Magnetospheric solitary structure maintained by 3000 km/s ions as a cause of westward moving auroral bulge at 19 MLT M. Yamauchi 1 , I. Dandouras 2 , P.W. Daly 3 , G. Stenberg 4 , H. Frey 5 , P.-A. Lindqvist 6 , Y. Ebihara 7 , R. Lundin 1 , H. Nilsson 1 , H. Reme 2 , M. Andre 4 , E. Kronberg 3 , and A. Balogh 8 (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
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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+)
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.