structures through large-scale magnetic coupling. We build a realistic environment of the solar corona on 2011 February 15 using a global magnetohydrodynamics (MHD) model and initiate coronal mass ejections (CMEs) in active region (AR) 11158 by inserting Gibson-Low analytical flux ropes. We show that a CME's impact on the surrounding structures depends not only on the magnetic strength of these structures and their distance to the source region, but also on the interaction between the CME with the large-scale magnetic field. Within the CME expansion domain where the flux rope field directly interacts with the solar structures, expansion-induced reconnection often modifies the overlying field, thereby increasing the decay index. This effect may provide a primary coupling mechanism underlying the sympathetic eruptions. The magnitude of the impact is found to depend on the orientation of the erupting flux rope, with the largest impacts occurring when the flux rope is favorably oriented for reconnecting with the surrounding regions. Outside the CME expansion domain, the influence of the CME is mainly through field line compression or post-eruption relaxation. Based on our numerical experiments, we discuss a way to quantify the eruption impact, which could be useful for forecasting purposes.

Authors: M. Jin, C. J. Schrijver, M. C. M. Cheung, M. L. DeRosa, N. V. Nitta, A. M. Title
Projects: SDO-AIA

Publication Status: Published by Astrophysical Journal
Last Modified: 2016-03-16 11:28
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Abstracts by Author
Probing the Puzzle of Behind-the-limb γ-Ray Flares: Data-driven Simulations of Magnetic Connectivity and CME-driven Shock Evolution
Data Constrained Coronal Mass Ejections in A Global Magnetohydrodynamics Model
Chromosphere to 1 AU Simulation of the 2011 March 7th Event: A Comprehensive Study of Coronal Mass Ejection Propagation
A Numerical Study of Long-Range Magnetic Impacts during Coronal Mass Ejections

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