Cluster workshop, 2009-5-15

Magnetospheric solitary structure maintained by 3000 km/s ions as a cause of westward moving auroral

bulge at 19 MLTM. Yamauchi1, I. Dandouras2, P.W. Daly3, G. Stenberg4, H. Frey5, P.-A. Lindqvist6, Y. Ebihara7, R. Lundin1, H. Nilsson1, H. Reme2, M. Andre4, E. Kronberg3, and A. Balogh8

(1) IRF, Kiruna, Sweden, (2) CESR, Toulouse, France, (3) MPS, Katlenburg-Lindau, Germany, (4) IRF, Uppsala, Sweden, (5) UCB/SSL, Berkeley, CA, USA, (6) Alfvén Lab., KTH, Stockholm, Sweden, (7) IAR, Nagoya U., Nagoya, Japan, (8) Blackett Lab., ICL, London, UK

Cluster workshop, 2009-5-15

* Z ≈ 0 RE

* 60 GMLat

* 19 MLT

S/C

sun

tail

Cluster Perigee

IMAGE(FUV)

ions ≈ 3000 km/s

ions > 5000 km/s

0.01~40 keV

P/A

P/A

overview

06:42 06:46 06:4806:44

Sudden change in fieldExB (>50 km/s) is observede.g., 57 km/s : He+ ~ 70 eV H+ ~ 17 eV

Timing (B ≠ E)

(1) single peak of E: lead by SC-3 by 1~10 sec

(2) Pi2-like rarefaction of B: simultaneous at all SC

propagate

Timing from ExB convection

SC-3 leads against SC-1 by 10 sec: agree with field data

Timing Sunward propagation of E& E is nearly // to Propagation direction

1000~2000 km

06:43 UT event (arrival of auroral bulge)

(a)Sunward propagation (5~10 km/s) of DC field * depletion of |B|≈BZ up to 25%

* polarization E≈-EX of up to 10 mV/m

* ExB convection (up to 50 km/s) of cold He+ (without O+)

increase in ion flux

decrease in ion flux

H+ < 90 keV

H+ > 160 keV

increase in ion flux

decrease in ion flux

He < 350 keV

He > 700 keV

O < 0.9 MeV

O > 1.4 MeV

All relevant ion channel

3000 km/s = 50 keV (H), 190 keV (He), 740 keV (O)5000 km/s = 130 keV (H), 500 keV (He), 2 MeV (O)

06:43 UT event (arrival of auroral bulge)

(a) Sunward propagation (5~10 km/s) of DC field * depletion of |B|≈BZ up to 25%

* polarization E≈-EX of up to 10 mV/m

* ExB convection (up to 50 km/s) of cold He+

(b) Net flux Increase of selectively 3000 km/s ions* ∆P3000km/s = 3 nPa = - ∆PB. * net decrease of other energetic particles.

Drift motionVB energy (mass independent)

VExB = constant (energy mass)

50 keV H+ drift = 15 km/s190 keV He+ drift = 60 km/s740 keV O+ drift = 220 km/s

Simultaneous appearance & much faster than the motion of the E-structure a solitary structure to maintain the flux peak

ion-scale ?gradient is less than 500 km (5~10 km x 50 sec)

cf. RB (= mv/qB) for B ≈ 200 nT condition

50 keV 200 keV 1 MeV

H+ v = 3000 km/s

RB = 150 km

v = 6000 km/s

RB = 300 km

v = 14000 km/s

RB = 700 km

He+ v = 1500 km/s

RB = 300 km

v = 3000 km/s

RB = 600 km

v = 7000 km/s

RB = 1400 km

O+ v = 700 km/s

RB = 600 km

v = 1500 km/s

RB = 1200 km

v = 3500 km/s

RB = 3000 kmRB(H+) ≤ gradient ≤ RB(He+) << RB(O+)

06:43 UT event (arrival of auroral bulge)

(a) Sunward propagation (5~10 km/s) of DC field * depletion of |B|≈BZ up to 25%

* polarization E≈-EX of up to 10 mV/m

* ExB convection (up to 50 km/s) of cold He+

(b) Net flux Increase of selectively 3000 km/s ions* ∆P3000km/s = 3 nPa = - ∆PB. * net decrease of other energetic particles. * propagating solitary structure.* scale size ~ gyro radius

IMAGE(FUV)

ions ≈ 3000 km/s

ions > 5000 km/s

0.01~40 keV

P/A

P/A

overview

06:42 06:46 06:4806:44

At around 06:44 UT, appearance of 7 keV // O+ from both hemisphere, within 40 sec difference

// keV ion

06:43 UT event (arrival of auroral bulge)

(a) Sunward propagation (5~10 km/s) of DC field * depletion of |B|≈BZ up to 25%

* polarization E≈-EX of up to 10 mV/m

* ExB convection (up to 50 km/s) of cold He+

(b) Net flux Increase of selectively 3000 km/s ions* ∆P3000km/s = 3 nPa = - ∆PB. * Net decrease of other energetic particles.* propagating solitary structure.* scale size ~ gyro radius

(c) Conjugate with auroral bulge* Parallel O+ of ≈ 7 keV is detected

Cluster observed westward moving auroral bulge at 19 MLT on 2002-5-19 is caused by a solitary structure in the magnetosphere.

The solitary structure consists of polarization E-field (up to 10 mV/m) and depletion of B≈Bz.

