O2(a1 Δg) dayglow limb observations on Mars by SPICAM IR on Mars-Express and connection to water vapor distribution

The 1.27-mu m O-2(a(1)Delta(g)) dayglow on Mars is a product of the ozone photolysis by solar UV radiation. The intensity of the O-2(a(1)Delta(g)) emission rate depends on ozone concentration, atmospheric density and kinetic parameters of involved photochemical reactions. In turn, the distribution of ozone is sensitive to the vertical and spatial distribution of water vapor, which is an effective destructor of O-3. SPICAM IR on the Mars-Express mission measures the O-2((1)Delta(g)) dayglow with spectral resolving power of 2200. The results of 147 limb observations from 2004 to 2013 are reported. Limb resolution of the instrument is variable and exceeds the scale height of the atmosphere. The slant emission rate reaches a maximum at the high Northern latitudes at northern and southern springs L-s = 0-50 degrees and 160-190 degrees, respectively and a minimum in middle and low latitudes at southern summer L-s = 200-300 degrees. We have compared the SPIVAM O-2(a(1)Delta(g)) limb profiles with the General Circulation Model simulation by the Laboratoire de Meteorologie Dynamique (LMD GCM, Lefevre, F., Lebonnois, S., Montmessin, F., Forget, F. [2004]. J. Geophys. Res. 109, E07004. http://dx.doi.org/10.1029/2004JE002268; Lefevre, F., et al. [2008]. Nature 454(7207), 971-975) reduced to the vertical resolution of the instrument. The GCM includes the radiative effect of the water clouds and an interactive dust scheme, and well reproduces Martian Climate Sounder (MCS) temperature profiles (Clancy, R. Todd et al. [2012]. J. Geophys. Res. 117, 10. http://dx.doi.org/10.1029/2011JE004018). The model underestimates the emission for L-s = 0-50 degrees, L-s = 160-180 degrees and overestimates it from L-s = 60 degrees to L-s = 150 degrees at high Northern latitudes. In the Southern hemisphere the model underestimates the emission for L-s = 170-200 degrees and overestimates it for L-s = 200-230 degrees at high Southern latitudes. The disagreement could be related to the water vapor distribution as the model reproduces it. The most recent version of the LMD GCM including microphysical representation of cloud formation taking into account the effect of dust scavenging by water ice clouds (Navarro, T., Madeleine, J.-B., Montmessin, F., Forget, F., Spiga, A., Millour, E. [2013]. Modeling of the martian water cycle with an improved representation of water ice clouds. European Planetary Science Congress 2013, EPSC Abstracts, vol. 8, EPSC2013-203) gives much better agreement with SPICAM O-2(a(1)Delta(g)) dayglow limb observations. Characterization of the Mars water cycle by GCMs continues to improve, and the observations of the O-2(a(1)Delta(g)) dayglow offer a powerful tool for its validation. (C) 2014 Elsevier Inc. All rights reserved.