Influence of EMIC Waves on Radiation Belt Dynamics T. Kersten, R. B. Horne, N. P. Meredith, S. A. Glauert ESWW11 Liège, 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 spacecraft Source: 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 Magnetosonic waves 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 Magnetosonic waves Plasmaspheric hiss 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 + : f cHe < f < f cH –He + : f cO < f < f cHe Chorus EMIC waves Sun Magnetosonic waves Plasmaspheric hiss 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 + : f cHe < f < f cH –He + : f cO < f < f cHe –May be important loss process Objective of Study: Quantify losses caused by EMIC waves Chorus EMIC waves Sun Magnetosonic waves Plasmaspheric hiss Magnetopause Plasmaspause

Fokker-Planck Equation BAS Radiation Belt Model

Fokker-Planck Equation BAS Radiation Belt Model Radial transport

Fokker-Planck Equation BAS Radiation Belt Model Radial transportPitch angle diffusion

Fokker-Planck Equation BAS Radiation Belt Model Energy diffusionRadial transportPitch angle diffusion

Fokker-Planck Equation BAS Radiation Belt Model Energy diffusionLossesRadial transportPitch angle diffusion

Fokker-Planck Equation Drift & bounce averaged diffusion coefficients D LL, D αα, D EE are activity, location and energy dependent Details in: Glauert et al BAS Radiation Belt Model Energy diffusionLossesRadial transportPitch 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: I W

Calculating the Diffusion Coefficients Use the PADIE code (Glauert and Horne, 2005) Requires Gaussian distribution –Peak power: I W –Peak of the Gaussian fmfm

Calculating the Diffusion Coefficients Use the PADIE code (Glauert and Horne, 2005) Requires Gaussian distribution –Peak power: I W –Peak of the Gaussian –Width of the Gaussian fmfm df

Calculating the Diffusion Coefficients Use the PADIE code (Glauert and Horne, 2005) Requires Gaussian distribution –Peak power: I W –Peak of the Gaussian –Width of the Gaussian –Cut-off frequencies fmfm df

Calculating the Diffusion Coefficients Use the PADIE code (Glauert and Horne, 2005) Requires Gaussian distribution –Peak power: I W –Peak of the Gaussian –Width of the Gaussian –Cut-off frequencies Model for plasma density fmfm df

Calculating the Diffusion Coefficients Use the PADIE code (Glauert and Horne, 2005) Requires Gaussian distribution –Peak power: I W –Peak of the Gaussian –Width of the Gaussian –Cut-off frequencies Model for plasma density Ion composition fmfm df

CRRES EMIC Wave Database Contains: Peak frequency f m Spectral width d f Peak intensity I 0 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 Rates Pitch angle diffusion coefficient (s -1 )

EMIC Diffusion Rates 1 MeV

Combined EMIC and Chorus Diffusion Rates

Electron flux: 100 day simulation – 90° 90° flux (cm -2 sr -1 s -1 keV -1 ) for 6MeV electrons With EMIC Without EMIC

Electron flux: 100 day simulation – 90° 90° flux (cm -2 sr -1 s -1 keV -1 ) for 6MeV electrons With EMIC Without EMIC

Electron flux: 100 day simulation – 45° 45° flux (cm -2 sr -1 s -1 keV -1 ) for 6MeV electrons With EMIC Without EMIC

Electron flux: 100 day simulation – 45° 45° flux (cm -2 sr -1 s -1 keV -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/ ) under grant agreements number (SPACECAST) and number (MAARBLE), and is also supported in part by the UK Natural Environment Research Council

Wave parameters ParameterHydrogen band wavesHelium band waves f m /f cH df/f cH 0.02 f lc /f cH f uc /f cH XmXm 0.0 ΔXΔXtan 15° X cut 2 ΔX Resonances-10 ≤ n ≤ 10 f pe /f ce 10.0 Ion composition94% H + 5% He + 1% O +