FWF - Elektronenverlust Mesosphäre - Electron Scavenging in the Mesosphere

The free electrons in the ionosphere are formed by ionisation through various processes such as solar UV, solar X- rays, cosmic rays or energetic particles originating in the solar wind. The reverse reaction which limits the fraction of the atmosphere which is ionised, is either recombination by which the original neutral molecules are restored, or attachment to neutrals, including aerosols. These negatively charged particles thus formed in a further stage recombine with positive ions and lead to the original neutral atmosphere or indeed produce atmospheric trace constituents. The attachment process of electrons to the most abundant atmospheric constituents is reasonably well understood from laboratory measurements, but observations in the real atmosphere show that the attachment of electrons ("scavenging") varies much more than could reasonably be expected due to any uncertainty in the laboratory data or the assumptions made concerning the background atmosphere. The most likely explanation for this large scatter is that attachment of free electrons does not only occur with molecules, but - notably in the mesosphere - with ablated meteorites which are theoretically expected and experimentally known to abound at these altitudes, but whose number density varies erratically. Most of the hitherto available data concerning night-time electron scavenging were obtained from rocket flights without associated measurements of parameters expected to be relevant to test the concept of electron attachment to meteoric smoke particles. Four sounding rockets which will be launched in two campaigns carry instruments that are very relevant to test the hypotheses by which night-time electron loss in the mesosphere can be explained. The prime goals of these campaigns are to study the dynamics and energy balance of the mesosphere, and to establish the size and height distribution of meteoric dust particles. The inclusion of the Austrian plasma diagnostic instruments in these four payloads is mutually beneficial, i.e. on the one hand crucial for the prime objectives of the two campaigns, and on the other hand the data on atomic oxygen, solar Lyman-alpha flux and meteor dust distribution contribute importantly towards the understanding the highly variable loss of free electrons. Three of the four sounding rockets will be launched in the same campaign, and one on its own a year later, but in a different season.