Intense magnetic field lines trap
Explosive ejection of gas and plasma from the sun
A space hazard…
Typical concentration of particles near Earths ~1 particle / cm3
Typical velocity ~400 km/sec;
Sievert – measure of radiation energy
absorbed (in gamma ray equivalent)
(joules per kg)
Multiply rem x 10 to get mSv
about 11 years. GCR are maximum when solar activity is minimum and vice-versa. The
resulting dose equivalent at aircraft also varies quite strongly with altitude and latitude
The following table provides estimates of the radiation dose equivalent at the times of a
recent solar minimum (10/86) and solar maximum (7/89) for representative high and low
latitude locations at 90 degrees west longitude as a function of altitude. These values
were obtained through the use of the CARI-6 program developed by the Civil
Aeromedical Institute of the Federal Aviation Administration.
The atmosphere protects us from the solar
Dose Equivalent Rate (micro-sieverts per hour (uSv/h)
Solar Minimum (10/86)
Solar Maximum (7/89)
We are continually exposed to dose equivalent rates of about 6 to 12 uSv per day at sealevel due to GCR and radiation from the ground which is dependent on our location, as
well as radiation from within our own bodies. Thus a two-hour flight at conventional
altitudes (20,000 - 40,000 ft) may approximately double one's radiation dose for the day.
Mostly, it is the mass of the atmosphere that shields us from
solar wind radiation, but the magnetic field helps too
Solar particle events of sufficient size to provide significant exposure increases are rare1.
In 11 years one could expect up to three events, each of which might produce an
All else being equal, this is what the Earth’s field would
look like from far away
Magnetopause – delimits boundary between solar wind and Earth’s magnetosphere.
Magnetosheath – region between the bow shock and the magnetopause
Outside the bow shock the solar wind wins, Inside the magnetopause the Earth’s field wins,
in between is a messy competition
Earth’s magnetosphere are very different
Much quieter inside
Occurs where the magnetic field switches from south to north, and
the field lines are stretched out by the solar wind
Circles show the sense of the magnetic field around parallel wires
(with current into page). For a ‘sheet’ of current, the magnetic field
Would be given by the red and green lines.
Controlled by off-axis dipole, and ~27 day solar rotation.
Magnetic equator precesses; from Earth it appears to oscillate
up and down
where field lines and particle trajectories are most nearly parallel
Outer belt: 4 to 5 Re, electrons
Inner belt: 0.01 to 1.5 Re, protons, particles
Multiply rem x 10 to get mSv
SAA is the closest approach of Van Allen radiation belt to the
Happens b/c magnetic pole is tilted relative to Earth’s axis, and
b/c Earth’s magnetic field is not uniform
If you are an astronaut or a satellite you want to avoid the area
(Hubble shuts down).
SAA is drifting westward ~0.3o per year
Saturn Uranus Neptune
1.4-1.6 R M 6-12 RE 50-100 RJ 16-22 RS 18-19 RU 23-26 RN
Saturn sometimes sits within Jupiter’s magnetosphere
(Jupiter’s magnetotail extends beyond Saturn)
Io is a major source of plasmaSulphur dioxides photo dissociates…