Non‐Maxwellian Characteristics of the Energy Distribution of Thermal Electrons in the Upper Atmosphere

The Result of Measurements of the energy distribution of thermal electrons in a midlatitude ionosphere is presented. A comparison is made in particular between the characteristics at sunrise and sunset periods because of the effect of vibrationally excited nitrogen molecules. At sunrise the distribution has a little‐irregularity but the middle and higher energy parts (0.2‐0.5 eV) deviate from the Maxwellian distribution only slightly at all heights. The electron temperature varies from 900 K to 1300 K between 130 km and 300 km. These values are higher than the kinetic temperature of neutral particles but comparable with the theoretical values of the vibration temperature of N 2 . At sunset small bumps due to non‐thermal electrons are seen on the high energy tail between 108 and 160 km, their density being from 5 × 10 −3 to 1 × 10 −2 of that one of the thermal electrons. Above 170 km (F‐layer) the deviation of the distribution from the Maxwellian one becomes smaller. The electron temperature varies from 500 K to 900 K between 100 km and 220 km. These values are higher than the kinetic temperature but lower than the theoretical values of the vibration temperature of N 2 . A mechanism of the appearance of non‐thermal electrons is considered to be due to super‐elastic collisions with vibrationally excited N 2 .