This joint session invites papers that are related to the mesosphere and lower thermosphere. It addresses the topical fields of the VarSITI (Variability of the Sun and Its Terrestrial Impact) program initiated by SCOSTEP, focusing on the role of the sun and the middle atmosphere/thermosphere/ionosphere in climate (ROSMIC). Contributions studying radiation, chemistry, energy balance, atmospheric tides, planetary waves, gravity waves, neutral-ion coupling, and the interaction of the various processes involved are welcome. This includes work on model data as well as measurements from satellites and ground based platforms such as ALOMAR.