Rarefaction n. : The act or process of rarefying; the state of being rarefied; -- opposed to condensation; as, the rarefaction of air.

Example:
The distance between the center of a condensation and the center of an adjacent Rarefaction is 65.23 cm.?

Taxonomy
Rarefaction, free encyclopedia, layers of the atmosphere, Rarefaction waves, rarefaction wave, natural example, behaviour, compression, search, Unsourced, reduction, density, decompression, to the Earth, relation to, self-similar expansion, pressure increases, relative pressure.

Defination from the web:
rarefaction of the medium. Another natural example of rarefaction is in the layers of our atmosphere. ...