Martian Global Dust Storm Research Articles

Effects of the 2007 Martian Global Dust Storm on Boundary Positions in the Induced Magnetosphere

Mars's magnetosphere is a sensitive system, varying due to external and internal factors, such as solar wind conditions and crustal magnetic fields. A signature of this influence can be seen in the position of two boundaries; the bow shock and the induced magnetospheric boundary (IMB). The bow shock moves closer to Mars during times of high solar activity, and both the bow shock and IMB bulge away from Mars over crustal magnetic fields in the southern hemisphere. This study investigates whether large-scale atmospheric events at Mars have any signature in these two magnetic boundaries, by investigating the 2007 storm. The 2007 global storm lasted for several months and increased atmospheric temperatures and densities of both water vapor and carbon dioxide in the atmosphere, leading to an increase in atmospheric escape. Using Mars Express, we identified boundary locations before, during, and after the event, and compared these to modeled boundary locations and areographical locations on Mars. We find that, while it is unclear whether the bow shock position is impacted by the storm, the IMB location does change significantly, despite the orbital bias introduced by Mars Express. The terminator distance for the IMB peaks at longitudes 0°–40° and 310°–360°, leaving a depression around 180° longitude, where the boundary usually extends to higher altitudes due to the crustal magnetic fields. We suggest this may be due to the confinement of ionospheric plasma over crustal fields preventing mixing with the dust, creating a dip in ionospheric pressure here.

Enhanced Hydrogen Escape on Mars during the 2018 Global Dust Storm: Impact of Horizontal Wind Field

Mars has undergone a substantial water loss, transforming from the early warm and wet state to the current cold and arid state. Observations and modeling efforts suggest that hydrogen escape is a metric of water loss on Mars. As a consequence of the vertical transport of water vapor by deep convection, hydrogen escape is significantly enhanced during Martian global dust storms. Motivated by the established scenario that the horizontal wind field could substantially enhance thermal escape, here we evaluate, for the first time, how the escape of H and H2 on Mars during a typical global dust storm is modified by the enhanced horizontal wind field during the period. By combining kinetic model calculations and the Mars Climate Database outputs, we reach the conclusion that a nonnegligible enhancement of the H and H2 escape flux could be driven by horizontal winds near the exobase, reaching 15% for H and 60% for H2 at dawn near the equator during the dust storm. Although the enhancement of the global hydrogen escape rate by the horizontal wind is insignificant, it plays a crucial role in the redistribution of H and H2 escape flux. The results presented here make useful contributions to a thorough understanding of enhanced hydrogen escape during the global dust storms.

Effect of the 2018 Martian Global Dust Storm on the Main Species in the Upper Ionosphere: Observations and Simulations

AbstractMartian global dust storms have significant influences on its atmosphere and ionosphere. In this research, the behavior of , , and O+ density profiles during the 2018 global dust storm is studied based on the observations of Neutral Gas and Ion Mass Spectrometer (NGIMS) onboard Mars Atmosphere and Volatile Evolution. The observations show increased density, decreased O+ density, and relatively stable density at 170–500 km during the dust storm. Using a photochemical model, we reproduced the behavior of , , and O+ density at 170–200 km during the dust storm based on the behaviors of NGIMS observed neutral density profiles. The behaviors of those neutral and ion density profiles should be the combined effects of the variations of latitude, longitude, season, local time, Solar Zenith Angle (SZA), and the activity of the global dust storm. Two different methods, one based on the Mars Climate Database and another based on a parametric model, are used to remove the effects of latitude, longitude, season, local time, and SZA variations on the neutral atmosphere and ionosphere. Both methods indicate that density at 170–200 km should increase, rather than stay unchanged under the 2018 global dust storm‐specified effect.

