From 15 September 1997 through 21 January 2006, only a single planet-encircling martian dust storm was observed by MGS-MOC. The onset of the storm occurred on 26 June 2001 (
L
s
=
184.7
°
), earliest ...recorded to date. It was initiated in the southern mid-to-low latitudes by a series of local dust storm pulses that developed along the seasonal cap edge in Malea and in Hellas basin
(
L
s
=
176.2
°
–
184.4
°
)
. The initial expansion of the storm, though asymmetric, was very rapid in all directions (3–32 m s
−1). The main direction of propagation, however, was to the east, with the storm becoming planet encircling in the southern hemisphere on
L
s
=
192.3
°
. Several distinct centers of active dust lifting were associated with the storm, with the longest persisting for 86 sols (Syria–Claritas). These regional storms helped generate and sustain a dust cloud (“haze”), which reached an altitude of about 60 km and a peak opacity of
τ
dust
∼
5.0
. By
L
s
=
197.0
°
, the cloud had encircled the entire planet between 59.0° S and 60.0° N, obscuring all but the largest volcanoes. The decay phase began around
L
s
∼
200.4
°
with atmospheric dust concentrations returning to nominal seasonal low-levels at
L
s
∼
304.0
°
. Exponential decay time constants ranged from 30–117 sols. The storm caused substantial regional albedo changes (darkening and brightening) as a result of the redistribution (removal and deposition) of a thin veneer of surface dust at least 0.1–11.1 μm thick. It also caused changes in meteorological phenomena (i.e., dust storms, dust devils, clouds, recession of the polar caps, and possibly surface temperatures) that persisted for just a few weeks to more than a single Mars year. The redistribution of dust by large annual regional storms might help explain the long period (∼30 years) between the largest planet-encircling dust storms events.
•The derivation of the Mars Exploration Rover opacity record is described.•Dust aerosol size variations are characterized across seasons and storm events.•Clouds contribute to northern summer optical ...depth at the Opportunity site.•The dust significantly affects the energy balance and frequency of dust devils.
Dust aerosol plays a fundamental role in the behavior and evolution of the martian atmosphere. The first five Mars years of Mars Exploration Rover data provide an unprecedented record of the dust load at two sites. This record is useful for characterization of the atmosphere at the sites and as ground truth for orbital observations. Atmospheric extinction optical depths have been derived from solar images after calibration and correction for time-varying dust that has accumulated on the camera windows. The record includes local, regional, and globally extensive dust storms. Comparison with contemporaneous thermal infrared data suggests significant variation in the size of the dust aerosols, with a 1μm effective radius during northern summer and a 2μm effective radius at the onset of a dust lifting event. The solar longitude (LS) 20–136° period is also characterized by the presence of cirriform clouds at the Opportunity site, especially near LS=50° and 115°. In addition to water ice clouds, a water ice haze may also be present, and carbon dioxide clouds may be present early in the season. Variations in dust opacity are important to the energy balance of each site, and work with seasonal variations in insolation to control dust devil frequency at the Spirit site.
Deep convection, as used in meteorology, refers to the rapid ascent of air parcels in the Earth's troposphere driven by the buoyancy generated by phase change in water. Deep convection undergirds ...some of the Earth's most important and violent weather phenomena and is responsible for many aspects of the observed distribution of energy, momentum, and constituents (particularly water) in the Earth's atmosphere. Deep convection driven by buoyancy generated by the radiative heating of atmospheric dust may be similarly important in the atmosphere of Mars but lacks a systematic description. Here we propose a comprehensive framework for this phenomenon of dusty deep convection (DDC) that is supported by energetic calculations and observations of the vertical dust distribution and exemplary dusty deep convective structures within local, regional, and global dust storm activity. In this framework, DDC is distinct from a spectrum of weaker dusty convective activity because DDC originates from pre-existing or concurrently forming mesoscale circulations that generate high surface dust fluxes, oppose large-scale horizontal advective-diffusive processes, and are thus able to maintain higher dust concentrations than typically simulated. DDC takes two distinctive forms. Mesoscale circulations that form near Mars's highest volcanoes in dust storms of all scales can transport dust to the base of the upper atmosphere in as little as two hours. In the second distinctive form, mesoscale circulations at low elevations within regional and global dust storm activity generate freely convecting streamers of dust that are sheared into the middle atmosphere over the diurnal cycle.
