Diurnal Variations in the Aphelion Cloud Belt as Observed by the Emirates Exploration Imager (EXI)

Wolff, Michael; Fernando, Anton; Smith, M. D.; Forget, F.; Millour, Ehouarn; Atwood, Samuel A.; Jones, A. R.; Osterloo, M. M.; Shuping, R. Y.; Shamsi, Mariam Al; Jeppesen, C.; Fisher, Charles D.

doi:10.1029/2022gl100477

Cited by 14 publications

(18 citation statements)

References 20 publications

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“…For instance, the data set of τ ice−column for more than 3.5 MY derived in M. D. Smith (2009) from THEMIS instrument on-board Mars Odyssey does not appear to show a minimum in τ ice−column for Ls ∼ 70°. Similar conclusions are drawn from the τ ice−column values derived in Wolff et al (2022) and Atwood et al (2022) from observations by instruments on-board the Emirates Mars Mission. For the same period analyzed in this work, the column aerosol optical depth (dust plus water ice cloud) derived in M. D. Smith et al (2023) from MEDA-TIRS observations does not display a minimum around aphelion either.…”

Section: The Decrease In Cloud Activity Around Ls 70°tsupporting

confidence: 79%

Twilight Mesospheric Clouds in Jezero as Observed by MEDA Radiation and Dust Sensor (RDS)

et al. 2023

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The Mars Environmental Dynamics Analyzer instrument, on board NASA's Mars 2020 Perseverance rover, includes a number of sensors to characterize the Martian atmosphere. One of these 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°, Mars Year 36) 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°–150° (cloudy period), and dust from Ls 150°–262°. A total of 161 twilights were analyzed in the cloudy period using a radiative transfer code and we found: (a) signatures of clouds/hazes in the signals in 58% of the twilights; (b) most of the clouds had altitudes between 40 and 50 km, suggesting water ice composition, and had particle sizes between 0.6 and 2 µm; (c) the cloud activity at sunrise is slightly higher that at sunset, likely due to the differences in temperature; (d) the time period with more cloud detections and with the greatest cloud opacities is during Ls 120°–150°; and (e) a notable decrease in the cloud activity around 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.

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Section: The Decrease In Cloud Activity Around Ls 70°tsupporting

confidence: 79%

Twilight Mesospheric Clouds in Jezero as Observed by MEDA Radiation and Dust Sensor (RDS)

et al. 2023

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“…(2021) and Wolff et al. (2022)) and Emirates Mars InfraRed Spectrometer (EMIRS, Atwood et al. (2022) and Smith et al.…”

Section: Resultsmentioning

confidence: 99%

Seasonal, Latitudinal, and Longitudinal Trends in Nighttime Ozone Vertical Structure on Mars From MAVEN/IUVS Stellar Occultations

et al. 2023

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Stellar occultation measurements conducted by the Mars Atmosphere and Volatile and EvolutioN/Imaging UltraViolet Spectrograph instrument were able to make vertically resolved measurements of ozone density in the middle atmosphere of Mars that offered good coverage with respect to latitude, longitude, and local time. These measurements were used to identify systematic variations in the vertical structure of ozone with longitude that could be distinguished from general trends in the evolution of ozone with respect to season and latitude. A total of 583 individual nightside occultations between Martian years 32 and 36 were analyzed, of which 224 were confirmed to have ozone, all found between Ls = 15°–165°. Close to aphelion (Ls = 60°–90°), peak ozone densities between 30 and 40 km altitude were observed to be within error of model predictions at all measured latitudes, but diverged from model predictions before and after this time. At low latitudes, seasonal changes were seen to have the greatest effect on the observed vertical structure of ozone, with detached ozone layer densities at altitudes above 30 km usually varying within approximately a factor of two along a given latitudinal band at a given time of year. Nonetheless, evidence of a persistent regional enhancement of ozone abundance was observed over equatorial latitudes during the aphelion season, spanning a longitude range of approximately 50°–130°E longitude. Planetary waves were clearly observed at higher Southern latitudes during Southern winter, often resulting in order of magnitude variations in ozone density with longitude.

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“…For this purpose, we use retrievals from MARCI on board MRO and from the Emirates Exploration Imager (EXI) on board the EMM Hope probe. The retrieval pipelines for these data sets are described in Wolff et al (2019Wolff et al ( , 2022, respectively.…”

Section: Comparison With Marci/emirates Exploration Imager Water-ice ...mentioning

confidence: 99%

Five Mars Years of Cloud Observations at Gale Crater: Opacities, Variability, and Ice Crystal Habits

Hayes,

Kloos,

Innanen

et al. 2024

Planet. Sci. J.

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We update the record of cloud opacity observations conducted by the Mars Science Laboratory (MSL) Curiosity rover to cover the first five Mars Years (MYs) of the mission (L s = 160° of MY 31 to L s = 160° of MY 36). Over the three MY period that we add to the previously analyzed two MY record, we achieve good diurnal coverage between 07:00 and 17:00 with nearly 1200 new observations. We derive a new scattering phase function for the clouds of the Aphelion Cloud Belt (ACB) using results from the Zenith and Suprahorizon movie data sets. Our phase function is generally smooth and featureless, which is consistent with the overall lack of atmospheric optical phenomena on Mars aside from a single instance of an observed halo. Applying our new phase function to the data, we find that there is very minimal variability in the ACB's opacity, either diurnally, intraseasonally, or interannually, noting that our observations are only sensitive to ice clouds and cannot detect any ice hazes that may be present over Gale. This contrasts with previous results, which observed a 57% difference in the opacity of morning and afternoon clouds in MY 33. The MY 33 results now appear to be an outlier, not replicated at any point during the MSL mission. We conclude that the higher morning opacities in MY 33 were a consequence of an incomplete understanding of the nature of the scattering phase function close to the Sun.

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Diurnal Variations in the Aphelion Cloud Belt as Observed by the Emirates Exploration Imager (EXI)

Cited by 14 publications

References 20 publications

Twilight Mesospheric Clouds in Jezero as Observed by MEDA Radiation and Dust Sensor (RDS)

Twilight Mesospheric Clouds in Jezero as Observed by MEDA Radiation and Dust Sensor (RDS)

Seasonal, Latitudinal, and Longitudinal Trends in Nighttime Ozone Vertical Structure on Mars From MAVEN/IUVS Stellar Occultations

Five Mars Years of Cloud Observations at Gale Crater: Opacities, Variability, and Ice Crystal Habits

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