Charged Dust in the Earth's Middle Atmosphere

We discuss the few existing in situ rocket observations of dust and plasma during the radar backscatter phenomenon Polar Mesospheric Summer Echoes (PMSE). We show from one recent observation, where the rocket flew directly through the radar beam during observation of a PMSE, that there is a very good correspondence between the charge density of dust layer and the PMSE. A surprising observation is that only a small amount of charged dust can be associated with a considerable PMSE signal strength. By estimating the relationship between radar backscatter and dust charge density for other rocket measurements we have found a total relationship between radar backscatter strength and dust charge density. This shows a rapid increase of radar backscatter strength at low NdZd, a more or less constant level for a considerable range in NdZd and a decrease to low values for large values of NdZd where most of the negative charge will be on the dust.