Lecture 19

• at distance greater than ~10 Earth radii, the geomagnetic field is significantly distorted by the solar wind
• solar wind

  • coronal mass ejection (plasma and magnetic field)
  • associated with sunspot activity on the sun
  • consists of plasma (electrons, protons, hydrogen and helium nuclei) overall neutrally charged
  • particles travel outwards at velocities of ~400 km/s
  • normally ~5 particles per cm^3
• how does the solar wind interact with the geomagnetic field

  as the solar wind approaches the geomagnetic field two things can happen:

  1. the particles in the solar wind are deflected around the field
  2. the magnetic field is pushed out of the way by the solar wind
• bow shock

  where the solar wind particles are slowed from supersonic speeds by the magnetic pressure of the Earth's field
• solar wind is stopped at the magnetopause
• region between the magnetopause and bow shock is called the magnetosheath
• low field regions near polar regions are called cusps
• magnetic field on the night is reduced at large distances - this is the magnetotail
• the magnetotail contains a narrow zone of very low field, over which the magnetic field direction reverses - this is the neutral sheet
• variable solar wind can give some radiation belt particles enough energy to spiral into atmosphere and create aurorae. most solar wind particles deflected on past planet but a few leak into magnetosphere to get trapped in radiation belts
• a charged particle from CME collides with stable electrons of an oxygen atom causing it to get excited and 'jump' a orbit. unstable excited electrons rapidly de-excites 'jumps' down orbits and releases a radiation and a photon as a result. the photon emitted has a wavelength of 550 nm giving visible green light
• in the absence of a magnetosphere:

  • the solar wind will not be deflected
  • high energy particles enter the atmsophere
  • increase rick of cancer
  • high energy particles in the region occupied by man made satellites
  • may induce currents in subsurface and disrupt power lines
  • in the longer time-scale:
  • will degrade atmosphere - eventually removing most of it
  • lower pressure will mean lower boiling point of water
  • liquid water will not be possible even at normal temperatures of 25 C
  • lack of liquid water will mean life on planet surface will be impossible