Some theories for the observed anomalous radar backscatter during the summer (polar mesospheric summer echoes, or PMSE) and electron bite outs measured by rockets require the presence of charged dust. To investigate this, two dust probes have been launched in 1994 from Andøya Rocket Range and we here report the results from the dust and an electron probe on the two payloads. The dust probes were designed to block out the electron and ion components at the mesopause but to detect primary currents due to impacts of charged dust and also to detect secondary plasma production during dust impacts. The results indicate that both during PMSE and noctilucent cloud (NLC) conditions, large amounts of dust, with average sizes apparently of about 0.1 μm and less, were present. The number densities Nd can be up to many thousand per cubic centimeter, and the charge density NdZd likewise. Large local gradients in density and charge density of dust are detected. Dust carrying both positive and negative charges can apparently be present on different occasions. In some parts of the NLC/PMSE layers we find that the negative charge density locked in grains is so large that the number of free electrons is significantly reduced there because the dust acts like sinks for electrons, and an electron bite out results. We also find that in one case the presence of positive dust leads to an increase in the local electron density by photoionization. The main uncertainties in the data analysis are the structure of the dust and the secondary plasma production at the comparatively low dust impact velocities (1 km s−1) in the experiment.

[1] We have developed a numerical model that solves the time-dependent, onedimensional, coupled continuity and momentum equations for an arbitrary number of charged and neutral particle species. The model includes production and loss of particles due to ionization, recombination, and attachment of ions and electrons by heavy aerosol particles, and transport due to gravity and multipolar diffusion. The model is used to study the response of the mesopause plasma to small-scale, aerosol particle density perturbations. We find that for aerosol structures on the order of a few meters, electron attachment and ambipolar diffusion are the dominant processes, leading to small-scale electron perturbations that can cause polar mesosphere summer echoes (PMSEs). Moreover, for small aerosol particles, with radii on the order of 10 nm or less, ambipolar diffusion leads to an anticorrelation between electron and ion densities, which is in agreement with most rocket observations. These small-scale structures persist as long as the aerosol layer persists, which will be limited by aerosol particle diffusion. For 10-nm particles, this diffusive lifetime will be on the order of hours. The few instances where rocket observations find instead a correlation between electron and ion densities can be explained either by the aerosol particles becoming large, on the order of 50 nm or more, in which case ion attachment becomes important, or by rapid evaporation of aerosol particles. In the latter case, evaporation must be sufficiently fast to overcome ambipolar diffusion. Citation: Lie-Svendsen, Ø., T. A. Blix, U.-P. Hoppe, and E. V. Thrane, Modeling the plasma response to small-scale aerosol particle perturbations in the mesopause region,

Abstract. We report the results from simultaneous radar and rocket measurements of a PMSE event where for the first time the rocket measured dust and plasma within the radar beam. We find very clear correspondence between the measured dust charge density profile and the radar backscatter profile as a function of height. We find that even very small amounts of charged dust is associated with an appreciable PMSE radar backscatter. Although we find it likely that the dust layer corresponds fully with the PMSE layer there is a possibility that the upper part of the PMSE layer may be influenced by ion clusters which are too small to be detected by the rocket dust probe.

[1987] that large cluster ions and charged aerosols will result in a reduced mobility of the electrons (since they are electrically bound to the 'heavy' aerosols), therefore to Schmidt numbers larger than unity, and to an increase of the plasma PSD at the 3m scales. These aerosols can only exist at the very low temperatures of the summer mesopause region and presumably consist of water ice.In this paper we present new measurements and model calculations which elucidate the importance of negatively charged aerosols in modifying the turbulent spectrum thereby creating PMSEs. We will derive Sc from the microphysical properties of the charged aerosols, and then compare this result with the turbulent spectra of the electron and neutral density fluctuations.

The paper presents and discusses a large set of in situ measurements of fine‐scale structure in the mesosphere and lower thermosphere at high latitudes. The experimental technique used is a rocket‐borne electrostatic positive ion probe with linear amplification and high precision and time resolution. This type of probe has proved to be very efficient. The accuracy and limitations of the experiment are discussed. The measured ion density fluctuations are used as passive tracers for motions in the nonionized air. Quantitative estimates of the characteristics of turbulence have been derived. The method of analysis is carefully discussed and related to previous work, and a revision of earlier methods is proposed. The results show a characteristic minimum in turbulent intensity at or below the mesopause region.