Mars General Circulation Model Research Articles

CO2frost cap thickness on Mars during northern winter and spring

The thickness of seasonal CO2frost that covers the north pole of Mars during the winter and spring seasons is studied using gamma ray and neutron data measured using the gamma ray spectrometer suite of instruments aboard Mars Odyssey. The resultant seasonal variation of CO2ice/frost thickness for latitudes greater than +85° is in close agreement (within 9% at maximum) with those predicted using all three major Mars general circulation models presently in use. These observed CO2ice results are significantly different from those inferred from the Mars Obiter Laser Altimeter experiment aboard Mars Global Surveyor (MGS). A possible explanation is that the density of the CO2ice/frost cap is considerably lower than that inferred from observed variations of the MGS orbit. Other significant results are that the thermal neutron counting rates provide evidence for variations in the abundance of noncondensable components of the polar atmosphere of Mars and that the basement terrain below the seasonal cover of CO2frost within about 10° of the pole is nearly 100% water ice.

Modelling the martian atmosphere

Mars general circulation models, used to study the atmosphere of Mars, have developed almost in parallel with terrestrial weather and climate models. These models are now being confronted with a large amount of new spacecraft data, which is allowing the models to be validated more rigorously. This paper briefly reviews the current state of Mars models, highlighting areas of current development and particular challenges. The way in which models can be used to help to interpret observations, via data assimilation, and the way in which model results can be of help in planning for future missions are both discussed.

On the orbital forcing of Martian water and CO2 cycles: A general circulation model study with simplified volatile schemes

Variations in the Martian water and CO2 cycles with changes in orbital and rotational parameters are examined using the Geophysical Fluid Dynamics Laboratory Mars General Circulation Model. The model allows for arbitrary specification of obliquity, eccentricity, and argument of perihelion as well as the position and thickness of surface ice. Exchange of CO2 between the surface and atmosphere is modeled, generating seasonal cycles of surface ice and surface pressure. Water is allowed to exchange between the surface and atmosphere, cloud formation is treated, and both cloud and vapor are transported by modeled winds and diffusion. Exchange of water and CO2 with the subsurface is not allowed, and radiative effects of water vapor and clouds are not treated. The seasonal cycle of CO2 is found to become more extreme at high obliquity, as suggested by simple heat balance models. Maximum pressures remain largely the same, but the minima decrease substantially as more CO2 condenses in the more extensive polar night. Vapor and cloud abundances increase dramatically with obliquity. The stable location for surface ice moves equatorward with increasing obliquity, such that by 45° obliquity, water ice is stable in the tropics only. Ice is not spatially uniform, but rather found preferentially in regions of high thermal inertia or high topography. Eccentricity and argument of perihelion can provide a second‐order modification to the distribution of surface ice by altering the temporal distribution of insolation at the poles. Further model simulations reveal the robustness of these distributions for a variety of initial conditions. Our findings shed light on the nature of near‐surface, ice‐rich deposits at midlatitudes and low‐latitudes on Mars.

Cyclones, tides, and the origin of a cross‐equatorial dust storm on Mars

We investigate the triggering mechanism of a cross‐equatorial dust storm observed by Mars Global Surveyor in 1999. This storm, which had a significant impact on global mean temperatures, was seen in visible and infrared data to commence with the transport of linear dust fronts from the northern high latitudes into the southern tropics. However, other similar transport events observed in northern fall and winter did not lead to large dust storms. Based on off‐line Lagrangian particle transport analysis using a high resolution Mars general circulation model, we propose a simple explanation for the diurnal, seasonal and interannual variability of this type of frontal activity, and of the resulting dust storms, that highlights the cooperative interaction between northern hemisphere fronts associated with low pressure cyclones and tidally‐modified return branch of the Hadley circulation.

