Extending MGS-TES temperature retrievals in the martian atmosphere up to 90 km: Retrieval approach and results

This paper describes a methodology for performing temperature retrievals in the martian atmosphere in the 60–90 km altitude range using spectrally integrated 15 μm CO2 limb emissions measured by the Thermal Emission Spectrometer (TES), the infrared spectrometer on-board the Mars Global Surveyor (MGS). We show that a limited number of limb-geometry sequences observed by this instrument are characterized by a high enough signal-to-noise ratio (SNR) to extend the upper limit of the retrievals to ∼90 km. Using the methodology described in the paper, we have retrieved ∼1200 individual temperature profiles from the MGS TES limb observations in the altitude range between 60 and 90 km. The set of retrieved temperature profiles is available for download in supplemental materials of this paper. The temperature retrieval uncertainties are mainly caused by noise in the observed radiance, and are estimated to be about ±2 K at 60 km, ±3 K at 70 km, ±5 K at 80 km, and ±13 K at 90 km. We compare the retrieved profiles to the martian Year 24 (MY 24) dataset of the Mars Climate Database (MCD) and SPICAM measured temperature profiles for MY 27 and find good qualitative agreement. Quantitatively, our retrieved profiles are in general warmer and demonstrate strong profile-to-profile variability. The warm bias is partially explained by the selection of high SNR limb scans and can be estimated and taken into account. Overall, the average difference between the TES-retrieved temperatures corrected for warm bias and the MCD MY 24 dataset is 4 K at 60 km, 4 K at 70 km, 2 K at 80 km, and −2 K at 90 km. The root-mean-square of the temperature variability caused by gravity waves estimated in this work is 7 K at 60 km, 11 K at 70 km, 18 K at 80 km, and 25 K at 90 km.