Aurora

What is an Aurora?

Auroras occur in both Northern ( Aurora Borealis ) and Southern hemispheres ( Aurora Australis ), aand are often visible as far as 40 degrees from the poles. They are most visible at close to the equinoxes - March/April and September/October.

Auroras are usually observed as coloured lights or a glow coming from the upper atmosphere, and appear to be associated with instability in the geomagnetic field of the Earth. The glow is caused by solar flares colliding with atoms of Oxygen and Nitrogen in the upper atmosphere, causing ionsation of the atoms.

Auroras typically occur at altitudes of 80km to 150km, and usually occur between 65 and 70 degrees geomagnetic latitude, but can occur up to 40 degrees latitude.

Auroral Propagation

This usually occurs at frequencies above 20MHz - below this, radio waves are usually absorbed. The maximum frequencies reflected by auroras are around 400MHz - optimal frequencies are usually in the 6 metres band

Links

The Northern Lights and Six Metres