influence of emic waves on radiation belt dynamics t. kersten, r. b. horne, n. p. meredith, s. a....
TRANSCRIPT
Influence of EMIC Waves on Radiation Belt Dynamics
T. Kersten, R. B. Horne, N. P. Meredith, S. A. Glauert
ESWW11Liège, 17-21/11/2014
British Antarctic Survey, UK
Van Allen Radiation Belts
• Inner belt: stable
• Outer belt: highly variable
• Main cause for variability: Plasma waves
• Risk for spacecraftSource: NASA
Types of Plasma Waves
• Chorus waves: – Major cause of acceleration and loss
Chorus
Sun
Magnetopause
Plasmaspause
Types of Plasma Waves
• Chorus waves: – Major cause of acceleration and loss
• Magnetosonic waves: – May be an important acceleration
mechanism
Chorus
Sun
Magnetosonicwaves
Magnetopause
Plasmaspause
Types of Plasma Waves
• Chorus waves: – Major cause of acceleration and loss
• Magnetosonic waves: – May be an important acceleration
mechanism
• Plasmaspheric hiss: – Major loss process
Chorus
Sun
Magnetosonicwaves
Plasmaspherichiss
Magnetopause
Plasmaspause
Types of Plasma Waves
• Chorus waves: – Major cause of acceleration and loss
• Magnetosonic waves: – May be an important acceleration
mechanism
• Plasmaspheric hiss: – Major loss process
• ElectroMagnetic Ion Cyclotron (EMIC) waves:– H+: fcHe < f < fcH
– He+: fcO < f < fcHe
Chorus
EMIC waves
Sun
Magnetosonicwaves
Plasmaspherichiss
Magnetopause
Plasmaspause
Types of Plasma Waves
• Chorus waves: – Major cause of acceleration and loss
• Magnetosonic waves: – May be an important acceleration
mechanism
• Plasmaspheric hiss: – Major loss process
• ElectroMagnetic Ion Cyclotron (EMIC) waves:– H+: fcHe < f < fcH
– He+: fcO < f < fcHe
– May be important loss process
Objective of Study: Quantify losses caused by EMIC waves
Chorus
EMIC waves
Sun
Magnetosonicwaves
Plasmaspherichiss
Magnetopause
Plasmaspause
• Fokker-Planck Equation
BAS Radiation Belt Model
),()(
)(
1)(
)(
12
2
E
f
E
fDEA
EEA
fDg
gL
f
L
D
LL
t
f
L
EE
ELJ
LL
• Fokker-Planck Equation
BAS Radiation Belt Model
),()(
)(
1)(
)(
12
2
E
f
E
fDEA
EEA
fDg
gL
f
L
D
LL
t
f
L
EE
ELJ
LL
Radial transport
• Fokker-Planck Equation
BAS Radiation Belt Model
),()(
)(
1)(
)(
12
2
E
f
E
fDEA
EEA
fDg
gL
f
L
D
LL
t
f
L
EE
ELJ
LL
Radial transport Pitch angle diffusion
• Fokker-Planck Equation
BAS Radiation Belt Model
),()(
)(
1)(
)(
12
2
E
f
E
fDEA
EEA
fDg
gL
f
L
D
LL
t
f
L
EE
ELJ
LL
Energy diffusionRadial transport Pitch angle diffusion
• Fokker-Planck Equation
BAS Radiation Belt Model
),()(
)(
1)(
)(
12
2
E
f
E
fDEA
EEA
fDg
gL
f
L
D
LL
t
f
L
EE
ELJ
LL
Energy diffusion LossesRadial transport Pitch angle diffusion
• Fokker-Planck Equation
• Drift & bounce averaged diffusion coefficients DLL , Dαα , DEE
are activity, location and energy dependent
• Details in: Glauert et al. 2014
BAS Radiation Belt Model
),()(
)(
1)(
)(
12
2
E
f
E
fDEA
EEA
fDg
gL
f
L
D
LL
t
f
L
EE
ELJ
LL
Energy diffusion LossesRadial transport Pitch angle diffusion
Calculating the Diffusion Coefficients
• Use the PADIE code (Glauert and Horne, 2005)
