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Abstract This study involving both observations and simulations furthers our understanding of water transport in the Martian northern polar region, a critical component of the global water cycle, and explores strengths and weaknesses in simulations of the polar atmosphere. Observations of the northern polar winter by the Mars Climate Sounder (MCS) onboard the Mars Reconnaissance Orbiter show extensive water ice clouds over the polar ice cap throughout the 300–3 Pa (∼10–50 km) vertical column within the vortex during the entire winter season. The observations also indicate that the vortex evolves throughout its depth on a broad range of timescales, from sub‐diurnal to seasonal. Time sequences of these data together with results from a Mars global circulation model and Ensemble Mars Atmosphere Reanalysis System reanalysis (EMARS) are used to study the evolution of the winter polar atmosphere and to examine dynamic mechanisms for transporting water across the vortex boundary. Model simulations and reanalysis show a similar temperature structure to observations, although they struggle to reproduce some of the detailed features such as the extent of polar warming above the vortex and the magnitude of the temperature minima inside the vortex. The free run simulation also fails to capture the vertically distributed water ice cloud due to a general absence of transport across the vortex boundary. EMARS results, with assimilated MCS temperatures, show a greater amount of water entering the vortex at pressures below 200 Pa, leading to a more vertically extended cloud within the vortex and improving agreement with observations.
Gillespie et al. (Wed,) studied this question.