The focus of this session is the role of the interaction between the middle atmosphere (i.e. the
stratosphere and mesosphere between about 10 and 80 km) and the troposphere in a changing
climate, in particular to assess the impact of a changing middle atmosphere on surface climate and weather.

The middle atmosphere and troposphere are coupled by radiative, dynamical and chemical processes.
Radiatively active gases in the stratosphere, like ozone, water vapour and carbon dioxide, determine
the radiative forcing (RF) of the troposphere-surface system and influence tropospheric temperature.
In addition, the stratosphere in winter is largely influenced by upward propagating tropospheric
dynamical disturbances that decelerate the stratospheric polar night jet. High correlations between
stratospheric and tropospheric variability patterns, like the Northern and Southern Annular Modes
(NAM, SAM), exist with a possible downward influence of stratospheric dynamical anomalies on
tropospheric weather (e.g., the occurrence of extreme events) and climate.

The session will address the following aspects:
• the vertical coupling from the mesosphere to the troposphere-surface system
• the radiative forcing of changing middle atmospheric composition and its effects on the
troposphere-surface system
• the response of the Arctic and Antarctic troposphere-surface system to past and future ozone
changes
• the role of increasing greenhouse gas concentrations for stratosphere-troposphere coupling
• the role of changes in solar forcing
• the relevance of the stratosphere for tropospheric predictability
• the role of feedback processes between stratospheric changes and the ocean – sea ice system.

The session invites contributions from observational, theoretical and modeling studies. Mechanistic
model studies to understand the processes of vertical coupling are encouraged, as well as papers on
past and future simulations with climate and chemistry climate models including the middle
atmosphere and the oceans.