HR: 11:20h
AN: SA22A-05    [Abstracts]
TI: Weather in Mesospheric Ice Layers
AU: * Lübken, F
EM: luebken@iap-kborn.de
AF: Leibniz Institute of Atmospheric Physics, Schloss Str. 6, Kühlungsborn, 18225 Germany
AU: Berger, U
EM: berger@iap-kborn.de
AF: Leibniz Institute of Atmospheric Physics, Schloss Str. 6, Kühlungsborn, 18225 Germany
AB: We have recently developed a new model of the atmosphere called LIMA (Leibniz Institute Middle Atmosphere Model) which, amongst others, nicely reproduces the mean conditions of the summer mesopause region at middle and polar latitudes, in particular temperatures, winds, and trace gases such as water vapor. The major improvements of LIMA compared to its precursor concern spatial resolution and coupling to the lower atmosphere by nudging to ECMWF data. These new features lead to significant variability in the thermal, dynamical, and compositorial structure of the upper atmosphere. We have run our ice particle model using the background conditions from LIMA which vary with season and height. The ice model is interactively coupled with water vapor and thereby includes the redistribution of water vapor by the so called `freeze drying' effect. It turns out that the background variability has a severe effect on the geographical distribution of the ice clouds. For example, ice particle related phenomena such as noctilucent clouds (NLC) and polar mesosphere summer echoes (PMSE) have been observed at mid latitudes (e.g., at Kühlungsborn, 54°N, or at Logan, 42°N) where they should never appear according to the mean conditions. In the new LIMA/ice model a region of cold and ice loaded air indeed can drift down to mid latitudes leading to NLC and PMSE. Furthermore, LIMA/ice shows from time to time a significant depletion of ice particles at polar latitudes (`ice holes') which explains the decrease of polar mesosphere cloud occurrence intermittently observed from satellites. This also explains the temporal reduction of PMSE occasionally detected at very high latitudes. It is important to note that the average layer characteristics such as mean NLC altitude and brightness agree nicely with observations, despite all the variability mentioned above. The new model allows us to study in detail the physical processes leading to temporal and spatial variability of ice layers in the upper atmosphere and the role of the background atmosphere.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0340 Middle atmosphere: composition and chemistry
DE: 2461 Plasma interactions with dust and aerosols (7849)
DE: 3315 Data assimilation
DE: 3332 Mesospheric dynamics
SC: SPA-Aeronomy [SA]
MN: Fall Meeting 2005