Great Dust Storms Research Articles

Pressure Deficit in Gale Crater and a Larger Northern Polar Cap After the MY34 Global Dust Storm

AbstractWe describe the model‐independent analysis technique of Mars Science Laboratory (MSL) pressure and Mars Climate Sounder (MCS) data in de la Torre Juárez et al. (2019, https://doi.org/10.22541/essoar.169945479.90436599/v1) that compared multiple years of surface pressures on Gale before, during, and after the Global Dust Storm of Mars Year 34. The analysis found (a) representative pressure scale heights over Gale; (b) that the storm was followed by a pressure deficit at Gale; (c) the following C storms did not eliminate the deficit; (d) changes in the duration of the polar caps condensation seasons, with an early start of the North Polar (NP) ice cap growing season the year before the Great Dust Storm (GDS) and a late signature of the end of the expansion season thereafter, changes consistent with a larger growth phase of the NP cap; (e) MCS observed a larger than usual NP cap; and (f) cold temperature anomalies over the NP and warm over the Southern Pole after the storm. We also show that the analysis of observed MSL pressure data alone filters out effects on the pressure signal that are attributable to dynamical and orographic processes in a recent model analysis that makes similar interpretations as our 2019 study. One additional Mars year of observations is included to eliminate early concerns about sensor drifts. Noting that a similar NP anomaly was observed with MCS data after the last early GDS in MY25, and not the later GDS of MY27, the results suggest a possible unique effect of early GDSs.

Mars: Abundant Recurring Slope Lineae (RSL) Following the Planet‐Encircling Dust Event (PEDE) of 2018

AbstractRecurring slope lineae (RSL) are dark linear markings on Mars that regrow annually and likely originate from the flow of either liquid water or granular material. Following the great dust storm (or planet‐encircling dust event, PEDE) of Mars year (MY) 34, Mars Reconnaissance Orbiter/High Resolution Imaging Science Experiment has seen many more candidate RSL than in typical Mars years. They have been imaged at more than 285 unique locations from August 2018 (when the atmosphere was clearing as the PEDE decayed) to August 2019, about half (157) of which are locations where RSL have not been documented previously. In MY34, 150 active RSL sites were identified in the southern middle latitudes (SML, ‐60° to ‐30°), whereas an average of 36 active sites were observed in each previous year (MY28–33). Post‐PEDE RSL are also present during southern summer over a wider range of latitude, slope aspect, andLs(areocentric longitude of the sun) than in prior years. These RSL sites usually show evidence for recent dust deposition: obscuration of relatively dark areas, an overall brighter and redder surface than in prior years, and dust devil tracks, which indicate dust lifting by several mechanisms. We speculate that dust‐lifting processes may initiate and sustain RSL activity. The RSL may form from flows of dust (perhaps clumped) and/or sand that is destabilized by dust movement or directly mobilized by dust devils. If this is the case, then the otherwise puzzling recurrence and year‐to‐year variability of RSL activity can be at least partly explained. The dust replenishment varies from year to year, which could explain interannual variations in RSL activity.

A rare case of haboob in Tehran: Observational and numerical study

A great dust storm occurred in Tehran on 2 June 2014 and caused severe damage to properties and involved loss of human life. From the visual evidence available, it can be regarded as a case of haboob. As a lower latitude phenomenon, its occurrence in Tehran was unprecedented in the last 50years.This paper aims to present a detailed analysis of the weather conditions, the pathways by which dust particles were ingested by the haboob, as well as the impact of the urban boundary layer on the intensity and propagation of the dust storm. Using numerical simulation carried out by the WRF-Chem model and various observational techniques, the coupling of a low-level small-scale deformation field with a lower-tropospheric cold pool produced by precipitating mid-tropospheric clouds is identified as the main process involved in shaping this rare dust storm.

Numerical simulations of the regional characteristics of dust transport on Mars

Using a Martian general circulation model (GCM), regions favorable for expansion of dust storms on Mars are identified. Dust transport simulations for the northern fall provide global maps of dust expansibility. These global maps show that dust injected from certain areas in the northern mid-latitudes tends to spread widely within a few days. The high expansibility of dust in such areas results from thermal tides, baroclinic waves, and quasi-stationary disturbances. Dust injected into the vast regions around Tharsis and the Sirenum–Aonia regions also tends to spread extensively. However, dust expansion around these two regions largely depends on the local time of dust injection. On the other hand, dust injected at high latitudes in either hemisphere does not spread extensively. Such global maps indicating regions favorable for dust storm expansion are a clue to understanding the expansion processes and climatology of great dust storms on Mars.

How well do we understand Mars great dust storms?

How well do we understand Mars great dust storms?

