Magnetospheric Solitary Structure maintained by 3000 km/s ions

and its relation to Auroral Bulge after a Substorm

M. Yamauchi1, H. Nilsson1, I. Dandouras2, P.W. Daly3, H. Frey4, G. Stenberg1,5, P.-A. Lindqvist6, Y. Ebihara7, R. Lundin1, H. Reme2, M. Andre5, E. Kronberg3, A. Balogh8, and M. Henderson9 (1) IRF-Kiruna, Sweden, (2) CESR, Toulouse, France, (3) MPS, Katlenburg-Lindau, Germany, (4) UCB, Berkeley, USA, (5) IRF-Uppsala, Sweden, (6) KTH, Stockholm, Sweden, (7) Nagoya U., Nagoya, Japan, (8) ICL, London, UK, (9) LANL, Los Alamos, USA

302-MON-P1716-0570

Recently Published in Ann. Geophys, 27(7), 2947-2969, 2009

ions ≈ 3000 km/s

ions > 5000 km/s

keV

P/A

P/A

06:42 06:46 06:4806:44

IMAGE (FUV)

Fig 1: overview

(a) Sunward propagation (5~10 km/s) of Solitary DC field Fig 2 * depletion of |B|≈BZ up to 25%

Fig 2 * polarization E≈-EX of up to 10 mV/m

Fig 2 * ExB convection (up to 50 km/s) of cold He+ Fig 3 * timing of ∆E speed = 5~10 km & size = 1000~2000 km

(b) Solitary structure is maintained by 3000 km/s ions Fig 4 * net flux increase of 50 keV H+, 200 keV He, 700 keV O

* ∆P3000km/s = 3 nPa = - ∆PB * scale size ~ gyro radius* magnetic drift velocity is faster than propagation velocity

(c) The auroral bulge is caused by this solitary structure Fig 5 * parallel O+ ≈ 7 keV is detected but not in direction Fig 5 * size, speed, and potential structure agree with auroral bulge

Outline

Fig 2: Sudden change in field

ExB (>50 km/s) is also observede.g., 57 km/s : He+ ~ 70 eV H+ ~ 17 eV

Fig 3: timing Sunward propagation of E

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

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

1000~2000 km

E-field

3000 km/s = 50 keV (H), 190 keV (He), 740 keV (O) = Flux increase RB = 200 km (H), 800 km (He), 3200 km (O)

5000 km/s = 130 keV (H), 500 keV (He), 2 MeV (O) = Flux decrease

Fig 4: mass-dependent change

Fig 5: auroral ion

Cf. Aurora motion (Fig 1): sunward < 0.1 MLT/min (stagnate at 06:44) ≈ 10 km/s at Cluster (L=4, equator)

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

Conclusion

On 2002-5-19, Cluster observed westward moving auroral bulge at 19 MLT, which 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 the carrier ions.

1000~2000 km

E