New nitric oxide (NO) nightglow measurements with SPICAM/MEx as a tracer of Mars upper atmosphere circulation and comparison with LMD‐MGCM model prediction: Evidence for asymmetric hemispheres

In the upper atmosphere of Mars, CO2 and N2 are photo-dissociated by solar UV and EUV on the day side, producing O and N atoms. They are carried to the night side by planet rotation and general circulation in the thermosphere. When they recombine to form nitric oxide (NO), they emit light in the UV in the so-called δ and γ bands, producing a UV nightglow that was discovered by SPICAM/Mars Express in 2005 during dedicated limb observations. Therefore, it provides an important tracer of thermospheric circulation, tracing mostly descending air. A new data set has been produced by using more frequent star occultations (more than 2000), which in about 10% cases revealed the presence of the NO emission in addition to the star signal. We have developed a method allowing to retrieve the vertical profile of the NO emission intensity, after disentangling the star signal from the limb signal. We have made a first-order comparison with the MGCM LMD model. The peak intensity (a few KiloRayleigh) and the peak altitude (50-100 km) are in reasonable agreement with model predictions. There is a clear seasonal pattern of the latitude location of the emission. The latitude of the emission as a function of season (solar longitude Ls) can be approximated with a relationship of the form Lat= -80 sin (Ls). At solstices (Ls=90 and 270°) this is in agreement with the MGCM model, which predicts an emission in the depth of the winter polar night. At equinoxes (Ls=0 and 180°), the emission is observed near the equator, in total contradiction with the model, which predicts on the contrary an emission simultaneously at both polar regions. The significance of this major discrepancy for the general circulation of the upper atmosphere of Mars will be discussed, and the NO and O2 observed nightglows will be compared.

[1]  D. Fussen,et al.  Stellar occultations observed by SPICAM on Mars Express , 2006 .

[2]  E. Millour,et al.  A ground‐to‐exosphere Martian general circulation model: 1. Seasonal, diurnal, and solar cycle variation of thermospheric temperatures , 2009 .

[3]  A. Dalgarno,et al.  The radiative association of N and O atoms , 1990 .

[4]  A. Spiga,et al.  Gravity waves, cold pockets and CO2 clouds in the Martian mesosphere , 2012 .

[5]  S. Bougher,et al.  Vertical dust mixing and the interannual variations in the Mars thermosphere , 2007 .

[6]  F. Montmessin,et al.  NO emissions as observed by SPICAV during stellar occultations , 2010 .

[7]  G. Sonnabend,et al.  Modelling the atmospheric CO2 10-μm non-thermal emission in Mars and Venus at high spectral resolution , 2011 .

[8]  F. Forget,et al.  The martian mesosphere as revealed by CO2 cloud observations and General Circulation Modeling , 2011 .

[9]  S. Murchie,et al.  Correction to "Extensive MRO CRISM observations of 1.27 µm O2 airglow in Mars polar night and their comparison to MRO MCS temperature profiles and LMD GCM simulations" , 2012 .

[10]  L. Esposito,et al.  Ultraviolet Spectroscopy of Venus: Initial Results from the Pioneer Venus Orbiter , 1979, Science.

[11]  A. Dalgarno,et al.  INFRARED EMISSION SPECTRA OF NITRIC OXIDE FOLLOWING THE RADIATIVE ASSOCIATION OF NITROGEN ATOMS AND OXYGEN ATOMS , 1996 .

[12]  S. Murchie,et al.  Extensive MRO CRISM observations of 1.27 mm O2 airglow in Mars polar night and their comparison to MRO MCS temperature profiles and LMD GCM simulations , 2012 .

[13]  P. Feldman,et al.  Identification of the UV nightglow from Venus , 1979, Nature.

[14]  Franck Lefèvre,et al.  Three-dimensional modeling of ozone on Mars , 2004 .

[15]  Jean-Pierre Bibring,et al.  First detection of O 2 1.27 μm nightglow emission at Mars with OMEGA/MEX and comparison with general circulation model predictions , 2012 .

[16]  Oleg Korablev,et al.  Nightglow in the Upper Atmosphere of Mars and Implications for Atmospheric Transport , 2005, Science.

[17]  F. Leblanc,et al.  SPICAM on Mars Express: Observing modes and overview of UV spectrometer data and scientific results , 2006 .

[18]  J. Gérard,et al.  Distribution of the ultraviolet nitric oxide Martian night airglow: Observations from Mars Express and comparisons with a one‐dimensional model , 2008 .

[19]  W. Traub,et al.  O2/1 Delta/ emission in the day and night airglow of Venus , 1979 .