We report on the direct measurements of zonal winds around 80 km altitude during the 2018 planet-encircling dust event (PEDE) by infrared (IR) heterodyne spectroscopy. The observed Doppler shifts assume intense retrograde (easterly) winds (208 ± 17 m s−1, 159 ± 20 m s−1, 211 ± 20 m s−1 on June 21, June 27, August 31, 2018, respectively) in the equatorial region during the 2018 PEDE. This is significantly stronger than those during non-storm conditions reported by the previous study (Sonnabend et al., 2012, https://doi.org/10.1016/j.icarus.2011.11.009). The substantial retrograde wind during the PEDE is qualitatively consistent with the predictions by the Mars general circulation models (MGCMs), however, the observed wind on 31, August, are of a larger magnitude. We evaluated the mechanism of acceleration using the output from a high-resolution MGCM. We find out that the stronger winds are related to strengthening the meridional circulation across the equator and forcing by gravity waves.
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