AAS/SPD, 2005 (#SH13A-06)
"The MHD simulation on the coronal plasma in radially shrinking open magnetic flux tubes"
Hayashi, K., Zhao, X. P. and Poduval, B.
Open field regions in the corona, or coronal holes, have been believed
to be rapidly expanding with their flux tube expansion factors, FTEs,
greater than 1. We present the MHD simulation results of three-dimensional
solar corona, focusing on the open field regions with FTEs less than 1.
Most of such radially shrinking magnetic flux tubes are found to be rooted
on the weak open field region sandwiched between two strong open field
regions with FTEs greater than 1 and with same magnetic polarity
as the weak region. The flow speeds at the shrinking magnetic flux tubes
obtained with our MHD simulation are less dependent on FTEs, while the
inverse relationship between the flow speed and FTE is obtained at the
usual expanding magnetic flux tubes. This finding increases the complex
in using the FTE to predict the solar wind speed, and may be used to better
understand the coronal plasma expansion.
AGU fall meeting, 2003 (#SH42B-0524)
"Solar corona obtained with MHD simulation using various boundary treatments
based on characteristic projection method"
Hayashi, K.
We will present the results of the experimental time-dependent MHD simulation
of the solar corona, with various boundary treatments based on the concept of
characteristics projection method. This method allows us to make the choices
of the boundary treatment rather arbitrarily, and it is possible that the
results may depend on them. We examined this point using TVD-MUSCL MHD code
and found that, among the choice we made, a two-stage boundary treatment,
where (i) the plasma density and temperature are fixed if 0 ≤ Vr ≤ Vc and
(ii) the radial flow speed is reset to be Vc and instead the temperature
is changeable if Vr ≥ Vc, with the criteria flow speed Vc = 5.0 km/s,
provides the steady solar wind best matching the reality, for example,
the uniform plasma and magnetic field at the high heliographic latitude regions.
This study is a part of our effort to construct the three-dimensional MHD
simulation model of solar corona using SOHO/MDI data.
AGU fall meeting, 2001 (#SH31A-0697)
"MHD tomography using IPS observations"
Hayashi, K., Kojima, M., Tokumaru, M., and Fujiki, K.
We will present the tomography analysis method to derive three-dimensional
solar wind structures from IPS observations using MHD simulation.
By incorporating MHD simulation in tomography analysis, we can treat
the nonlinear MHD interactions in solar wind and examine the spatial variation
at the stream-stream interaction regions and spiral structure of IMF.
Therefore, MHD tomography will improve the global solar wind structure
derived from IPS measurement data. The method is based on the concept of
the tomography, and the practical calculation is done as iteration procedure.
At the first step of iteration, MHD simulation is carried out with
given provisional boundary conditions, and the numerical three-dimensional
solar wind is made. At the next step, the IPS observations are simulated
in this three-dimensional solar wind. The differences between the actual
IPS measurement and the numerically reproduced ones are traced back along
streamlines onto the inflow boundary surface. Then, the velocity distribution
on the boundary surface is modified so that the differences may be cancelled.
For the MHD simulation, the boundary conditions of other solar wind parameters,
density, temperature and magnetic field, are determined as follows.
The density and temperature are determined by empirical relations to the velocity,
and magnetic field is determined from the potential field approximation.
The three-dimensional solar wind structures derived from this analysis were compared
with the in-situ measurement data made by Ulysses and WIND,
and good agreements were contained among them.
JGUM, 2001
"The three-dimensional structure of the solar wind determined by
combining the MHD simulation and the IPS observation data"
Keiji Hayashi, Masayoshi Kojima, Munetoshi Tokumaru, and Ken'ichi Fujiki
The MHD simulation model to determine the three-dimensional solar wind structure
by introducing the IPS observation data made at STEL of Nagoya University is presented.
Giving the inner boundary conditions that are determined from the IPS observations data
and some assumptions, we can calculate the solar wind structure in the space
from 0.25 to 5 AU that are consistent with both the basic equations and the observed data.
Various agreements are seen in the comparison with the nearby-Earth and Ulysses data,
while these in-situ data have been made independently of our simulation model.
COSPAR scientific assembly, 2000 (#PSW1-0073)
"The speed of the solar wind and the solar surface and coronal magnetic field"
K. Hayashi and H. Yoshimura
We found that there is a positive correlation between the speed of the solar
wind flow at about 20 solar radii and an index of the solar surface magnetic
field at the footpoint of the streamline of the solar wind flow in a series
of numerical simulation experiment of the nonlinearly coupled solar wind
flow and magnetic field. The solar wind flow is faster when the footpoint of its
streamline is more distant from the nearest closed boundary line at the solar
surface made by the footpoints of the closed coronal magnetic field lines, and
when the surface magnetic field along the distance is stronger.