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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

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Van Allen Radiation Belts Inner belt: stable Outer belt: highly variable Main cause for variability: Plasma waves Risk for spacecraft Source: NASA

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Types of Plasma Waves Chorus waves: –Major cause of acceleration and loss Chorus Sun Magnetopause Plasmaspause

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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

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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

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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

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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

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Fokker-Planck Equation BAS Radiation Belt Model

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Fokker-Planck Equation BAS Radiation Belt Model Radial transport

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

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

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

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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. 2014 BAS Radiation Belt Model Energy diffusionLossesRadial transportPitch angle diffusion

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Calculating the Diffusion Coefficients Use the PADIE code (Glauert and Horne, 2005) Requires Gaussian distribution

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

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

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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

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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

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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

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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

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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

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Modelling the Radiation Belts

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EMIC Diffusion Rates Pitch angle diffusion coefficient (s -1 )

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EMIC Diffusion Rates 1 MeV

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Combined EMIC and Chorus Diffusion Rates

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

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

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

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

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Pitch-angle distribution: 1 MeV

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Pitch-angle distribution: 6 MeV

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Pitch-angle distribution: 10 MeV

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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

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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

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Wave parameters ParameterHydrogen band wavesHelium band waves f m /f cH 0.40.15 df/f cH 0.02 f lc /f cH 0.360.11 f uc /f cH 0.440.19 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 +

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