Parameter Tree:
EARTH SCIENCE > SUN-EARTH INTERACTIONS > SOLAR ENERGETIC PARTICLE PROPERTIES > PARTICLE DENSITY

Definition:
The number of particles present per unit volume (typically a cubic centimeter).

Reference:
Online Glossary of Plasma Physics and Fusion Energy Research (Princeton Plasma
Physics Laboratory). URL:
http://www.pppl.gov/~rfheeter/fusion-faq/glossary.html