Observations by the Mars Color Imager (MARCI) onboard the Mars Reconnaissance Orbiter (MRO) in the ultraviolet (UV, Band 7; 320 nm) are used to characterize the spatial and temporal behavior of ...atmospheric water ice over a period of 6 Mars Years. Exploiting the contrast of the bright ice clouds to the low albedo surface, a radiative transfer-based retrieval algorithm is developed to derive the column-integrated optical depth of the ice (τice). Several relatively unique input products are created as part of the retrieval development process, including a zonal dust climatology based on emission phase function (EPFs) sequences from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), a spatially variable UV-reflectance model for Band 7 (as well as for Band 6, 260 nm), and a water ice scattering phase function based on a droxtal ice habit. Taking into account a radiometric precision of 7%, an error analysis estimates the uncertainty in τice to be ∼0.03 (excluding particle size effects, which are discussed separately). Zonal trends are analyzed over the full temporal extent of the observations, looking at both diurnal and interannual variability. The main (zonal) features are the aphelion cloud belt (ACB) and the polar hoods. For the ACB, there can be an appreciable diurnal change in τice between the periods of 14h30–15h00 and 15h00–15h30 Local True Solar Time (LTST). The amplitude of this effect shows relatively large interannual variability, associated mainly with changes in the earlier time block. When averaged over the interval 14h00–16h00 LTST, the interannual differences in the ACB structure are appreciably smaller. When the MARCI τice are compared to those from the Thermal Emission Spectrometer (TES), there is a good correlation of features, with the most significant difference being the seasonal (LS) evolution of the ACB. For TES, the ACB zonal profile is relative symmetric about LS = 90°. In the MARCI data, this profile is noticeably asymmetric, with the centroid shifted to later in the northern summer season (LS = 120°). The MARCI behavior is consistent with that observed by several other instruments. The correspondence of MARCI τice zonal and meridional behaviors with that predicted by two Global Circulation Models (GCM) is good. Each model captures the general behavior seen by MARCI in the ACB, the polar hoods, and the major orographic/topographic cloud features (including Valles Mariners). However, the mismatches between GCM results and MARCI reinforce the challenging nature of water ice clouds for dynamical models. The released τice are being archived at Malin Space Science Systems at https://www.msss.com/mro_marci_iceclouds/.
•The zonal behavior is dominated by aphelion cloud belt (ACB) and polar hood structures.•The MARCI ACB can demonstrate appreciable diurnal change and annual variability.•MARCI ACB observations show differences with those of Thermal Emission Spectrometer.•Dynamical models can capture the general behavior seen by the MARCI ACB and polar hoods.
The Context Camera (CTX) on the Mars Reconnaissance Orbiter (MRO) is a Facility Instrument (i.e., government‐furnished equipment operated by a science team not responsible for design and fabrication) ...designed, built, and operated by Malin Space Science Systems and the MRO Mars Color Imager team (MARCI). CTX will (1) provide context images for data acquired by other MRO instruments, (2) observe features of interest to NASA's Mars Exploration Program (e.g., candidate landing sites), and (3) conduct a scientific investigation, led by the MARCI team, of geologic, geomorphic, and meteorological processes on Mars. CTX consists of a digital electronics assembly; a 350 mm f/3.25 Schmidt‐type telescope of catadioptric optical design with a 5.7° field of view, providing a ∼30‐km‐wide swath from ∼290 km altitude; and a 5000‐element CCD with a band pass of 500–700 nm and 7 μm pixels, giving ∼6 m/pixel spatial resolution from MRO's nearly circular, nearly polar mapping orbit. Raw data are transferred to the MRO spacecraft flight computer for processing (e.g., data compression) before transmission to Earth. The ground data system and operations are based on 9 years of Mars Global Surveyor Mars Orbiter Camera on‐orbit experience. CTX has been allocated 12% of the total MRO data return, or about ≥3 terabits for the nominal mission. This data volume would cover ∼9% of Mars at 6 m/pixel, but overlapping images (for stereo, mosaics, and observation of changes and meteorological events) will reduce this area. CTX acquired its first (instrument checkout) images of Mars on 24 March 2006.
