Multi‐Spacecraft Observation of Compressional Mode ULF Waves Excitation 

and Relativistic Electron Acceleration

X. Shao1, L. C. Tan1, A. S. Sharma1, S. F. Fung2, Mattias Tornquist3,Dimitris Vassiliadis3

1. University of Maryland, College Park, MD, USA2.Goddard Space Flight Center, NASA, Greenbelt, MD, USA3. 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, 2001. [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, Dst = 14 nT

AE > 1000 nT

Recovery

Spacecraft Configuration during Sept. 25, 2011

Magnetic conjunction b/w Cluster 3 & LANL91 @ 20:21 UT, MLT= 10, L = 6.6

• Long period of Pc5 ULF waves observed by Geotailin 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 azimuthalwave mode number:

m = 3.3 ± 1.2 at day sidem = 0.9 ± 0.4 at night side

9

Cluster 3RAPID/IES

LANL91

Cluster 3EFW

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

225-315 keV

1.1-1.5 MeV

1.1-1.5 MeV

500-750 keV

Observations from LANL Geosynchronous Satellites

Threshold Value of Accelerated Electron EnergiesIs about 300-500 keV

Observed Result on Threshold Value of Accelerated Electron Energies

SM33A‐1759 2008 AGU Fall Meeting 11

Energy Threshold ~ 0.3‐0.4 MeV

• First two adiabtic invariants are conserved..

• W 0 from azimuthal drift-resonant interactions

ddt m d

dt 0 or md

Acceleration of MREs by Drift‐Resonant Interaction with ULF Waves

W qE

E

Driftperiod

V d dt

Eulf ~ eim i t

ei t t wave phase in

particle frame

W qE ulf d

s Driftpath

qE

E z

E ds

Driftpath

Particle energy change

wave electric

fieldPoloidalmode

Toroidalmode

PoloidalmodeToroidal

mode

Drift‐Resonant Acceleration by E Perturbations (Compressional (Poloidal) Mode)

Eφ ~ 10 mV/mWave period: 5 minW ~ 200 keV gain/drift period

E f (t) * cos( 2

)g(L)

X (Re)

Y (R

e)

W qE

E

Driftperiod

V d dt qE

Driftperiod

V d dt

qE

Driftperiod

ddt

ddt

dt

e E Driftperiod

dE 0

E > E0

300 keV

20

0

30

MrqMm

m

Drift ResonantCondition: 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 : 276.6

• Coordinate System for the Output: SM 

• Output step: every 3 min. (Improving output interval to every 30 seconds is worked on.) 

GOES Satellite Observation Comparison

GOES 10GOES 8

Science Questions for RBSP

• 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

Our Experience with L* Coordinate CalculationXi Shao, Lun C. Tan (UMD) and Shing F. Fung (NASA/GSFC)

• NOAA POES (NOAA‐05 to NOAA14, >20 years) Energetic Proton and Electron data processed and derived McIlwain B/Bmin and L* coordinate at 1 min resolution.

• 4 magnetic field models used including T89, T96.• Hourly solar wind and geomagnetic parameters obtained from OMNI to drive the T89 (Kp), and T96 (Pdym, Dst etc.) model. 

• NASA Linux cluster is used. (Intensive field line tracing performed with MPI.)

• Products archived at NASA SPDF/CDAWeb.

Electron (> 300 keV) Belt Dynamics (1979-1999) (from NOAA 5-14 POES Satellites)

• Inner (peak near L=1.6 ) and Outer (peak near L= 4-5) Electron Belts• Variability of outer belt; Relative stable inner belt.

Proton (> 80 MeV) Belt Dynamics (1979-2005) (from NOAA 5-14 POES Satellites)

• Only one (peak near L=1.5 ) Proton Belt.• Stably Trapped for years.