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Taming Earth’s space radiation environment through scientific understanding

Taming Earth’s space radiation environment through scientific understanding. J.C. Green Space Environment Center June 22, 2005. Outline. Intro to the radiation belts Hazards of the radiation belts Current modeling solutions Statistical/empirical modeling

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Taming Earth’s space radiation environment through scientific understanding

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  1. Taming Earth’s space radiation environment through scientific understanding J.C. Green Space Environment Center June 22, 2005

  2. Outline • Intro to the radiation belts • Hazards of the radiation belts • Current modeling solutions • Statistical/empirical modeling • Physics based modeling • Combination of empirical and physics based • Testing electron acceleration mechanisms • Testing electron loss mechanisms • Looking forward

  3. Introduction to the Electron Radiation Belts • Particle energies >.1 MeV • Inner belt 1.5-3 Re Outer belt 3-10 Re. • Slot region: flux minimum at ~3 Re formed by enhanced loss due to interaction with waves caused by lightening and VLF transmitters. • Structure and dynamics of proton and electron belts differs so they are studied separately. • Radiation belt electrons = relativistic electrons

  4. High energy electrons can penetrate through shielding causing internal charge to build up. A sudden discharge may temporarily flip bits or permanently damage electronics as in the loss of the Telestar satellite. Telestar Failure >1.5 MeV Electron dose Electron Radiation Belt Hazards [Violet and Frederickson, 1993]

  5. >2 MeV Electron Flux at Geosynchronous electron flux Day of Year The Challenge to Modelers • Relativistic electron flux is extremely variable. • Flux may increase or decrease on rapid timescales of less than one day.

  6. Empirical/Statistical Modeling Solutions Nowcast/Forecast: Electron flux nowcasts provide situational awareness for analyzing satellite upsets while forecasts provide the ability to prepare for potential upsets. • REFM: predicts flux at geosynchronous • 1day PE=80%, 2day PE=-24%, 3day PE=-49% • Statistical Asynchronous Regression: specifies geosynchronous flux at any local time based on a measurement at one local time. • State space model with Kalman filter: predicts flux at low altitude based on previous SAMPEX measurements. Relativistic Electron Forecast Model Observed daily flux Predicted flux flux Day

  7. Testing Loss Mechanisms

  8. The Earth’s Radiation Belts Discovered accidentally in 1958 by Dr. Van Allen’s cosmic ray experiment onboard explorer I spacecraft. • Energies >.1 MeV • Inner belt 1.5-3 Re, Outer belt 3-10 • Slot region: flux minimum near ~3 Re formed by enhanced precipitation due to interaction with whistler waves generated by lightening and VLF transmitters. • Radiation belt electrons = relativistic electrons

  9. Contrary to intuition, relativistic electron flux does not always increase during geomagnetic storms [Reeves et al., 2003] Flux levels are determined by the outcome of a continuous competition between acceleration and loss. >2 MeV Electron Flux at Geosynchronous electron flux Day of Year Goal: To understand and specify radiation belt variability.

  10. Motion due to magnetic fields + Gyro-motion around filed lines: ~sec Bounce motion along field lines: ~seconds-minutes Drift motion around the earth: many minutes = All motion + +

  11. Radiation Belt Basics Discovered accidentally in 1958 by Dr. Van Allen’s cosmic ray experiment onboard explorer I spacecraft. • Energies >.1 MeV • Inner belt 1.5-3 Re, Outer belt 3-10 • Slot region: flux minimum near ~3 Re formed by enhanced precipitation due to interaction with whistler waves generated by lightening and VLF transmitters. • Radiation belt electrons = relativistic electrons

  12. Scientific Puzzle: What causes the extreme temporal variability?

  13. Contrary to intuition relativistic electron flux does not always increase during geomagnetic storms. Reeves et al. [2003] found that 53% produced elevated relativistic electron fluxes at geosynchronous altitude, 19% produced decreased fluxes, and 28% produced no change. Flux levels are determined by the outcome of a continuous competition between acceleration and loss.

  14. Societal impact High radiation levels may cause satellites to electrically charge. A sudden discharge may cause minor problems, temporarily disabling satellites due to flipped program bits or more cataclysmic situations, permanently satellites due to damaged electronics. High radiation levels cause slow degradation of solar arrays.

  15. High radiation levels harmful to astronauts.

  16. Goal: To Better understand and specify radiation belt variability. High radiation levels may cause satellites to electrically charge. A sudden discharge may temporarily disable satellites due to flipped program bits or permanently destroy satellites due to damaged electronics.

  17. Magnetopause Loss Adiabatic motion can lead to real loss if electrons move out far enough to encounter the magnetopause. Kim and Chan [1997] examined one storm and based on theoretical calculations concluded that electrons at geosynchronous could be pushed out to the magnetopause. Currently, there is no observational support in favor of this loss mechanism. solar wind Earth SUN e Magnetopause

  18. Are the electrons scattered into atmosphere? Yes, SAMPEX > 400 keV electron data shows increased flux in the bounce loss cone within .5 days.

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