Assimilation of temperatures and column dust opacities measured by
ExoMars TGO-ACS-TIRVIM during the MY34 Global Dust Storm
Abstract
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 LMD Mars
Global Climate Model. The assimilation period is Mars Year 34 Ls = 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 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.