What causes halo shape of aurora over poles?

[Gene B]

Can aurora halo shape be explained, versus full pole capping by aurora? What could cause the sharp boundaries?

Are oxygen ions ejected too vigorously from directly above poles due to B field strength or orientation? If so, are those ions lost to the heliosphere?

Calling all ion chasers...

 

[Vancanneyt Sander]

It’s a simple explanation. The earths core is magnetic, so that’s deep below your feet. Our atmosphere is way above. So like every magnet, magnetic field lines come from the poles in the core and reconnect with the other pole. So those field lines go through our atmosphere around the poles and form a halo like shape called the Van Allen belt. 

so during southward directed interplanetary magnetic field, a part of solar wind particles are injected along the earths magnetic field lines into the earths atmosphere and light up the auroral oval. Northward directed interplanetary magnetic field deflects it.

[Curious in NC]

I am struggling to understand northward vs southward IMF. Certainly this basic concept is obvious, once it’s conceived of properly, but I’m not grasping it, given the diagrams I’ve seen so far. Would love to see two diagrams: one showing a southward IMF and a separate one showing a northward IMF. Thanks!

 

 

 

[Vancanneyt Sander]

It’s simple, northward directed IMF deflects near the poles like in the last image. Southward directed IMF will cause the solar wind to be injected towards the poles.