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.

The auroral electron data obtained during the flight of Polar 3 over an auroral arc (Maynard et al., 1977) were utilized as an input to a computation of the Hall and Pedersen conductivities of the auroral ionosphere produced by the particle precipitation. These conductivities, together with the in situ electric field measurements made on board the rocket, allowed an analysis of the electrodynamics of this auroral arc to be carried out. It was found that the local electric field variations correlated very well with the reciprocal of the height‐integrated Pedersen conductivity, a result suggesting that the auroral ionosphere was, to an extent, electrically isolated from the source of the electric field in the outer magnetosphere. The Joule power dissipation associated with ionospheric current flow was found to decrease abruptly from a value of ∼12 ergs/cm²/s column equatorward of the arc to a very low value within the confines of the arc. However, the sum of the Joule dissipation and the electron energy flux, which is the total energy input to the neutral atmosphere, did not display any abrupt variation across the equatorward boundary of the arc. The auroral electrojet, inferred from J = σ · E by assuming no neutral winds, was not directed parallel to this arc, nor was the current intensified within this arc. Instead, the electrojet flowed in a sheet extending equatorward from this arc for a distance of at least 100 km. The presence of an E region neutral wind will greatly affect the current patterns within this arc but will have only a first‐order effect on the current system equatorward of this arc. These observations are generally consistent with a model of auroral arc in which resistivity along the magnetic field lines linking the auroral ionosphere to the outer magnetosphere isolates these two regions from one another and results in magnetic‐field‐aligned potential differences which may accelerate auroral electrons.

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.

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