SPD 2013 (#302.04)
"A data-driven time-dependent three-dimensional MHD simulation of solar active regions with HMI vector magnetic field data"
K. Hayashi, J. Todd Hoeksema, Yang Liu, Xudong Sun, Monica Bobra and Aimee Norton
We investigate the dynamics of the solar active regions
by means of our data-driven time-dependent three-dimensional MHD simulation model
using the HMI vector magnetic field data.
The simulations start with pre-emergence phase, or very early phase of the
active region so that the development of the loop structures and other
signatures of the active regions will be traced.
We tested several cases, mainly for AR 11158 of Feb. 2011.
Either of the plasma motion or electric field, inferred from the
DAVE4VM (Schuck, 2008) is given to the solar-surface boundary surface of the
simulation box to which the method of projected normal characteristics (Nakagawa
et al. 1987; Wu and Wang, 1987) is applied to ensure the numerical stability and consistency in physics.
As our first attempt, we choose the ideal MHD equations without any additional terms except gravity.
The results of the simulation show that the method can trace some signatures
of the solar active regions, such as development of the magnetic-field loop and (nonlinear) twist.
Not having all information at the simulation initial time, nor all physics
processes on the photosphere, at transition region, and in the solar corona,
agreements in plasma quantities with the other observation such as AIA image data are limited.
No flare-like eruptions were obtained under a simulation setting we currently test.
The temporal sequences of three-component vector data can give good
constraints on the MHD simulation studies of the sub-Alfvenic region, though,
we will need more observations, and probably assumptions, to fulfill the physics system.
The MHD simulation can be a powerful tool to bridge the measurements and
observation, helping interpretation and giving requirement.
GONG2012 / LWS-SDO5 / SOHO 27 (#80)
"Making global map of the solar surface Br from the HMI vector magnetic field observations"
Keiji Hayashi, J. T. Hoeksema, Y. Liu, A. Norton, X. Sun, R. Centeno, G. Barnes and K. D. Leka
The Helioseismic Magnetic Imager (HMI) has made full-disk vector magnetic field measurement of the Sun
with a cadence of 12 minutes. We can determine the three-component solar surface magnetic field from
the HMI observations with the data process pipeline modules, VFISV (Very Fast Inversion of the Stokes Vector)
for Milne-Eddington inversion (Borrero et al, 2010) and
the minimum-energy disambiguation algorithm (Metcalf 1994, Leka et al, 2009).
For the modelings of the global corona and solar wind, such as
the PFSS (potential-field source-surface) model and the MHD simulations,
the global maps, typically in the synoptic map format, of the radial (Br) component must be prepared.
Because of weak magnetic signals at the quiet sun regions and geometric effects near solar disk limb,
we need to apply specific care to the quiet sun regions and the polar regions
in order to make a global map usable by these models.
In this presentation, we will present maps of solar-surface Br derived from the HMI vector measurements
with several treatments for the weak field regions and compare results of models with other observations,
such as coronal images taken by the SDO's AIA (Atmospheric Imaging Assembly).
SDP 2012 (220th AAS meeting) (#521.21)
"Daily Coronal MHD Simulation Using HMI Near-Real-Time Magnetograms",
Keiji Hayashi and HMI team
SDO/HMI is making full-disk line-of-sight magnetogram measurements with a cadence of 45 seconds.
The HMI analysis pipeline regularly generates two types of synoptic map of the solar surface magnetic field.
Definitive calibrated data maps are created every Carrington Rotation, about every 27 days and
a preliminary synoptic map is updated on a near-real-time basis.
As an application of the near-real-time data,
we have been running a daily MHD simulation of the global solar corona
using the photospheric map as the boundary condition ( http://hmi.stanford.edu/MHD ).
The daily MHD model assumes a polytropic gas with the specific heat ratio of 1.05, and
the simulation is conducted in a 4-pi spherical grid system
with latitudinal and longitudinal grid sizes of pi/64.
