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