Assimilation of Temperatures and Column Dust Opacities Measured by ExoMars TGO-ACS-TIRVIM During the MY34 Global Dust Storm

We assimilate atmospheric temperature profiles and column dust optical depth observations from the ExoMars Trace Gas Orbiter Atmospheric Chemistry Suite thermal infrared channel (TIRVIM) into the Mars Planetary Climate Model. The assimilation period is Mars Year 34 L_s = 182.3°–211.4°, covering the onset and peak of the 2018 global dust storm. We assimilated observations using the Local Ensemble Transform Kalman Filter with 36 ensemble members and adaptive inflation; our nominal configuration assimilated TIRVIM temperature profiles to update temperature and dust profiles, followed by dust column optical depths to update the total column dust abundance. The observation operator for temperature used the averaging kernels and prior profile from the TIRVIM retrievals. We verified our analyses against in-sample TIRVIM observations and independent Mars Climate Sounder (MCS) temperature and dust density-scaled opacity profiles. When dust observations were assimilated, the root-mean-square temperature error verified against MCS fell by 50% during the onset period of the storm, compared with assimilating temperature alone. At the peak of the storm the analysis reproduced the location and magnitude of the peak in the nighttime MCS dust distribution, along with the surface pressure diurnal cycle measured by Curiosity with a bias of less than 10 Pa. The analysis winds showed that, at the peak of the storm, the meridional circulation strengthened, a 125 m s⁻¹ asymmetry developed in the midlatitude zonal jets, the diurnal tide weakened near the equator and strengthened to 10–15 K at midlatitudes, and the semi-diurnal tide strengthened almost everywhere, particularly in the equatorial lower atmosphere.