Comparison of the Effects of Regional and Global Dust Storms on the Composition of the Ionized Species of the Martian Upper Atmosphere Using MAVEN

The densities of three ion species in the Martian upper atmosphere were compared during the MY33 and MY34 Martian regional and global dust storms (RDS 2016 and GDS 2018, respectively) using data from the neutral gas and ion mass spectrometer of the Mars atmosphere and volatile evolution mission. The trends of the ion species and their relative abundances in altitudes compared to some neutral species were examined from 10 September–4 October 2016 and 27 May–18 June 2018, at altitudes of 160–240 km. Both RDS 2016 and GDS 2018 caused variations in the ion species abundance of the upper atmosphere at their onsets in 18–21 September 2016 and 5–8 June 2018 respectively. The densities of O2+, CO2+, and O+ increased during RDS 2016. Meanwhile, O2+ and O+ densities decreased and CO2+ density increased during GDS 2018. Ion species’ relative abundances indicate that during RDS 2016, the increase in O2+ density may be caused by the increase of CO2+ or O+ densities rather than the increase of O or CO2 densities. Meanwhile, the decrease in O2+ density during GDS 2018 may be caused by the decrease of O or O+ densities rather than the decrease in CO2+ or CO2 densities.

Effects of the June 2018 Global Dust Storm on the Atmospheric Composition of the Martian Upper Atmosphere as Observed by MAVEN

AbstractThe densities of six neutral species in the Martian upper atmosphere were analyzed before and during the 2018 Martian global dust storm (GDS 2018) using data from the Neutral Gas and Ion Mass Spectrometer of the Mars Atmosphere and Volatile EvolutioN mission. The trends of the dayside densities of the neutral species and their relative abundances were investigated between May 27 and June 17, 2018, at altitudes of 160–210 km. GDS 2018 caused variations in the neutral species abundance of the upper atmosphere at its onset in June 5–8, 2018, with the CO2, Ar, CO, O, N2, and He densities decreasing relative to prestorm conditions. The densities of the examined neutral species increased during the storm, except those of O and He. During the storm, the relative abundances of CO2 and Ar increased, while those of CO and O decreased and those of N2 and He remained the same. The variation in the neutral species with altitude was consistent with the regular atmospheric conditions and unrelated to the GDS 2018 drivers. The higher thermospheric temperature observed during the storm onset suggested that changes in the composition of the neutral species were caused by storm‐induced thermal enhancements.

Enhanced Super‐Rotation Before and During the 2018 Martian Global Dust Storm

AbstractSuper‐rotation affects—and is affected by—the distribution of dust in the martian atmosphere. We modeled this interaction during the 2018 global dust storm (GDS) of Mars Year 34 using data assimilation. Super‐rotation increased by a factor of two at the peak of the GDS, as compared to the same period in the previous year which did not feature a GDS. A strong westerly jet formed in the tropical lower atmosphere, with strong easterlies above 60 km, as a result of momentum transport by thermal tides. Enhanced super‐rotation is shown to have commenced 40 sols before the onset of the GDS, due to dust lifting in the southern mid‐latitudes and tropics. The uniform distribution of dust in the tropics resulted in a symmetric Hadley cell with a tropical upwelling branch that could efficiently transport dust vertically; this may have significantly contributed to the rapid expansion of the storm.

Dust particle size, shape and optical depth during the 2018/MY34 martian global dust storm retrieved by MSL Curiosity rover Navigation Cameras

Martian planet-encircling dust storms or global dust storms (GDS), resulting from the combined influence of local and regional storms, are uncommon aperiodic phenomena: with an average frequency of approximately one every 3–4 MY, they produce a substantial rise in the atmospheric dust loading that lasts from weeks to months and have a significant impact on the atmospheric properties, energy budget, and global circulation. During the 2018/MY34 global dust storm, initiated at LS = 185° (30–31 May 2018), an intensive atmospheric science campaign was carried out by the Mars Science Laboratory (MSL) rover to monitor the environmental parameters at Gale Crater. We contribute to previous studies with independent retrievals to constrain the dust opacity and characterise the aerosol particle properties, including: size, shape and single scattering phase function. An iterative radiative transfer retrieval procedure was implemented to determine the aerosol parameters that best fit the angular distribution of sky radiance at forward and backward scattering regions observed by MSL Navigation Cameras (Navcams) during the 2018/MY34 GDS. The MOPSMAP aerosol database and Double Henyey-Greenstein (DHG) analytical single scattering phase functions were used to model the Martian dust aerosol. Outcomes of this study show a steep rise in dust opacity from pre-storm levels of 1.2 up to τ > 9, correlated to particle size variations from 1 to 4 μm. DHG phase functions are characterised with an average asymmetry parameter of g = 0.60 ± 0.11 during the storm, diverging from values of around 0.71 ± 0.06 for the same period in previous MY. Best fitting simulations to backscatter observations for high-opacity periods were generated by a mixture of spheroids following a log-normal distribution of aspect ratios centred on 2.8 ± 0.9, in contrast to values of 1.8 in post-storm sols, thus pointing to more irregular particle shapes at the peak of the dust storm.

