title: Bite-outs and other depletions of mesospheric electrons.
abstract: The ionised mesosphere is less understood than other parts of the ionosphere because of the challenges of making appropriate measurements in this complex region. We use rocket bornein situmeasurements of absolute electron density by the Faraday rotation technique and accompanying DC-probe measurements to study the effect of particles on theD-region charge balance. Several examples of electron bite-outs, their actual depth as well as simultaneous observations of positive ions are presented. For a better understanding of the various dependencies we use the ratioβ/αi(attachment rate over ion-ion recombination coefficient), derived from the electron and ion density profiles by applying a simplified ion-chemical scheme, and correlate this term with solar zenith angle and moon brightness. The probable causes are different for day and night; recentin situmeasurements support existing hypotheses for daytime cases, but also reveal behaviour at night hitherto not reported in the literature. Within the large range ofβ/αivalues obtained from the analysis of 28 high latitude night flights one finds that the intensity of scattered sunlight after sunset, and even moonlight, apparently can photodetach electrons from meteoric smoke particles (MSP) and molecular anions. The large range of values itself can best be explained by the variability of the MSPs and by occasionally occurring atomic oxygen impacting on the negative ion chemistry in the night-time mesosphere under disturbed conditions.
authors: Graz University of Technology, Graz, Austria.
authors: Martin
authors: M
authors: Friedrich
authors: Leibniz Institute of Atmospheric Physics, Kühlungsborn, Germany.
authors: Markus
authors: M
authors: Rapp
authors: University of Leeds, Leeds, UK.
authors: John M C
authors: JM
authors: Plane
authors: Space Research Institute, Austrian Academy of Sciences, Graz, Austria.
authors: Klaus M
authors: KM
authors: Torkar
keywords: Bite-out; Mesosphere; Meteoric dust; Noctilucent clouds