Hubble Space Telescope Wide-Field Camera 3 (HST/WFC3) observations spanning 2015 to 2021 confirm a brightening of Uranus’ north polar hood feature with time. The vertical aerosol model of Irwin et al. (2023) (IRW23), consisting of a deep haze layer based at ~5 bar, a 1 - 2 bar haze layer, and an extended haze rising up from the 1 - 2 bar layer, was applied to retrievals on HST Space Telescope Imaging Spectrograph (HST/STIS) observations (Sromovsky et al., 2014, 2019} revealing a reduction in cloud-top CH4 by an average of 0.19 {plus minus} 0.03% between 40 - 80{degree sign}N between 2012 and 2015. A combination of latitudinal retrievals on the HST/WFC3 & HST/STIS datasets, again employing the IRW23 model, reveal a temporal thickening of the 1 - 2 bar haze layer to be the main cause of the polar hood brightening, finding an average increase of 1.09 {plus minus} 0.08 at 0.8 μm north of ~45{degree sign}N, concurrent with a decrease in the imaginary refractive index spectrum of the 1 - 2 bar haze layer north of ~40{degree sign}N and longwards of ~0.7 μm, and between 60{degree sign}N and 80{degree sign}N at ~0.5 μm. Small contributions to the brightening were found from a thickening of the deep aerosol layer, with an average increase in integrated opacity of 0.6 {plus minus} 0.1 north of 45{degree sign}N between 2012 and 2015, and from the aforementioned decrease in cloud-top CH4 abundance. Our results are consistent with the slowing of a meridional circulation, exhibiting strong subsidence at the poles.

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 Mars Environmental Dynamics Analyzer (MEDA) on board Perseverance includes first-of-their-kind sensors measuring the incident and reflected solar flux, the downwelling atmospheric IR flux, and the upwelling IR flux emitted by the surface. We use these measurements for the first 350 sols of the Mars 2020 mission (Ls ~ 6-174 deg; in Martian Year 36) to determine the surface radiative budget on Mars, and to calculate the broadband albedo (0.3-3 μm) as a function of the illumination and viewing geometry. Together with MEDA measurements of ground temperature, we calculate the thermal inertia for homogeneous terrains without the need for numerical models. We found that: (1) the observed downwelling atmospheric IR flux is significantly lower than model predictions. This is likely caused by the strong diurnal variation in aerosol opacity measured by MEDA, which is not accounted for by numerical models. (2) The albedo presents a marked non-Lambertian behavior, with lowest values near noon and highest values corresponding to low phase angles (i.e., Sun behind the observer). (3) Thermal inertia values ranged between 180 (sand dune) and 605 (bedrock-dominated material) SI units. (4) Averages across Perseverance’ traverse of albedo and thermal inertia (spatial resolution of ~3-4 m2) are in very good agreement with collocated retrievals of thermal inertia from THEMIS (spatial resolution of 100 m per pixel) and of bolometric albedo in the 0.25-2.9 μm range from (spatial resolution of ~300 km2). The results presented here are important to validate model predictions and provide ground-truth to orbital measurements.

Observations by several cameras on the Perseverance rover showed a 22° scattering halo around the Sun over several hours on the morning of sol 292 (15 December 2021). Such a halo has not previously been seen off Earth. The halo occurred during the aphelion cloud belt season and the cloudiest time yet observed from the Perseverance site. The halo required crystalline water-ice cloud particles in the form of hexagonal columns large enough for refraction to be significant, at least 11 µm in diameter and length. Near 44 km altitude, fall speeds would have been 0.3-1 m/s for the smallest allowed particles. Over the 3.3-hour duration of the halo, particles could have fallen 3-12 km, causing downward transport of water and dust. Halo-forming clouds are likely rare due to the high supersaturation of water that is required but may be more common in northern subtropical regions during mid-northern summer.

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.

Rovers and landers on Mars have experienced local, regional, and planetary-scale dust storms. However, in situ documentation of active lifting within storms has remained elusive. Over 5-11 January 2022 (LS 153°-156°), a dust storm passed over the Perseverance rover site. Peak visible optical depth was ~2, and visibility across the crater was briefly reduced. Pressure tides and temperatures responded to the storm. Winds up to 20 m s-1 rotated around the site before the wind sensor was damaged. The rover imaged 21 dust-lifting events—gusts and dust devils—in one 25-minute period, and at least three events mobilized sediment near the rover. Rover tracks and drill cuttings were extensively modified, and debris was moved onto the rover deck. Migration of small ripples was seen, but there was no large-scale change in undisturbed areas. This work presents an overview of observations and initial results from the study of the storm.