Trends In the Middle Atmosphere

Prof. Dr. F.-J. Lübken, Prof. Dr. E. Becker, Dr. U. Berger, Dr. P. Hoffmann
Leibniz-Institute of Atmospheric Physics

The aim of TIMA is to study trends in the middle atmosphere and their relevance for climate issues. Within this project we intend to perform model calculations and compare with various temperature time series to clarify the discrepancy between observed and predicted trends in the mesosphere. For example, we aim to estimate the relative importance of greenhouse gas increase in the mesosphere compared to tropospheric/stratospheric effects in the mesosphere. To this end we expand our previous studies based on a nudged model by including longer reanalysis time series (back to the late 19th century) and also climate change scenarios.

Since gravity waves represent the key dynamical component for the upper mesosphere and its coupling to the troposphere, we also want to investigate trends in mean winds and gravity waves in the middle atmosphere. This will be done by using long-term radar measurements at IAP and mechanistic model simulations. There is strong experimental evidence that trends in winds indeed exist. However, a quantitative explanation in terms of physical processes involved has not yet been given. Trends are also detected in gravity waves in the mesosphere, but the physical processes involved regarding sources and filtering are unclear. We will perform global model studies on trends with resolved gravity waves from the surface to the lower thermosphere, and try to identify potential trends in tropospheric gravity waves sources and their impact on the mesosphere.

An additional scientific aim is to apply the trend results to mesospheric ice layers applying microphysical ice modelling. Long-term trends of occurrence, brightness, and height of polar mesospheric clouds (PMC, NLC, PMSE) will be derived and compared with ground-based and satellite measurements. We will expand our investigation to trends in polar mesosphere summer echoes (PMSE). Furthermore, we want to solve the mystery why NLC have obviously not been reported before the eruption of Krakatau in 1883. We also want to explain why NLC heights observed more than 130 years ago are practically identical to modern observations.

References (some selected):

U. Berger and F.-J. Lübken. Mesospheric temperature trends at mid-latitudes in summer. Geophys. Res. Lett., 2011.

Becker, E. (2009), Sensitivity of the upper mesosphere to the Lorenz energy cycle of the troposphere, J. Atmos. Sci., pp. 647-666, doi:10.1175/2008JAS2735.1.

P. Hoffmann, M. Rapp, W. Singer, and D. Keuer. Trends of mesospheric gravity waves at northern middle latitudes during summer. J. Geophys. Res., 116, 2011.

F.-J. Lübken and U. Berger. Latitudinal and interhemispheric variation of stratospheric effects on mesospheric ice layer trends. J. Geophys. Res., 116, 2011.

F.-J. Lübken, U. Berger, J. Kiliani, G. Baumgarten, and J. Fiedler. Solar variability and trend effects in mesospheric ice layers. In F.-J. Lubken, editor, Climate And Weather of the Sun-Earth System (CAWSES): Highlights from a priority program. Springer, Dordrecht, The Netherlands, 2012.