Equatorial signatures of an auroral bulge and a

filamentation/demarcation of a transpolar arc observed by Cluster

M. Yamauchi1, I. Sandahl1, R. Lundin1, H. Nilsson1, G. Stenberg1, I. Dandouras2, H. Reme2, H. Frey3, P.W. Daly4, E. Kronberg4, M. Andre5, P.-A. Lindqvist6, Y. Ebihara7, and A. Balogh8.

(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., 2001-10-21 event: JGR, 111, A11S09, 2006).

One obvious exception is 2002-5-19 event, which we examine here.

Fig 1

Fig 2:

11 LT 06 LT 08 LT 07 LT

camera’s FOV is not optimum (aurora is active>)

16:28 UT

onset SIE SIEonset

18:28 UT

SIE

02:40 UT

We examined asymmetric events when FUV data is available. Most of them are related to substorm activity.

2002-5-19 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 62.0 61.0 60.6 60.9 61.6

Fig 3

event #1 event #2

06:26 UT 06:32 UT 06:38 UT

06:40 UT 06:42 UT 06:44 UT 06:46 UT 06:48 UT 06:50 UT

06:52 UT 06:54 UT 06:56 UT 06:58 UT 07:00 UT 07:02 UT

07:05 UT 07:07 UT 07:09 UT 07:11 UT 07:13 UT 07:15 UT

Fig 4: IMAGE/FUV Cluster conjugate

Fig 5: Sudden change in field

Onset of AC burst & // beamsimultaneous 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

∆PB = -3 nPa = -∆P3000km/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|≈BZ up to 25%

* polarization E≈-EX 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+ (RB= 200 km), He+ (RB= 800 km), and O+ (RB= 3000 km)* ∆P3000km/s = 3 nPa = - ∆PB * 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 2001-2010).* 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 (2001-2005). We examined 6 events: 2001-10-21 (already reported), 2002-5-19, 2002-10-1, 2002-12-14, 2004-11-7, 2004-11-10.

(1) Five events are explained by on-going substorm injection.

(2) In the last event (2002-5-19) 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:∆P3000km/s = 3 nPa = - ∆PB. note: RB, 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.