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

## TL;DR

This study analyzes seasonal variations in near-surface relative humidity on Mars, identifying key regions with higher humidity linked to surface properties and nighttime condensation processes, using model and measurement data.

## Contribution

It provides new insights into how thermal inertia and surface dust properties influence Martian humidity and condensation phenomena across seasons.

## Key findings

- Identified three regions with consistently higher near-surface humidity.
- Demonstrated the role of thermal inertia in humidity levels.
- Observed nighttime water vapor condensation near the surface.

## 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.