FIRST DETECTION OF CHARGED DUST PARTICLES IN THE EARTHS MESOSPHERE

Some theories for the observed anomalous radar backscatter during the summer (polar mesospheric summer echoes, or PMSE) and electron bite ou ts measured by rockets require the presence of charged dust. To invest igate this, two dust probes have been launched in 1994 from Andoya Roc ket 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 primar y 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 mu m and less, were p resent. The number densities N-d can be up to many thousand per cubic centimeter, and the charge density N(d)Z(d) likewise. Large local grad ients in density and charge density of dust are detected. Dust carryin g both positive and negative charges can apparently be present on diff erent 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 f ind that in one case the presence of positive dust leads to an increas e in the local electron density by photoionization. The main uncertain ties in the data analysis are the structure of the dust and the second ary plasma production at the comparatively low dust impact velocities (1 km s(-1)) in the experiment.