INCOHERENT-SCATTER RADAR CONTRIBUTIONS TO HIGH-LATITUDE D-REGION AERONOMY

Recent aeronomical work on the high latitude D-region is reviewed, res tricting the discussion to observations of the D-region by the incoher ent scatter technique. Emphasis is given to chemical aeronomy, which g overns part of the coupling between the neutral atmosphere and the ion osphere, and forms the basis for the global role of the high latitude D-region. Details of the dynamics of the high latitude D-region, and t hus the actual coupling with regions below and above, are, however, no t discussed in this context. The aeronomical consequences of special h igh-latitude phenomena are discussed. These include the effects of the polar summer, precipitation of high energy electrons during auroral s ubstorms and high ionization of the D-region during solar proton event s. A detailed discussion is given on selected studies concerning the s eries of solar proton events that occurred in 1989. Problems of ion an d neutral chemistry are readily accessible with incoherent scatter mea surements through chemical modelling of the D-region. In this way the continuous nature of incoherent scatter measurements can be utilized t o expand our knowledge of the D-region, which earlier was mainly based on momentarily sounding rocket experiments. However, it is pointed ou t how the interpretation of incoherent scatter data from the D-region strongly benefits from multi-instrument configurations. An outline is given of a possible new development based on the combined use of the T romso heating facility and the EISCAT incoherent scatter radars.