I don't think of "aura" as most people do (to my knowledge). But through the use of ritual and magic in general, you have to look at the scientific aspects of energy.
When you focus your will to cause change you are focusing energy to move in the way that you wish it to. By doing this you are creating an "aura" of magical power surrounding the ritual area.
I've been to many different ritual chambers, and many different rituals in the past, and you can "feel" the power in the air. The human senses are very perceptive to things that science hasn't quite put a label on.
Eventually the energy will dissipate, but at that point in time the "aura" was present.
"Six seconds left until your eyes turn green and you begin to question everything you've ever seen."