Ions, Clusters, Ice Particles - Feedback Mechanisms in the Summer Mesosphere

Dr. Jörg Gumbel
Universities Space Research Association /
Naval Research Laboratory

In the cold summer mesopause region (80-90 km) ice particles can form that give rise to phenomena like noctilucent clouds (NLC) and polar mesosphere summer radar echoes (PMSE). The presence of these ice particles is closely coupled to ionospheric processes. This talk presents a model that for the first time combines detailed ion chemistry, clustering processes and ice particle charging. Case studies illustrate these interactions for various ionospheric conditions. As an example, the response of the mesosphere to the Solar Proton Event of the Bastille Day 2000 is discussed.

An important open question concerns the origin of the small-scale charge fluctuations that are needed for the generation of PMSE. This talk describes a positive feedback mechanism involving electron capture by ice particles, cluster growth and particle nucleation. It is argued that these ion-chemical processes can give rise to local structures in the charge distribution and, hence, provide a possible explanation of PMSE.