Global seasonal variations of the near-surface relative humidity levels on present-day Mars

Abstract

We investigate the global seasonal variations of near-surface relative humidity and relevant attributes, like temperature and water vapor volume mixing ratio on Mars using calculations from modelled and measurement data. We focus on 2 am local time snapshots to eliminate daily effects related to differences in insolation, and to be able to compare calculations based on modelling data from the LMDZ GCM with the observations of MGS TES. We study the seasonal effects by examining four specific dates in the Martian year, the northern spring equinox, summer solstice, autumn equinox and winter solstice. We identify three specific zones, where the near-surface relative humidity levels are systematically higher than in their vicinity regardless of season. We find that these areas coincide with low thermal inertia features, which control surface temperatures on the planet, and are most likely covered with unconsolidated fine dust with grain sizes less than $\sim$ 40$\mu$m. By comparing the data of relative humidity, temperature and water vapor volume mixing ratio at two different heights (near-surface, $\sim$ 23 m above the surface), we demonstrate that the thermal inertia could play an important role in determining near-surface humidity levels. We also notice that during the night the water vapor levels drop at $\sim$ 4 m above the surface. This, together with the temperature and thermal inertia values, shows that water vapor likely condenses in the near-surface atmosphere and on the ground during the night at the three aforementioned regions. This condensation may be in the form of brines, wettening of the fine grains or deliquescence. This study specifies areas of interest on the surface of present day Mars for the proposed condensation, which may be examined by in-situ measurements in the future.

25 pages, 20 figures, revision under review in Icarus

References in corpus (1)

• Possibility of microscopic liquid water formation at landing sites on Mars and their observational potential

Cited by in corpus (5)

• Annual and daily ideal periods for deliquescence at the landing site of InSight based on GCM model calculations
• Modelling Slope Microclimates in the Mars Planetary Climate Model
• A modern-day Mars climate in the Met Office Unified Model: dry simulations
• Deliquescence probability maps of Mars and key limiting factors using GCM model calculations
• Observations of Water Frost on Mars with THEMIS: Application to the Presence of Brines and the Stability of (Sub)Surface Water Ice