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。