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Electron temperatures are a key parameter for understanding the ionosphere‐thermosphere system. This study uses in situ data from the MAVEN mission to investigate the level of coupling between the Martian ionospheric electrons and the neutral thermosphere below the altitude of 190 km. Such coupling is responsible for significant diurnal variations and dawn/dusk asymmetries in both the neutral and plasma portions of the ionosphere‐thermosphere system. Earlier theoretical studies suggested that neutral species controlled the electron temperature by collisional cooling thus implying a diurnal trend in electron temperatures due to the diurnal variability of the neutrals. This hypothesis is evaluated across the dayside ionosphere in the present work. Observations of neutral densities confirm that neutral‐electron collisions are the primary process controlling the cooling of electrons in the Martian ionosphere below ~190 km. The consequence of this is that electron temperatures can be anticorrelated with the extreme ultraviolet (EUV) irradiance due to enhanced electron cooling brought about by an expansion of neutral densities. The results also indicate that in the afternoon sector, neutral densities are less responsive to changes in EUV. This might be associated with enhanced winds leading to dynamic cooling that mitigates the thermal expansion of the thermosphere in the afternoon region. Subsequently, the electron temperature as a function of EUV is relatively uncorrelated in the afternoon sector. The upper atmospheres of planets are partially composed of an ionized plasma. The plasma component is important to understanding the behavior of this region as well as how radio transmissions travel through it. Plasma temperatures are especially important as they determine the rates of many chemical reactions in the upper atmosphere. This analysis confirmed that at Mars, plasma temperatures are made cooler by collisions with carbon dioxide. The upper atmosphere expands when the amount of solar ultraviolet light increases leading to increased amounts of carbon dioxide at any given altitude. Therefore, more solar ultraviolet radiation generally leads to cooler plasma in the upper atmosphere. We find that there is significant variation to this phenomenon across the planet's dayside with dawn, noon, and dusk each having a different atmospheric and plasma temperature response to solar ultraviolet light. Electron temperature in the Martian ionosphere is anticorrelated with ultraviolet irradiance; this is consistent with neutral collisional coolingThe change in electron temperatures with ultraviolet irradiance is strongest near the morning and noon sectorsElectron temperatures exhibit little response to ultraviolet irradiance in the afternoon

Gravity waves are a key mechanism that facilitates coupling between the lower and upper atmosphere of Mars. In order to better understand the mean, large‐scale impacts of gravity waves on the thermosphere, a modern whole atmosphere, nonlinear, non‐orographic gravity wave parameterization scheme has been incorporated into a three‐dimensional ground‐to‐exosphere Mars general circulation model, the Mars Global Ionosphere‐Thermosphere Model (M‐GITM). M‐GITM simulations utilizing the gravity wave parameterization indicate that significant gravity wave momentum is deposited in the thermosphere, especially within the altitude range of 90–170 km. This impacts the winds in the thermosphere; in particular, M‐GITM simulations show a decrease in speed of the wind maximum in the summer hemisphere by over a factor of two. Gravity wave effects also impact the temperatures above 120 km in the model, producing a cooler simulated thermosphere at most latitudes. M‐GITM results were also compared to upper atmospheric temperature and wind data sets from the MAVEN (Mars Atmosphere and Volatile Evolution) spacecraft. Some aspects of wind data‐model comparisons improved once the gravity wave scheme was added to M‐GITM; furthermore, a cooler temperature profile produced by these new M‐GITM simulations for the MAVEN Deep Dip 2 observational campaign resulted in a closer data‐model comparison, particularly above 180 km. Overall, these modeling results show that gravity waves play an important role for the energy and momentum budget of the Martian thermosphere. Atmospheric gravity waves are an important physical process in the upper atmosphere of Mars. To better understand the average effects of gravity waves on the temperatures and winds above 100 km, a modern numerical scheme designed to represent the relevant physics has been added to a 3‐D general circulation model, M‐GITM (Mars Global Ionosphere‐Thermosphere Model), which extends from the surface to about 250 km. Results from these M‐GITM simulations show that in the upper atmosphere, the wind maximum in the summer hemisphere decreases in speed by over a factor of