The Magnetosphere

Internet resources

A very readable overview
Exploration of Earth's Magnetosphere Section #19 & #20
Windows to the Universe Magnetosphere Page
The magnetosphere section in the Physics of the Aurora webcast

More detailed info:
University of Oulu's (Finland) Magnetosphere section in their Space Physics Textbook

Magnetospheric structure

The basic structure was previously described as part of the atmospheric structure, but the internal structure of the magnetosphere is rather complex with often overlapping structures depending on whether the region is defined by high energy charged particles, low energy charged particles or neutral (uncharged) particles.

  • The Magnetopause: the boundary between the magnetosphere and the solar wind
  • The Polar Cusps (or Clefts): the funnel-shaped region delineated by the (open) magnetic field lines that sweep into the magnetotail
  • The Entry Zone: the boundary just inside the magnetopause on the day side
  • The Geocorona: the glow (in the far UV) from the shroud of neutral hydrogen atoms surrounding the Earth

  • The Inner Magnetosphere
  • The Magnetotail

    There is no sharp boundary between the ionosphere and the magnetosphere. The mid and low latitude ionosphere is connected to the plasmasphere, whereas the high latitude ionosphere is directly connected to the outer magnetosphere through the polar cusps. The high latitude ionosphere receives a polar rain (actually it's more like a drizzle) of electrons from the solar wind and is also the source of a polar wind of O+ ions into the magnetosphere.

    "Sounds" of the Magnetosphere

    Natural radio waves are associated with lightning, aurora and magnetospheric processes. Some of these radio waves occur at audio frequencies (about 100 Hz to 10 kHz). These radio waves are not sound waves and can not be heard directly, but a radio receiver can convert eletromagnetic (radio) waves into acoustic (sound) waves with the same frequency so as to allow the magnetosphere to be "heard". The radio waves that travel through the magnetosphere provide signatures for magnetospheric instabilities and mechanisms which transport particles or cause particles to be lost from the magnetosphere.

    Where are the "noises" coming from? Some prefer to call them Earth Songs.
    Samples and live audio stream from the INSRIRE VLF radio receiver at the Marshall Space Flight Center in Huntsville, Alabama.
    Excellent examples of whistlers, hiss, and chorus (as .wav files) recorded by the Polar spacecraft
    A menu of ground-based recordings

    Historical Outline

    May 7,1895Alexander Popov demonstrates that radio waves ("sferics") are generated by lightning
    1903Kristian Birkeland proposes idea to explain aurora (incorrectly) that turns out to be basis of "polar rain"
    1915"Whistler" radio waves detected
    1931Sydney Chapman and Vincent Ferraro develop theory for Earth's magnetic cavity
    1953Owen Storey proves interhemispheric propagation of "whistler" radio waves from lightning
    1959Thomas Gold coins word "magnetosphere"
    1961James Dungey proposes idea of magnetic reconnection as mechanism of transferring solar wind energy into Earth's magnetosphere
    1961Explorer 12 detects magnetopause
    1963Equatorial plasmapause is identified through analysis of "whistler" radio waves by D.L. Carpenter
    1963Hannes Alfvén describes theory of magnetohydrodynamic (MHD) waves and existence of bow shock
    1964IMP-1 (Interplanetary Monitoring Platform) probe detects bow shock and existence of magnetotail
    1970Alfvén awarded Nobel Prize
    1974Existence of polar rain confirmed
    1976Ed Shelley and others find evidence for polar wind
    2001Four Cluster spacecraft detect rippling of the magnetospause