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F. Jegou, E. Chassefiere, F. Forget, F. Hourdin (Laboratoire de Meteorologie Dynamique (LMD), Paris France), E. Lellouch, T. Encrenaz (Departement d'etudes spaciales (DESPA), Meudon France), R. Moreno (Institut de Radio Astronomie Millimetrique (IRAM), Bure France)
Measurements of the Doppler shift winds and thermal structure of the Mars middle atmosphere (40-70 km) have been obtained for ten years from ground-based millimeter-wave observations. Recently, new measurements were obtained with I.R.A.M. 30m single dish antenna in april 1997, april 1999 and in november 1999. This set of data was completed in april 1999 by interferometric observations (IRAM Plateau de Bure), with a 5-fold improvement in spatial resolution.
The Doppler shift wind measurements are of particular interest. The winds of the middle atmosphere infered from the observations are almost always retrograde and stronger than expected, compared to the winds deduced from T.E.S. temperature observations and GCM simulations. This discrepancy may result from our poor understanding of the actual dynamic of the Martian middle atmosphere, but may also be due to the fact that the measured signal includes some contributions from a large range of altitude and locations in a way difficult to interpret directly.
To address this issue we have developed a geometric-radiative transfer model able to synthesize the CO rotational lines emitted by a 3D varying temperature wind fields on Mars as it would be observed from Earth. The synthetic lines can then be compared with the ground-based millimeter-wave observations.
The model can be applied to GCM simulations, providing a good diagnostic for the martian GCM in the middle atmosphere, especially with regard to the interactions between the atmospheric tides and the mean flow.