• Requires Gaussian distribution
Calculating the Diffusion Coefficients
• Use the PADIE code (Glauert and Horne, 2005)
• Requires Gaussian distribution– Peak power: IW
Calculating the Diffusion Coefficients
• Use the PADIE code (Glauert and Horne, 2005)
• Requires Gaussian distribution– Peak power: IW
– Peak of the Gaussian
fm
Calculating the Diffusion Coefficients
• Use the PADIE code (Glauert and Horne, 2005)
• Requires Gaussian distribution– Peak power: IW
– Peak of the Gaussian– Width of the Gaussian
fm
df
Calculating the Diffusion Coefficients
• Use the PADIE code (Glauert and Horne, 2005)
• Requires Gaussian distribution– Peak power: IW
– Peak of the Gaussian– Width of the Gaussian– Cut-off frequencies
fm
df
Calculating the Diffusion Coefficients
• Use the PADIE code (Glauert and Horne, 2005)
• Requires Gaussian distribution– Peak power: IW
– Peak of the Gaussian– Width of the Gaussian– Cut-off frequencies
• Model for plasma density
fm
df
Calculating the Diffusion Coefficients
• Use the PADIE code (Glauert and Horne, 2005)
• Requires Gaussian distribution– Peak power: IW
– Peak of the Gaussian– Width of the Gaussian– Cut-off frequencies
• Model for plasma density
• Ion composition fm
df
CRRES EMIC Wave Database
• Contains: Peak frequency fm Spectral width df Peak intensity I0
• EMIC wave events binned by: L*, MLT, 5 magnetic activity levels
Average intensities – Helium band
Average intensities – Hydrogen band
Modelling the Radiation Belts
EMIC Diffusion RatesPi
tch
angl
e di
ffusi
on c
oeffi
cien
t (s
-1)
EMIC Diffusion Rates
1 MeV
Combined EMIC and Chorus Diffusion Rates
Electron flux: 100 day simulation – 90°90° flux (cm-2sr-1s-1keV-1) for 6MeV electrons
With EMIC
Without EMIC
Electron flux: 100 day simulation – 90°90° flux (cm-2sr-1s-1keV-1) for 6MeV electrons
With EMIC
Without EMIC
Electron flux: 100 day simulation – 45°45° flux (cm-2sr-1s-1keV-1) for 6MeV electrons
With EMIC
Without EMIC
Electron flux: 100 day simulation – 45°45° flux (cm-2sr-1s-1keV-1) for 6MeV electrons
With EMIC
Without EMIC
Pitch-angle distribution: 1 MeV
Pitch-angle distribution: 6 MeV
Pitch-angle distribution: 10 MeV
Conclusions
• EMIC waves lead to significant losses at pitch-angles < 60°
• EMIC waves are effective at scattering electrons for E > 2MeV
• There is no significant energy diffusion
• EMIC waves will result in a peaked particle distribution for 70° < α < 90°
• Therefore, we suggest: Looking for particle distributions peaked near 90° and E > 2MeV in Van Allen Probes data
Acknowledgements
• The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreements number 262468 (SPACECAST) and number 284520 (MAARBLE), and is also supported in part by the UK Natural Environment Research Council
Wave parameters
Parameter Hydrogen band waves Helium band waves
fm/fcH 0.4 0.15
df/fcH 0.02 0.02
flc/fcH 0.36 0.11
fuc/fcH 0.44 0.19
Xm 0.0
ΔX tan 15°
Xcut 2 ΔX
Resonances -10 ≤ n ≤ 10
fpe/fce 10.0
Ion composition 94% H+ 5% He+ 1% O+
