LOWER IONOSPHERE ELECTRON DENSITIES MEASURED DURING SOLAR ECLIPSE OF NOVEMBER 12,1966

The University of Illinois and the GCA Corporation, supported by NASA, launched four Nike‐Apache rockets from Cassino, Brazil, during the solar eclipse of November 12, 1966. The measurement of D‐region ionization loss rates was the principal aeronomic objective of the four rockets. Each rocket carried a 3385‐kHz radio propagation experiment and a Langmuir probe. The probe data were calibrated by the radio data to give electron number densities. At the mesopause (82 km) the electron densities were 800, 400, 300, and 100 cm‐3 at full sun (2 hours after totality), at 2.5% visibility of the solar disk, at second contact and at third contact, respectively. The full‐sun measurement of electron density at 65 km was 100 cm−3. By the time of second contact, the electron density diminished to less than 10 cm−3 at 70 km and below. At the time of third contact, the electron density was less than 10 cm−3 at 75 km and below. No significant differences were visible between the electron densities observed at second and third contact and at 2.5% visibility for altitudes between 95 and 100 km. A well‐defined sporadic‐E layer was observed at 104 km. Copyright 1969 by the American Geophysical Union.