This solitary structure is maintained by energetic ions of 3000 km/s speed for all ions.

Size (gradient < 500 km) of this solitary structure is comparable to the ion gyro radius of carrier ions.

conclusion1000~2000 km

End

Many other interesting topics

(1) Qualitative inter-SC difference

(2) Inter-SC time-of-flight examination

(3) Decoupling technique of different plasma using conservation of magnetic moment

Qualitative difference within Rgyro

Distribution function Difference cannot be explained by the slight difference in effective energy between SC.

RB >> inter-SC distance cannot be due to finite gyroradius effect.

gradient is substantially large?

TOF (7 keV O+ = 250 km/s & SC-1 -100km- SC-4 -150km- SC-3)or Phase-angle dependence?

TOF effect or phase effect?

TOF (7 keV O+ = 250 km/s) SC-1/SC-4/SC-3 = 100 km/150 kmor Phase-angle dependence?

Energy-time dispersion (flux increase)

time-of-flight? (No) ∆T ~ 10 sec for ∆VD ~ 10 km/s source < 1000 km No

finite gyroradius? (Yes) ∆T ~ 10 sec for ∆RB ~ 100 km agree with propagation

VDB = 20~30 km/s

VDB = 10~20 km/s

VDB = 30~50 km/s

VDB = 50~100 km/s

Energetic electron vs B

observed flux

Synchronize with B field variation

|B|

µB = W/B conserved? not really

increasing flux

under µB = const df(µB) = 0

(∂f/∂W)B > 0 (∂f/∂B)W > 0

= real

Linear decoupling

observed flux after decoupling the conservation of µB = W/B

End

Westward surging aurora

Akasofu et al., 1966

Fujii et al., 1994

= strong upward FAC

conclusion - continuedThe 3000 km/s ions are the main carrier of the propagating diamagnetic current that caused the magnetic depletion propagating sunward.

The sunward propagation of this solitary structure caused the sunward propagation of field-aligned potential drop and hence of the auroral bulge.

sunward propagation

E

prof

ile

Global condition: minor storm Dst ≈ -60 nT

3000 km/s

> 5000 km/s

0.01~40 keV

overview

P/A

P/A

IMAGE/FUV 06:26~06:56 UT

06:26 UT

06:28 UT

06:30 UT

06:32 UT

06:34 UTS/C

06:36 UT

06:38 UT

06:40 UT

06:42 UT

06:44 UT

06:46 UT

06:48 UT

06:50

06:52

06:54

06:56

~06:43 event

AE and Bx

1. Main phase of minor storm (Dst ~ -60 nT).

2. Substorm onset at around 06:25 UT but ceased in ~10 min.

3. New activity started at around 06:38 UT.

4. Aurora bulge arrived Cluster’s conjugate ~19 MLT at around 06:42~06:44 UT.

ion-scale ?All SC should observe the same behavior of ions if ion gyro-radius (RB = mv/qB) >> inter-S/C distance

RB for B ≈ 200 nT condition

10 keV 100 keV 1 MeV

H+ v = 1400 km/s

RB = 70 km

v = 4000 km/s

RB = 200 km

v = 14000 km/s

RB = 700 km

He+ v = 700 km/s

RB = 140 km

v = 2000 km/s

RB = 400 km

v = 7000 km/s

RB = 1400 km

O+ v = 350 km/s

RB = 300 km

v = 1000 km/s

RB = 800 km

v = 3500 km/s

RB = 3000 km

µB conservation: W W//, but

06:43

consolation

S/C distance ≈ 100 km in z direction & 50 km in x-y direction

≈ RB for 10~20 keV H+ << RB for Ring current ions

H+ > 20 keV (O+ > 2 keV) should behave the same at all SCs if the gyrotropic assumption is correct

06:43 UT event (arrival of auroral bulge)

(a) Sunward propagation (5~10 km/s) of DC field * depletion of |B|≈BZ up to 25%

* polarization E≈-EX of up to 10 mV/m

* ExB convection (up to 50 km/s) of cold He+ (without O+)

(b) Net flux Increase of selectively 3000 km/s ions (∆P3000km/s = 3 nPa = - ∆PB).

* Net flux decrease of other energetic particles. * Energy-time dispersion* 100 keV H+ ~ ∆E, and 50 keV H+ ~ ∆B

(c) Ionospheric plasma that is accelerated by parallel potential of about 7 kV.

But, there is inter-SC difference

RAPID (SSD) data

How about CIS (MCP) data?

Inter-SC difference: trapped H+ for CIS

For flux increase: (1) SC-2 < SC-1 < SC4=SC3

H+: 80~160 keVHe+: 200~300 keV

(2) SC-2 > SC-1 > SC4=SC3H+: ~60 keV O+: 500~600 keV

For flux decrease: (3) SC-2 < SC-1 < SC4=SC2

He+: 400~700 keV(4) SC-2 > SC-1 > SC4=SC3

O+: ~400 keV

inter-SC difference !

Hybrid: (5) SC-2 > SC-1 > SC4 > SC3

O+: 400~500 keV

End

no wave@06:43 UT, wave@06:48 UT

ion

dE

dB

S//

E/B

dBZ

dBXstagnant

BB-EM

spin effects

150 nT ΩP = 4 Hz

ΩHe?

Composition from energy ratio(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+

18eV 70eVH+ He+

//

//

End

Ground conj.

06:43 06:48

Nothing special

only 50 nT activity