Multi-Spacecraft Observation of Compressional Mode ULF Waves Excitation and Relativistic Electron Acceleration X. Shao 1, L. C. Tan 1, A. S. Sharma 1, S. F. Fung 2, Mattias Tornquist 3,Dimitris Vassiliadis 3 1. University of Maryland, College Park, MD, USA 2.Goddard Space Flight Center, NASA, Greenbelt, MD, USA 3. West Virginia University, Morgantown, WV, United States. Acknowledgement: K. Papadopoulos, M. Hudson, I. Mann 1

Abstract Observations by Cluster spacecraft, ground magnetometer station measuring ULF waves, and LANL, GOES spacecraft measuring energetic electron fluxes during a SSC event on September 25, [Tan et al., JGR, 2011] Evidence of relativistic electron acceleration by the compressional-mode ULF waves. Energetic electron flux measured by LANL shows modulation of low-energy electrons and acceleration of high-energy electrons by the compressional poloidal-mode electric field oscillations within 2-3 hours. Preliminary global MHD simulation through NASA/CCMC Remaining Questions and Implication for RBSP Mission 2

Solar Wind Condition and Geomagnetic Response during September 25, 2001 Vsw > 500 km s - 1 SSC, D st = 14 nT AE > 1000 nT Recovery

Spacecraft Configuration during Sept. 25, 2011 Magnetic conjunction b/w Cluster 3 & 20:21 UT, MLT= 10, L = 6.6

Long period of Pc5 ULF waves observed by Geotail in the solar wind, GOES satellite, and ground magnetometer Solar wind with broadband ULF wave fluctuations drive the ULF oscillations observed by GOES and on the ground. LANL MRE flux enhancements ~ 3-4 times GOES MRE flux increases 4-5 times. ULF Wave Excitation and Magnetospheric Relativistic Electron (MRE) Acceleration

ULF Electric Field Fluctuations observed by Cluster-3 and Geomagnetic Field Fluctuations Sept. 25, 2001 Cluster 3 observed strong Pc5 ULF waves in electric field [Max Edusk (1 - 8 mHz) ~ 20 mVm-1 (p-p)] Ground magnetometer observation shows that ULF activity occurs largest at L =9.5 and decreases inward, Favors radial diffusion. Cluster-3

Evidence of Compressional Mode ULF Wave Excitation Compressional mode ULF wave supports harmonic oscillations across substantial radial distances inside the magnetosphere The observed ULF wave frequency spectra are of wide band with multiple peaks. During the entire solar wind driving process we see broadband ULF oscillations existing at all observation points. Within the shaded gray region, we see significant spectral strength for magnetic field amplitude at ULF wave frequency. Therefore, the observed ULF waves are compressional in nature.

Day-night Asymmetry in Azimuthal Wave Number for Compressional Mode From ground station magnetometer observation to determine azimuthal wave mode number: m = 3.3 ± 1.2 at day side m = 0.9 ± 0.4 at night side

9 Cluster 3 RAPID/IES LANL91 Cluster 3 EFW Coherent Electron & E-Field Modulations Seen by CLUSTER and LANL91 on Sept 25, 2001 (20:00-24:00 UT) Conjunction of LANL 91 and Cluster 3 Flux peak correlated with negative E  Cluster-3 LANL91

50-75 keV keV MeV keV Observations from LANL Geosynchronous Satellites Threshold Value of Accelerated Electron Energies Is about keV

Observed Result on Threshold Value of Accelerated Electron Energies SM33A AGU Fall Meeting11 Energy Threshold ~ MeV

First two adiabtic invariants are conserved..  W  0 from azimuthal drift- resonant interactions Acceleration of MREs by Drift-Resonant Interaction with ULF Waves  Particle energy change wave electric field Poloidal mode Toroidal mode Poloidal mode Toroidal mode

Drift-Resonant Acceleration by E  Perturbations (Compressional ( Poloidal) Mode ) Eφ ~ 10 mV/m Wave period: 5 min  W ~ 200 keV gain/drift period X (Re) Y (Re)   

E > E0 300 keV Drift Resonant Condition: Degeling et al., 2007 Explanation of the threshold by theory of Drift-Resonant Acceleration

Global MHD Simulation Conducted real event simulation with Lyon-Fedder-Mobbary (LFM) 3D global MHD model through NASA/CCMC Time-Dependent Inflow Boundary Conditions Start Time: 2001/09/25 18:00 End Time: 2001/09/25 23:59 Dipole tilt updated with time Ionospheric conductance model 10.7 cm Radio Flux : Coordinate System for the Output: SM Output step: every 3 min. (Improving output interval to every 30 seconds is worked on.)

Dayside Magnetosphere Compression during the Event UT = 21:30 UT = 21:00 UT = 20:30 UT = 20:00 y

Dayside Magnetosphere Compression during the Event: Density Map in Log scale UT = 21:30 UT = 21:00 UT = 20:30 UT = 20:00

Magnetospheric Magnetic Field Configuration in the North-South Plane during the Event UT = 21:30UT = 21:00 UT = 20:00

GOES Satellite Observation Comparison GOES 10 GOES 8

Remaining Science Questions ULF Wave Excitation and distribution – Solar wind driving: narrow band vs. broadband; Pdyn, IMF, and MC – K-H Instability: high speed stream – Toroidal vs. Poloidal mode; FLR vs. Compressional – Azimuthal mode number difference at dayside and nightside during SSC. Related to Alfven Velocity difference? – Plasmasphere and movements of plasma-pause effects MRE acceleration by ULF waves – Acceleration efficiency difference by FLR vs. coimpressional model – Understanding ULF wave modulation of low-energy electrons and the acceleration of high-energy electrons by the ULF waves. – Distribution of ULF waves for effective MRE acceleration Simultaneous multi-spacecraft and ground magnetometer observations are needed to understand above questions Look forward to RBSP