We analyze the onset and initial expansion of the 2018 Martian Global Dust Storm (GDS 2018) using ground‐based images in the visual range. This is the first case of a confirmed GDS initiating in the ...Northern Hemisphere. A dusty area extending about 1.4×105 km2 and centered at latitude +31.7°±1.8° and west longitude 18°±5°W in Acidalia Planitia was captured on 30 and 31 May 2018 (Ls = 184.9°). From 1 to 8 June, daily image series showed the storm expanding southward along the Acidalia corridor with velocities of 5 m/s and simultaneously progressing eastward and westward with horizontal velocities ranging from 5 to 40 m/s. By 8 June the dust reached latitude ‐55° and later penetrated in the South polar region, whereas in the North the dust progression stopped at latitude approximately +46°. We compare the onset and expansion stage of this GDS with the previous confirmed storms.
Key Points
May‐June 2018 ground‐based images show the onset and early evolution of a Martian Global Dust Storm (GDS)
The outbreak took place at location (North hemisphere) and time (solar longitude 184.9°) unusual for most GDSs
The expansion involved horizontal velocities in all directions in the range 5‐40 m/s
Thermal tides are atmospheric planetary‐scale waves with periods that are harmonics of the solar day. In the Martian atmosphere thermal tides are known to be especially significant compared to any ...other known planet. Based on the data set of pressure timeseries produced by the InSight lander, which is unprecedented in terms of accuracy and temporal coverage, we investigate thermal tides on Mars and we find harmonics even beyond the number 24, which exceeds significantly the number of harmonics previously reported by other works. We explore comparatively the characteristics and seasonal evolution of tidal harmonics and find that even and odd harmonics exhibit some clearly differentiated trends that evolve seasonally and respond to dust events. High‐order tidal harmonics with small amplitudes could transiently interfere constructively to produce meteorologically relevant patterns.
Plain Language Summary
In analogy to the string of a guitar, which can oscillate in integer harmonics, planetary atmospheres exhibit oscillations that are harmonics of the solar day (Harmonic 1 with a period of 24 hr; harmonic 2, 12 hr; harmonic 3, 8 hr; etc.). These oscillations are part of the so‐called “atmospheric thermal tides”, which retain a complex global structure. They are conceptually related to ocean gravitational tides, and they have been observed in atmospheres of the solar system whose main source of energy is the light from the sun: Earth, Mars, Venus, and Titan. On Mars, thermal tides are particularly strong and they play a key role in atmospheric dynamics, presenting interactions with meteorological phenomena such as dust storms. Most studies on thermal tides focus on low‐order harmonics (1, 2, 3, and sometimes 4). In this study, we use a particularly sensitive pressure sensor that landed on Mars with the InSight mission to explore the existence of high‐order harmonics, and we find clear harmonics with very small amplitudes even beyond harmonic 24, which corresponds to 24 oscillations per solar day. We compare the characteristics of those harmonics and analyze their seasonal behavior, and we find that even and odd harmonics exhibit clearly different behaviors.
Key Points
Analysis of an unprecedented data set of pressure obtained by InSight suggests that tidal harmonics beyond 24 are present on Mars
Even and odd modes exhibit distinct patterns with a seasonal dependency centered on equinoxes and solstices, and response to dust events
We study the 2018 Martian global dust storm (GDS 2018) over the Southern Polar Region using images obtained by the Visual Monitoring Camera (VMC) on board Mars Express (MEx) during June and July ...2018. Dust penetrated into the polar cap region but never covered the cap completely, and its spatial distribution was nonhomogeneous and rapidly changing. However, we detected long but narrow aerosol curved arcs with a length of ~2,000–3,000 km traversing part of the cap and crossing the terminator into the nightside. Tracking discrete dust clouds allowed measurements of their motions that were toward the terminator with velocities up to 100 m/s. The images of the dust projected into the Martian limb show maximum altitudes of ~70 km but with large spatial and temporal variations. We discuss these results in the context of the predictions of a numerical model for dust storm scenario.
Plain Language Summary
Dust storms of different scales (local, regional, etc.) are common on Mars. Some Martian years a regional storm activates secondary storms and dust encircles the planet, in a dust event usually called a global dust storm. The last global dust storm took place in 2018, and we are not currently able to predict when a new one will occur. Global dust storms affect the global dynamics of the Martian atmosphere, and the dynamics of the polar regions is a good proxy to the global situation. In this paper, we take advantage of the polar orbit of Mars Express to study the Southern Polar Region during 2018 global dust storm using the Visual Monitoring Camera onboard the spacecraft. We show how the dust penetrated into the polar cap, the apparition of aerosol arcs curved around the pole, and the presence of winds blowing up to 100 m/s, not following the usual patterns expected with no global dust storm.