Rapid Expansion and Evolution of a Regional Dust Storm in the Acidalia Corridor During the Initial Growth Phase of the Martian Global Dust Storm of 2018

AbstractA vigorous regional dust storm substantially altered both the global atmospheric thermal structure and the magnitude and spatial distribution of dust loading within the Mars atmosphere between 1 and 9 June 2018. We examine the development and decay of this storm in latitude, longitude, altitude, and time, employing observations by the Mars Climate Sounder on board the Mars Reconnaissance Orbiter. Dust layer top altitudes rose from seasonal‐normal values of ~40 to ~70 km. Dust lofting to high altitudes was localized between 0° and ~60°W longitude, and between 60°N and 60°S latitude. Intensification of paired meridional overturning circulation cells within the study area is confirmed by strong nighttime dynamical heating in higher latitudes of both hemispheres. By the end of this episode, significant dust loading was present at altitudes greater than 50 km above all longitudes on Mars, and other dust lifting centers had been activated.

Effect of the 2018 Martian Global Dust Storm on the CO2 Density in the Lower Nightside Thermosphere Observed From MAVEN/IUVS Lyman‐Alpha Absorption

AbstractThe MAVEN/Imaging Ultraviolet Spectrograph (IUVS) instrument measures Lyman‐α emissions from interplanetary and Martian hydrogen at the limb and through the extended corona of Mars. In June 2018, a global dust storm (GDS) surrounded Mars for a few months, heating the lower atmosphere and leading to an expansion of the Martian atmosphere. Nightside IUVS observations before and throughout this GDS showed the altitude of CO2 absorption of Lyman‐α photons in the thermosphere to increase by 4.5±1.0 km on 8 June 2018. This shift is attributed to an increase of the CO2 density by a factor 1.9±0.2 at 110 km due to the heating of the lower atmosphere. These nightside observations, not previously used to study dust storms, in an altitude range not sampled by other instruments, are consistent with dayside MAVEN observations and allow for more comprehensive determination of the global changes produced by the GDS on the Martian thermosphere.

The 2018 Martian Global Dust Storm Over the South Polar Region Studied With MEx/VMC

AbstractWe 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.

The Onset and Growth of the 2018 Martian Global Dust Storm

AbstractWe 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.

Replication of the historic record of martian global dust storm occurrence in an atmospheric general circulation model

The MarsWRF Mars general circulation model (GCM) with radiatively active dust and orbit-spin coupling reproduces the observational record of Mars years with and without global dust storms (GDS) with a success rate of 77%. Atmospheric conditions diagnostic to the occurrence or non-occurrence of GDS were successfully simulated in 17 of the 22 Mars years of the available historic record. Statistical significance at the 99% level is obtained in a comparison of success rates between an occurrence model with stochastic forcing and those of the GCM forced by orbit-spin coupling. These results provide proof of concept for the orbit-spin coupling hypothesis as a factor contributing to the observed interannual variability of the weather and climate of Mars.

Enhanced carbon dioxide causing the dust storm‐related increase in high‐altitude photoelectron fluxes at Mars

AbstractSeveral studies have shown that the Martian global dust storm occurred in 2001 had a long‐term influence on high‐altitude photoelectron fluxes by analyzing the observations of the magnetometer/electron reflectometer instrument on board Mars Global Surveyor, most likely because the dust altered the neutral atmosphere in a significant way in terms of photoelectron production and loss. This study investigates candidate atmospheres that can replicate observations, especially focusing on the role that thermospheric composition and density play in high‐altitude photoelectrons. Through the simulations of our SuperThermal Electron Transport model, it is found that high‐altitude photoelectron fluxes at more field‐aligned pitch angles are very sensitive to composition change and surprisingly independent of density. For more perpendicular pitch angles, both composition and density take part in determining photoelectron fluxes. Also, a CO2 atmosphere is the only one of the tested atmospheres that can qualitatively match the observation, which suggests that the global dust storm might have altered the photoelectron fluxes via causing CO2 to be the dominant species at a much larger altitude range than usual.

