Spokesperson: Dr. Bernd Kaifler
The middle atmosphere comprises the stratosphere and the mesosphere and extends from about 10 km to 100 km altitude. Within this region, the thermal structure at polar latitudes exhibits extreme deviations from the radiative equilibrium temperature, leading to temperatures as low as -150°C at 85 km altitude in the summer hemisphere. These are the lowest temperatures in the Earth system. The reason for this is the global residual circulation which is driven by atmospheric gravity waves: air masses rise above the summer pole and at the same time cool adiabatically before being transported across equator to the winter pole, where they subside and heat up. Moreover, planetary waves and atmospheric tides, whose amplitudes can reach up to 100 m/s in the horizontal, affect significantly the mesosphere. But also the stratosphere is a region of extreme conditions with jet streams controlling the vertical and horizontal propagation of gravity waves. On the one hand, the stratosphere acts as a valve layer for upward propagating gravity waves, on the other hand the stratospheric jet streams can act as wave sources themselves. Important tropospheric sources of gravity waves, for example, are thunder cells and flow across mountains.
Like all waves, atmospheric gravity waves transport energy and momentum and thus contribute significantly to the redistribution of momentum in the atmosphere and the middle atmosphere in particular. The main goal of the Middle Atmosphere matrix group is the investigation of the resulting vertical coupling. Main research foci are:
For this research we combine numerical simulations of atmospheric waves, model studies based on data of numerical weather prediction models, and in situ and remote sensing measurements of atmospheric parameters obtained from the ground as well as from aircrafts, balloons, sounding rockets and satellites.
The research aircraft HALO during a test of the lidar system ALIMA: A powerful laser is used here, reaching up to 100 km. Its backscatter provides information about the atmosphere above HALO, e.g. for the detection and analysis of gravity waves (Photo: ©bigair).