auras
The current expansive list of magic schools is kind of a pain when it comes to defining auras. I think that there's not really any point having an aura based on the school of magic if there are so many schools to keep straight and just having the school doesn't really tell you much, if anything, about the source of the aura. Most of the time the aura doesn't really matter, as you only care about two things: Is there something magic, and is it dangerous.
magical auras as detected by the detect magic function of an arcana check tell the following things:
school of magic:
duration: temporary or permenant
source: area, object, or creature
ambiguity: each spell has a ambiguity value, the ambiguity of the aura is that base value, plus the caster's character level. The lower the ambiguity, the easier it is to notice the spell's aura, as you make an arcana skill check to detect magical auras, and the amount by which you roll under your arcana score is compared to the ambiguity of the spell auras in your target area, any with lower ambiguity are detected by you.