PowerPoint プレゼンテーション - On the origin and dynamics

Contents
1. Introduction
2. T96 磁場モデルとは
入力パラメータと使用方法
3. 磁気圏対流と電場計算
Weimer 1996モデルと共回転電場
4. 磁気圏モデル内粒子軌道追尾計算の例
磁気圏内プラズマ輸送問題
(研究の背景と計算例)
5. Summary
Earth’s Magnetosphere
Tsyganenko 1996 (T96) model
A data-based model of the geomagnetospheric magnetic
field with an explicitly defined realistic magnetopause,
large-scale region 1 and 2 Birkeland current systems, and
the IMF penetration across the boundary.
[Tsyganenko, JGR, p27187, 1996]
Input parameters:
1. Geodipole tilt angle,
Click here for details
2. Solar wind pressure (0.5~10 nPa),
3. Dst index (-100~+20),
4. IMF By and Bz (-10~+10 nT),
)
Click here for details
Click here for details
5. GSM position of the observation point.
Tsyganenko 1996 model (2)
Effects of Geodipole Tilt
From http://www-spof.gsfc.nasa.gov/Modeling/group.html
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Movie
The animation above shows how the magnetospheric field varies in response to the dipole wobbling. The background
color coding displays the distribution of the scalar difference DB between the total model magnetic field and that of
the Earth's dipole only. Yellow and red colors correspond to the negative values of DB (depressed field inside the ring
current, in the dayside polar cusps, and in the plasma sheet of the magnetotail). Black and blue colors indicate a
compressed field (in the subsolar region on the dayside and in the magnetotail lobes on the nightside).
Solar Wind Pdyn and Dst Index
Dst Index とは
地上磁場観測の各ステーションのH成分から
長期磁場変動
日変化・季節変化
を取り除いた北向き磁場擾乱の世界平均
Dstは ring currentの強度の指標
ストーム時には負に大きくふれる。
Tsyganenko 1996 model (3)
Effects of Time Variation in the Solar Wind Flow Speed
From http://www-spof.gsfc.nasa.gov/Modeling/group.html
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Movie
The animation above illustrates the dynamical changes of the global magnetic field in the course of a disturbance: a
temporary compression of the magnetosphere by enhanced flow of the solar wind is followed by a tailward stretching
of the field lines. Eventually, the increase of the tail magnetic field results in a sudden collapse of the nightside field
(a substorm ) and a gradual recovery of the magnetosphere to its pre-storm configuration. Format of the figure is the
same as the previous one.
IMF By and Bz and Dst Index
Magnetospheric Convection
during Southward IMF Periods
Weimer 1996 Model + corotation
Weimer 1996 model: A data-based model of electric potentials in the
high-latitude ionosphere based on spherical harmonic coefficients derived by
a least error fit of the double-probe electric field measurements by DE-2 with
simultaneous IMF data from ISEE-3 or IMP-8.
Input parameters:
[Weimer, GRL, p2549, 1996]
1. Solar Wind Velocity,
2. IMF By and Bz (-11~11 nT),
3. Geodipole tilt angle,
4. MLT, ILAT of the observation point.
Corotation: Assuming 0-tilt dipole magnetic field.
Formulation:
M: dipole moment, W: angular velocity of the Earth's rotation, Ri: radial
distance from the center of Earth to ionospheric altitude.
Example of
Weimer 1996
Electric
Potential
IMF northward
IMF dawnward
IMF duskward
IMF southward
Tsyganenko 1996 model (4)
Effects of Magnetospheric Convection
From http://www-spof.gsfc.nasa.gov/Modeling/group.html
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Movie
The animation above illustrates the magnetospheric convection during southward IMF periods. In this case the
geomagnetic and interplanetary field lines connect across the magnetospheric boundary, which greatly enhances the
transfer of the solar wind mass, energy, and electric field inside the magnetosphere. As a result, the magnetospheric
field and plasma become involved in a convection, as illustrated in the above animation.
