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The Importance of Wave Acceleration and Loss for Dynamic Radiation Belt Models Richard B. Horne M. M. Lam, N. P. Meredith and S. A. Glauert, British Antarctic Survey, Cambridge, UK 3 rd European Space Weather Week Brussels, 14 November 2006

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CRRES ~1 MeV Electron Flux Rapid variations in radiation belt –Damage spacecraft –Hazard to astronauts Object To develop a dynamic radiation belt model Use of dynamic models –To specify periods of risk –To analyse events –To determine extreme events –To specify conditions where little (no) data is available

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Importance of Wave Processes Structure of ‘quiet-time’ radiation belt controlled by losses due to waves –Lyons and Thorne [1973] Losses due to lightning (whistlers), ground based transmitters, hiss –Abel and Thorne [1998a, b] Losses due to microbursts precipitation (chorus waves) –Obrien et al. [2003] Losses due to EMIC waves –Summers and Thorne [2005], Albert [2005] Flux increases during 2003 Halloween due to chorus wave acceleration –Horne et al. Nature [2005], Shprits et al. [2006] Wave acceleration on global scale –Varotsou et al. [2005], Horne et al. [2006]

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Radiation Belt Model Solve the Fokker Planck equation in 1d –1 st term is transport across B (for constant 1 st +2 nd invariants J 1, J 2 ) –2 nd term is losses due to wave-particle interactions Focus only on losses due to whistler mode hiss Use BAS wave database and PADIE code to calculate losses Use data at GEO and calculate flux near L=3-4 –GPS satellites –Galileo satellites

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CRRES Data at L=6 Note energy dependence in flux variations Outer boundary condition requires flux at different energies

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Inward Transport Conservation of adiabatic invariants (J 1, J 2 ) –electrons accelerated when transported inward At GEO - need observations at 0.05 – few MeV

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Contribution of Wave-Particle Interactions: Which Waves?

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Intensity of Whistler Mode Hiss Wave intensity increases with Kp Changes in high density plasmapause region is critical for wave power Note plume region on dayside Latitude: 5 o – 30 o

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Latitude Coverage of Hiss Hiss observed to 30 o latitude Averaged over 06:00-21:00 MLT Include wave-particles interactions along magnetic field due to distribution of waves

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Pitch Angle Diffusion – PADIE Results Assume Peak wave frequency at 550 Hz and width of 200 Hz Peak power in field aligned direction with 20 o spread 10 harmonic resonances Bounce –average to mirror point Electron loss to atmosphere when diffusion rates are high near the loss cone (~ 4 degrees at L=4) Losses increase for fpe/fce small –fpe/fce =2 purple –Fpe/fce = 18 red E = 1 MeV L=4 Fpe/fce = 2, 6, 10, 14, 18

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Pitch Angle Diffusion Matrix for Hiss

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Model – Satellite Comparison - 1 MeV Drive model by time series of Kp Use flux at L=6 as outer boundary Look up fpe/fce and wave power according to Kp Scale diffusion matrix and obtain loss rates at all MLT Solve Fokker-Planck eqn. and obtain flux CRRES Model

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Radial diffusion only Radial diffusion and chorus waves Horne et al. [2006]

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Conclusions Model predicts MeV flux at L=3 – 4 from observations at L=6 using RD + wave losses Losses inside plasmapause near L~4 are major importance Predictions better than empirical models Flux L>4 underestimated – suggests local acceleration required Model improvements –Include wave acceleration outside plasmapause - chorus waves Varotsou et al. [2005]; Horne et al [2006] –Include losses due to other waves modes EMIC, chorus, whistlers, transmitters, magnetosonic waves Data requirements –Electron flux at 0.1 – few MeV at GEO –Galileo and GPS data for verification at L~4 –Wave database with different wave modes

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Timescale for Inward Transport If flux at outer boundary drops by a factor of 100 for 10 days –Flux at L=4 responds after 2 days If flux drops for only 1 day –Almost no response at L<4

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