Annual Cycle of Gravity Wave Activity Derived From a High‐Resolution Martian General Circulation Model

Abstract

The paper presents results of simulations with a high‐resolution (equivalent to ∼67‐km grid size) Martian general circulation model (MGCM) from the surface up to the mesosphere for a full Martian year. The obtained climatology of the small‐scale disturbances can serve as a proxy for gravity waves (GWs) that are largely not resolved by MGCMs with conventional grid resolution and thus have to be parameterized. GW activity varies greatly with season and geographical location, which contradicts with the constant in space and time sources in the lower atmosphere adopted by GW parameterizations employed by coarse‐grid MGCMs. In particular, lower‐atmospheric GW activity is smaller in polar regions of the troposphere throughout all seasons, and the intensity is larger in southern spring and summer and in winter hemisphere at both solstices. In the mesosphere, the peak of GW activity shifts toward middle and high latitudes, and the interhemispheric symmetry is much larger compared to the lower atmosphere. The detailed climatology created in this study can be used for prescribing sources of GWs in parameterizations utilized by MGCMs as well as for validating the parameterizations in the middle and upper atmosphere.

Density Fluctuations in the Lower Thermosphere of Mars Retrieved From the ExoMars Trace Gas Orbiter (TGO) Aerobraking

“…The amplitude of density fluctuations steadily grows from ∼5 to 10% (in the average sense) during the southern winter. This is consistent with the recent simulations using a GW-resolving Martian GCM [29], which also demonstrate the increase of GW activity at the southern high-latitudes during the aphelion season. Note that the results of simulations are shown at~80 km, whereas the majority of aerobraking data come from passes with pericenter altitudes between 105 km and 111 km (see red lines in Figure 1A).…”

“…Larger-scale background winds strongly influence the vertically propagating harmonics via wave refraction and filtering, thus modulating the spatiotemporal and spectral characteristics of the GW field. Some of these phenomena have been explored in the lower and middle atmosphere using a high-resolution (GW-resolving) Martian general circulation model (MGCM) [27][28][29]. Thus, GW activity in the thermosphere is a complex result of the local wave excitation and processes of wave generation and propagation from below.…”

Impact of Gravity Waves on the Middle Atmosphere of Mars: A Non‐Orographic Gravity Wave Parameterization Based on Global Climate Modeling and MCS Observations

“…Medvedev et al (2015) implemented a nonlinear spectral gravity wave parameterization (Yiǧit & Medvedev, 2010) in their GCM, extended up to 130 km, and their simulations showed that (1) GW decelerate zonal winds at all seasons, (2) they produce jet reversals similar to those observed in the terrestrial mesosphere and lower thermosphere, and (3) GW weaken the meridional wind and modify the zonal mean temperature by up to 15 K. However, modeling efforts for Mars suffer from lack of measurements to validate predicted wind fields and from no observational constraints on the GW forcing (Creasey et al, 2006a). Other studies performed high‐resolution simulations ( 60 km grid size) with a general circulation model in order to resolve a significant portion of small‐scale GWs and to capture the impact of GWs on the dynamics and energetics of Mars atmosphere without any parameterizations (Kuroda et al, 2015, 2016, 2019). Those authors showed that the GW activity varies greatly with season and geographical location, with stronger wave generation in the northern hemisphere winter in the mesosphere and smaller activity in polar regions of the troposphere throughout all seasons.…”

Gravity Waves in Planetary Atmospheres: Their Effects and Parameterization in Global Circulation Models

“…The Martian surface is much rougher and near-surface winds are stronger than on Earth. Simulations using Martian GCMs with increased resolution clearly demonstrate enhanced wave activity over mountainous regions [5][6][7][8]. A large bow-shaped stationary GW signature was observed at the cloud tops of Venus [9].…”

“…Weather on Mars, Venus and, especially, Jupiter [15] is more volatile than that on Earth. Simulations with high-resolution GCMs show that the seasonal variations of GW activity both in the lower and upper atmospheres of Mars are tightly linked with the behavior of the circumpolar vortex and its instability, in particular [8].…”