Cyclic absorption of solar radiation generates oscillations in atmospheric fields. These oscillations are called atmospheric or thermal tides, which are furthermore modified by topography and surface properties. This leads to a complex mix of sun-synchronous and non sun-synchronous tides that propagate around the planet eastward and westward. This study focuses on analyzing the ter-diurnal component (period of 8 hr) from surface pressure observations by Mars Science Laboratory (MSL), InSight, Viking Lander (VL) 1, and VL2. General Circulation Model (GCM) results are used to provide a global context for interpreting the observed ter-diurnal tide properties. MSL and InSight have a clear and similar seasonal cycle, with local amplitude peaks at around solar longitude (Ls) 60◦ , Ls 130◦ and Ls 320◦ . The amplitude peak at Ls 320◦ is related to the annual dust storm, while the dust storm around Ls 230◦ is not detected by either platforms. During the global dust storms, MSL, VL1, and VL2 detect their highest amplitudes. GCM predicts the weakest amplitudes at the equinoxes, while the strongest ones are predicted in summertime for both hemispheres. GCM amplitudes are typically lower than observed, but match better during the aphelion season. During this time, model results suggest that the two most prominent modes are the sun-synchronous ter-diurnal tide (TW3) and an eastward propagating resonantly-enhanced Kelvin wave (TE3). Simulations with and without the effect of radiative heating by water ice clouds indicate the clouds may play a significant role in forcing the ter-diurnal tide during northern hemisphere summer season.

Mars present-day middle and upper atmosphere, above ~100 km, connects the deep atmosphere to the Martian space environment. This region is important to understand for many reasons, including for more general insights into the evolution of atmospheres, as a comparison to other planetary atmospheres, and for current and future mission development and interpretation. The middle/upper atmosphere is greatly influenced by the physics of the lower atmosphere (water cycle, dust cycle, waves, etc.) and the solar environment (solar magnetic activity, solar events). It contains the upper branch of the overturning meridional circulation and the transitional point of the main heating source from near-IR to UV radiation. These influences feed on a primitive property of an atmosphere: temperature. This work will break down the radiative processes that drive the Martian’s thermal structure above ~100 km as a function of latitude and season. We demonstrate the on-going work on extending the NASA Ames Mars Global Climate Model (MGCM), now using the NOAA/GFDL FV3 dynamical core. The MGCM nominally extends from the surface up to ~80 km but new physics packages will extend the MGCM’s vertical domain up to ~250 km. We present the heating and cooling mechanisms that dominate this atmospheric region, discuss the parametrizations used, the state of the seasonal/diurnal thermal structure, and finally, we discuss the work in progress for the development and implementation of physics schemes in our model.

We are using radio occultation (RO) measurements from Mars Global Surveyor to investigate the nighttime structure and dynamics in the lower atmosphere of Mars. High-resolution temperature profiles retrieved from the RO data contain unique information about nocturnal mixed layers (NMLs) – detached layers of neutral stability that form at night in response to radiative cooling by a water-ice cloud layer. Basic properties of the NMLs and constraints on their spatial distribution and seasonal evolution can be obtained through analysis of the RO profiles. We have examined more than 3000 RO profiles in a latitude band centered on the Phoenix landing site (234°E, 68°N), where nighttime water-ice clouds were observed by the LIDAR instrument (Whiteway et al., Science 325, 68-70, 2009). NMLs appear routinely in the western hemisphere in RO observations at 5 h local time from early summer of MY27. There is a close resemblance in both thickness (a few km) and altitude (about 4 km above the surface) to the cloud layer observed at the same local time by the Phoenix LIDAR in MY29. The NMLs confirm that radiative cooling by the Phoenix cloud is sufficient to trigger convective instability, as predicted by a Large Eddy Simulation (Spiga et al., Nat. Geosci. 10, 652-657, 2017). We have also analyzed more than 800 RO profiles from the northern tropics near summer solstice of MY28. Tropical NMLs are largely confined to regions of elevated terrain, where the daytime convective boundary layer is deep. At 4 h local time, the top of the NML is about 10 km below the peak of Olympus Mons. The spatial distribution of the NMLs appears to be influenced by diverse processes ranging from topographic circulations to planetary-scale thermal tides. In addition, we are using a Mars Global Circulation Model and Large Eddy Simulations to interpret the RO results. Goals of the modeling effort include: to identify the atmospheric processes that control the formation of nocturnal water ice clouds; to understand the spatial distribution of the clouds and their evolution with time of day and season; and to assess the impact of NMLs on the nighttime weather and water transport in the lowest scale height above the surface.

