NOCTILUCENT CLOUDS AND REGIONS WITH POLAR MESOSPHERIC SUMMER ECHOES STUDIED BY MEANS OF ROCKET-BORNE ELECTRON AND ION DC-PROBES

During the Noctilucent Cloud Campaign from Esrange, Kiruna, Sweden in July-August 1991, detailed in situ mesurements were performed by means of plasma probes in the TURBO rocket payload. When launched through NLC and PMSE layers, these probes indicate that the NLC layer was associated with a one kilometer thick region containing heavy positive ions. Embedded in this layer were structures only a few tens of metres in vertical extent. These structures exhibited strongly enhanced ion current and corresponding sharp decreases of electron current. The observations indicate that the structures contain enhanced densities of light positive ions as well as heavy, negative charge carriers in the form of ions or particles. VHF radar measurements from the same site showed Polar Summer Mesospheric Echoes from a layer that at first was located just above the NLC layer, but the rocket results indicate that it later merged with the NLC-layer.