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

Fig 1: overview ions > 5000 km/s ions ≈ 3000 km/s P/A keV P/A 06:42 06:44 06:46 06:48 IMAGE (FUV)

Outline (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

Fig 2: Sudden change in field ExB (>50 km/s) is also observed e.g., 57 km/s : He+ ~ 70 eV H+ ~ 17 eV

Fig 3: timing  Sunward propagation of E 1000~2000 km E-field (1) single peak of E: lead by SC-3 by 1~10 sec (2) Pi2-like rarefaction of B: simultaneous at all SC

Fig 4: mass-dependent change 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

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

Conclusion 1000~2000 km 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. E