reconnection electric fields in the ”2 null - 2...
TRANSCRIPT
惑星間空間磁場北向き時の交換型リコネクションによる対流
渡辺正和1 ,藤田茂2,田中高史1 1. 九州大学
2. 気象大学校
Interchange cycle Z (north)
X (Sun) Interchange-type merging cell
Reciprocal cell
Expected ionospheric convection at θIMF~20°
R: Reciprocal cell L: Lobe cell M: Merging cell
Interchange cycleの一帰結:電離圏対流 (θIMF~20°の場合)
Interchange cycleを支持する観測
IMF BY > 0 北半球 IMF BY < 0 北半球
8 March 2008 22 March 2008
Reproduction of reciprocal cells in MHD modeling
dusk dawn dusk dawn
Sun Sun
+ − + −
+ − +
−
R R
BIMF = 5 nT, θIMF = 20°(BY > 0) VSW = 350 km/s, NSW = 5 #/cc, TSW = 50,000 K
Contours every 3 kV
Reconnection in 3D
A necessary and sufficient condition for a general magnetic reconnection (Schindler et al., 1988):
recR E∝ Reconnection rate
0E ds ≠∫ Integration along a field line
In MHD modeling, is useful to identify the reconnection mode.
E
Direct proof of interchange cycle: Field-aligned electric field on separatrices
Field-aligned electric field calculation
0 0 0L vηη
µ=
0 6370 kmL = 0 53.2 km/sv =
70 4 10 H/mµ π −= ×
Normalized electric resistivity
m nη η η= +
m nη η
( )( ) ( )
20
2 220 0
0.0010.0010.003
m
J J
B B l Lη = ≈
+ ∆2
0 1.26 nA/mJ =0 10 nTB =
Model resistivity : numerical resistivitynη
η+ × =E v B J E Jη=
Ohm’s law
Separatrix Torus: open-closed boundary Cylinder: open-interplanetary boundary
dawn dusk
The “2 null – 2 separator” topological structure
BY > 0 and BZ > 0 view from the Sun
Torus の半分 Separator circleより南側、夕方側の部分
Cylinder の半分 Separator circleより北側、朝方側の部分
(X, Y, Z)=(20, 2, 0)を通る流線
に沿って磁力線トポロジーの変化を追ってみると
Interchange cycleの間接的証拠2
① ②
④ ③ ② ③
④ ⑤
結論
• Interchange cycleはMHDモデルで確実に
再現されており、現実の磁気圏でも起こっている可能性が高い。