Positive ions and the winter anomaly.

A coordinated rocket program to study winter variability in D-region ionization was conducted at White Sands Missile Range, New Mexico, during the winter of 1970-1971. Parachute-borne blunt probes that measure positive-ion and electron conductivities were flown, in conjunction with other experiments, on Jan. 22 and 26 and Feb. 1, 1971. Both A1 and A3 radiowave absorption techniques were used to indicate anomalous winter days. The two rocket shots in January occurred on such days of high absorption. The first of these was one of quiet solar activity, whereas the second was preceded by a major solar proton event on January 24. The third flight occurred on a normal winter day. We tentatively conclude that we have observed two days of 'anomalous' winter absorption of very different character, one possibly related to a solar disturbance, and one probably entirely induced by meteorological effects. The former day was probably characterized by inhibition of the formation of negative ions due to increased detachment and the latter by decreased ionization loss rate.