Thermal Tides on Mars Before and During the 2018 Global Dust Event as Observed by TIRVIM‐ACS Onboard ExoMars Trace Gas Orbiter

Abstract

Migrating tides dominate the tropical climate on Mars and are known to reach high amplitudes during global dust events (GDE). In this study, we characterize the amplitude, phase and vertical wavelength of the diurnal and semi‐diurnal migrating tides in Mars’ lower atmosphere (up to 50km) by exploiting temperature vertical profiles retrieved from TIRVIM, an infrared spectrometer onboard the ExoMars Trace Gas Orbiter covering multiple local times. Observations from the Mars Climate Sounder onboard the Mars Reconnaissance Orbiter are used to complement the local time coverage when needed, and to estimate a seasonal trend to subtract from TIRVIM observations. We focus on two time periods in Martian Year 34, near Ls=150° and near Ls=200° (during the 2018 GDE). The characteristics of the migrating tides at Ls=150° agree very well with tidal theory: a downward propagation, amplitudes of typically 2–5K, and a larger vertical wavelength for the semi‐diurnal compared to the diurnal mode. Comparisons with model predictions from the Mars Planetary Climate Model reveal an excellent agreement, except for a slightly different phase of the diurnal tide. During the GDE, the tide pattern changes spectacularly: the diurnal tide amplitude reaches 35K at 65°S and 17K at 50°N, being vertically trapped up to 10Pa. The semi‐diurnal tide is maximum near 20–30°S with an amplitude of 8–12K. The phase of this mode is tilted with latitude, which was not the case before the storm. This indicates a significant contribution of the asymmetric Hough modes due to hemispheric asymmetry in the dust distribution.

Analyzing the Instabilities in the Venus Atmosphere Using Bred Vectors

“…Thermal tides commonly occur in the rapidly rotating atmospheres of terrestrial planets such as Earth, Mars, and Venus (Wu et al., 2021). The amplitude of thermal tide in the Earth's atmosphere is small (Guerlet et al., 2023). For the thermal tide in the Martian atmosphere, dust and water ice are important excitation sources because they absorb the visible sunlight and the infrared radiation emitted from the ground (Wu et al., 2020).…”

Seasonal and Diurnal Variations of Dust Storms in Martian Year 36 Based on the EMM‐EXI Database

“…In contrast, the semidiurnal component is more evident for dust storm occurrences over southern mid-latitudes (Barnes et al, 2017;Forbes et al, 2020). At these latitudes, the storm occurrences peak around 14-16 hr, which coincides more with the peak of the semi-diurnal mode (Forbes et al, 2020;Guerlet et al, 2023). Considering the hemispheric differences, the occurrence of northern mid-latitude storms is greater than its southern counterpart only around noon, whereas the low-latitude storms differ noticeably between each hemisphere during morning (8-10 LT) and evening (16-18 LT) hours.…”

Atmospheric Tides in the Middle and Upper Atmosphere of Mars at Northern High Latitudes: A Comparison of MAVEN‐EUVM and MRO‐MCS Observations With Model Results

“…It can be seen from Equation 2that |s n| is the wavenumber associated with longitudinal variation in a fixed local time reference frame. A few previous studies have successfully delineated values of s and n; however, many of these were focused on identifying migrating tides in the lower atmosphere Guerlet et al, 2023;Kleinböhl et al, 2013). Wu et al (2015) successfully separated the values of s and n to identify both migrating and nonmigrating tides in the middle atmosphere using MCS observations.…”

“…It can be seen from Equation that | s − n | is the wavenumber associated with longitudinal variation in a fixed local time reference frame. A few previous studies have successfully delineated values of s and n ; however, many of these were focused on identifying migrating tides in the lower atmosphere (Fan, Forget, et al., 2022; Fan, Guerlet, et al., 2022; Guerlet et al., 2023; Kleinböhl et al., 2013). Wu et al.…”