Isobar Altitude Variations in the Upper Mesosphere Observed With IUVS-MAVEN in Response to Martian Dust Storms

We report limb measurements of the oxygen dayglow emission at 297.2 nm performed during four Martian dust storms. The emission peak provides a good remote sensing tool to probe changes of the altitude of the 39 mPa pressure level for the first time during dust storms. We illustrate the time variation of these changes and compare them with the infrared opacity in the lower atmosphere. We find that the 39 mPa level rises in response to the increase in dust opacity. It reaches a plateau, and additional dust load does not significantly increase its altitude. Numerical simulations with the LMD global circulation model shows a similar response, except for the event observed during MY33 regional storm when the model fails to reproduce the observed variations. Observations collected during the onset of the global dust storm in June 2018 show that the upper atmosphere rapidly responds within two Martian days to the increased amount of tropospheric dust.