JapaneseHighlights
We performed a multi-wavelength observation of a solar flare that occurred on 2006 December 13 with the Hinode satellite, the RHESSI satellite, and the Nobeyama Radioheliograph (NoRH), in order to study the electron acceleration site and mechanisms. A photospheric vector magnetogram obtained from the Solar Optical Telescope on board Hinode and a hard X-ray (HXR) image taken by RHESSI reveal that the HXR sources are located at the region where the horizontal magnetic fields change direction, i.e., the magnetic separatrix. Microwave images taken with NoRH suggest that the accelerated electrons are distributed parallel rather than perpendicular to the magnetic field lines. We conclude that these observations are evidence of the electron acceleration due to the curvature drift near the magnetic separatrix (Minoshima et al. 2009, ApJ).
(Figure caption) Vector magnetogram taken by Hinode and 35-100 keV HXR image observed with RHESSI (black contours). From left to right, the strengths of the horizontal magnetic fields (east-west and south-north directions), and the longitudinal magnetic field are shown in units of Gauss. The horizontal magnetic fields are also indicated as gray arrows in the right image. The white dashed lines correspond to the position of the flare ribbons. These images show that the HXR sources are located only at places where the horizontal magnetic fields change direction.
To understand particle acceleration and transport mechanisms in solar flares, we have developed a new numerical code with the drift-kinetic Vlasov equation. Our code can describe the time evolution of the particle distribution function with coronal actual parameters, and then the numerical result can be directly compared with the observations. Using the code, we have investigated the particle acceleration by convective electric fields generated through the flare. We found that the particles are affected by two different mechanisms: Fermi acceleration in open magnetic field lines, and drift acceleration in closed field lines.
(Figure caption) Spatial distribution of 20 keV electrons in a solar flare, obtained from the drift-kinetic Vlasov simulation. The x- and z-axes correspond to the tangential and normal directions relative to the solar surface, respectively. The calculation domain covers ~10 Mm in the x direction, and ~13 Mm in the z direction. The white solid lines are the magnetic field lines, and the white dashed line corresponds to the magnetic separatrix.
GEMSIS-Ring Current Simulation
We have almost finished development of a prototype GEMSIS-RC model, which is a new self-consistent numerical simulation code solving the five-dimensional Vlasov equation for the ring-current ions in the inner-magnetosphere coupled with the Maxwell equations.
Please refer to the GEMSIS-Magnetosphere working team page for more information.
GEMSIS-Radiation Belt Simulation
We have developed a numerical code to trace the trajectory of relativistic electrons in the outer radiation belt precisely and efficiently. The initial result has been submitted to a scientific journal.
Please refer to the GEMSIS-Magnetosphere working team page for more information.
Empirical Model of Large-Scale Field-Aligned Currents
An empirical model of large-scale field-aligned currents (LSFACs) has been developed in collaboration with The Institute of Statistical Mathematics (ISM) and The Johns Hopkins University Applied Physics Laboratory (JHU/APL). With a huge amount of data from the DMSP and DE2 satellites, the model is parameterized by the solar wind speed, the interplanetary magnetic field (IMF), the tilt angle of the Earth’s magnetic field, and the solar activity indices to give a realistic spatial profile of LSFACs. The present model has adopted a new method in which positions of upper/lower latitude boundaries and intensities of LSFACs are averaged separately.
Inductive Model of Electric Potential
With data from the SuperDARN radars and ground-based magnetic observatories, an inductive model of the electric potential has been developed to reconstruct the electric potential during magnetic storms.
Deductive Model of Electric Potential
By applying Ohm’s law, we can calculate the electric potential for given electric currents flowing along a field line (field-aligned current) and the ionospheric conductance. From left to right, an example of the calculated electric potential, field-aligned current, and ionospheric conductance is shown.