The output available at hmi.stanford.edu/MHD includes the three-dimensional volume data,
the shape of the open-field regions corresponding to the coronal holes, and
the LoS-integration of the coronal density mimicking coronagraph observations.
For validation, we compare the results of the low-resolution daily MHD simulation and
the high-resolution PFSS calculation with SDO/AIA and SOHO/C2 and C3 image data.
In the future the simulation region will be extended to 1 AU,
and models of coronal heating and acceleration will be applied to allow a timely prediction of solar wind
at the Earth for space weather purposes.
SDP 2012 (220th AAS meeting) (#207.16)
"Making The Daily-updated Synoptic Map Of HMI Line-of-sight Magnetogram Cooperating With The HARP module",
K. Hayashi, Y. Liu, X. Sun and M. J. Turmon
The synoptic map of the magnetogram is widely used for the global coronal modeling, and the daily or
more frequently updated maps help enhance understanding of the solar corona and interplanetary space,
especially the space weather related topics.
The daily-updated synoptic map is made by superimposing the latest meridional bin of the full disk data
to the map. In the HMI data pipeline,
the width of the bin is chosen 80 degrees in longitude around the central meridian.
A problem occurs when the boundary of the bin happens to separate the bipolar pair of the strong field:
The updated part of the synoptic map may have magnetic flux unbalanced, then, the global map will have
unbalanced flux and the models of the global corona, such as the PFSS, will give wrong solution.
To avoid this problem, one choice is to include all (or exclude all) of the bipolar pair.
The HARP, HMI Active Region Patch, will be automatically and routinely monitoring the HMI magnetogram data
and recognizing the Active Region, therefore,
the HARP will help minimize such unbalance of the magnetic field.
In this presentation, we will show the daily updated maps and the outputs of the coronal models,
the PFSS and MHD, with the new maps,compare with the other coronal observations such as SDO/AIA images.
AGU fall meeting 2007 (#SH53A-1072)
"An MHD simulation model of the global solar corona with the time-varying
boundary magnetic field driven with the current at the lower corona",
K. Hayashi
A time-dependent three-dimensional MHD simulation model to treat the response of the solar corona
to the temporal variations of the global solar photospheric magnetic field is proposed.
In order to avoid the computational difficulties in calculating the vector quantities of
the magnetic field and plasma motion on the boundary surface fully matching the measured
variations, we assumed the shallow spherical layer at the lowermost corona for which
the "differential potential field" is calculated and superimposed to the existing corona.
The differential potential field uses differential synoptic map that is calculated by
subtracting two successive synoptic maps of the solar photospheric magnetic field measurement data.
The radial component of the differential field at the upper sphere set at 1.1 Rs sphere is zero.
The differential potential field confined in a shallow spherical layer can be regarded as the
proxy of the global variation of the coronal magnetic field during one Carrington rotation
period of about 27 days.
By gradually adding the differential potential field to the existing numerical coronal magnetic field,
we can simulate the continuous coronal variations in the global scale. The potential field is
calculated by the spherical harmonics up to 5th term, which corresponds to about 10-degree
spatial resolution to treat only the global scale and to neglect the small-scale quick surface variations.
This model assumes the strong current at the upper sphere of the shallow spherical layer that
we here chose at 1.1 Rs, which may not represent the real corona. It is, however,
beneficial to examine a lot of new features numerically obtained, such as the twisted magnetic loops
and the mass condensations along the magnetically neutral lines,
and the magnetic reconfigurations at the streamer.
AAS/SPD, 2005 (#SH13A-06)
"The MHD simulation on the coronal plasma in radially shrinking open magnetic flux tubes",
K. Hayashi, X. P. Zhao, and B. Poduval
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",
K. Hayashi
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",
K. Hayashi, M. Kojima, M. Tokumaru, and K. Fujiki
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 canceled.
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.