Heavy ionospheric ions in the formation process of noctilucent clouds

Abstract

Results from a multinational rocket experiment in noctilucent cloud (NLC) conditions are presented. Weak NLC was detected at 83 km by visible photometry. Two separate ion mass spectrometer experiments both detected a narrow layer of very heavy positive ions at 90 km. The mass distribution of the large ions showed an increase of “most abundant mass” with height up to 90 km, indicating a temperature decrease up to that altitude. At 90 km the ion size approached the critical size at which nucleation of ice particles can start. If water ice particles would be formed in such a layer, they would continue to grow, as long as the ambient temperature is low enough and the water supply sufficient. While sedimenting through the atmosphere, they would add to the existing population of aerosol particles and thereby increase the total surface area of particles. Such an increased surface area of small particles would increase the loss rate for electrons and cause a deficiency of electrons at heights below the nucleation layer. A pronounced deficiency of electrons below 90 km was found in the measurements. With a theoretically modeled mesospheric H2O concentration, ice particle growth at 90 km is impossible. This situation may, however, change completely under the influence of an upwelling in the mesosphere. In addition to lowering the sink rate of the particles, such an upwelling would increase the concentration of H2O by vertical transport, and lower the gas temperature, which would also enhance the probability of particle growth. The upwelling would have to terminate in a horizontal motion above 90 km. At this height the rocket measurements show marked changes in the atomic oxygen concentration, electron/positive ion ratio and inferred concentrations of nitric oxide and negatively charged aerosol particles in addition to abrupt changes in positive ion composition.

Coordinated optical and radar image measurements of noctilucent clouds and polar mesospheric summer echoes

“…Subsequent ground-based and rocket-borne measurements have determined their remarkably consistent altitude, occurring in the upper mesosphere at a mean height of $83 km (e.g. Jesse, 1896;Strö rmer, 1933;Paton, 1964;Grahn and Witt, 1971;Witt et al, 1971;Bjorn et al, 1985;Taylor et al, 1984, Gadsden and Taylor, 1994, von Zahn et al, 1998Chu et al, 2001;Collins et al, 2003;Thayer et al, 2003;Fiedler et al, 2005;Gerding et al, 2007). NLC are seasonal, appearing during the summer months in close association with the observed rapid decrease in mesopause temperatures that result from strong upwelling in the summer polar region in response to the gravity wave-driven mean meridional circulation (e.g.…”

Photochemistry of Ions at D-region Altitudes of the Ionosphere: A Review

“…The results of the rocket experiment carried out over Esrange on July 30, 1978 at 23:33 UT in noctilucent cloud conditions were presented by Björn et al (1985). Between 91.5 and 106 km, the dominant ion was NO ?…”

“…(H 2 O), and NO ? (H 2 O), and some proton hydrates appeared (Björn et al 1985 ? ], and the total number density of positive cluster ions measured during this experiment were presented by Balsiger et al (1995Balsiger et al ( , 1996.…”

Rocket-Borne Probes for Charged Ionospheric Aerosol Particles

“…When a sufficient number of aerosol particles are present, the aerosol surfaces scavenge electrons, thus creating localized reduction or "biteouts" in the electron density. Rocket-borne mass spectrometers have shown the existence of proton hydrates at the mesopause that may be the condensation nuclei of these cloud particles [7]. Enhanced radar returns called polar mesospheric summer echoes (PMSEs) often occur with NLCs [8]- [10].…”