Contents
1. Introduction
2. T96 磁場モデルとは
入力パラメータと使用方法
3. 磁気圏対流と電場計算
Weimer 1996モデルと共回転電場
4. 磁気圏モデル内粒子軌道追尾計算の例
磁気圏内プラズマ輸送問題
(研究の背景と計算例)
5. Summary
Conventional View before GEOTAIL
Ionospheric Contribution
From low-altitude observations
[Yau et al., AGU Monogr., 1988]
[Chappell, JGR, 1988]
From magnetotail observations
[Candidi et al., JGR, 1984]
[Orsini et al., JGR, 1990]
Example of Multi-Composition Ion
Flows in the Lobe/Mantle Regions
[Seki et al., JGR, 1999]
Location of Lobe/Mantle and
Multi-Component Ion Flows
observed by GEOTAIL
[Seki et al., JGR, 1999]
Possible Supply Scenarios
[Seki et al., JGR, 1998]
O+ Trajectory Tracings in
Empirical Magnetospheric Models
Assumption:
1. Magnetic field line is equi-potential.
2. Geodipole tilt angle is zero.
3. Solar wind conditions are constant in time.
・ Magnetic field model: Tsyganenko 1996 model
A data-based model of the geomagnetospheric magnetic field.
Input parameters: Solar wind pressure (0.5~10 nPa), Dst index (-100~+20),
IMF By and Bz (-10~+10 nT), Geodipole tilt angle, GSM position of the
observation point.
・ Electric potential model: Weimer 1996 + corotation
Weimer 1996 model: A data-based model of electric potentials in the
high-latitude ionosphere. Input parameters: Solar wind velocity, IMF By
and Bz (-11~11 nT), Geodipole tilt angle, MLT, ILAT of the observation
point.
Corotation: Assuming 0-tilt dipole magnetic field.
Initial Conditions
O+ Trajectory Tracing: initial 500 eV
Purely Southward IMF Case:
Pdyn=2nPa,
Dst=100,
By = 0nT,
Bz=-10nT,
Vsw=450 km/s
initial condition:
L=10Re,
MLT=12h,
Energy=500eV
Examples of O+ Trajectory Tracing
Purely Southward IMF Case:
Pdyn=2nPa,
Dst=100,
By = 0nT,
Bz=-10nT,
Vsw=450 km/s
Initial Conditions (2)
O+ Trajectory Tracing: initial 500 eV
Purely Southward IMF Case:
Pdyn=2nPa,
Dst=100,
By = 7.01nT,
Bz= -7.01nT,
Vsw=450 km/s
initial condition:
L=11Re,
MLT=12h,
Energy=500eV
Dependence on Pitch Angle and Energy
O+ Remaining in Magnetosphere
[%]
Ratio of O+ Ions Remaining in Magnetosphere
70
60
50
solid points: Case 1 (IMF By=0)
open diamons: Case 2 (IMF By=0)
red: Eo=10 keV
green: Eo=2.5 keV
blue: Eo=500 eV
40
Average Probability of
Transport to Magnetotail
Lo
Energy
Case 1
10 Re
11Re
Case 2
11 Re
30
500 eV
31.0%
21.3%
22.3%
20
2.5 keV
7.8%
6.9%
5.1%
10 keV
0.0%
0.3%
3.8%
10
0
0
22.5
45
67.5
90
initial pitch angle at equator [degrees]
Conclusions
On the basis of obtained results, new aspects are added by
this study to the conventional view. Namely, the lobe/mantle
plasma is considered to have at least the following four
supply routes:
• Direct entry of dayside polar ionospheric outflows in the
near-Earth regions,
• Plasma entry from the magnetosheath through the
magnetopause,
• Extra energization of polar outflows by a pressure pulse
and possibly other mechanisms,
• Transport of trapped plasma with isotropic and/or beam
distributions in the dayside magnetosphere via dayside
reconnection.
Plasma Supply to Lobe/Mantle
How to Get Started
T96磁場モデルのソースコードは、
以下のwebページで公開されています:
http://www-spof.gsfc.nasa.gov/Modeling/group.html
公開プログラム概要:
T96-01.for:
T96モデル
GEOPACK.for: IGRF, Dipole,
座標変換, 磁力線traceなど
GEOPACK Utilities
各インプットパラメータの時定数
Input parameters:
1. Geodipole tilt angle,
〜1日
予測難しい
2. Solar wind pressure (0.5~10 nPa),
3. Dst index (-100~+20),
〜数日
4. IMF By and Bz (-10~+10 nT),
予測は難しい
5. GSM position of the observation point.