Airglow remote sensing of the seasonal variation of the Martian upper atmosphere: MAVEN limb observations and model comparison

We apply a new technique to remotely sense the seasonal altitude variation of the isobar level in this region. We present results from observations of airglow limb profiles collected during two Martian years with the Imaging UltraViolet Spectrograph (IUVS) onboard MAVEN. IUVS has collected tens of thousands of Martian airglow limb profiles since the Fall of 2014. We analyze the global dayglow dataset of the 297.2 nm emission corresponding to the O(3P-1S) forbidden transition. The vertical profile of this unique emission shows two peaks: one around 120 km and a second one near 80 km. We use both peaks to trace the altitude changes of the isobars in this atmospheric region. We map and compare them with the seasonal variations of the O(1S) with CO
UV doublet peak. We find that the altitude of the level varies by up to 20 km. We show that the dayglow model overpredicts the lower peak altitude by 2–5 km from the observations while it underpredicts the upper peak altitude with the same offset. The best agreement near 80 km is obtained by decreasing the CO density by the Mars Climate Database (MCD) by about 40%.