A new Mars Global Ionosphere-Thermosphere Model (M-GITM) is presented that combines the terrestrial GITM framework with Mars fundamental physical parameters, ion-neutral chemistry, and key radiative processes in order to capture the basic observed features of the thermal, compositional, and dynamical structure of the Mars atmosphere from the ground to the exosphere (0-250 km). Lower, middle, and upper atmosphere processes are included, based in part upon formulations used in previous lower and upper atmosphere Mars GCMs. This enables the M-GITM code to be run for various seasonal, solar cycle, and dust conditions. M-GITM validation studies have focused upon simulations for a range of solar and seasonal conditions. Key upper atmosphere measurements are selected for comparison to corresponding M-GITM neutral temperatures and neutral-ion densities. In addition, simulated lower atmosphere temperatures are compared with observations in order to provide a first-order confirmation of a realistic lower atmosphere. M-GITM captures solar cycle and seasonal trends in the upper atmosphere that are consistent with observations, yielding significant periodic changes in the temperature structure, the species density distributions, and the large-scale global wind system. For instance, mid afternoon temperatures near ∼200 km are predicted to vary from ∼210 to 350 K (equinox) and ∼190 to 390 k (aphelion to perihelion) over the solar cycle. These simulations will serve as a benchmark against which to compare episodic variations (e.g., due to solar flares and dust storms) in future M-GITM studies. Additionally, M-GITM will be used to support MAVEN mission activities (2014)(2015)(2016).

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Coupling between the lower and upper atmosphere, combined with loss of gas from the upper atmosphere to space, likely contributed to the thin, cold, dry atmosphere of modern Mars. To help understand ongoing ion loss to space, the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft made comprehensive measurements of the Mars upper atmosphere, ionosphere, and interactions with the Sun and solar wind during an interplanetary coronal mass ejection impact in March 2015. Responses include changes in the bow shock and magnetosheath, formation of widespread diffuse aurora, and enhancement of pick-up ions. Observations and models both show an enhancement in escape rate of ions to space during the event. Ion loss during solar events early in Mars history may have been a major contributor to the long-term evolution of the Mars atmosphere.

[1] Warming of the martian lower thermosphere (100-130 km) at north polar latitudes near the perihelion/winter solstice (Ls = 270) was recently observed. No analogous warming has been observed within the south polar thermosphere during its aphelion/winter season (Ls $ 90). Detailed global model simulations are required to investigate the physical processes driving these seasonal variations. New simulations are conducted for conditions approximating the atmosphere during these Mars Global Surveyor (MGS) and Odyssey (ODY) aerobraking periods. Strong northern winter polar warming features are calculated near 120 km, yielding nightside mean temperatures 10 -15 K warmer than observed ODY values. No southern winter polar warming trend is simulated; however, nightside mean temperatures are 20-30 K warmer than observed by MGS. The stronger interhemispheric circulation during northern winter is clearly driven by stronger insolation and dust heating near perihelion, resulting in subsidence and warmer temperatures in the northern polar night.

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