I may be wrong myself here, but I'll share my thoughts at the risk of making a fool of myself...
Just clicked onto todays spaceweather to find them carrying a story on South Pole Auroras www.spacweather.com - In the body of text its says 'Just before he took the picture, the interplanetary magnetic field (IMF) near Earth tipped south, opening a crack in our planet's magnetosphere.'
Now, I know this is the case in the northern hemisphere, but in the southern hemishpere would it be the opposite - should they be saying a northward tilt? I'm know i'm being a bit pedantic here, I just need to satisfy my curiousity... Any of you folks know whats what here? or am I just barking up the wrong tree?
Yep, the premise is correct. Don't forget that the magnetic field of the earth has the usual two poles and the field "flows" out of the north and down to the south. (Not strictly correct but it'll do) Now if we go through a field which is oriented the same way the coupling will be poor but if we go through a field which is reversed with respect to us, the coupling is much better so more particles can get in both over the north and south magnetic poles.
A good way to visualise this and understand what is going on is to do a wee experiment with two magnets.
As you'll know if you try to bring the two north or south poles together they will repel each other, similarly if you hold the magnets length wise and parallel to each other with both north ends and the same end they will also repel as n pushes against n and s pushes against s.
Now turn one of the magnets so that the n sees the others s end the reverse at the other end and they will pull together, voila just as what happens with the earths field and the interplanetary field when they are anti parallel. The best aurora happen during this configuration.
I have a look at the spaceweather.com site most days and they have some fantastic NLC images. However, I find it frustrating that they don't list NLC events in double-date format - very ambiguous if no times are included!