two once the effects of gravity waves are added to the model. Additionally, above 120 km, the model now produces a cooler upper atmosphere, on average. The new M‐GITM results were also compared to select upper atmospheric temperature and wind data sets from the MAVEN (Mars Atmosphere and Volatile Evolution) spacecraft. Data‐model comparisons in upper atmospheric wind speeds for a January 2017 observational campaign improve with the addition of gravity wave effects, as do data‐model comparisons for upper atmospheric temperatures for a MAVEN Deep Dip campaign. Overall, these model results show that gravity waves can have significant impacts on the winds and temperature structure in the Martian upper atmosphere. Large‐scale impacts of gravity waves in the thermosphere are examined using a modern gravity wave scheme in a Mars general circulation modelSignificant gravity wave momentum deposition is found in model simulations from 90 to 170 km altitudeGravity waves which propagate to the upper atmosphere of Mars can have an appreciable impact on thermospheric winds and temperatures Large‐scale impacts of gravity waves in the thermosphere are examined using a modern gravity wave scheme in a Mars general circulation model Significant gravity wave momentum deposition is found in model simulations from 90 to 170 km altitude Gravity waves which propagate to the upper atmosphere of Mars can have an appreciable impact on thermospheric winds and temperatures

In the present study, we investigate the characteristics of helium (He) bulges in the Martian upper atmosphere using He densities and winds measured by the Neutral Gas and Ion Mass Spectrometer (NGIMS) aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. The observations are compared with those predicted by the Mars Global Ionosphere Thermosphere Model (M‐GITM). The results of the present study show that the nightside He bulge is a persistent feature of the Martian upper atmosphere in all seasons. The He densities inside the bulges are 1–2 orders of magnitude greater than those on the dayside. In solstices, the bulges are observed in the winter polar region which is in accordance with the model predictions. In equinoxes, however, the bulges are observed to extend from mid‐latitudes into the southern polar regions (>60°S), which is contrary to the model predictions at mid‐latitudes. These anomalous bulges are predominantly observed in the northern spring equinox and are 10–30 × greater than the modeled ones. During the autumnal equinox, the observed winds depart from the modeled winds. Furthermore, the observed winds point to the southern polar regions where the bulges are observed. Thus, the results of the present study indicate that in equinoxes the regions of local vertical advection, that are responsible for the formation of the bulges, are displaced toward the southern polar regions. The results of the present study point to the need of a larger wind database from NGIMS in southern polar region, particularly during equinoxes. Helium in the upper atmospheres of Earth, Venus, and Mars is known to accumulate on the nightside which is often referred as “He bulge.” The upwelling of winds on the dayside and their downwelling on the nightside, combined with large‐scale circulation, is the primary driver of the bulge formation. The densities inside the He bulge are, in general, 1–2 orders of magnitude greater than those on the dayside. In the present study, the He bulge in the Mars upper atmosphere is investigated using the neutral densities measured by the Mars Atmosphere and Volatile EvolutioN spacecraft and those of a global model. In the northern summer, the He bulge occurs in the winter polar nightside which is in accordance with the model predictions. In spring and autumn, however, the observed He bulges extend from mid‐latitudes into the southern polar region whereas the model predicts their presence at mid‐latitudes. The southern polar bulges in autumn are observed in regions where the observed winds point toward the southern pole. Inclusion of the effects of the upward propagating small‐scale waves on the Martian upper atmosphere in the model, along with a larger observational wind database, is likely to address the data‐model differences. In equinoxes, helium bulges are observed to extend from mid‐latitudes in to the southern polar regions (>60°S)The observed helium densities in the southern polar regions in equinoxes are 10–30 × greater than the modeled onesThe observed winds seem to support the formation of helium bulge in the southern polar region during the autumnal equinox In equinoxes, helium bulges are observed to extend from mid‐latitudes in to the southern polar regions (>60°S) The observed helium densities in the southern polar regions in equinoxes are 10–30 × greater than the modeled ones The observed winds seem to support the formation of helium bulge in the southern polar region during the autumnal equinox