Why does the solar wind follow magnetic field lines?

[Thynazgul]

My physics teacher said that the northern lights are the product of charged particles coming from the sun and interactign with our atmosphere. I believe he said that these are deflected by Earth's magnetic field and directed towards the North and South poles.

When I look at pictures on this topic, the Earth's magnetic field is shown to be similar to a bar magnet's field. The solar wind then goes perpendicular to it and seems to follow the lines. Shouldn't the particles experience a magnetic force that is perpendicular to both their velocity and the magnetic field, and therefore end somewhere else that's not the North or South? For example, in the picture attached the arrows at the centre impact the field when its going up, with a velocity vector pointing right. Why is the force vector not going "out of the page"?

 

[davenn]

I believe he said that these are deflected by Earth's magnetic field and directed towards the North and South poles.

poor wording ... some of these are trapped by the Earth's magnetic field ... would have been much better
Note ... Not ALL of the particles are trapped, many are deflected ... it's the trapped ones that cause the aurora

When I look at pictures on this topic, the Earth's magnetic field is shown to be similar to a bar magnet's field.

yes

The solar wind then goes perpendicular to it and seems to follow the lines.

a very basic and as a result a very poor drawing
The charged particles in the solar wind, namely protons and electrons, actually spiral down the field lines, rather than following them straight down. The spiralling effect is a direct cause of a moving charged particle in a magnetic field.

Shouldn't the particles experience a magnetic force that is perpendicular to both their velocity and the magnetic field, and therefore end somewhere else that's not the North or South? For example, in the picture attached the arrows at the centre impact the field when its going up, with a velocity vector pointing right. Why is the force vector not going "out of the page"?

they do, see my previous comment ... again forget about that pic ... it is VERY BAD

This is better ...

http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/aurora.html

https://www-spof.gsfc.nasa.gov/Education/wtrap1.html

Dave