The Earth's middle atmosphere, mesosphere, and lower thermosphere (MLT) region provide a great platform for studying ionospheric dynamics, disturbances, eddy mixing, atmospheric drag effects, and space debris tracking. The thermal structure of these regions is influenced by numerous energy sources such as solar radiation, chemical, and dynamical processes, as well as forces from both above (e.g. solar and magnetospheric inputs) and below (e.g. gravity waves and atmospheric tides). Solar atmospheric tides, related to global-scale variations of temperature, density, pressure, and wind waves, are responsible for coupling the lower and upper layers of the atmosphere and significantly impact their vertical profiles in the upper atmosphere. With evidence of climate change impacts on the middle and upper atmosphere, monitoring and understanding trends through observational data is critical. There has been a contraction of the stratosphere and a decrease in the density of the upper atmosphere, which could impact the accumulation of space debris. This session invites presentations on scientific work related to various experimental/observational techniques, numerical and empirical modeling, and theoretical analyses on the dynamics, chemistry, and coupling processes in the altitude range of ~ 20 km to 180 km of the middle atmosphere and MLT regions, including long-term climatic changes.