NASA’s Mars 2020 (M2020) rover mission includes a suite of sensors to monitor current environmental conditions near the surface of Mars and to constrain bulk aerosol properties from changes in atmospheric radiation at the surface. The Mars Environmental Dynamics Analyzer (MEDA) consists of a set of meteorological sensors including wind sensor, a barometer, a relative humidity sensor, a set of 5 thermocouples to measure atmospheric temperature at ∼1.5 m and ∼0.5 m above the surface, a set of thermopiles to characterize the thermal IR brightness temperatures of the surface and the lower atmosphere. MEDA adds a radiation and dust sensor to monitor the optical atmospheric properties that can be used to infer bulk aerosol physical properties such as particle size distribution, non-sphericity, and concentration. The MEDA package and its scientific purpose are described in this document as well as how it responded to the calibration tests and how it helps prepare for the human exploration of Mars. A comparison is also presented to previous environmental monitoring payloads landed on Mars on the Viking, Pathfinder, Phoenix, MSL, and InSight spacecraft.

In this paper we show that Sun-viewing images obtained by the Mars Science Laboratory (MSL) Navigation Cameras (Navcam) can be used for retrieving the dust optical depth and constrain the aerosol physical properties at Gale Crater by evaluating the sky brightness as a function of the scattering angle. We have used 65 Sun-pointing images covering a period of almost three Martian years, from MSL mission sol 21 to sol 1646 (MY 31 to 33). Radiometric calibration and geometric reduction were performed on MSL Navcam raw image data records to provide the observed sky radiance as a function of the scattering angle for the near-Sun region (scattering angle from 4º to 30º). These curves were fitted with a multiple scattering radiative transfer model for a plane-parallel Martian atmosphere model using the discrete ordinates method. Modelled sky brightness curves were generated as a function of two parameters: the aerosol particle size distribution effective radius and the dust column optical depth at the surface. A retrieval scheme was implemented for deriving the parameters that generated the best fitting curve under a least-square error criterion. The obtained results present a good agreement with previous work, showing the seasonal dependence of both dust column optical depth and the effective particle radius.

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We study a seasonally recurrent cyclone and related cloud phenomena observed on Mars at L s 120°, latitude~60°N, and longitude 90°W from images obtained with cameras in different spacecraft between 1995 and 2018. A remarkable double cyclone formed in 2012 and we present a detailed study of its dynamics using images from Mars Express and Mars Reconnaissance Orbiter obtained between 6 June and 9 July. A double cyclone was also observed in 2006 and 2008. In other Martian years the primary cyclone showed an annular cloud morphology with a large water ice cloud observed eastward of it. The cyclones have a size of~600-800 km with a cloud-free core of a radius~100-300 km. Tangential velocities measured from cloud tracking in 2012 images are~5-20 m/s À1 at 10-km altitude and double cyclone moved eastward with a velocity of 4 m/s À1 during its lifetime of one month. The vortices grow in the morning hours, but with the increasing insolation as the sol progresses, a part of the clouds evaporate, the winds weaken, and the vortices lose coherence. This phenomenon forms under high-temperature gradients in a region with a large north-south topographic slope and has been recurrent each Martian year between 1995 and 2018. We argue the interest of studying its changing properties each Martian year in order to explore their possible relationship to the state of the Martian atmosphere at L s~1 20°. Plain Language SummaryWe study a remarkable annular vortex observed some years to be formed by two coupled cyclones that grow every Martian northern summer at the same longitude and latitude of the planet. Each vortex has a size of 700 km and its center is a cloud-free area with a radius of about 200 km. The vortex is formed by water ice clouds at about 10-km altitude where the winds blow with speeds of 5 to 20 m/s. The clouds grow in the morning hours and sublimate as the vortex weakens with increasing insolation. Dynamical models show that the vortex forms in a region with a large north-south terrain slope that combines with north-south temperature gradient. The study mainly uses images taken in 2012, but a survey shows that the vortex recurrently forms every Martian year between 1995 and 2018. This vortex system can be used as a proxy, studying its variability, to characterize the state of the atmosphere at the time of its formation.

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