Recent studies show in connection with SSWs an enhancement of tidal waves that are considered as key processes for influences of changes in the ionosphere. These enhancements are not really understood. To answer the question: What causes the enhancement of tidal activity in the MLT region after SSW, we will investigate the temporal development of planetary, tidal and gravity waves in connection with SSW based on long-term observations with MF - and Meteor radar observations in Andenes (69°N, 16°E) since 1999 at polar latitudes and in Juliusruh (55°N, 13° E) since 1990 at middle latitudes. For case studies, the altitudinal dependence of long period waves with periods of 8 - 20 days that are present throughout the atmosphere and may induce SSWs, are additionally investigated by temperatures derived from the MLS experiment on board of the AURA satellite and by ozone and water vapor variations in the upper stratosphere/ lower mesosphere derived from microwave observations in Bern (47°N, 8°E) and Sodankylä (67°N, 26°E). The interpretation of the observational diagnostics is provided by complementary modeling efforts.

The presentation gives an overview about interdisciplinary studies of the ISSI team 152: Bridging the gap between the middle and upper atmosphere - Coupling processes due to winds and waves over an extended altitude range. The International Space Science Institute (ISSI) at Bern (Switzerland) acts as a catalysator for scientists and experts from all over the world who like to combine their theoretical, experimental, observational, empirical and analytical skills for solving open problems in Earth system and space science. A well-known observational lack exists in remote sensing of neutral winds of the lower mesosphere and lower thermosphere where strong wind jets appear. Neutral wind retrieval from incoherent scatter (IS) radar data can partly remove this shortcoming. Using wind observations with MF-, Meteor- and IS radars at polar and middle latitudes together with long period variations of ozone and water vapor in the upper stratosphere/ lower mesosphere derived from microwave observations, the main project activities are concentrated on concrete case studies about dynamical coupling processes from the stratosphere up to the lower thermosphere a) during sudden stratospheric warming events and to investigate possible coupling processes between different layers with emphasis on the influence on the ionosphere, and on b) temporal development of wind reversals and their influence on waves and temperature up to thermospheric heights during fall transition. The interpretation of the observational diagnostics and the elucidation of the impact of the associated processes on the MLT are provided by complementary modelling efforts and by the additional evaluation of global satellite data.