The effects and characteristics of atmospheric dust during martian global dust storm 2001A

We present retrieved trends in dust optical depth, dust effective radius and surface temperature from our analysis of Mars Global Surveyor Thermal Emission Spectrometer daytime data from global dust storm 2001A, and describe their significance for the martian dust cycle. The dust optical depth becomes correlated with surface pressure during southern spring and summer in years both with and without a global dust storm, indicating that global dust mixing processes are important at those seasons. The correlation is low at other times of the year. We found that the observed decay of optical depths at the later stages of the dust storm match, to first-order, theoretical values of clearing from Stokes–Cunningham fallout of the dust. Zonally averaged effective radius is constant within standard deviation of results (between 1.2 and 2.0 μm, with a global mean for all seasons of 1.7 μm), at all latitudes and seasons except at southern latitudes of 35° and higher around equinoxes in both martian years, where it is larger than average (2–3 μm). The emergence and disappearance of these larger particles correlates with observations of polar cap edge storms at those latitudes. Northern latitude observations under similar conditions did not yield a similar trend of larger average effective radii during the equinoxes. We also report on a linear correlation between daytime surface temperature drop and rise in optical depth during the global dust storm. Global dust storm 2001A produced a significant optical depth and surface temperature change.

Mars surface and atmospheric temperature during the 2001 global dust storm

The dramatic growth and evolution of the 2001 martian global dust storm were captured using the Submillimeter Wave Astronomy Satellite (SWAS). While the lower and middle atmosphere (pressures greater than 50 μbar, up to ∼45 km altitude) showed rapid heating of up to 40 K, the average surface brightness temperature plummeted by ∼20 K at the peak of the storm. The storm appears to have had little impact on the global temperature structure at altitudes above ∼ 10 μbar (∼ 60 km).

Interannual variability of Mars global dust storms: an example of self-organized criticality?

Previous simulations of martian global dust storms with a simple low-order model showed the desired interannual variability of storms if one of the model parameters—the threshold wind speed for starting saltation and lifting dust from the surface—was finely tuned. In this paper we show that the fine-tuning of this parameter could be the result of negative feedback in which processes associated with global dust storms raise the threshold and small-scale processes like dust devils, which are active in years between the storms, lower the threshold.

Interannual Variability of Martian Global Dust Storms: Simulations with a Low-Order Model of the General Circulation

We present simulations of the interannual variability of martian global dust storms (GDSs) with a simplified low-order model (LOM) of the general circulation. The simplified model allows one to conduct computationally fast long-term simulations of the martian climate system. The LOM is constructed by Galerkin projection of a 2D (zonally averaged) general circulation model (GCM) onto a truncated set of basis functions. The resulting LOM consists of 12 coupled nonlinear ordinary differential equations describing atmospheric dynamics and dust transport within the Hadley cell. The forcing of the model is described by simplified physics based on Newtonian cooling and Rayleigh friction. The atmosphere and surface are coupled: atmospheric heating depends on the dustiness of the atmosphere, and the surface dust source depends on the strength of the atmospheric winds. Parameters of the model are tuned to fit the output of the NASA AMES GCM and the fit is generally very good. Interannual variability of GDSs is possible in the LOM, but only when stochastic forcing is added to the model. The stochastic forcing could be provided by transient weather systems or some surface process such as redistribution of the sand particles in storm generating zones on the surface. The results are sensitive to the value of the saltation threshold, which hints at a possible feedback between saltation threshold and dust storm activity. According to this hypothesis, erodable material builds up as a result of a local process, whose effect is to lower the saltation threshold until a GDS occurs. The saltation threshold adjusts its value so that dust storms are barely able to occur.

