We present water vapor vertical distributions on Mars retrieved from 3.5 years of solar occultation measurements by Nadir and Occultation for Mars Discovery onboard the ExoMars Trace Gas Orbiter, which reveal a strong contrast between aphelion and perihelion water climates. In equinox periods, most of water vapor is confined into the low‐middle latitudes. In aphelion periods, water vapor sublimated from the northern polar cap is confined into very low altitudes—water vapor mixing ratios observed at the 0–5 km lower boundary of measurement decrease by an order of magnitude at the approximate altitudes of 15 and 30 km for the latitudes higher than 50°N and 30–50°N, respectively. The vertical confinement of water vapor at northern middle latitudes around aphelion is more pronounced in the morning terminators than evening, perhaps controlled by the diurnal cycle of cloud formation. Water vapor is also observed over the low latitude regions in the aphelion southern hemisphere (0–30°S) mostly below 10–20 km, which suggests north‐south transport of water still occurs. In perihelion periods, water vapor sublimated from the southern polar cap directly reaches high altitudes (>80 km) over high southern latitudes, suggesting more effective transport by the meridional circulation without condensation. We show that heating during perihelion, sporadic global dust storms, and regional dust storms occurring annually around 330° of solar longitude (LS) are the main events to supply water vapor to the upper atmosphere above 70 km.
Abstract. We have determined the MLT distribution and K P dependence of the ion up¯ow and down¯ow of the thermal bulk oxygen ion population based on a data analysis using the EISCAT VHF radar CP-7 data obtained at Tromsù during the period between 1990 and 1996: (1) both ion up¯ow and down¯ow events can be observed at any local time (MLT), irrespective of dayside and nightside, and under any magnetic disturbance level, irrespective of quiet and disturbed levels; (2) these up¯ow and down¯ow events are more frequently observed in the nightside than in the dayside; (3) the up¯ow events are more frequently observed than the down¯ow events at any local time except midnight and at any K P level and the dierence of the occurrence frequencies between the up¯ow and down¯ow events is smaller around midnight; and (4) the occurrence frequencies of both the ion up¯ow and down¯ow events appear to increase with increasing K P level, while the occurrence frequency of the down¯ow appears to stop increasing at some K P level.
The Martian upper atmosphere is the reservoir region for an atmospheric escape to space. The escape rates of O 2 + , O + , and CO 2 + ions of Martian origin and their relative ratios have been measured by ion mass spectrometers aboard Mars Express (e.g.,
We report a new set of stellar occultation measurements for nightside temperature profiles made by the Mars Atmosphere and Volatile EvolutioN/Imaging Ultraviolet Spectrograph that provide evidence for a recurring layer of warm air between 70 and 90 km altitudes in the nightside mesosphere of Mars during Ls = 0–180° in Martian Year 33–34. The nightside profiles reveal a recurring peak of atmospheric temperature around 80 km over the equator to the middle latitudes in the northern hemisphere. The predictions of the Mars Climate Database have a warm layer with much smaller amplitudes. The observed peak amplitudes are larger than those predicted by the model by up to 90 K. Wavenumber‐3 structures are seen in the warm layer that are potentially signatures of thermal tides or stationary planetary waves, with amplitudes two times larger than predicted.
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