Gravity Wave Activity in the Atmosphere of Mars During the 2018 Global Dust Storm: Simulations With a High‐Resolution Model

Abstract

Gravity waves (GWs) exist in atmospheres of all planets with convectively stable stratification. They transport energy and momentum from denser tropospheres to thinner upper levels (Yiğit & Medvedev, 2019). Effects produced by GWs are particularly strong in the middle and upper atmospheres of Earth and Mars (see recent reviews of Medvedev & Yiğit, 2019; Yiğit & Medvedev, 2015, correspondingly), thus making them a major dynamical mechanism that couples the lower and upper atmospheres on both planets. Being relatively small in size (from tens to hundreds of kilometers in horizontal wavelength) and short-lived (periods from a few minutes to several hours), GWs are thought to strongly affect the Martian global circulation. They close and even reverse zonal jets in the middle atmosphere (Barnes, 1990; Gilli et al., 2020; Medvedev et al., 2011a) and enhance the meridional circulation, which has implications for the meridional transport of tracers and important dynamical effects. The upwelling part of the meridional cell amplifies the transport of water into the thermosphere (Shaposhnikov et al., 2019), and the descending branch leads to thermospheric polar warmings (Bougher et al., 2006; Medvedev et al., 2011b). GW-induced downward transport Abstract Gravity wave (GW) activity in the lower and middle atmosphere of Mars during the global dust storm of 2018 has been studied for the first time using a high-resolution (GW-resolving) general circulation model. Dust storm simulations were compared with those utilizing the climatological distribution of dust in the absence of storms. Both scenarios are based on observations of the dust optical depth by the Mars Climate Sounder instrument on board the Mars Reconnaissance Orbiter. The modeling reveals a reduction of the wave activity by a factor of 2 or more in the lower atmosphere, which qualitatively agrees with recent observations. It is associated with a decline of GW generation due to baroclinic and convective stabilization of the Martian troposphere induced by the increased amount of airborne aerosols during the storm. Contrary to the decrease of GW activity in the lower atmosphere, wave energy and momentum fluxes in the middle atmosphere increase by approximately the same factor. This enhancement of GW activity is caused by the changes in the large-scale circulation, most importantly in the mean zonal wind, which facilitate vertical wave propagation by allowing for a greater portion of GW harmonics originated in the lower atmosphere to avoid filtering on their way to upper layers. Plain Language Summary Gravity waves (GWs) are oscillations of wind, temperature, pressure, and density that originate in the dense lower atmosphere. They grow in amplitude upon propagation upward and represent a major driving force in the thinner middle and upper atmosphere. GWs are difficult to account for in general circulation models because their scales are smaller than the resolution of the majority of such models. To circumvent this, we employ a high-resolution model that can explicitly ...

Abnormal Phase Structure of Thermal Tides During Major Dust Storms on Mars: Implications for the Excitation Source of High‐altitude Water Ice Clouds

“…For instance, the diurnal variability of gravity wave drag is suggested to modify the DW1 propagation in the Earth's atmosphere (Meyer, 1999;Ortland & Alexander, 2006). Recent observation and simulation studies suggested that the diurnal variability of gravity wave activity in the Martian lower atmosphere is significantly reduced during dust storms (Heavens et al, 2020;Kuroda et al, 2020), which could remove its constraint on the DW1. Such effect of small-scale gravity wave flux in modifying the tidal structure on Mars needs more studies in the future.…”

Dust Storm‐Enhanced Gravity Wave Activity in the Martian Thermosphere Observed by MAVEN and Implication for Atmospheric Escape

“…Since the gravity wave energy and momentum flux are proportional to the square of the wave amplitude, the increase in observed amplitude is, in fact, even higher in terms of these dynamically important quantities. An overall effect of storms on the lower atmosphere is the convective (Figure 1c of Kuroda et al, 2020) and baroclinic (Figure 2 of Kuroda et al, 2007) major mechanisms of GW generation in the lower atmosphere. Observations by Mars Climate Sounder provided evidence of a reduction of GW activity below 30 km by several times during the 2018 GDS (Heavens et al, 2020).…”

Intense Zonal Wind in the Martian Mesosphere During the 2018 Planet‐Encircling Dust Event Observed by Ground‐Based Infrared Heterodyne Spectroscopy

“…Finally, we have to note that the measured wind velocities maintain its high values on 31 August as seen in Figure 3; while, the dust storm was significantly weaker by the end of August (Fedorova et al, 2020;Luginin et al, 2020). According to the model prediction by Kuroda et al (2020), the impact of dust storms on the zonal winds is essentially the same regardless of the extent of the storm. The discrepancy between our result and dust storm evolution might suggest a bias of the wind determination in our result.…”

“…The observed enhancement of the retrograde (easterly) equatorial wind in the mesosphere during dust storms has been captured by the MGCMs (Kuroda et al, 2020;Medvedev et al, 2013;Ruan et al, 2019). Medvedev et al (2013), with a horizontal resolution of ∼5.6° in both longitude and latitude and a gravity wave drag parameterization empirical for terrestrial thermosphere (Yiǧ;, presented simulations based on the zonally averaged dust distributions observed by the Thermal Emission Spectrometer instrument (TES) onboard the Mars Global Surveyor (MGS) during the 2001 PEDE (MY25), which started at almost the same season as the one in 2018.…”

“…To discriminate the effect of PEDE from the nominal seasonal variation, we checked the zonal winds from MGCMs. The maximum equatorial retrograde wind velocities obtained by an MGCM with a horizontal resolution of ∼1.1° in both longitude and latitude (Kuroda et al, 2019(Kuroda et al, , 2020 for the corresponding season are imposed on Figure 3. The wind velocities shown here are the zonal (diurnal) and meridional maximum easterly velocities averaged in 75-85 km geopotential height and 10° in longitude and latitude within the central latitudes of less than 20°, followed by the time smoothing for five sols.…”