Observations made in Gale Crater by instruments on the MSL Curiosity Rover show that the diurnal amplitude of the surface pressure is increased and the depth of the Convective Boundary Layer (CBL) is decreased relative to other lander locations on flatter regions of Mars (Haberle et al., 2014; Moores et al., 2015). Mesoscale modeling studies of Gale Crater suggest that crater circulations produce these effects. Tyler & Barnes (2013) show that local upslope/downslope flows along the crater rim and Mt. Sharp amplify the diurnal pressure cycle. These same flows are thought to be at least partly responsible for the suppression of the CBL because upward air flow at the rim and in the center (due to Mt. Sharp) forces subsidence over the lowest regions of the crater during the day. Regional flows, largely due to the location of Gale near the dichotomy boundary, may also play a role in shaping the circulation internal to the crater. Whether the behavior of the CBL and the amplified diurnal pressure cycle are phenomena observed in craters morphologically different from Gale (i.e. bowl-shaped, irregular, degraded) is not yet understood. We will explore these questions by characterizing the behavior of these processes as they are shaped by the morphology of craters greater than 100 km in diameter. We use the NASA Ames Mars Global Circulation Model (GCM) that now utilizes the NOAA/GFDL cubed-sphere finite-volume dynamical core to examine ~100 craters of varying size and shape from a database of known Martian craters (Robbins & Hynek, 2014). Run at 7.5 km resolution, the GCM is capable of resolving surface winds, temperature, and pressure inside craters of this size allowing for the analysis of dozens of craters simulated at various seasons and within the context of synoptic and global-scale phenomena.

The B storm is an annually recurring, regional-scale dust storm that occurs over the south pole of Mars during southern summer solstice season during years lacking a global dust storm [1]. The B storm begins just after perihelion (Ls = 251°), reaches peak strength around southern summer solstice (Ls = 270°), and decays through ~Ls = 290° [2]. The B storm is associated with mid-level atmospheric warming in which 50 Pa (2.5 scale heights) temperatures increase to over 200 K. Mid-level dust concentrations more than triple during the B storm, exceeding 4 ppm throughout the duration of the storm and exceeding 10 ppm at peak strength (Ls = 270°) [1,2]. Our observational analysis, which was presented at AGU in 2020, shows that elevated dust concentrations (> 4 ppm) and associated warming (> 200 K) are observable as high as 25 Pa during peak intensity, and that the B storm is a southwestward-propagating storm that develops over 60° S and strengthens as it travels poleward [2,3]. We have since carried out simulations of B storms using the NASA Ames Mars Global Climate Model (MGCM), which is based on the NOAA/GFDL cubed-sphere finite volume dynamical core, at high spatial (1x1°, 60x60 km) resolution. We find that B storm dust is lofted upwards of 50 Pa by episodic pluming events somewhat resembling the rocket dust storms described in Spiga et al. (2013) [4]. Detached dust layers sometimes form from these plumes at altitudes between 25-3 Pa (3-5 scale heights). These detached layers maintain altitude for ~1 sol before the sedimentation rate of the dust exceeds the upward vertical velocity generated by the radiative heating of the suspended dust [5]. We will present results from the MGCM-simulated B storm using three-dimensional animations to illustrate the hourly evolution of the dust that is lofted during the storm. 1. Kass D. M. et al. (2016). Geophs. Res. Letters, 43, 6111–6118. 2. Batterson, C.M.L. et al. (2021). Scholarworks, SJSU Master’s Theses, 5174. 3. Batterson, C.M.L. et al. (2020). Martian B Storm Evolution: Modeling Dust Activity over the Receding South Polar CO2 Ice Cap at Southern Hemisphere Summer Solstice, Abstract (P080-0002) presented at 2020 AGU Fall Meeting, 1-17 Dec. 4. Spiga, A. et al. (2013). JGR: Planets, 118(4), 746-767. 5. Daerden, F. et al. (2015). Geophs. Res. Letters, 42, 7319-7326.