MID-LATITUDE LOWER IONOSPHERE STRUCTURE AND COMPOSITION MEASUREMENTS DURING WINTER

Measurements of total positive ion densities by use of electrostatic probes and measurements of total negative ion densities and the positive ion composition by use of cryogenically pumped mass spectrometers were conducted in the lower ionosphere during winter anomaly. The measurements which were part of the Western Europe Winter Anomaly Campaign 1975/76 show strong enhancements of D-region positive ion densities while the lower E-region behaves quite normally. Negative ions are important only below about 68 km. The positive ion composition shows a dominance of NO+ above 77 km while proton hydrates become most abundant below this height. Atomic metal ions reach high fractional abundances also in the D-region. The anomalous behaviour of positive ions is interpreted mainly in terms of an enhanced production of NO+, O2+ and electrons and a lowering of the bulk recombination coefficient for positive ions and electrons. The first cause seems to be mainly associated with enhanced densities of nitric oxide, the second cause seems to be related to high temperatures and an enhanced ion-electron production. The enhanced O2+-production may be associated with higher solar fluxes in the relevant region of the spectrum or with higher photoionisation cross sections. On one of the two days studied an enhanced O2(1Δg) associated with high atomic oxygen densities may have also contributed. © 1979.