Detection and characterization of clouds at twilight by MEDA-RDS for the first 365 sols

<p>Clouds on Mars are primary elements for understanding the past and present climate of the planet. Cloud particles can affect the energy balance of the planet, and so the atmospheric dynamic, as well as influence the vertical distribution of dust particles through dust scavenging. The dust scavenging by clouds has critical consequences in the water cycle of the planet; e.g. regions in the atmosphere with insufficient quantity of dust particles (or condensation nuclei) can inhibit the formation of H₂O clouds and thus lead to the presence of water vapor in excess of saturation [1]. The study of these interactions requires observations whose analysis allows us to infer simultaneously the properties of both the clouds and dust. To address these observations, the Radiation and Dust Sensor (RDS) [2] is part of the Mars Environmental Dynamics Analyzer (MEDA) [3] payload onboard of the Mars 2020 rover Perseverance. RDS instrument compromises two sets of 8 photodiodes (RDS-DP) and a camera (RDS-SkyCam). One set of photodiodes is pointed upward (TOP sensors), with each one covering a different wavelength range between 190-1200 nm. The other set is pointed sideways (LAT sensors), 20 degrees above the horizon, and they are spaced 45 degrees apart in azimuth to sample all directions at a single wavelength.</p><p>In this work we will present the radiative transfer analysis of the RDS TOP sensors observations at twilight for the first 365 sols. The twilight period was selected to: i) better constrain the vertical distribution of dust particles for the cloud-free days; ii) detect aerosol layers with very low opacities (lower than 0.1); iii) estimate the cloud altitude [4]. We will discuss the implication of our observations and analyses for Mars aerosol structure and timescales. For example, we find a period of a few days with a notable increase in the presence of clouds during twilight, and for which we derived cloud altitudes higher than 40 km and settling timescales of a few hours (involving a rapid vertical transport of dust particles).</p><p><strong>References:</strong></p><p>[1] Maltagliati, Luca, et al. "Evidence of water vapor in excess of saturation in the atmosphere of Mars." science 333.6051 (2011): 1868-1871.</p><p>[2] Apestigue, Victor, et al. "Radiation and Dust Sensor for Mars Environmental Dynamic Analyzer Onboard M2020 Rover." Sensors 22.8 (2022): 2907.</p><p>[3] Rodriguez-Manfredi, Jos&#233; Antonio, et al. "The Mars Environmental Dynamics Analyzer, MEDA. A suite of environmental sensors for the Mars 2020 mission." Space science reviews 217.3 (2021): 1-86.</p><p>[4] Toledo, D., et al. "Measurement of aerosol optical depth and sub-visual cloud detection using the optical depth sensor (ODS)." Atmospheric Measurement Techniques 9.2 (2016): 455-467.</p>