ISSI POLARIS Team: Octav Marghitu 1, Joachim Vogt 2, Andreas Keiling 3, Rumi Nakamura 4, Tomas Karlsson 5, Maria Hamrin 6, Olaf Amm 7, Harald Frey 3, Costel Bunescu 1, Eugen Sorbalo 2, Vlad Constantinescu 1, Hans Nilsson 8, Joshua Semeter 9 MPE Symposium on Auroral Physics and Plasma Boundary Analysis, Garching, 1–5 July, 2013 Multi-Scale M–I Coupling Effects of Magnetotail Flow Bursts: Event Study by Cluster, THEMIS, GOES, and Ground Stations Magnetosphere–Ionosphere Coupling Associated with Magnetotail Flow Bursts: A Conjugate THEMIS/Cluster/Ground Event 1. Institute for Space Sciences, Bucharest, Romania 2. School of Engineering and Science, Jacobs University Bremen, Bremen, Germany 3. Space Sciences Laboratory, University of California at Berkeley, USA 4. Space Research Institute, Austrian Academy of Sciences, Graz, Austria 5. Space and Plasma Physics, Royal Institute of Technology, Stockholm, Sweden 6. Department of Physics, Umeå University, Umeå, Sweden 7. Arctic Research Unit, Finnish Meteorological Institute, Helsinki, Finland. 8. Swedish Institute of Space Physics, Kiruna, Sweden. 9. Department of Electrical and Computer Engineering, Boston University, Boston, USA

Introduction  While the large scale scene, in space and time, is set by the Sun, the terrestrial control may dominate at the M – I coupling end of the solar-terrestrial interaction.  An M – I coupling event, observed by several in-situ platforms and ground stations, during a relatively quiet interval, illustrates the internal dynamics of the M – I system.  In this case flow bursts in the tail, observed by THEMIS, appear to be related to:  large-scale Pi2 pulsations over a wide range of latitudes and longitudes, observed by the THEMIS GBO and by GOES in-situ.  meso-scale vortical motion in the ionosphere, observed by equivalent ionospheric current (EIC) maps;  small-scale electron acceleration by dispersive Alfvén waves, observed by Cluster-1 at about 2R E altitude.

Outline  Event context  IMF, SuperDARN, Magnetic indices  Spacecraft location, mapping  Tail flow bursts association with:  Large scale Pi2 pulsations, THEMIS / GOES / ground data  Meso-scale ionospheric vortical motion, THEMIS / ground data  Alfvénic electron acceleration, THEMIS / Cluster data  Summary  Open questions

Feb. 25, 2008 – IMF, SuperDARN B_gsm_z B_gsm_y B_gsm_x He++/H+ Tp Np :00 UT 44 kV 4 nT 10:20 UT 44 kV 5 nT

Magnetic indices, Ground magnetic field Feb. 2008, Sol. rot Kp=1+

Event Context – Spacecraft Location TH-A TH-D TH-E C1 C2 C3 C4 GOES-12 TH-A TH-E TH-D C1 C2 C3 C4 GOES-12

THEMIS GBO ASI / SuperDARN :03:00 UT P5/TH-A P3/TH-D P4/TH-E C2 C1 C3 C4 GOES-12 P3P4 P5

THEMIS GBO ASI / SuperDARN :24:00 UT P5/TH-A P3/TH-D P4/TH-E C2 C1 C3 C4 GOES-12 P3 P4 P5

THEMIS GBO ASI / SuperDARN

THEMIS flow bursts TH-A N B V_gsm V_perp_gsm V_para_gsm TH-D TH-E

Flow bursts Pulsations Keiling et al., Chapman Conference, Iceland, 2013

Flow bursts Pulsations Keiling et al., Chapman Conference, Iceland, 2013

Flow bursts Pulsations Keiling et al., Chapman Conference, Iceland, 2013

 During the first burst, 3 intensifications of the flow are observed, starting at about 10:03, 10:05, and 10:08 (TH-A is multiplied by 6 => actually quite small).  The flow speed decreases progressively, from the first to the last intensification.  During the first intensification, Vx on TH-D is largest, but Vy and Vz are also significant. On TH-E, all three components have comparable values.  During second and third intensifications, Vx on TH-D is small, but Vy and Vz are significant. On TH-E, Vx becomes negative.  Overall, the velocity components suggest 3D oscillatory motion, consistent with the expectations in the flow braking region. Flow bursts Ionospheric vortical motion P5/TH-A*6P3/TH-DP4/TH-E Vx V Vz Vy

THEMIS flow bursts Nakamura et al., manuscript in preparation

Flow bursts Ionospheric vortical motion 10:03 EIC 10:24 EIC 10:03 FAC 10:24 FAC

Flow bursts Ionospheric vortical motion 10:01:40 – 10:09:50 EIC

Flow bursts Ionospheric vortical motion 10:21:40 – 10:30:50 EIC

 Paralel and anti-paralel low energy electron bursts are associated with the 3 intensifications of the flow.  The low energy counter-streaming electrons are suggestive for Alfvénic acceleration.  According to recent theoretical models and simulation studies, dispersive Alfvén waves launched by tail flow braking can indeed accelerate the electrons. Flow bursts Alfvénic acceleration 10:00 10:02 10:04 10:06 10:08 10: V (km/s) TH-A*6 TH-D TH-E

Flow bursts Alfvénic acceleration FYKN KIAN

Summary  Two flow bursts episodes in the tail are observed by THEMIS spacecraft during a globally quiet magnetospheric interval. First episode is more prominent in TH-D and TH-E data, near midnight, while second episode is visible also in TH-A data, some 2.5 h in MLT to the dusk.  Both episodes are associated with large scale Pi2 pulsations, visible both in- situ, by THEMIS and GOES, as well as on ground, by THEMIS GBO.  The flow bursts are observed in the inner plasma sheet, presumably in the flow braking region. The flow features suggest oscillatory vortical motion – consistent with theoretical models, simulations, and recent observations by THEMIS.  The vortical motion in the tail is supported also by conjugate meso-scale EIC maps, showing as well vortical plasma convection.  On small scale, Cluster-1, conjugate to TH-D during the first flow burst, observes Alfvénically accelerated electrons, presumably related to dispersive Alfvén waves launched by the flow braking.  Overall, the event provides a remarkable illustration of the M–I system internal dynamics, which can be properly addressed only by multi-point in-situ observations and comprehensive networks of ground equipment.  With the launch of the ESA 3-satellite Swarm mission, now scheduled at the end of the year, future M–I coupling studies will benefit from multi-point in-situ observations also at ionospheric level.

Open Questions  Oscillatory braking of one BBF or three separate BBFs? The progressive decrease of the oscillations’ amplitude supports rather the first option. Also, the large scale pulsation episode suggests one driver, not three. On the other hand, C1 maps to 24 R E, 51 R E, and 58 R E in the equatorial plane, suggesting three different BBFs (Rumi).  Pulsations scenario?  Others?