Equatorial signatures of an auroral bulge and a filamentation/demarcation of a transpolar arc observed by Cluster M. Yamauchi 1, I. Sandahl 1, R. Lundin 1, H. Nilsson 1, G. Stenberg 1, I. Dandouras 2, H. Reme 2, H. Frey 3, P.W. Daly 4, E. Kronberg 4, M. Andre 5, P.-A. Lindqvist 6, Y. Ebihara 7, and A. Balogh 8. (1) IRF-Kiruna, Sweden, (2) CESR, Toulouse, France, (3) UCB/SSL, Berkeley, USA, (4) MPS, Katlenburg-Lindau, Germany, (5) IRF- Uppsala, Sweden, (6) KTH, Stockholm, Sweden, (7) Kyoto U., Uji, Japan, (8) ICL, London, UK #F-9 Chapman Conference on Aurora, 2011, Fairbanks, Alaska

Sub-keV and few-keV ion patterns (pink arrows in Fig 1) in the inner magnetosphere are explained by remainder of substorm injections after long-time (several hours) ExB and magnetic drifts (Ann. Geophys., 27, 1431, 2009). The patters are therefore normally north-south symmetric. However, some spectrograms are difficult to explain with this drift scenario. Most of them (asymmetric ones: Fig 2) are explained by on-going substorm injection in the morning sector (e.g., event: JGR, 111, A11S09, 2006). One obvious exception is event, which we examine here. Fig 1

Fig 2: 11 LT06 LT08 LT07 LT camera’s FOV is not optimum (aurora is active>) 16:28 UT onset SIE onset 18:28 UT SIE 02:40 UT We examined asymmetric events when FUV data is available. Most of them are related to substorm activity.

event: There are two different ion signatures at equatorial conjugate region of substorm-related aurora. One signature (light-blue marked area in Fig 3) corresponds to evening auroral bulge (Ann. Geophys., 27, 2947, 2009), and the other (pink marked area in Fig 3) corresponds to filamentation/demarcation of aurora at the conjunction to transpolar arc. #1 Arrival of auroral bulge: Cluster observed a solitary structure of DC field, which is maintained by main carrier of the ring current, and propagates at the same velocity as the auroral bulge with respect to B. #2 filamentation/demarcation: Cluster observed sudden onset of bi-directional ion beam at sub-keV range (uniquely high intensity in 10-years Cluster observations), change of energetic ions, and DC and AC electromagnetic disturbances. Traversed the conjugate region of aurora at 19 MLT.

ions ≈ 3000 km/s ions > 5000 km/s T89 lat Fig 3 event #1event #2

06:26 UT06:32 UT06:38 UT 06:40 UT06:42 UT06:44 UT06:46 UT06:48 UT06:50 UT 06:52 UT06:54 UT06:56 UT06:58 UT07:00 UT07:02 UT 07:05 UT07:07 UT07:09 UT07:11 UT07:13 UT07:15 UT Fig 4: IMAGE/FUV Cluster conjugate

Fig 5: Sudden change in field Onset of AC burst & // beam simultaneous at all SC (1) Different timing between SC:  5~10 km/s & 1000~2000 km wide (2) ExB drift velocity >50 km/s:  He + ~ 70 eV, H + ~ 17 eV ∆|B|~-25% E~10 mV/m single peak of E: lead by SC-3 by 1~10 sec Pi2-like rarefaction of B: simultaneous at all SC ∆P B = -3 nPa = -∆P 3000km/s.

geometry for event #1 Fig 6: Auroral ions 1000~2000 km E-field * mainly in parallel direction * keV ions ( ) + sub-keV ions ( ) keV sub-keV=same velocity keV

summary (event #1) 1000~2000 km E (a) Solitary DC field * depletion of |B|≈B Z up to 25% * polarization E≈-E X of up to 10 mV/m * ExB convection (up to 50 km/s) * 5~10 km/s sunward propagation * 1000~2000 km wide (b) maintained by 3000 km/s ions * increase of 3000 km/s H + (R B = 200 km), He + (R B = 800 km), and O + (R B = 3000 km) * ∆P 3000km/s = 3 nPa = - ∆P B * decrease of other energetic ions * scale size ~ gyro radius (c) relation to auroral bulge * location, size, speed, & potential structure agree with auroral bulge * // O + ≈ 7 keV is detected but not in  O +

summary (event #2) both // directions (a) Sudden onset of DC/AC field + ion burst at 06:48:30 UT * Unique event in 9 years of Cluster data (examined ). * both DC and AC fields * Poynting flux is stagnant (SC are in the source region) * same velocity for H+, He+, O+ (= TOF-like with discrete sources) * both // & -// ions simultaneously (boundary crossing) * all SC registered nearly simultaneously  quickly moving boundary * decrease of energetic particles mainly for O+ (why?) (b) relation to aurora * map to demarcation point of transpolar arc * transpolar arc is becoming “string of beads” * same timing (06:48~07:02 UT) as ion burst

We examined when the low-energy ion data (sub-keV ~ several keV) in the inner magnetosphere showed strong asymmetry between inbound (southern hemisphere) and outbound (northern hemisphere) for all Cluster perigee passes when IMA/FUV data is available ( ). We examined 6 events: (already reported), , , , , (1) Five events are explained by on-going substorm injection. (2) In the last event ( ) which is the evening sector observation, sudden onsets of unique ion signatures (06:43 UT and 06:49 UT) are conjugate to auroral bulge and a transpolar arc right after a substorm. (3) Bulge is strongly related to energetic ions (3000 km/s H +, He +,O + ). (4) Deformation of the transpolar arc coincides with a region of bursty sub-keV ions and electromagnetic fields. Conclusion

3000 km/s = 50 keV (H), 190 keV (He), 740 keV (O) = Flux increase: ∆P 3000km/s = 3 nPa = - ∆P B. note: R B, 3000km/s = 200 km (H), 800 km (He), 3200 km (O)) 5000 km/s = 130 keV (H), 500 keV (He), 2 MeV (O) = Flux decrease extra: Energetic ions: mass-dependent Only for the first event. Second event terminates this.