Water Vapor Vertical Distribution on Mars After Six Years of TGO/NOMAD Solar Occultations: 1. Global Climatology

Abstract We present vertical profiles of water vapor obtained during six continuous years of solar occultation observations in the infrared by the Nadir and Occultation for MArs Discovery (NOMAD) instrument on board Trace Gas Orbiter. The retrievals have been performed with an inversion code previously applied to smaller samples of this data set, but improved to combine pairs of diffraction orders allowing for sounding water vapor up to about 120 km altitude. As a first part of a set of two papers, this study presents the most extended data set of water vapor measurements from the NOMAD instrument to date, covering three full and consecutive Martian Years. Building upon previous researches primarily focused on the perihelion season, this analysis now includes the aphelion season, offering a comprehensive view of Mars' water cycle. Observations from April 2018 to December 2023 were analyzed, covering perihelion of Mars Year (MY) 34 to aphelion of MY 37 and presenting water vapor vertical profiles from approximately 5–10 km to 110–120 km in altitude. This study reveals consistent seasonal and latitudinal water vapor patterns, showing water vapor systematically more vertically extended during the perihelion season than during the aphelion. We present an extensive analysis of the water vapor local time variability, confirming overall larger abundances during the evenings than during mornings. These data provide new insights into the vertical distribution of atmospheric water vapor on Mars, aiding future comparisons and global climate model validation.