Key Points
The 2018 global dust storm propagated unevenly over the South Polar Region, not covering it fully, and forming elongated narrow dust arcs
Overall, dust moved toward the terminator, reaching velocities up to 100 m/s in the morningside
During June–July 2018, the top altitude of dust showed both spatial and temporal variability, ranging from 10–70 km
This review describes the dynamic phenomena in the atmosphere of Mars that are visible in images taken in the visual range through cloud formation and dust lifting. We describe the properties of ...atmospheric features traced by aerosols covering a large range of spatial and temporal scales, including dynamical interpretations and modelling when available. We present the areographic distribution and the daily and seasonal cycles of those atmospheric phenomena. We rely primarily on images taken by cameras on Mars Express.
We present the first systematic study of clouds observed during twilight on Mars. We analyze images obtained by the Visual Monitoring Camera on Mars Express between 2007 and 2020. Using an automated ...retrieval algorithm, we found 407 cases of clouds observed at twilight, in which the geometry of the observations allows to derive the minimum altitude, revealing that many of these clouds are in the mesosphere (above 40 km and up to 90 km). The majority of these mesospheric clouds were detected in mid‐latitudes at local autumn and winter, a new trend only hinted at by previous studies. In particular, we find a massive concentration of clouds in the southern mid‐latitudes between Terra Cimmeria and Aonia, a region where high altitude events have been previously observed. We propose that there is an unknown mechanism in these regions that enhances the probability to host high altitude clouds around the southern winter solstice.
Plain Language Summary
During twilight, when the sun is below the horizon, its light can still reach clouds or mountains high above the surface, making them bright features on the dark background. This effect is sometimes seen on noctilucent clouds on Earth, and also in the mountains on the Moon. On Mars, it was first observed by ground based observers in the 1890s, and occasional observations have been later reported. We present here the first systematic study of such clouds on Mars as observed from space by the Visual Monitoring Camera (also known as the Mars webcam) onboard Mars Express. The study of clouds at twilight reveals information about their altitude, and the state of the atmosphere at this moment of the daily cycle. We analyze the occurrence of these clouds and find some new trends that previous observations had only hinted at.
Key Points
We present a new methodology to detect clouds at twilight and measure their altitude. We find 407 cases, some at altitudes over 80 km
High altitude clouds appear most often in mid‐latitudes during the local winter. This is a new trend when compared to previous studies
High altitude clouds concentrate aerographically in a southern belt that includes Terra Cimmeria, and in clusters on northern planitias
In a previous work (Hernández‐Bernal et al., 2021, https://doi.org/10.1029/2020je006517) we performed an observational analysis of the Arsia Mons Elongated Cloud (AMEC), which stands out due to its ...impressive size and shape, quick dynamics, and the fact that it happens during the Martian dusty season. Observations show that its morphology can be split in a head, on the western slope of the volcano of around 120 km in diameter; and a tail, that expands to the west reaching more than 1,000 km in length, making the AMEC the longest orographic cloud observed so far in the solar system. In this work we run the Laboratoire de Météorologie Dynamique Mesoscale Model to gain insight into the physics of the AMEC. We note that it is coincident in terms of local time and seasonality with the fastest winds on the summit of Arsia Mons. A downslope windstorm on the western slope is followed by a hydraulic‐like jump triggering a strong vertical updraft that propagates upwards in the atmosphere, causing a drop in temperatures of down to 30 K at 40–50 km in altitude, spatially and temporarily coincident with the observed head of the AMEC. However the model does not reproduce the microphysics of this cloud: the optical depth is too low and the expansion of the tail does not happen in the model. The observed diurnal cycle is correctly captured by the model for the head of the cloud. This work raises new questions that will guide future observations of the AMEC.
Plain Language Summary
This is the second paper of our research on the Arsia Mons Elongated Cloud (AMEC), which is a visually impressive cloud on Mars. It appears on the western flank of the Arsia Mons volcano during a specific season right at sunrise. For 3 hr it grows, developing a thin elongated tail that has been observed to be as long as 1,800 km. In our previous work we described available observations. In this work we run a high resolution atmospheric model that captures the effect of the Arsia Mons volcano on the atmosphere. This model shows that due to the presence of the volcano and its effect on the wind, air is forced upwards next to the volcano, leading to a drop in temperatures of 30°C, which causes the formation of the cloud under extreme conditions of humidity. This is a success of the model that provides a new understanding of this outstanding cloud, however, the accurate physics behind the extreme expansion of the AMEC are not fully understood yet. This work solves some questions and raises many new ones, which will be an aid in the planning of new observations.
Key Points
We performed mesoscale model dynamic simulations of the Arsia Mons Elongated Cloud observed in the Martian southern solstice
Topography‐induced circulation causes temperatures to drop by about 30 K at the observed origin location and local time of the cloud
The cloud tail is much more elongated in the observations than in the model, which challenges our understanding of winds and microphysics
We report a previously unnoticed annually repeating phenomenon consisting of the daily formation of an extremely elongated cloud extending as far as 1,800 km westward from Arsia Mons. It takes place ...in the solar longitude (Ls) range of ∼220°–320°, around the Southern solstice. We study this Arsia Mons Elongated Cloud (AMEC) using images from different orbiters, including ESA Mars Express, NASA MAVEN, Viking 2, MRO, and ISRO Mars Orbiter Mission (MOM). We study the AMEC in detail in Martian year (MY) 34 in terms of local time and Ls and find that it exhibits a very rapid daily cycle: the cloud growth starts before sunrise on the western slope of the volcano, followed by a westward expansion that lasts 2.5 h with a velocity of around 170 m/s in the mesosphere (∼45 km over the areoid). The cloud formation then ceases, detaches from its formation point, and continues moving westward until it evaporates before the afternoon, when most sun‐synchronous orbiters make observations. Moreover, we comparatively study observations from different years (i.e., MYs 29–34) in search of interannual variations and find that in MY33 the cloud exhibits lower activity, while in MY34 the beginning of its formation was delayed compared with other years, most likely due to the Global Dust Storm. This phenomenon takes place in a season known for the general lack of clouds on Mars. In this paper we focus on observations, and a theoretical interpretation will be the subject of a separate paper.
