Prof. Dr. Franz-Josef Lübken
Various layers exist in the summer mesosphere at middle and polar latitudes which owe their existence to water ice particles. These layers are called `noctilucent clouds' (NLC), `polar mesosphere clouds'(PMC), and `polar mesosphere summer echoes' (PMSE) which reflects different observation geometry or entirely different physical processes involved. These layers are very sensitive to temperature (and to a lesser extent on H2O) and are therefore best suited to indicate long term and solar cycle changes. Indeed, variations on decadal time scales of different layer parameters (occurrence frequency, layer brightness etc.) have been reported from ground and satellite based observations. However, the physical and photo-chemical processes involved are not understood and some of the observations contradict expectations. In this proposal we want to study the formation of layers in the polar summer mesopause region, in particular their sensitivity to variations of background conditions caused by solar forcing and anthropogenic increase of greenhouse gases. We investigate and complement the available observations on layers (NLC/PMSE) and trace gases (ground based microwave and satellite observations of H2O) and perform model calculations with the COMMA/IAP and LIMA GCM models, and with a microphysical model to interpret the observations. In particular we will model the feed back mechanisms of ice formation on the atmosphere (e.\ g., through freeze drying) and the coupling mechanisms to above and below.