Space Weather

Coronal loops Intense magnetic field lines trap plasma main_TRACE_loop_arcade_lg.jpg

Coronal mass ejection Explosive ejection of gas and plasma from the sun A space hazard…

Normal conditions Typical concentration of particles near Earths ~1 particle / cm3 Typical velocity ~400 km/sec; (Protons)

During a solar flare, particle flux increases by a factor > 100,000

Ionized radiation is bad for you… Sievert – measure of radiation energy absorbed (in gamma ray equivalent) (joules per kg)

Multiply rem x 10 to get mSv Solar Flare Ionized radiation is bad for you…

10 km 20 km Mostly, it is the mass of the atmosphere that shields us from solar wind radiation, but the magnetic field helps too The atmosphere protects us from the solar flares Fukashima Reactor #1 500 uSv/hr

Interaction of the solar wind and Earth’s magnetic field All else being equal, this is what the Earth’s field would look like from far away

But the solar wind cannot cross fields lines, so what happens?

Bow shock – where velocity of solar wind drops sharply as it approaches the magnetopause 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

The polar auroral fountain sprays ions - oxygen, helium, and hydrogen - from Earth's upper ionosphere into deep space. The loss is miniscule compared to the immense ocean of air covering our world, but is significant in terms of what drives space weather around our world.

Outside Inside The magnetic conditions inside and outside the Earth’s magnetosphere are very different Much quieter inside

Generation of a current sheet in the magneto-tail. 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.

The solar current sheet (or magnetic equator) Controlled by off-axis dipole, and ~27 day solar rotation. Magnetic equator precesses; from Earth it appears to oscillate up and down

Some small amount of charged particles can enter magnetopause where field lines and particle trajectories are most nearly parallel

Go to notes on electron orbits in magnetic fields….

Aurora Borealis (northern lights)

From space

Van Allen radiation belts Outer belt: 4 to 5 Re, electrons Inner belt: 0.01 to 1.5 Re, protons,  particles

mSv/hour

Multiply rem x 10 to get mSv 1 hour in Van Allen Belt

The South Atlantic Anomaly SAA is the closest approach of Van Allen radiation belt to the surface. 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 ~0.3 o per year

Magnetic fields on other planets…. Saturn sometimes sits within Jupiter’s magnetosphere

Jupiter’s radiation belt (Jupiter’s magnetotail extends beyond Saturn)

Aurora on Jupiter

Io is a major source of plasma- Sulphur dioxides photo dissociates… Jupiter’s northern lights

Saturn too…