Temperature, water vapour and aerosol studies in the middle atmosphere

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The objective of the proposal is to analyze correlative measurements of temperature, water vapour and aerosols throughout the middle atmosphere (20-100 km height) and study the coupling of the stratosphere and mesosphere. Temperature, water vapour and aerosols are the three main themes in this proposal. Temperature is a central theme that links the presence of thin aerosol layers (e.g. Polar Stratospheric Clouds, Polar Mesospheric Clouds) to the amount of H2O, CO2 and CH4 in the stratosphere and upper mesosphere. The temperature is also a key factor in determining the dynamical structure of the mesosphere/lower thermosphere region. Water vapour content is also a central theme since it can be used as a tracer for various dynamical processes in the stratosphere and the upper mesosphere far from its source region in the lower atmosphere. Water in the middle atmosphere is the most important greenhouse gas crucial to climate change, because of its influence on Earth's radiative budget, and the human influence on the production of CH4, which is an important source of H2O in the middle atmosphere. Temperature change is a critical element in the conversion of water from vapour to liquid form, so the formation of solid water is an indicator of global change that can readily be monitored. Aerosols in the stratosphere can significantly impact atmospheric chemistry, dynamics, radiation and climate by absorbing outgoing long-wave radiation and thus change the thermal balance of the middle atmosphere. They can also affect climate by enhancing upward air motion in the lower stratosphere and alter stratospheric dynamics, in turn influencing the dynamics of the mesosphere. Knowledge of the properties of stratospheric aerosol is also important in analyzing data from space-borne instruments, whose measurements are affected by aerosol presence. The stratospheric aerosols could be quite sensitive to input from the tropical troposphere (volcanic eruption, burning), while meteoric material descending into the stratosphere from the mesosphere may be important to the morphology of stratospheric aerosols, particularly in polar air and perhaps globally, similar to their role in the summer mesosphere.