Orbital change experiments with a Mars general circulation model

We use a Mars general circulation model to examine the effect of orbital changes on the planet’s general circulation and climate system. Experiments are performed for obliquities ranging from 0° to 60° for two different longitudes of perihelion. Each experiment simulates a full Mars year assuming a fixed atmospheric dust distribution and fixed amount of CO 2 in the atmosphere/cap system. We find that global mean surface temperatures and pressures decline with increasing obliquity due to the increasing extent of the winter polar caps. The seasonal CO 2 cycle and intensity of the solstice circulation amplify considerably with increasing obliquity such that global dust storms are likely at both solstices. The most significant feature of the high obliquity solstice circulations is the development of an intense low-level jet associated with the return branch of the Hadley circulation. Model surface stresses are used to map regions of preferred dust lifting, which are defined in terms of an annual deflation potential. For the present obliquity, the model-predicted regions of high deflation potential are in good agreement with Cantor et al.’s (2001, J. Geophys. Res. 106, 23653–23688) observations, which gives us some confidence in the model’s ability to predict where lifting might occur when Mars’ orbit parameters are different than they are today. In general we find that the dust lifting potential increases sharply with obliquity and is greatest at times of high obliquity when perihelion coincides with northern summer solstice. Over an obliquity cycle, the model global annual deflation potential ranges from several tenths of a millimeter at 0° obliquity to almost 15 mm at 60° obliquity. Much higher values are possible when the atmosphere is very dusty. We find a strong correlation between the deflation potential and surface thermal inertia: regions of high deflation potential correspond to regions of high thermal inertia (high rock abundance), and regions of low deflation potential correspond to regions of low thermal inertia (high dust/sand abundance). Furthermore, while the regions of preferred lifting (high deflation potential) expand somewhat with increasing obliquity and dust loading, the central parts of Tharsis, Arabia, and Elysium show no tendency for significant lifting at any obliquity or longitude of perihelion. These regions may therefore be very old and represent net long-term sinks for atmospheric dust. It is the topography of the planet, through its influence on surface pressure and wind systems, which ultimately determines where dust accumulates. Finally, as was found by Fenton and Richardson (2001, J. Geophys. Res. 106, 32885–32909), we find no tendency for the development of east-southeasterly winds at the Pathfinder site for any of our orbital change experiments. This suggests that the ancient wind regime discussed by Greeley et al. (2000, J. Geophys. Res. 105, 1829–1840) was produced by other factors, such as polar wander.

Stationary planetary waves in the atmosphere of Mars during southern winter

We report new observations of stationary planetary waves in the Southern Hemisphere of Mars by Mars Global Surveyor (MGS). We focus on a period during midwinter (Ls = 134°–160°) when independent observations were acquired by two techniques. Radio occultation experiments sounded the atmosphere at essentially fixed latitude (∼68°S) and local time (∼1030), yielding profiles of geopotential and temperature between the surface and the 9 Pa pressure level. Observations by the Thermal Emission Spectrometer (TES) included systematic limb sounding at nine discrete latitudes and two local times (∼0200 and ∼1500), yielding temperature profiles at pressures of 1–100 Pa. We supplemented these data with a simulation by a Mars general circulation model (MGCM), which provides an accurate synthesis of the observations. These stationary planetary waves have significant amplitudes at zonal wave numbers s = 1 and 2. The s = 1 component propagates vertically, as reflected by a westward tilt with increasing height in the geopotential and temperature fields and a net poleward eddy heat flux. The peak amplitude at s = 1 is ∼1 km in geopotential height and ∼7 K in temperature. The geopotential field of the s = 2 component is “barotropic” in character, which results through hydrostatic balance in a distinctive temperature field. The peak amplitude at s = 2 is ∼700 m in geopotential height and 4–6 K in temperature.

Modeling the Martian dust cycle 2. Multiannual radiatively active dust transport simulations

Multiannual dust transport simulations have been performed using a Mars general circulation model containing a dust transport scheme which responds to changes in the atmospheric state. If the dust transport is “radiatively active,” the atmospheric state also responds to changes in the dust distribution. This paper examines the suspended dust distribution obtained using different lifting parameterizations, including an analysis of dust storms produced spontaneously during these simulations. The lifting mechanisms selected are lifting by (1) near‐surface wind stress and (2) convective vortices known as dust devils. Each mechanism is separated into two types of parameterization: threshold‐sensitive and ‐insensitive. The latter produce largely unrealistic annual dust cycles and storms, and no significant interannual variability. The threshold‐sensitive parameterizations produce more realistic annual and interannual behavior, as well as storms with similarities to observed events, thus providing insight into how real Martian dust storms may develop. Simulations for which dust devil lifting dominates are too dusty during northern summer. This suggests either that a removal mechanism (such as dust scavenging by water ice) reduces opacities at this time or that dust devils are not the primary mechanism for storm production. Simulations for which near‐surface wind stress lifting dominates produce the observed low opacities during northern spring/summer, yet appear unable to produce realistic global storms without storm decay being prevented by the occurrence of large‐scale positive feedbacks on further lifting. Simulated dust levels are generally linked closely to the seasonal state of the atmosphere, and no simulation produces the observed amount of interannual variability.