Correction to “The Martian annual atmospheric pressure cycle: Years without great dust storms” by James E. Tillman, Neal C. Johnson, Peter Guttorp, and Donald B. Percival

Correction to “The Martian annual atmospheric pressure cycle: Years without great dust storms” by James E. Tillman, Neal C. Johnson, Peter Guttorp, and Donald B. Percival

Western boundary currents in the atmosphere of Mars

WESTERN boundary currents (WBCs) are an intensification of north–south flow adjacent to an eastward-facing meridional boundary. Although most familiar in the oceans (where the Gulf Stream is the best known example), WBCs also occur in the Earth's troposphere, the main example being the East African Jet1, which is thought to play an important role in the Asiatic monsoon. Here we identify boundary currents in a different geophysical context: a numerical simulation of the atmosphere of Mars. In our simulation, WBCs exist in association with significant cross-equatorial flow and the presence of equatorial martian topography, which has vertical scale far exceeding terrestrial relief2. The intensity and width of these currents depend on model parameters, notably the surface drag. From a comparison of our results with other martian models we suggest that WBCs have already been simulated, although they were not previously identified as such3. The available observational evidence appears to be consistent with the presence of martian WBCs, which may be important in the generation of global and great dust storms.

The Martian annual atmospheric pressure cycle: Years without great dust storms

A model of the annual cycle of pressure on Mars has been developed for a 2‐year period chosen to include 1 year at Lander 2 and to minimize the effect of great dust storms at the 22°N Lander 1 site. The model was developed by weighted least squares fitting of the Viking Lander pressure measurements to an annual mean, and fundamental and the first four harmonics of the annual cycle. The very close agreement between the two years suggests that an accurate representation of the annual CO2 condensation‐sublimation cycle can be established for such years. The two annual mean pressures are identical to 0.006 mbar out of 7.9 mbar, and the differences in amplitudes for the first five periodic components between the two years range from 0.017 to 0.001 mbar. The phase angles, primarily dependent on solar insolation determined orbital dynamics, differ by −3.0° Ls for the second harmonic (year 1 minus year 2), and drop to ≤ 0.7° for the fundamental and fourth harmonic. Although the slight year‐to‐year differences appear to be real, this model is proposed as a “nominal” Martian annual pressure cycle and applications are suggested. By analogy, the corresponding first year's representation at Lander 2 is also proposed as the “nominal” cycle, although it has not been verified by data from a subsequent year. These models provide a method of removing low frequencies from the annual pressure cycle for spectral analyses of baroclinic, tidal, and normal mode oscillations, and for comparisons of the interannual variability.

On the Microphysical State of the Martian Seasonal Caps

Carbon dioxide in the martian seasonal polar caps can metamorphose into an annealed polycrystalline layer, provided freshly condensed grains are smaller than 10 μm. Densification is not expected for coarse-grained (grain size larger than 10 μm) CO2 snow. These conclusions are based on an analysis of the micro-physical processes involved in pressureless sintering. The presence of low porosity CO2 deposits over large areas could lead to the millimeter- to centimeter-sized path lengths required to explain several weak absorption features observed in the 1.5- and 2.3-μm spectral regions, provided grain boundaries scatter light very inefficiently and the layer is sufficiently flawless, i.e., devoid of scattering centers such as air bubbles, cracks, and impurities. The latter condition may well be satisfied in the seasonal caps on Mars, where CO2 condenses in the near absence of an inert gas, the cap temperature is almost constant, and the average abundance of impurities is not expected to exceed 0.1% by volume. A nonporous layer may also explain the low thermal emissivity inferred from Viking measurements. In addition, an annealed layer could become sufficiently transparent during the later stages of spring sublimation to allow the albedo dichotomy between the northern and southern cap to be associated with the underlying substrate and thus be permanent; this would explain the exposure of the northern residual H2O cap even during years when no great dust storms occur. The measurements to be carried out by instruments onboard the Mars Observer spacecraft may help to distinguish locations where fine-grained frost is forming on the ground from areas covered by coarse-grained CO2 snow.

Observations of Martian surface winds at the Viking Lander 1 Site

Partial failure of the wind instrumentation on the Viking Lander 1 (VL1) in the Martian sub tropics (22.5°N) has limited previous analyses of meteorological data for this site. We describe a method for reconstructing surface winds using data from the partially failed sensor and present and analyze a time series of wind, pressure, and temperature at the site covering 350 Mars days (sols). At the beginning of the mission during early summer, winds were controlled by regional topography, but they soon underwent a transition to a regime controlled by the Hadley circulation. Diurnal and semidiurnal wind oscillations and synoptic variations have been analyzed and compared with the corresponding variations at the Viking Lander 2 middle latitude site (48°N). Diurnal wind oscillations were controlled primarily by regional topography and boundary layer forcing, although a global mode may have been influencing them during two brief episodes. Semidiurnal wind oscillations were controlled by the westward propagating semidiurnal tide from sol 210 onward. Comparison of the synoptic variations at the two sites suggests that the same eastward propagating wave trains were present at both sites, at least following the first 1977 great dust storm, but discordant inferred zonal wave numbers and phase speeds at the two sites cast doubt on the zonal wave numbers deduced from analyses of combined wind and pressure data, particularly at the VL1 site where the signal to noise ratio of the dominant synoptic waves is relatively small.

