68 research outputs found
Magnetohydrodynamic Simulations for Studying Solar Flare Trigger Mechanism
In order to understand the flare trigger mechanism, we conducted
three-dimensional magnetohydrodynamic simulations using a coronal magnetic
field model derived from data observed by the Hinode satellite. Several types
of magnetic bipoles were imposed into the photospheric boundary of the
Non-linear Force-Free Field (NLFFF) model of Active Region NOAA 10930 on 2006
December 13 to investigate what kind of magnetic disturbance may trigger the
flare. As a result, we confirm that certain small bipole fields, which emerge
into the highly sheared global magnetic field of an active region, can
effectively trigger a flare. These bipole fields can be classified into two
groups based on their orientation relative to the polarity inversion line: the
so called opposite polarity (OP) and reversed shear (RS) structures as it was
suggested by Kusano et al. (2012). We also investigated the structure of the
footpoints of reconnected field lines. By comparing the distribution of
reconstructed field lines and the observed flare ribbons, the trigger structure
of the flare can be inferred. Our simulation suggests that the data-constrained
simulation taking into account both the large-scale magnetic structure and the
small-scale magnetic disturbance such as emerging fluxes is a good way to find
out a flare productive active region for space weather prediction.Comment: 28 pages, 10 figure
Development of a coronal mass ejection arrival time forecasting system using interplanetary scintillation observations
Coronal mass ejections (CMEs) cause disturbances in the environment of the
Earth when they arrive at the Earth. However, the prediction of the arrival of
CMEs still remains a challenge. We have developed an interplanetary
scintillation (IPS) estimation system based on a global magnetohydrodynamic
(MHD) simulation of the inner heliosphere to predict the arrival time of CMEs.
In this system, the initial speed of a CME is roughly derived from white light
coronagraph observations. Then, the propagation of the CME is calculated by a
global MHD simulation. The IPS response is estimated by the three-dimensional
density distribution of the inner heliosphere derived from the MHD simulation.
The simulated IPS response is compared with the actual IPS observations made by
the Institute for Space-Earth Environmental Research, Nagoya University, and
shows good agreement with that observed. We demonstrated how the simulation
system works using a halo CME event generated by a X9.3 flare observed on
September 5, 2017. We find that the CME simulation that best estimates the IPS
observation can more accurately predict the time of arrival of the CME at the
Earth. These results suggest that the accuracy of the CME arrival time can be
improved if our current MHD simulations include IPS data.Comment: 39 pages, 6 figures, accepted for publication in Earth, Planets and
Spac
MHD Modeling for Formation Process of Coronal Mass Ejections: Interaction between Ejecting Flux Rope and Ambient Field
We performed magnetohydrodynamic simulation of a formation process of coronal
mass ejections (CMEs), focusing on interaction (reconnection) between an
ejecting flux rope and its ambient field. We examined three cases with
different ambient fields: no ambient field, and cases with dipole field of two
opposite directions which are parallel and anti-parallel to that of the flux
rope surface. As a result, while the flux rope disappears in the anti-parallel
case, in other cases the flux ropes can evolve to CMEs and show different
amounts of rotation of the flux rope. The results imply that the interaction
between an ejecting flux rope and its ambient field is an important process for
determining CME formation and CME orientation, and also show that the amount
and direction of magnetic flux within the flux rope and the ambient field are
key parameters for CME formation. Especially, the interaction (reconnection)
plays a significant role to the rotation of the flux rope, with a process
similar to "tilting instability" in a spheromak-type experiment of laboratory
plasma.Comment: 24 pages, 5 figures. Accepted for publication in Ap
Magnetohydrodynamic Modeling of Solar Wind and Coronal Mass Ejections on the Basis of Solar Observations
第6回極域科学シンポジウム[OS] 宙空圏11月16日(月) 国立極地研究所 2階 大会議
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