Nonmigrating tides in the thermosphere of Mars

The vertical propagation of nonmigrating (i.e., longitude‐dependent or non–Sun‐synchronous) solar diurnal and semidiurnal tides into the thermosphere of Mars is investigated through numerical simulation. The waves are generated in the NASA Ames Mars general circulation model (MGCM) through solar radiative, topographic, and nonlinear processes using a comprehensive physics package and including a diurnal cycle. At an altitude near 70 km, zonal wave number decompositions of the diurnal and semidiurnal tidal fields are performed, and each wave component is extended from 70 to 250 km using a linear steady state global scale wave model for Mars (Mars GSWM). Conditions representative of aerocentric longitudes Ls = 30 (near equinox) and Ls = 270 (Southern Hemisphere summer solstice) are considered. Modeled total relative density variations of order ±10–40% near 125 km are analyzed in terms of the zonal wave numbers (ks) seen from the Sun‐synchronous perspective of the Mars Global Surveyor (MGS) accelerometer experiment, and yield reasonable agreement in amplitude and phase with the density measurements. The model indicates the two most important waves responsible for ks = 3 to be the eastward‐propagating diurnal and semidiurnal oscillations with zonal wave numbers s = 2 (∼15–40%) and s = 1 (∼8%), respectively. The eastward‐propagating diurnal component with s = 1 (∼15%) and the semidiurnal standing (s = 0) oscillation (∼4–23%) are concluded to be the main contributors to the ks = 2 longitudinal density variation seen from the Mars Global Surveyor (MGS). The standing (s = 0) diurnal oscillation (∼4–5%) and the westward‐propagating semidiurnal component with s = 1 (∼5–8%) emerge as the most likely contributors to ks = 1. Other waves that may make important secondary contributions include the westward‐propagating semidiurnal oscillations with s = 3 (∼4–6%) and s = 4 (∼3–9%). In addition, above 100 km the wind and temperature fields associated with the above waves represent ∼15–30% perturbations on the Sun‐synchronous wind and temperature fields driven in situ by EUV and near‐IR solar radiation absorption. Nonmigrating tides primarily arise from zonal asymmetries in wave forcing associated with Mars' topography; our results show for the first time that the dynamical effects of Mars' topography extend throughout the atmospheric column to Mars' exobase (∼200–250 km).

A mesoscale model for the Martian atmosphere

The Pennsylvania State University/National Center for Atmosphere Research Mesoscale Model Version 5 (MM5) has been converted for use on Mars. Modifications are based on schemes implemented in the Geophysical Fluid Dynamics Laboratory Mars General Circulation Model (GCM). Validation of the Mars MM5 is conducted by comparison to the Mars GCM, examining the large‐scale dynamics in the two models. Agreement between the two models on similar scales (a few hundred kilometers) is good. Validation is also performed against both Viking Landers and Mars Pathfinder meteorological observations with the model run at higher vertical (lowest level at 1.6 m) and horizontal resolution (a few kilometers). We find reasonable agreement with near‐surface air temperature, pressure, and wind direction observations, with caveats. The results demonstrate that the model accurately simulates surface heat balance and the propagation of global thermal tides. However, wind speeds are underpredicted. The model generates the correct phasing of wind speeds with local time at the Viking Lander 2 site during winter but does not generate the correct phasing at the other sites or seasons. We examined the importance of slopes and global tides in generating the diurnal cycle of winds at the lander sites. We find that tides are at least as important as slopes, in contrast to previous studies. This study suggests that when used in combination with a GCM, the Mars MM5 promises to be a powerful tool for the investigation of processes central to the Martian climate on scales from hundreds of kilometers to tens of meters.

Traveling waves in the Northern Hemisphere of Mars

Analysis of temperature retrievals from Mars Global Surveyor Thermal Emission Spectrometer data has revealed the presence of regular, eastward propagating waves in the Northern Hemisphere. A large amplitude, zonal wave 1 with a long (∼20 sol) period is particularly prominent during early winter (Ls = 220–270°). After Ls = 270°, a weaker and more rapidly propagating (6.5 sol period) zonal wave 1 is dominant. These waves have a deep vertical structure (>40 km) correlated with the axis of the winter hemisphere westerly jet. Simulations with a Mars general circulation model suggest that the fast wave is associated with baroclinic instability due to the strong meridional temperature gradient at the surface and is consistent with surface pressure oscillations seen in Viking Lander data. By contrast, the slow wave has the appearance of a large‐amplitude Rossby wave that is coupled with an inertially unstable region in the subtropics.

