The Mars Environmental Dynamics Analyzer (MEDA) instrument, on board the NASA’s Mars 2020 Perseverance rover, includes a number of sensors to characterize the Martian atmosphere. One of this sensors is the Radiation and Dust Sensor (RDS) that measures the solar irradiance at different wavelengths and geometries. We analyzed the RDS observations made during twilight for the period between sol 71 and 492 of the mission (Ls 39◦-262◦) to characterize the clouds over the Perseverance rover site. Using the ratio between the irradiance at zenith at 450 and 750 nm, we inferred that the main constituent of the detected high-altitude aerosol layers was ice from Ls= 39◦ to 150◦ (cloudy period), an dust from Ls 150◦-262◦. A total of 161 twilights were analyzed in the cloudy period using a radiative transfer code and we found: i) signatures of clouds/hazes in the signals in the 58 % of the twilights; ii) most of the clouds had altitudes between 40-50 km, suggesting water ice composition, and had particle sizes between 0.6 and 2 μm; iii) the cloud activity at sunrise is slightly higher that at sunset, likely due to the differences in temperature; iv) the time period with more cloud detections and with the greatest cloud opacities is during Ls 120◦-150◦; and v) a notable decrease in the cloud activity around the aphelion, along with lower cloud altitudes and opacities. This decrease in cloud activity indicates lower concentrations of water vapor or cloud condensation nuclei (dust) around this period in the Martian mesosphere.

The Finnish Meteorological Institute (FMI) provides a relative humidity measurement sensor (HS) for NASA’s Mars 2020 rover. The sensor is a part of the Mars Environmental Dynamic Analyzer (MEDA), a suite of environmental sensors provided by Spain’s Centro de Astrobiología. The main scientific goal of the humidity sensor is to measure the relative humidity of the Martian atmosphere near the surface and to complement previous Mars mission atmospheric measurements for a better understanding of Martian atmospheric conditions and the hydrological cycle. Relative humidity has been measured from the surface of Mars previously by Phoenix and Curiosity. Compared to the relative humidity sensor on board Curiosity, the MEDA HS is based on a new version of the polymeric capacitive humidity sensor heads developed by Vaisala. Calibration of humidity devices for Mars conditions is challenging and new methods have been developed for MEDA HS. Calibration and test campaigns have been performed at the FMI, at University of Michigan and the German Aerospace Center (DLR) in Berlin to achieve the best possible calibration. The accuracy of HS and uncertainty of the calibration has been also analysed in detail with VTT Technical Research Centre of Finland. Assessment of sensor performance after landing on Mars confirms that the calibration has been successful, and the HS is delivering high quality data for the science community.

We characterize the vortex and dust devil activity at Jezero from pressure and winds obtained with the MEDA instrument on Mars 2020 over 415 sols (Ls=6-213º). Vortices are abundant (4.9 vortices per sol with pressure drops >0.5 Pa when correcting from gaps in coverage) and peak at noon. At least one in every 5 vortices carries dust from RDS-MEDA data, and intense vortices are more likely to carry dust. Seasonal variability was small but dust devils were abundant during a dust storm (Ls=152-156º). Vortices are more frequent and intense over terrains with lower thermal inertia favoring a higher daytime surface-to-air temperature gradient. We fit measurements of wind and pressure during dust devil encounters to models of vortices, and investigate their physical characteristics. Diameters range from 5 to 135 m with a mean of 20 m. Three 100-m size events passed within 30 m of the rover. From the close encounters we estimate a dust devil activity of 2.0-3.0 dust devils km$^{-2}$ sol$^{-1}$. A comparison of MEDA observations with a Large Eddy Simulation of Jezero at Ls=45º produces a similar result. We estimate that large dust devils with diameters $>100$ m have a density of 0.1 dust devils km-2sol-1, implying that dust lifting is dominated by the largest vortices in the region. At least one vortex had a central pressure drop of 9.0 Pa and internal winds of 25 ms-1. The MEDA wind sensors were partially damaged during two dust devil encounters, and we detail these events.

Mars 2020 Mars Environmental Dynamics Analyzer (MEDA) instrument data acquired during half of a martian year (Ls 13º-180º), and modeling efforts with the Mars Regional Atmospheric Modeling System (MRAMS) and Mars Climate Database (MCD) allow us to study the seasonal evolution and variability of nocturnal atmospheric turbulence at Jezero crater. Nighttime conditions in Mars’s Planetary Boundary Layer are highly stable because of strong radiative cooling that efficiently inhibits convection. However, MEDA nighttime observations of simultaneous, rapid fluctuations in horizontal wind speed and air temperatures suggest the development of nighttime turbulence in Jezero crater. Mesoscale modeling with MRAMS also shows a similar pattern and enables us to investigate the origins of this turbulence and the mechanisms at play. As opposed to Gale crater, less evidence of turbulence from breaking mountain/gravity wave activity was found in Jezero during the period studied with MRAMS. On the contrary, the model suggests that nighttime turbulence at Jezero crater is explained by mechanical turbulence produced by increasingly strong wind shear related to the development of a bore-like disturbance at the nocturnal inversion interface. The enhanced wind shear leads to a reduction in the Ri and an onset of mechanical turbulence. Once the critical Richardson Number is reached (Ri ∼< 0.25), shear instabilities can mix warmer air aloft down to the surface.

We utilise SuperCam’s Mars microphone to provide information on wind speed and turbulence at high frequencies on Mars. This is achieved through a correlation analysis between the microphone and meteorological data which shows that the microphone signal power has a consistent relationship with wind speed and air temperature. A calibration function is constructed using Gaussian process regression (a machine learning technique) to use the microphone signal and air temperature to produce an estimate of the wind speed. This wind speed estimate is at a high rate for in situ measurements on Mars, with a sample every 0.01 s. As a result, we determine the fast fluctuations of the wind at Jezero crater which highlights the nature of wind gusts over the martian day. We evaluate the normalised wind standard deviation (gustiness) on the estimated wind speed to analyse the turbulent behaviour. Correlations are shown between the evaluated gustiness statistic and pressure drop rates, temperature, energy fluxes and optical opacity to characterise the behaviour of high frequency turbulent intensity at Jezero crater. This has implications for future atmospheric models on Mars, taking into account turbulence at the finest scales.