Investigation of the photochemistry of oxygen species in the mesopause region

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Atomic oxygen (O) is one of the most important chemical constituents of the terrestrial mesopause region. It plays an essential role for the energy balance of this atmospheric region. Due to its long chemical lifetime it is capable of transporting chemical potential energy over large distances. It participates indirectly in the radiative cooling of the mesopause region and it is directly coupled to the less abundant ozone, which in turn governs diabatic solar heating of mesosphere. The number of O measurements in the mesopause region is rather limited, and most of the available observations are based on measurements of the O2, O and OH airglow emissions. These measurements are indirect measurements and generally require knowledge of a large number of photochemical rate constants. Existing studies provide clear evidence that the currently used models to describe the O2 A-band, the O green line and the OH Meinel emissions, which are all driven by atomic oxygen, are inconsistent. Within the frame of this proposal we are planning on investigating the consistency of the existing photochemical models of the three airglow emissions mentioned. This will be done using the synergy of simultaneous satellite observations of all three emissions and dedicated model simulations. The satellite measurements to be used were carried out with the SCIAMACHY (Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY) instrument on the Envisat spacecraft, which operated from 2002 to 2012. SCIAMACHY is uniquely suited for this purpose, because with its broad spectral range it covers all the airglow emissions relevant for this proposal and provides simultaneous and spectrally resolved observations of these emissions. The planned model simulations will be performed with a suite of established photochemical and global models. Using an inverse modelling approach, we plan on carrying out an optimization of photochemical model parameters by simultaneously minimizing the differences between model results and the SCIAMACHY observations. In addition, we plan on performing a thorough characterization of the spatial and temporal variability of O in the mesopause region, with particular focus on solar influence and potential long-term variations over the period from 2002 to 2012. Furthermore, our aim is to improve the existing climatological models of O in the mesopause region (e.g., MSIS) - which are clearly inadequate in different respects - using the O time series derived within this project. The applicants are established experts in their main research areas and have long-time experience in the area of satellite remote sensing using terrestrial airglow emissions and atmospheric modelling, respectively.