Vertical temperature profile and mesospheric winds retrieval on Mars from CO millimeter observations

Comparison with general circulation model predictions

¹ Université Bordeaux I, Laboratoire d'Astrophysique de Bordeaux, France e-mail: cavalie@obs.u-bordeaux1.fr
² CNRS/INSU, UMR5804, BP 89, 33270 Floirac, France
³ Observatoire de Paris-Meudon, Laboratoire d'Études Spatiales et d'Instrumentation en Astrophysique, France
⁴ Université Paris VI, Institut Pierre Simon Laplace, Laboratoire de Météorologie Dynamique, France

Received: 20 March 2008
Accepted: 3 June 2008

Abstract

Aims. We have recorded high spectral resolution spectra and derived precise atmospheric temperature profiles and wind velocities in the atmosphere of Mars. We have compared observations of the planetary mean thermal profile and mesospheric wind velocities on the disk, obtained with our millimetric observations of CO rotational lines, to predictions from the Laboratoire de Météorologie Dynamique (LMD) Mars General Circulation Model, as provided through the Mars Climate Database (MCD) numerical tool.

Methods. We observed the atmosphere of Mars at CO(1-0) and CO(2-1) wavelengths with the IRAM 30-m antenna in June 2001 and November 2005. We retrieved the mean thermal profile of the planet from high and low spectral resolution data with an inversion method detailed here. High spectral resolution spectra were used to derive mesospheric wind velocities on the planetary disk. We also report here the use of ¹³CO(2-1) line core shifts to measure wind velocities at 40 km.

Results. Neither the Mars Year 24 (MY24) nor the Dust Storm scenario from the Mars Climate Database (MCD) provides satisfactory fits to the 2001 and 2005 data when retrieving the thermal profiles. The Warm scenario only provides good fits for altitudes lower than 30 km. The atmosphere is warmer than predicted up to 60 km and then becomes colder. Dust loading could be the reason for this mismatch. The MCD MY24 scenario predicts a thermal inversion layer between 40 and 60 km, which is not retrieved from the high spectral resolution data. Our results are generally in agreement with other observations from 10 to 40 km in altitude, but our results obtained from the high spectral resolution spectra differ in the 40-70 km layer, where the instruments are the most sensitive. The wind velocities we retrieve from our ¹²CO observations confirm MCD predictions for 2001 and 2005. Velocities obtained from ¹³CO observations are consistent with MCD  predictions in 2001, but are lower than predicted in 2005.