Substorm-origin sub-keV ring current ions: wedge-like structure

M. Yamauchi, R. Lundin, H. Nilsson (IRF-Kiruna),

Y. Ebihara (Nagoya U.)I. Dandouras, H. Reme (CESR,

Toulouse)

Substorm : production of plasma

Sub-keV ring current : fossil of substorm

Question: source of sub-keV ring current?

ICS-9, Graz, 2008-5-3~7

Sub-keV Ring Current (RC)?

But, in reality, sub-keV ions exist

11 MLT

14 MLT

m>2

H+ cavity in sub-keV range

Traditional RC : > 5 keV only

15 MLT

Westward (magnetic) drift

Eastward (electric) drift

Viking statistics

6 MLT

9 MLT

12 MLT

15 MLT

18 MLT

Time-lag (hours)

(1) Moves eastward

(2) Decrease in time

Backward Superposed Epoch Analyses using 700 traversals. * 3h MLT bin & 3h window for time-lag* three categories: "clear structure", "marginal", and "quiet.

Morning: additional keV line= Eastward (electric) drift

Westward (magnetic) drift

Noon Early morning Late morning

(1) Total (wedge & >1 keV): Morning peak(2) > 1 keV: Morning only(3) Freja-Cluster difference: Mirror altitude?

only < 1 keV also > 1 keV also > 1 keV

day (12 MLT)

Midnigh (3 MLT)

UT 00:30 01:00 01:30 02:00

Substorm onset

difference

Case study : 2001-10-21

H+

O+South North

Substorm onset

+0.1° 0° -0.1°

SC-4 @ 23:50 UT: Yes

23:50 UT

23:40 UT

23:50 UT

SC-3 @ 23:40 UT: No

V(10 keV) = VE-VB << VE

V(0.1 keV) ~ VE

10 keV 0.1 keV

23:40 UT

Source estimation

∆t < 13 min (100 eV/C-3 & 10 keV/C-4) t < 30 min drift distance = VE * t < 20000 km

started at 7~9 MLT.

+0.1° 0° -0.1°

SC-4 @ 23:50 UT: Yes

23:50 UT

23:40 UT

23:50 UT

V(10 keV) = VE-VB << VE

V(0.1 keV) ~ VE

10 keV 0.1 keV

23:40 UTSC-3 @ 23:40 UT: No