Evidence for nonmigrating thermal tides in the Mars upper atmosphere from the Mars Global Surveyor Accelerometer Experiment

Mars Global Surveyor Accelerometer Experiment density measurements indicate the presence of planetary‐scale wave structure in the Mars upper atmosphere (∼130 km). In particular, Phase 2 aerobraking observations reveal large amplitude zonal wave 2 and 3 variations in dayside density between ±60° latitude. These spatial variations (in a fixed local solar time reference) can be qualitatively reproduced by a Mars general circulation model and are identified as a manifestation of eastward propagating nonmigrating thermal tides with long vertical wavelengths. The simulated wave 2 variation is dominated by a diurnal period wave 1 Kelvin mode while the principal components of the simulated zonal wave 3 structure are a diurnal period wave 2 Kelvin mode and a wave 1 semidiurnal tide. The characterization of these waves is important for understanding the structure and variability of the martian atmosphere at aerobraking altitudes.

Simulation of surface meteorology at the Pathfinder and VL1 sites using a Mars mesoscale model

The Fifth‐Generation Penn State/NCAR Mesoscale Model (MM5) has been adapted to study circulations in the Martian atmosphere. The NASA Ames Mars general circulation model (GCM) provides initial and boundary conditions. The meteorology of this Mars MM5 (the OSU MMM5) is compared with Pathfinder and Viking Lander 1 (VL1) data for late northern summer. The MMM5 uses an equator‐crossing semiglobal polar stereographic mother domain, significantly reducing the boundary reflections inherent in Martian mesoscale simulations. Using two‐way nests, simultaneous simulations of two regions are performed: (1) Chryse Planitia (Mars Pathfinder (MPF)/VL1) and (2) the central chasmas of Valles Marineris. Simulations are hydrostatic and dry. The MMM5 uses the same atmospheric radiation package as the GCM but a much enhanced near‐surface vertical resolution and a different Planetary Boundary Layer (PBL) scheme. Model topography, thermal inertia, and surface albedo maps have all been developed using the most recent data from the Mars Global Surveyor (MGS) Mars Orbiter Laser Altimeter (MOLA) and Thermal Emission Spectrometer (TES) experiments. The diurnal cycles of surface air temperature, surface pressure, and surface wind all show improvement in comparison with the GCM. For certain regions the local surface pressure tidal amplitudes are strongly dependent on the resolution of the model and/or the topography; VL1 and MPF are in such a region. The diurnal cycles of wind are complex, and for many locations the near‐surface winds are dominated by slope flows of multiple scales. Comparison with data indicates that resolving these slope flows is very important for simulating the diurnal wind cycle. At specific locations these slope flows dramatically influence the diurnal surface pressure cycle.

Transient eddies in the southern hemisphere of Mars

Mars Global Surveyor is providing the first observations of transient eddies in the southern hemisphere of Mars. We derive basic properties of the traveling eddies that appear in midwinter (Ls = 134°–148°) through analysis of radio occultation measurements at 67°–70°S latitude. The dominant mode has a period of ∼2 solar days and a zonal wavenumber s = 3. Strong zonal variations in eddy amplitude signal the presence of a possible “storm zone” at 150°–330°E longitude. Within this longitude band the eddies achieve peak amplitudes at the 300‐Pa pressure level of ∼7 K in temperature and 10–15 m s−1 in meridional wind speed. The minimum temperature associated with the eddies is ∼2 K colder than saturation of CO2, close to the threshold where nucleation and growth of new ice particles can occur. A simulation by a Mars general circulation model produces traveling eddies that closely resemble the observations.

Mars-GRAM 2000: A Mars atmospheric model for engineering applications

This paper presents Mars Global Reference Atmospheric Model 2000 Version (Mars-GRAM 2000) and its new features. All parameterizations for temperature, pressure, density, and winds versus height, latitude, longitude, time of day, and Ls have been replaced by input data tables from NASA Ames Mars General Circulation Model, for the surface through 80-km altitude, and the University of Arizona Mars Thermospheric General Circulation Model for 80 to 170 km. A modified Stewart thermospheric model is still used for higher altitudes and for dependence on solar activity. “Climate factors” to tune for agreement with general circulation model data are no longer needed. Adjustment of exospheric temperature is still an option. Consistent with observations from Mars Global Surveyor, a new longitude-dependent wave model is included, with user input to specify waves having one to three wavelengths around the planet. A simplified perturbation model has been substituted for the earlier one. An input switch allows users to select either East or West longitude positive. The paper includes instructions on obtaining Mars-GRAM source code, data files, and a users guide for running the program. The Mars-GRAM users guide provides sample input and output and gives an example for incorporating Mars-GRAM as an atmospheric subroutine in a trajectory code.

