D-region measurements during a solar eclipse

Observations of positive ion density in the _D-region during the solar eclipse of 1966 May 20, were made by means of a cylindrical Langmuir probe carried on a small rocket. the launch site was near Karystos in Greece. The ion density between 70 and 80 km was found to vary rapidly during the eclipse and the main ionising source at the time is considered to have been an X-ray emitting region on the Sun (McMath 8302). From the X-ray intensity of the Sun on this day, the maximum NO concentration at 80 km is found to be 1·8 × 10⁶cm⁻³. this is consistent with other D-region and some laboratory observations, but not with airglow measurements. Some evidence was also found for day-to-day variations in D-region density not associated with variations either in solar X-rays or in atmospheric density. These are presumed to be due to variations in the concentration of a minor atmospheric constituent such as NO, perhaps with atmospheric temperature.