What is a sounding rocket?
Sounding rockets are suborbital vehicles; they are launched into space but don’t reach orbital velocity, so they return to Earth along a parabolic path within 15-20 minutes.
Sounding rockets are commonly used to study the upper atmosphere and phenomena like aurora since the region below ~400 km is a very difficult altitude to keep a satellite orbiting, due to atmospheric drag. Auroral altitudes of ~100 km are too low to be reached by satellites so sounding rockets offer the best access.
For more information, visit: https://www.nasa.gov/missions/research/f_sounding.html and