Taming earth s space radiation environment through scientific understanding
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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

Taming Earth’s space radiation environment through scientific understanding

J.C. Green

Space Environment Center

June 22, 2005


Outline
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


Introduction to the electron radiation belts
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


Electron radiation belt hazards

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]


The challenge to modelers

>2 MeV Electron Flux at Geosynchronous causing internal charge to build up.

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.


Empirical statistical modeling solutions
Empirical/Statistical Modeling Solutions causing internal charge to build up.

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


Testing loss mechanisms
Testing Loss Mechanisms causing internal charge to build up.


The earth s radiation belts
The Earth’s Radiation Belts causing internal charge to build up.

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


Goal to understand and specify radiation belt variability

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.


Motion due to magnetic fields
Motion due to magnetic fields always increase during geomagnetic storms [

+

Gyro-motion around filed lines: ~sec

Bounce motion along field lines: ~seconds-minutes

Drift motion around the earth: many minutes

= All motion

+

+


Taming earth s space radiation environment through scientific understanding

Radiation Belt Basics always increase during geomagnetic storms [

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


Scientific puzzle what causes the extreme temporal variability
Scientific Puzzle: always increase during geomagnetic storms [What causes the extreme temporal variability?


Taming earth s space radiation environment through scientific understanding

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.


Societal impact
Societal impact always increase during geomagnetic storms.

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.


High radiation levels harmful to astronauts
High radiation levels harmful to astronauts. always increase during geomagnetic storms.


Goal to better understand and specify radiation belt variability
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.


Magnetopause loss
Magnetopause Loss variability.

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


Are the electrons scattered into atmosphere
Are the electrons scattered into atmosphere? variability.

Yes, SAMPEX > 400 keV electron data shows increased flux in the bounce loss cone within .5 days.