Assimilation of Mars Global Surveyor atmospheric temperature data into a general circulation model

We examined the observed temperature data from Thermal Emission Spectrometer (TES) between heliocentric longitude Ls = 141° and 146° (∼10 Martian days in northern summer) during the mapping phase, then compared them with the simulated results using the NASA/Ames Mars general circulation model. Both show a strong polar vortex at the winter pole, higher equatorial temperatures near the ground and larger tropospheric lapse rates during daytime than at night. However, the simulation is colder than the observation at the bottom and top of the atmosphere and warmer in the middle. The highest wave activities are found in the polar front in both the simulations and the observations, but it is at a much higher altitude in the former. Experiments show that larger dust opacity improves the temperature field in the lower atmospheric levels. Using a steady state Kalman filter, we attempted to obtain a model state that is consistent with the observations. The assimilation did achieve better agreement with the observations overall, especially over the north pole. However, it is hard to make any further improvement. Dust opacity is the key factor in determining the temperature field; correcting temperature alone improves the spatial and temporal variations, it degrades the mean state in the south pole. Assimilation cannot improve the simulation further, unless more realistic dust opacity and its vertical profile are considered.

Martian surface winds: Insensitivity to orbital changes and implications for aeolian processes

Aeolian features observed on the surface of Mars provide insight into current, and potentially past, surface wind systems. In some cases the features are clearly transient and related to the lifting and settling of atmospheric dust. Other features, like dunefields, yardangs, and ventifacts, are more persistent and likely require significant time to form. In this study we analyze the observed directions of selected aeolian features with the aid of the Geophysical Fluid Dynamics Laboratory Mars general circulation model (GCM). Initially, we examine bright and dark streaks which have been observed to form in association with global dust storms. The ability to match these features with Mars GCM wind directions provides an important validation of the model. More important, we are able to define best fit seasons and local times for both types of features which provide the basis for extension and modification of the Veverka et al. [1981] model of bright and dark dust streak formation. In addition these best fit times correspond well with the dark streak “wind storm” model of Magalhães and Young [1995]. The primary focus of this paper is to provide constraints on the range of mechanisms proposed to explain inconsistencies between current wind direction patterns and long‐term wind indicators (for example, the misalignment of rock tail and ventifact orientations at the Mars Pathfinder landing site). Specifically, we assess whether changes in planetary obliquity, precession, or global dust opacity could significantly alter patterns of surface wind directions. In all cases we find the seasonal and annual average wind direction patterns to be highly invariable. While changes in the dust loading (hence the partitioning of solar absorption between the surface and atmosphere) and in the surface latitude of maximum solstitial insolation cause the vigor of the large‐scale circulation to increase (especially the Hadley cell), the spatial patterns of the surface wind orientations remain essentially unchanged. In the case of perihelion during northern summer (opposite of the current perihelion position), the northern summer Hadley cell remains weaker than the southern summer cell despite the strengthened heating in the northern hemisphere. Taken together, these results cast significant doubt on orbital explanations for surface wind changes. It is thus suggested that significant changes in topography (e.g., Tharsis uplift, true polar wander) or climate (e.g., the existence of a significantly thicker atmosphere or an ocean at some point in the past) are more likely explanations for long‐term wind indicators such as the ventifact orientations at the Mars Pathfinder landing site.

Radio occultation measurements of forced atmospheric waves on Mars

Mars Global Surveyor performed a series of radio occultation experiments in December 1998, resulting in 36 profiles of the neutral atmosphere in late northern spring (Ls = 74.1°–77.3°). The measurements are confined in latitude (64.6°–67.2°N) and local time (0321–0418), but their distribution in longitude is fairly uniform. We used least squares spectral analysis to characterize the zonal structure of the atmosphere and constructed longitude‐height cross sections of both temperature and geopotential. Zonal variations of temperature exceed 12 K near the surface but are much smaller (2–3 K) at higher altitudes. Zonal variations of geopotential are ∼200 m throughout the vertical range of the measurements. These patterns of temperature and geopotential appear to be stationary relative to the surface with little day‐to‐day variation within the 7‐sol span of the measurements. We relied heavily on Mars general circulation models (GCMs) for guidance in understanding these data. Stationary planetary waves are responsible for some aspects of the temperature and geopotential fields, particularly at pressures exceeding 100–200 Pa. On the basis of strong similarities between a GCM simulation and the observations, we conclude that the disturbance takes the form of a planetary wave train excited by Alba Patera. The data also include the signature of non‐Sun‐synchronous thermal tides, which produce a pattern that appears to be stationary when sampled at fixed local time. Comparison between a GCM simulation and the measured geopotential field provides evidence for the presence of the resonantly enhanced, diurnal, wave‐1 Kelvin mode.

