L9 - Radiation Belt Physics Flashcards
What populates the Earth’s magnetosphere?
• The Earth’s magnetosphere is populated by energetic charged particles - electrons and ions, protons and alpha particles (helium nuclei) mainly
The Earth’s magnetic field traps what?
• The Van Allen radiation belt electrons are trapped in Earth’s dipolar magnetic field: their energies are from >40 keV to many MeV
What is the L- value for a dipolar geomagnetic field? (def)
• A dipolar geomagnetic field line is specified by its L-value, which is the distance at which the field line crosses the equatorial plane, measured from the centre of the Earth, in units of Earth radii
What is the Cyclotron (gyro) motion around geomagnetic field lines?
~1 millisecond, ms, for electrons at L ~ 4
What is the bounce motion from one hemisphere to another?
a few seconds, ~s, for 40 keV electrons at L ~ 4
What is the longitudinal drift motion?
> 1 hour, for 40 keV electrons
Cite the motions that characterize electrons in a magnetic field.
Cyclotron (gyro)
Bounce
Longitudinal Drift
Describe the charged particle populations in the outer Van Allen belt.
- Trapped charged particles: if pitch angle > loss cone
- Sources: (i) from solar wind – with entry on dayside magnetopause, or at cusp, or from magnetotail (ii) from ionosphere (polar wind)
- Losses: if pitch angle lies within the loss cone, charged particles precipitate into upper atmosphere
- Transport: in real space, x, y, z, and time t, or in phase space, also termed velocity space, i.e. acceleration or deceleration can occur
- Explore the balance between these three processes
Explain the Wave Particle Interaction
Cyclotron resonance (or gyroresonance) interaction between energetic electrons of the Van Allen belts and whistler mode waves moving in the opposite direction along geomagnetic field lines.
