Sources of < 10 keV ring current ions: supply mechanism? 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? IMC workshop, Espoo, 2008-7

Sub-keV Ring Current? m>2 H+ Eastward (electric) drift 15 MLT Sub-keV Ring Current? cavity in sub-keV range Eastward (electric) drift Westward (magnetic) drift Noon Early morning Late morning only < 1 keV also > 1 keV also > 1 keV

Statistics Morning peak Energy decrease with MLT poleward Viking 14 MLT Statistics eastward drift Morning peak Energy decrease with MLT Cluster = Viking ≠ Freja (less)  (1) Moves eastward (2) Decrease in time (3) Freja is below mirror altitude 6 MLT 9 MLT 12 MLT 15 MLT 18 MLT Time-lag (hr) from substorm onset

Sub-keV component is fossil of substorm activity UT 00:30 01:00 01:30 02:00 day (12 MLT) Midnight (3 MLT) difference Substorm onset Summary Sub-keV component is fossil of substorm activity Mirror altitude > 2000 km Seen at low-altitude (after substorm)

However: Questions (1) Too quick response (2) H+ - O+ difference (3) Freja-Cluster difference in both composition and distribution mainly O+ mainly H+

H+ - O+ difference

Case study : 2001-10-21 event Substorm onset H+ O+ South North

Oxygen feature H+: both directions O+: one direction PA PA Substorm onset O+ structure is only at 0.05-0.3 keV range (20 km/s ~ 50 km/s). 0.05 keV O+ takes 20~30 min to travel from the ionosphere to the Cluster location along B in best case. Therefore, O+ should not have mirror-bounced, and this is confirmed from nearly uni-direction pitch angle. Again, 20~30 min elapsed time (with morning source) ! H+: both directions O+: one direction PA PA

O+ trajectory (30 min trajectory) Tsyganenko T89 B-model & Weimer 2001 E-model Backward trace of 0.1 keV O+ (reference point S/C-3) Pitch angle: 0°, 45°, 90°, 135°, 180° Again, morning source

Inter-SC time-of-flight confirms the timing V(10 keV) = VE-VB << VE 10 keV 0.1 keV H+ 23:40 UT +0.1° 0° -0.1° SC-3 @ 23:40UT: No 23:40 UT SC-1,4 @ 23:50UT: Yes 9 MLT Substorm onset 23:50 UT V(0.1 keV) ~ VE 23:50 UT O+ ∆t < 13 min (100 eV/SC-3 & 10 keV/SC-4)  t < 30 min  drift = VE * t < 20000 km  started at 7~9 MLT.

Questions Q1.The source location (MLT + altitude) Q2.The source population (O+ source and H+ source can be different). Q3. Source energy, i.e., relation between two (keV+wedge) components. Q4.The exact relation to substorms Q5. Supply mechanism To invest these problems, we need * More observation/analyses * Numerical mapping

Source ? Observation = Back-trace to 8 Re Back-trace to 8 Re Bursty cold (0.1~0.2/cc) Isotropic Maxwellian (T=1 keV, N=0.5/cc)

Re-construction by simulation both component together

Summary Wedge-like dispersed sub-keV ring current is a fossil of substorm activity carried by VExB ≥ VB-drift. O+ source is different from H+ source. The source is cold ions, which is supplied from midnight to morning. A sample of morning source: 2003-10- 29 event (next figure).

IMAGE/FUV Ground ∆B 0611:40 UT evening-midnight: 2000 nT 0613:40 UT 2003-10-29 event evening-midnight: 2000 nT Wide morning source of upward current (O+ escape) nearly simultaneously with substorm onset 0613:40 UT 0615:40 UT morning: 2000 nT Yamauchi, Iyemori, Frey, & Henderson, 2006 JGR

Summary of 2001-10-21 event Case study from 2001-10-21 event (9 MLT) shows that * The "wedge" suddenly appeared in the magnetic flux tube in which no signature was recognized 10 minutes before. * The dispersion is formed within 3 Re distance from the spacecraft within 30 minutes before the observation. * Observed oxygen ions of the "wedge" were not mirrored, i.e., they directly came from northern ionosphere (ionospheric source) 20-30 minutes before.  Dispersion started and O+ is ejected from the morning (6~7 MLT).

Ground ∆B + auroral image 0611:40 UT 0615:40 UT evening-midnight Ground ∆B + auroral image IQA≈01 LT 0613:40 UT morning 0617:40 UT