New impact craters at five sites in the martian mid-latitudes excavated material from depths of decimeters that has a brightness and color indicative of water ice. Near-infrared spectra of the ...largest example confirm this composition, and repeated imaging showed fading over several months, as expected for sublimating ice. Thermal models of one site show that millimeters of sublimation occurred during this fading period, indicating clean ice rather than ice in soil pores. Our derived ice-table depths are consistent with models using higher long-term average atmospheric water vapor content than present values. Craters at most of these sites may have excavated completely through this clean ice, probing the ice table to previously unsampled depths of meters and revealing substantial heterogeneity in the vertical distribution of the ice itself.
Over the past several decades, orbital observations of lofted dust have revealed the importance of mineral aerosols as a climate forcing mechanism on both Earth and Mars. Increasingly detailed and ...diverse data sets have provided an ever-improving understanding of dust sources, transport pathways, and sinks on both planets, but the role of dust in modulating atmospheric processes is complex and not always well understood. We present a review of orbital observations of entrained dust on Earth and Mars, particularly that produced by the dust-laden structures produced by daytime convective turbulence called “dust devils”. On Earth, dust devils are thought to contribute only a small fraction of the atmospheric dust budget; accordingly, there are not yet any published accounts of their occurrence from orbit. In contrast, dust devils on Mars are thought to account for several tens of percent of the planet’s atmospheric dust budget; the literature regarding martian dust devils is quite rich. Because terrestrial dust devils may temporarily contribute significantly to local dust loading and lowered air quality, we suggest that martian dust devil studies may inform future studies of convectively-lofted dust on Earth.
As on Earth, martian dust devils form most commonly when the insolation reaches its daily and seasonal peak and where a source of loose dust is plentiful. However this pattern is modulated by variations in weather, albedo, or topography, which produce turbulence that can either enhance or suppress dust devil formation. For reasons not well understood, when measured from orbit, martian dust devil characteristics (dimensions, and translational and rotational speeds) are often much larger than those measured from the ground on both Earth and Mars. Studies connecting orbital observations to those from the surface are needed to bridge this gap in understanding. Martian dust devils have been used to remotely probe conditions in the PBL (e.g., CBL depth, wind velocity); the same could be done in remote locations on Earth. Finally, martian dust devils appear to play a major role in the dust cycle, waxing and waning in relative importance and spatial patterns of occurrence with the planet’s orbital state. Orbital studies of terrestrial dust devils would provide a basis for comparative planetology that would broaden the understanding of these dusty vortices on both planets.
A multiyear, planet‐wide survey of Martian dust devils was conducted using observations from Mars Global Surveyor Mars Orbiter Camera, acquired through 21 January 2006. A total of 223,350 images were ...surveyed and 11,456 dust devils were seen in 0.4% of the images, 11.5% in the Southern and 88.5% in the Northern Hemisphere. Dust devils were observed at latitudes from 71.9°S to 62.2°N, over a range of surface albedos (Am∼0.11–0.22) and elevations from Hellas (−8750 m) to Arsia Mons (+17,250 m). The light‐ and dark‐toned streaks created by dust devils were observed from 80°S to 80°N and changed on timescales as short as 1 month. At mid‐to‐high latitudes, seasonal changes in streak patterns contribute to the seasonal “wave of darkening” observed telescopically from Earth. Dust devils were observed in all seasons in both hemispheres with the exception of Ls = 202.8°–281.5° in the north. Peak activity occurred during midsummer in each hemisphere. Five regions in Amazonis, Syria‐Claritas, Meridiani, and Gusev were monitored regularly. Amazonis had the largest dust devils and was the most active planet‐wide, with annual activity occurring from Ls∼8.5°–197°. Interannual variability resulted from dust storms and planet‐encircling dust hazes, which were observed to initiate and abate dust devil activity. There was no evidence suggesting dust devils cause or lead to initiation of dust storms. Model‐derived tangential wind speeds of large vortices were >20 m s−1 at 20 m above the surface. Dust flux calculations suggest that dust devils are a contributor to the background dust opacity observed through northern spring and summer.
