Extending MGS-TES Temperature Retrievals in the Martian Atmosphere up to 90 km: Retrieval Approach and Results

This paper describes a methodology for performing a temperature retrieval in the Martian atmosphere in the 50–90 km altitude range using spectrally integrated 15 μm CO2 limb emissions measured by the Thermal Emission Spectrometer (TES), the thermal infrared spectrometer on board the Mars Global Surveyor (MGS). We demonstrate that temperature retrievals from limb observations in the 75-90 km altitude range require accounting for the non-local thermodynamic equilibrium (non-LTE) populations of the CO2(ν2) vibrational levels. Using the methodology described in the paper, we have retrieved ~1200 individual temperature profiles from MGS TES limb observations in the altitude range between 60 and 90 km. Our dataset of retrieved temperature profiles is available for download in supplemental materials of this paper. The temperature retrieval uncertainties are mainly caused by radiance noise, and are estimated to be about 2 K at 60 km and below, 4 K at 70 km, 7 K at 80 km, 10 K at 85 km, and 20 K at 90 km. We compare the retrieved profiles to Mars Climate Database temperature profiles and find good qualitative agreement. Quantitatively, our retrieved profiles are in general warmer and demonstrate strong variability with the following values for bias and standard deviations (in brackets) compared to the Martian Year 24 dataset of the Mars Climate Database: 6 (±20) K at 60 km, 7.5 (±25) K at 65 km, 9 (±27) K at 70 km, 9.5 (±27) K at 75 km, 10 (±28) K at 80 km, 11 (±29) K at 85 km, and 11.5 (±31) K at 90 km. Possible reasons for the positive temperature bias are discussed.