Evidence for diurnal period Kelvin waves in the Martian atmosphere from Mars Global Surveyor TES data

Midlevel (∼25 km) atmospheric temperatures derived from Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) spectra indicate the presence of stationary waves and thermal tides. Stationary waves are prominent at middle to high latitudes where westerly zonal flow is indicated by the meridional temperature gradient. Longitudinal variability within 30°S to 30°N is dominated by topographically‐forced nonmigrating thermal tides that have westward and eastward propagating components. The MGS mapping data are available at two fixed local times so that it is not possible to distinguish between these components or isolate the sun‐synchronous tide. A comparison with Mars general circulation model (MGCM) simulations suggests that the observed wave patterns are consistent with the presence of eastward propagating, diurnal period Kelvin waves with zonal wavenumbers one and two. These waves can propagate to great heights and may account for observed zonal variations in thermospheric density.

A comparison of MGS Phase 1 aerobraking radio occultation data and the NASA Ames Mars GCM

The NASA Ames Mars general circulation model (MGCM) is used to investigate how different phenomena in the Martian climate system combine to produce temperature profiles measured by the Radioscience Instrument (RS) aboard Mars Global Surveyor (MGS) in early 1998. When integrated with dust amounts consistent with Thermal Emission Spectrometer (TES) observations, and with a topography data set determined from the Mars Orbiting Laser Altimeter (MOLA), modeled temperature profiles are within 5–10 K of observations. Modeled and measured profiles in the winter subtropics are warmer than pure radiative‐convective considerations suggest, providing further evidence of strong dynamical warming associated with descent in the Hadley cell. South of 40°S, the best fit to the data is obtained by confining airborne dust to below 2 scale heights in this region. The differences in the strength of low‐level inversions found in the MGCM and in the RS data indicate the presence of either a low‐level radiative cooling mechanism such as isolated dust clouds or water‐ice clouds, or a dynamical mechanism such as low‐level gravity wave drag. When initialized with a mean surface pressure that gives the best fit to Viking lander measurements, the model matches RS surface pressure data to within 0.1 mbar. This consistency is a further validation of the MGCM and shows how GCMs can be used to interpret measurements of surface pressure taken at different locations using different methods.

Mars Global Surveyor Thermal Emission Spectrometer (TES) observations: Atmospheric temperatures during aerobraking and science phasing

Between September 1997, when the Mars Global Surveyor spacecraft arrived at Mars, and September 1998, when the final aerobraking phase of the mission began, the Thermal Emission Spectrometer has acquired an extensive data set spanning approximately half of a Martian year. Nadir‐viewing spectral measurements from this data set within the 15 μm CO2 absorption band are inverted to obtain atmospheric temperature profiles from the surface up to about the 0.1 mbar level. The computational procedure used to retrieve the temperatures is presented. Mean meridional cross sections of thermal structure are calculated for periods of time near Northern Hemisphere fall equinox, winter solstice, and spring equinox as well as for a time interval immediately following the onset of the Noachis Terra dust storm. Gradient thermal wind cross sections are calculated from the thermal structure. Regions of possible wave activity are identified using cross sections of rms temperature deviations from the mean. Results from both near‐equinox periods show some hemispheric asymmetry with peak eastward thermal winds in the north about twice the magnitude of those in the south. The results near solstice show an intense circumpolar vortex at high northern latitudes and waves associated with the vortex jet core. Warming of the atmosphere aloft at northern midlatitudes suggests the presence of a strong cross‐equatorial Hadley circulation. Although the Noachis dust storm did not become global in scale, strong perturbations to the atmospheric structure are found, including an enhanced temperature maximum aloft at high northern latitudes resulting from intensification of the Hadley circulation. TES results for the various seasonal conditions are compared with published results from Mars general circulation models, and generally, good qualitative agreement is found.