Sub-keV Phenomena of Dayside Ring Current

M. Yamauchi, R. Lundin, H. Nilsson (IRF-Kiruna), Dandouras, H. Reme (CESR, Toulouse), G. Stenberg, M. Andre (IRF, Uppsala), P.-A. Lindquvist (KTH, Stockholm), Y. Ebihara (Nagoya U.), C. Vallat (ESTEC, Nordwijk), P.W. Daly (MPS, Katlenburg-Lindau), A. Balogh (ICL, London)

Sub-keV Ring Current?

Traditional view of the ring current : > 5 keV only

Cluster (SC-1) CIS data over perigee traversal at noon

2002-7-20

ions

H+

He+

O+

Sub-keV Cavity

Viking

Cluster

westward drift

eastward drift

eastward drift

Perigee, 11 MLT

14 MLT

poleward

Example 1: wedge-like structureHowever

Motion and source

6 MLT

9 MLT

12 MLT

15 MLT

18 MLT

Time-lag (hours)Backward Superposed Epoch Analyses using 700 traversals.

Viking probability of event

Cluster

Case study : 2001-10-21 event

H+

O+

South North

Substorm onset

0.1 keV

+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

23:40 UT

10 keV

H+

O+

H+

O+

Inter-SC time-of-flight (at 9.0 MLT)

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

V(0.1 keV) ~ VE

SC-3

SC-4

∆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.

Wedge-summary

Wedge-like dispersed sub-keV ring current is a fossil of substorm activity (model is right!) by VExB ≥ VB-drift.

It's source extends from midnight to morning (both statistics and case study)

O+ source is different from H+ source

Example 2: heating

ions

H+

He+

O+

Viking , 8 MLT

e-

i+

heating?

Cluster , 19 MLT

No dispersion not drifted local energization

Energy normally < 100 eV observed all local time

Only one extremely intense event over 5 years Cluster obs.

heating?

Unusual heating on 2002-5-19Energy range: >900 eV & 5-900 eV

ion

+ (

C1)

ion

+ (

C3)

0645 0650 0655 0700

H+ (

C4)

Feature-1: Timingio

n+ (

C1)

ion

+ (

C3)

H+ (

C4)

06:48:30

simultaneous at all SC in 12sec resolution

0642 0646 0650

SC-3: 60s behind SC-1

SC-4: 25s behind SC-1

SC-1: leading

cf. SC-location

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Feature-2: Pitch angle: Mostly // direction

//

//

4s spin plots of ion

(spin)

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (LZW) decompressor

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V

n

dB

dE

B0

4s spin plots of ion

Feature-3: Wave

simultaneous!

SC-1: 06:48:30 UT

ion

more wave: broadband + stagnant

ion

dE

dB

S//

E/B

dBZ

dBXstagnant

BB-EM

spin effects

150 nT ΩP = 4 Hz

ΩHe?

Feature-4: DC field

SC separation up to 1 min: temporal structure

06:48:30 UT = heating

-50

0

50

100

150

200

250

0:40 0:43 0:46 0:49 0:52 0:55BX (nT) BY (nT) BZ (nT) B (nT)

already from 0643 UT

0640 0645 0650 0655

EY

potential

B

Substorm-level disturbance simultaneous with heating

Feature-5: >5 keV component

sudden decrease

ion+

ion+

ion+

E = 0.005~40 keV

P/A (> 5 keV)

P/A (< 0.2 keV)

H+

He+

+~O+

06:48:30: heating06:43precursor

for > 100 keV component

ion+

e-

H+

He+ & He+ +

C +, N + & O+

Feature-6: Precursor strong ExB drift

(spin)

direction of drift: rotate

X (sunward)

Y (duskward)

//

drift direction

- UxB (estimated E) direction

and agree with DC E-field

40 42 44 46 48 50

0600 0620 0640 0700

EX<0

EY>0

EY<0

ExB drift velocity = 25~35 km/s 3-6 eV for H+, 13-25 eV for He+, 50-100 eV for O+

Feature-7: Composition(1) From energy peak: plasmaspheric He+ rich

= 0°

= 180°

= 360°

10 100 [eV] 10 100 [eV]

Precursor (06:44 UT) Heating (06:49 UT)

H+ He+ O+

ratio=4: O+/He+ or He+/H+

18 eV 70 eV

He+ O+

//

//

Composition: Precursor part

O+

He+

He+ becomes detection range only when |E| is strong.

Composition

0643 0644 0645 0646 0647 0648 0649

precursor heating

H+

He++

He+

O+

contamination

(2) TOF mass analyser: He+ rich

Composition (3) >100 keV: plasmaspheric He+precursor heating

Feature-8: magnetospheric condition Not special (just a minor storm/substorm)

Feature-9 : ground conj.

precursor heating

Nothing special

only 50 nT activity

Indications from data (heating):

1. Simultaneous at SC-1, 4 and -3 sudden activation

2. Bi-directional along B local hearing (not propagated)

3. Simultaneous wave with randomly changing Pointing flux direction even the wave is locally generated?

4. DC disturbance in B and E substorm-level activity?

5. Change in >5 keV large-scale configuration change

6. Precursor with cold ExB drift, no energization related ???

7. Rich in He+ for cold, sub-keV and 100 keV component plasmaspheric He+ is supplied well before the event?

8. Only minor magnetospheric activity Mystery !

Summary

Sub-keV part of dayside ring current is not empty!

Wedge-like dispersed sub-keV ions (statistics + case study)

Fossil of substorm with eastward by VExB > VB-drift Some are originated from morning sector

O+ source is different from H+ source

Heating (case study, unusual event, not well understood)

Local heating at equatorial plane by sudden onset

He+ rich

Precursor with strong DC E-field (and E-B drift)

Not clear ground signature, before substorm onset

Thank you

All info

ET

PA

O+ 30~500 eVETPA

ET

PA

25~150 eV

5-25 eV

25~150 eV

5-25 eV

25~150 eV

5-25 eV

25~150 eV

5-25 eV

all at 06:48:30 UT (12s resolution)SC-1: leading

SC-3: 60s behind SC-1

SC-4: 25s behind SC-1

0642 0644 0646 0648 0650 0652 0654 0656

Particle vs. wave

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4s spin plots of ion

Feature-#

**: **

Feature-#

**: **

more: waveYes, of course

0645 0700

0630 0700 0730

dE

dB

S//

E/B

Cluster Examples

Eastward (electric) drift Westward (magnetic) drift

only < 1 keV also > 1 keV also > 1 keVNoon Early morning Late morning