Free and forced modes in the Martian atmosphere

Short‐period, apparently global oscillations are clearly present in the multiyear time series of surface pressure variations recorded at the two Viking Lander sites on Mars. Previous work has emphasized the contributions of solar‐driven thermal tides to the surface pressure field. Recent analyses of single‐station data on Earth and on Mars suggest that the planetary normal modes (i.e., free modes of planetary scale) may also contribute to the short‐term, seasonally modulated variability in surface pressure. In this paper the periods of free modes in the Martian atmosphere are computed, with due consideration to the short atmospheric radiative damping time and to the seasonal and interannual variation of globally representative temperatures, both of which differ by an order of magnitude from their terrestrial counterparts. The likelihood of atmospheric resonance (i.e., free modes) or of efficient excitation and possibly resonant amplification of forced modes is then discussed. In summary, a thermally forced diurnal Kelvin wave still seems the best explanation for the short‐period, transient mode which appears just prior to or during the episodic great dust storms on Mars. Resonant modes seem most likely to occur during northern spring and summer, as previously suggested by Tillman. However, the limited atmospheric temperature data appear to have the wrong seasonal trend for resonance alone to account for the transient surface pressure oscillations observed in mid to late northern summer at the Viking Landers. One possibility is that during this period, unobserved changes in the atmospheric static stability near the surface have temporarily amplified the resonant modes or have moved the resonant frequency through the frequencies of the solar thermotidal forcing.

Atmospheric Tidal Forcing of the Zonal-Mean Circulation: The Martian Dusty Atmosphere

Classical atmospheric tidal theory has been used to compute the bilinear tidal zonal-mean forcing per unit mass of the zonal-mean meridional and zonal winds, together with the tidal zonal-mean heating per unit mass for the dusty Martian atmosphere. The convergences of the tidal Eliassen-Palm (EP) flux have been computed for both clear and dusty atmospheric conditions, including the special case of a 'dusty corridor' in the summer southern subtropics that is meant to simulate the early stages of a planetary-scale Martian dust storm. The calculation of the tidal EP zonal forcing differs from Hamilton in that more realistic thermotidal forcings and basic state temperatures are used. The zonal-mean convergences of the tidal fluxes of heat and momentum are large during a Martian great dust storm and should alter significantly the zonal-mean circulation and its residual component driven by the zonal-mean heating. In particular, the tidal forcing of the meridional wind, which is an order of magnitude greater than its zonal counterpart, is likely to give rise to a complex pattern of significantly ageostrophic zonal-mean flow in the Martian tropics.

Clearing the Martian air: The troubled history of dust storms

This note is an attempt to resolve some misconceptions regarding the historical record of the Martian atmospheric phenomena referred to as “dust storms,” but often called yellow storms, yellow clouds, planetwide dust storms, global dust storms, great dust storms, etc. The known frequency of planet-encircling storms will be specifically addressed. Better knowledge of the sizes, frequencies, and locations of Martian dust storms is needed for atmospheric modeling and for future mission planning.

Martian great dust storms: Interpretive axially symmetric models

The simplified theory of steady, nearly inviscid, thermally forced axially symmetric atmospheric motions developed by Schneider (1977) is applied to the study of the problem of the Martian great dust storms. A highly idealized calculation of the atmospheric response to heating concentrated in a small latitude band is carried out. Qualitatively different local and global response regimes are identified. As the heating is increased from zero, some critical value is reached at which the response jumps from local to global. It is suggested that this transition from local to global response may be related to the observed explosive growth of great dust storms. Results from the idealized model indicate that subtropical latitudes are favored for the initiation of a dust raising global dust storm, as the meridional scale of the response to a heat source of fixed intensity is largest for the heat source located close to the equator, but the surface stress in the zonal direction produced by the response increases as the heat source is moved towards the poles. Also, the steady axially symmetric Martian response to solar forcing is examined. Modification to the solar forced response due to an added latitudinally localized heat source is briefly discussed, and it is indicated that similar transition behavior to that obtained in the more idealized model is to be expected in this case also. Implications of the dynamical model for the dependence of the occurence of great dust storms on orbital parameters are remarked on.