Downslope Windstorms in the Lee of Ridges on Mars

The semianalytical theory of downslope windstorms, originally developed to understand large increases in surface winds in the lee of major mountain chains on Earth, such as the famous windstorms in Boulder, Colorado, is applied to martian conditions. The focus of this work is to assess whether this theory can help us understand dark erosional wind streaks downstream of ridges on the martian surface. These streaks provide a well-documented example of dust raising on Mars. However, the formation of the streaks remains a mystery because atmospheric circulation models indicate surface friction velocities far lower than those required for the initiation of eolian activity. Downslope windstorms result from the interaction of topographically launched finite amplitude gravity waves with a level of zero wind, which vertically traps the waves. When this zero-wind level is at the proper height, large increases in downstream surface winds (up to a factor of 4) can be produced. During the martian night, downslope windstorms can occur in the lee of quite small ridges (heights ≥ tens of meters) when a level of zero-wind is present in the lowest few kilometers of the atmosphere. Three independent models of the martian atmospheric circulation indeed show levels of zero wind in the form of wind reversals at the appropriate height and season and at the locations where the ridge-related dark streaks are concentrated. The strong upstream/downstream difference in surface winds produced by the downslope windstorm mechanism when a suitable wind reversal is present, rather than a particularly strong upstream wind, is what controls the occurrence of the ridge-related dark streaks. Downslope windstorms also appear to be potentially useful in understanding the build-up of dust in the atmosphere preceding the martian global dust storms.

Martian global dust storms: Zonally symmetric numerical simulations including size‐dependent particle transport

The size‐dependent transport of dust particles in the Martian atmosphere away from a specified surface source is numerically investigated employing a coupled system of a zonally symmetric primitive equation grid point model of the Martian atmosphere and an aerosol transport/microphysical model. The coupled model accounts for diabatic heating due to a radiatively active evolving dust field but neglects feedbacks between atmosphere‐surface interactions and surface dust lifting, which is prescribed. The differing suspension lifetimes of various sized dust particles (radius = 1–80 μm) in conjunction with spatially varying atmospheric dynamics results in latitudinal differences in several measurements of the column integrated particle concentration. The latitudinal extent of dust (opacity) transport away from a southern subtropical source is enhanced by the presence in suspension of smaller dust particles (r < 1 μm) when compared to the presence of only a single dust particle size (2.5 μm). The input particle size distribution, that inferred by Toon et al. (1977) from Mariner 9 IRIS measurements, is not preserved in suspension at subsolar latitudes for spherical particles (r = 1–10 μm), counter to Toon et al.'s interpretation of IRIS spectra. Visible to 9‐μm dust opacity ratios, which provide an indication of the relative number of large particles, are generally smaller (<1.7) than values (2–2.5) inferred from both Mariner 9 and Viking measurements. The invocation of slower falling nonspherical (disk) shaped particles results in an improved maintenance in suspension of the input particle size distribution at subtropical latitudes and visible to‐9 μm opacity ratios in better agreement with inferred values. Calculated visible opacity values at the Viking lander latitudes increase less abruptly than was observed at the onsets of the two 1977 dust storms, which has implications for both source locations and magnitudes. This work indicates the importance of considering the full range of particle sizes (and shapes) of the suspended dust during Martian global dust storms and their impact upon the spatial extent and wavelength‐dependent radiative influence of such storms.

Numerical simulations of the decay of Martian global dust storms

The decay of Martian global (great) dust storms is investigated. One‐dimensional (vertical, static atmosphere) and two‐dimensional (latitude‐height, steady state circulation) simulations carried out with an aerosol transport‐microphysical model indicate that atmospheric motions play a significant role in the observed decay of global dust storms. Spacecraft observations (Mariner 9, Viking) of the 1971 and the two 1977 planet‐encircling dust storms have provided suggestions about some characterisrics of storm decay. Specifically, the dust particle size distribution is inferred to have remained essentially unchanged for particles with radii between 1 and 10 μm during decay of the 1971 storm, and surface visible opacity declined quasi‐exponentially with time in northern mid‐latitudes during the decay of the two 1977 storms. The results from this investigation indicate that two‐ and three‐dimensional dynamical processes play a significant role in the observed decay features of Martian global dust storms. The most important processes are the lofting of dust by vertical motions in the dust source region of the southern hemisphere subtropics and a continuing advective resupply of atmospheric dust into the dust sink regions of the northern hemisphere. Our work has implications for Viking data analyses and future Mars observer observations and requires that the particle size distribution be treated as a time and latitude dependent quantity.