Evidence for Joule Heating in Neutral Density and Temperature Anomalies Observed With Rocket Borne Ionization Gauges

Seven temperature and number density profiles for the auroral mesosphere and lower thermosphere (MLT) were obtained during four different sounding rocket campaigns between 2019 and 2024. Two types of commercial, off‐the‐shelf ionization gauges were used on suborbital payloads reaching apogees ranging from 145 to 325 km. The analysis of absolute total number densities relies on the accurate determination of the ram factor for supersonic, rarefied, molecular flow and the transition to continuum flow. The rocket campaigns took place under quiet, moderately, and majorly disturbed geomagnetic conditions. The profiles are examined for anomalies associated with Joule and particle heating in the lower thermosphere and compared with MSIS model profiles. The main findings are evidence for temperature increases of up to 200°K near 120 km and number density increases of up to 50% at 140 km during disturbed conditions. The lowest thermospheric layer was characterized by density depletions of up to 20% and a very steep temperature gradient possibly also associated with high‐latitude heating.