Martian great dust storms: An update

Observations by the Viking Orbiters and Landers have made substantial contributions to our understanding of the episodic, planetary-scale dust storms on Mars. These and other observations pertinent to the great dust storms are reviewed in this paper; most of the emphasis is on the atmospheric/climatic aspects of these great storms. Specifically, observations concerning the optical properties of the airborne dust, the frequency of occurrence of great dust storms, and the kinematics of their evolution are summarized. Special attention is given to the various estimates derived from Viking data of atmospheric dust opacity. Within this observational framework, various physical mechanisms underlying the generation, evolution, and decay of the Martian great dust storms are discussed.

Thermal Tides in the Dusty Martian Atmosphere: A Verification of Theory

Major features of the daily surface pressure oscillations observed by the Viking landers during the two great dust storms on Mars in 1977 can be explained in terms of the classical atmospheric tidal theory developed for the earth's atmosphere. The most dramatic exception is the virtual disappearance of only the diurnal tide at Viking Lander 1 just before the second storm. This disappearance is attributed to destructive interference between the usually westward-traveling tide and an eastward-traveling diurnal Kelvin mode generated by orographically induced differential heating. The continuing Viking Lander 1 pressure measurements can be used with the model to monitor future great dust storms.

Inference of dust opacities for the 1977 Martian great dust storms from Viking Lander 1 pressure data

Abstract A δ-Eddington radiative transfer algorithm is used to compute the thermal tidal heating of a dusty Martian atmosphere for a given set of dust optical depth, effective single scattering albedo, and phase function asymmetry parameter. The resulting thermal tidal forcing is used in a classical atmospheric tidal model to compute the amplitudes of the surface pressure oscillations at the Viking Lander 1 site for the two 1977 Martian great dust storms. Parametric studies show that the dust opacities and optical parameters derived from the Viking Lander imaging data are roughly representative of the global dust haze needed to reproduce the tidal surface pressure amplitudes also observed at Lander 1, except that the model-inferred asymmetry parameter is smaller during the onset of a great storm. The observed preferential enhancement during dust-storm onset of the semidiurnal tide at Viking Lander 1 relative to its diurnal counterpart is shown to be due primarily to the elevation of the tidal heating source in a very dusty atmosphere, although resonant enhancement of the main semidiurnal tidal mode makes an important secondary contribution.

Mars surface active

The surface of Mars has shown itself to be a moderately active place, according to information compiled by Stephen D. Wall, Jet Propulsion Laboratory, and Kenneth L. Jones, Planetary Research, Inc., Pasadena, and presented by Wall at the AGU Spring Meeting.Researchers think the planet undergoes great dust storms each Martian year. (A Martian year consists of 667 25‐hour‐long Martian days.) Investigators knew dust interacted with the atmosphere, but didn't know what effect that had on surface conditions.

Surface Pressure Response to Elevated Tidal Heating Sources: Comparison of Earth and Mars

Modern atmospheric tidal theory has shown that the dominance of the terrestrial semidiurnal surface pressure oscillation, relative to its diurnal counterpart, is the result of the elevated heating source generated by solar heating of stratospheric ozone. Observations of the daily surface pressure variation at the Viking Lander 1 site on Mars reveal a similar predominance of the semidiurnal surface pressure oscillation only during the onset of a Martian great dust storm. Application of a classical, analytic tidal model to the Viking Lander 1 data indicates that elevating the effective heat source due to solar heating of airborne dust by a few kilometers during the onset of a Martian great dust storm can account for the observed semidiurnal surface pressure variation.

Cloud microphysics: Analysis of the clouds of Earth, Venus, Mars and Jupiter

A simple method of deducing the probable microphysics of a cloud is developed that uses only information about cloud particle mean size, composition, number density, and atmospheric structure. This analysis is applied to the sulfuric acid clouds of Venus, the water ice and dust clouds of Mars, and the ammonia-water and ammonia ice clouds of Jupiter. The Venus cloud layer most closely resembles smog and haze layers on Earth with no sharp concentration gradients. The cloud microphysics is dominated by coagulation, sedimentation, and turbulent mixing. No precipitation is formed. The water ice clouds on Mars resemble tenuous, nonprecipitating cirrus clouds on Earth. Deposition of condensed water on Mars only occurs from surface fogs or direct condensation on the surface. These fogs can provide a very efficient dust deposition mechanism. The observed settling behavior of the great dust storm of 1971 suggests sedimentation at the surface from a turbulent cloud with coagulation growth of large particles to replace those lost by sedimentation, analogous to the nighttime evolution of submicron tropospheric aerosols on Earth. The ammonia-water and ammonia ice clouds on Jupiter produce precipitation on time scales <10 4 sec. The vertical structure of all clouds is significantly altered. The activity of the lower ammonia-water cloud has significant effects on the vertical distribution of other gases and aerosols, on the vertical transport of heat, and on the dynamics in this portion of the atmosphere.