Electron densities within aurorae and other auroral E-region characteristics

The L ‐band incoherent scatter radar located at Chatanika, Alaska ( L ≃ 5.6) has been used to measure the characteristics of the auroral E layer. In this paper, the term auroral E layer refers to nighttime ionization between altitudes of 90 to 150 km produced by particle precipitation. Electron density profiles have been measured using time resolutions as short as 0.2 sec and range resolutions of 5 to 10 km. For the shortest integration time, the statistical accuracy of the measurement is on the order of 10%. Results obtained to date show auroral ionization to align with the earth's magnetic field and to have lengths along the field of typically 20 to 30 km and thicknesses across the field of less than 5 km (both distances measured between the half‐peak‐density points). Within the auroral ionization, the maximum electron density at times approaches 2 × 10 6 el cm −3 . The measured quantities have been analyzed to deduce (a) energy of the particle precipitation, (b) flux of particle precipitation, (c) production rates, and (d) effective recombination coefficients. For a few cases, estimates of the pitch‐angle distribution of the primary electrons have been made.