•5 Mars years of MARCI daily global mapping ozone (O3) column retrievals presented.•MARCI ozone maps display rotation and wave deformation of North Polar (NP) vortex.•Winter/Spring transport from SP ...region drives Hellas Basin O3 and CO columns.•Heterogeneous chemistry on Mars water ice clouds is not apparent in O3 behaviors.
Since November of 2006, The Mars Color Imager (MARCI) onboard the Mars Reconnaissance Orbiter (MRO) has obtained multiple-filter daily global images of Mars centered upon a local time (LT) of 3pm. Ultraviolet imaging bands placed within (260nm) and longward (320nm) of Hartley band (240–300nm) ozone (O3) absorption support retrievals of atmospheric ozone columns, with detection limits (∼1μm-atm) appropriate to mapping elevated O3 abundances at low latitudes around Mars aphelion, and over mid-to-high latitudes during fall/winter/spring seasons. MARCI O3 maps for these regions reveal the detailed spatial (∼1°lat/long, for 8×8pixel binned resolution) and temporal (daily, with substantial LT coverage at pole) behaviors of water vapor saturation conditions that force large variations in water vapor photolysis products (HOx-OH, HO2, and H) responsible for the catalytic destruction of O3 in the Mars atmosphere. A detailed description of the MARCI O3 data set, including measurement and retrieval characteristics, is provided in conjunction with comparisons to Mars Express SPICAM ozone measurements (Perrier, S. et al. 2006. J. Geophys. Res. (Planets) 111) and LMD GCM simulated O3 abundances (Lefèvre, F. 2004. J. Geophys. Res. (Planets) 109). Presented aspects of the MARCI ozone mapping data set include aphelion increases in low latitude O3, dynamically evolving high latitude O3 maxima associated with planetary waves and weather fronts during northern early spring, and distinctive winter/spring O3 and CO increases within the Hellas Basin associated with transport of condensation-enhanced south polar air mass. Comparisons of coincident MARCI measurements and LMD simulations for ice cloud and O3 columns are considered in the context of potential heterogeneous photochemical processes (Lefèvre, F. 2008. Nature 454, 971–975), which are not strongly evidenced in the MARCI observations. Modest interannual variations are exhibited, most notably a 20% reduction in aphelion low latitude O3 columns following the 2007 perihelic global dust storm.
We used MGS–MOC and MRO–MARCI daily mapping images of the North Polar Region of Mars from 16 August 2005 (
L
s
=
270°) to 21 May 2009 (
L
s
=
270°), covering portions of three consecutive martian ...years (MY 27–MY 29), to observe the seasonal behavior of the polar ice cap and atmospheric phenomena. The rate of cap regression was similar in MY 28 and MY 29, but was advanced by 3.5° of
L
s (∼7–8
sols) in MY 29. The spatial and temporal behaviors of dust and condensate clouds were similar in the two years and generally in accord with prior years. Dust storms (>100
km
2) were observed in all seasons, with peak activity occurring at
L
s
=
10–20° from 50°N to 70°N and at
L
s
=
135–140° from 70°N to 90°N. The most active quadrant was 0–90°W in MY 28, shifting to 180–270°W in MY 29. The majority of regional storms in both years developed in longitudes from 10°W to 60°W. During late summer the larger storms obscure the North Polar Region in a cloud of dust that transitions to north polar hood condensate clouds around autumnal equinox.
Changes in the distribution of perennial ice deposits, especially in Olympia Planum, were observed between the 2
years, with the MY 29 ice distribution being the most extensive observed to date. Modeling suggests that the small, bright ice patches on the residual cap are not the result of slope or elevation effects. Rather we suggest that they are the result of local meteorological effects on ice deposition. The annual darkening and brightening of peripheral areas of the residual cap around summer solstice can be explained by the sublimation of a brighter frost layer revealing an underlying darker, ice rich layer that itself either sublimes to reveal brighter material below or acts as a cold trap, attracting condensation of water vapor that brightens the surface. An alternative explanation invokes transport and deposition of dust on the surface from the cap interior, and later removal of that dust. The decrease in cap albedo and accompanying increase in near surface atmospheric stability may be related to the annual minimum of polar storm activity near northern summer solstice.
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