Rocket measurements of plasma densities and temperatures in visual aurora

Direct measurements in active visual auroral forms using electrostatic plasma probes are described. On-board probes and an ejected Langmuir probe were used to provide maximum accuracy of measurement and freedom from perturbations. An electron density of 9.5 × 10 5 electrons/cm 3 was found within a visual band, with a background density of 1.5 × 10 5 electrons/cm 3 outside the band. The ionization maximum occurred at 107 km altitude, with a half-density vertical thickness of 7 km. The temperature of the thermal electrons over the interval 100 km to 168 km was found to range from 500 °K to 1400 °K. A hyperthermal electron component was also observed. A rocket-borne photometer determined the height of the optical emission region, and an array of optical, radio, and magnetic ground-based instruments were used to provide supporting geophysical data, and to define the position and variations of the auroral forms.