Plain Language Summary
In September and October 2018, the Visual Monitoring Camera onboard Mars Express observed a spectacular water ice cloud extending as far as 1,800 km westward from the Arsia Mons Volcano on Mars. This curious extremely elongated cloud caught the attention of the public (http://www.esa.int/Science_Exploration/Space_Science/Mars_Express/Mars_Express_keeps_an_eye_on_curious_cloud). We study this Arsia Mons Elongated Cloud (AMEC) with the aid of several instruments orbiting Mars. We find that the AMEC repeated regularly each morning for a number of months, and that it is an annually repeating phenomenon that takes place every Martian year around the Southern Hemisphere during spring and summer. The AMEC follows a rapid daily cycle: it starts to expand from Arsia Mons at dawn at an altitude of about ∼45 km, and for ∼2.5 h it expands westward as fast as 170 m/s (around 600 km/h). The cloud then detaches from Arsia Mons and evaporates before noon. In previous Martian years, few observations of this phenomenon are available because most cameras orbiting Mars are placed in orbits where they can only observe during the afternoon, whereas this cloud takes place in the early morning, when the observational coverage is much lower.
Key Points
We report a new phenomenon consisting of an extremely elongated water ice cloud (up to 1,800 km) extending westward from the Arsia Mons volcano
The cloud reaches the mesosphere (45 km), and expands at a velocity of around 170 m/s in Martian Year 34.
This cloud repeatedly forms in the early mornings, and repeats in a daily cycle between Ls 220° and 320° every Martian year
We present a study of textured local dust storms that develop at the northern polar cap boundary on Mars springtime. We have used images obtained with VMC and HRSC cameras onboard Mars Express and ...MARCI on MRO to analyze dust storms captured from March to July 2019 (Ls = 350° in MY 34–Ls = 54° in MY 35). The textured storms grow in the longitude sector 150°E-210°E centered at latitude ~60°N and exhibit spiral, filamentary and compact shapes that change and evolve rapidly in a daily basis. The storms translate by prevailing east and southeast winds with speeds 15–45 ms−1. In some areas of their interiors they show organized clusters of cells formed typically by 100 elements with sizes ~5–30 km with a length/width ratio ~ 1.2–3 in the wind direction. The cells have elongated downwind tails with lengths 4–8 times the cell size. The cells top altitudes are ~6–11 km above their surroundings. We propose that the spirals grow as baroclinic vortices within a vertically sheared eastward jet present at this epoch in Mars due to the intense meridional temperature gradient at the polar cap edge. We show using a simple one-dimensional model that the cells can be produced by shallow dry convection with dust acting as the heating source to generate the updrafts. These patterns resemble those seen in laboratory experiments and on clouds in Earth's atmosphere and can serve to comparatively elucidate and discern the different mechanisms at work in each case.
•Mars springtime dust storms at the edge of North Polar Cap show textured organized patterns at different scales.•Front-like and spiral cyclonic vortices originate from baroclinic instability in the intense high latitude zonal jet.•Mesoscale dry convection generates fields of cellular patterns ~10 km in size that reach ~5–10 km heights.
RESUMEN En la investigación de la percepción visual comúnmente se usan programas computarizados comerciales para la presentación de los estímulos, configurados por lo general para admitir una ...respuesta por cada estímulo presentado. Sin embargo, el estudio de la percepción multiestable, requiere la presentación de un estímulo que permanece invariable aunque la percepción de éste puede variar en dos o más configuraciones, lo que demanda que el programa admita respuestas para cada cambio en la percepción de un mismo estímulo. Se presenta PercepFiguras desarrollado con lenguaje de programación C++ que es un sistema de estimulación visual que permite al usuario: a) presentar imágenes y recibir una o varias respuestas a cada una, b) sincronizar las respuestas con un sistema de registro electroencefalográfico mediante el envío de pulsos TTL, c) generar un archivo conductual y d) generar un archivo con el total de respuestas y promedios de las latencias a cada tipo de figura. Se realizó un estudio piloto con una tarea de presentación continua de una figura ambigua alternando con dos variantes de menor ambigüedad, se obtuvo mayor frecuencia de cambios perceptuales y menor estabilidad perceptual para la figura ambigua respecto a las de menor ambigüedad, comprobándose la utilidad del programa.
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