共查询到20条相似文献，搜索用时 531 毫秒
1.
In this paper we analyze some Viking infrared thermal mapping (IRTM) measurements of local Martian dust storms observed in the southern tropical region of the planet between Ls=225 and 262°. The derived opacities of these storms show that in the most opaque regions of the cloud, the optical thickness may be ≈6. Away from the individual clouds, the opacity is ≈2, which is still about four times the background level of dustiness in the Martian atmosphere. We find considerable structure in the derived opacity which will create corresponding variations in the atmospheric heating, which in turn may have an important feedback upon the local winds. 相似文献
2.
Edwin K. Schneider 《Icarus》1983,55(2):302-331
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. 相似文献
3.
Richard W. Zurek 《Icarus》1981,45(1):202-215
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. 相似文献
4.
Experimental data on cohesion-free particle transport in fluid beds are applied, via a universal scaling relation, to atmospheric transport of fine grains on Mars. It may be that cohesion due to impact vitrification, vacuum sintering, and adsorbed thin films of water are absent on Mars—in which case the curve of threshold velocity versus grain size may show no turnup to small particle size, and one micron diameter grains may be injected directly by saltation into the Martian atmosphere more readily than 100 micron diameter grains. Curves for threshold and terminal velocities are presented for the full range of Martian pressures and temperatures. Suspension of fine grains is significantly easier at low temperatures and high pressures; late afternoon brightenings of many areas of Mars, and the generation of dust storms in such deep basins as Hellas, may be due to this effect. 相似文献
5.
Calculations of the daily solar radiation incident at the tops of the atmospheres of Mars and the outer planets and its variability with latitude and season are presented in a series of figures and tables similar to those for Earth in The Smithsonian Meteorological Tables. The changes in the latitudinal and seasonal distributions of daily surface insolation during the great Martian dust storm of 1971 (when Martian atmospheric optical depth increased from about τ = 0.1 to 2.0 were significant and dramatically illustrate the effect of atmospheric aerosols on surface insolation; i.e., the mean annual daily insolation at the poles decreased by more than a factor of 100 as τ increased from 0.1 to 2.0. 相似文献
6.
G.S. Golitsyn 《Icarus》1973,18(1):113-119
A short review is given of the observational data on the great Martian dust storms. It is noted that these storms are observed at the time of the great oppositions, when Mars is at its perihelion. It is then late spring-early summer in the Southern Hemisphere and the insolation is a maximum. Intense storms were observed during the 1892, 1924, 1941, 1956 and 1971 oppositions, but not in 1909 or 1939. These storms were of various duration and intensity which points out the importance of local time and space meteorological conditions at the moment of storm origin. Storm generation is caused by local conditions, but the fact that they frequently reach global scale implies that there are some feedback processes favoring the global spread of the dust. Possible such processes are described qualitatively together with the causes of storm declines. Those problems of Martian meteorology and micrometeorology are discussed which have to be studied for a better understanding of the generation, development and decay of a dust storm. 相似文献
7.
A euphotic zone seems to exist at about 1 cm subsurface in the Martian epilith. At this depth visible light is still intense enough to be utilized by conceivable photosynthetic organisms; but the germicidal ultraviolet intensities at the Martian surface have been reduced to values manageable by terrestrial life. Such euphotic zone organisms would experience moderately high Martian temperatures at equatorial latitudes and can be dispersed readily during global dust stroms. During such storms the Martian euphotic zone may reach the surface. The aerosol content of the Martian atmosphere can be monitored by multiband single line scans of the sun at large zenith angles by the Viking lander camera; and the postulated euphotic zone organisms can be searched for with the Viking lander sample arm and biology experiments. 相似文献
8.
A time-sequential set of bolometric albedo maps for Mars has been constructed from Viking Infrared Thermal Mapper data. The maps provide global coverage in longitude for latitudes -60° to +60° at 1° by 1° spatial resolution. Individual maps are constructed under strict geometric constraints for a narrow range of Ls. The set of albedo maps spans a Martian year and includes maps before, during, and after the global dust storms of 1977. Transient brightenings associated with local dust storms or condensate clouds are apparent in some of the maps. During dust-free periods, bolometric albedo maps are generally similar to classical, visual albedo map of Mars. The distribution of bolometric surface albedos is bimodal with typical, clear-sky, Lambert albedos of 0.27 and 0.16 for bright and dark areas, respectively. Atmospheric effects strongly influence apparent surface albedos, especially for dark areas. Neither bright nor dark regions show measurable, long-term variations of bolometric albedos during clear periods. 相似文献
9.
William K. Hartmann 《Icarus》1978,33(2):380-387
Mariner 9 high-resolution photos and topographic information were used to make a topographic analysis of “blue” and “red” cloud positions reported over a 66-year period in Lowell Observatory records. A sample of 77 “blue” cloud sites lay preferentially at the highest Martian elevations; 60% centered precisely on the seven major volcanic mountain peaks (unknown when the clouds were observed); another 16% lay on substantial slopes or contacts between cratered terrain and lower plains. The median altitude of blue cloud sites was 2.1 km above the global topographic median. These results agree with other evidence that most Earth-detected blue clouds are orographic uplift clouds, composed of condensates. Over half of 131 sporadic yellowish or red clouds were associated with blue clouds or volcanoes, and thus probably did not represent dust storm phenomena, contrary to a commonly held belief. Of 88 “possible dust clouds” (chosen by additional criteria), about two-thirds occur at borders between light and dark areas, in the light regions. These sites may have thin veneers of dust, and current depositional or denudational activity. Median altitude of “possible dust cloud” sites was 0.5 km below the global topographic median. Major dust storms begin in a few “core areas,” two of which associate with major basins Hellas and Isidis, probable reservoirs of mobile dust; but exact topographic control and causes of dust storms are unclear. 相似文献
10.
Michael D Smith 《Icarus》2004,167(1):148-165
We use infrared spectra returned by the Mars Global Surveyor Thermal Emission Spectrometer (TES) to retrieve atmospheric and surface temperature, dust and water ice aerosol optical depth, and water vapor column abundance. The data presented here span more than two martian years (Mars Year 24, Ls=104°, 1 March 1999 to Mars Year 26, Ls=180°, 4 May 2003). We present an overview of the seasonal (Ls), latitudinal, and longitudinal dependence of atmospheric quantities during this period, as well as an initial assessment of the interannual variability in the current martian climate. We find that the perihelion season (Ls=180°-360°) is relatively warm, dusty, free of water ice clouds, and shows a relatively high degree of interannual variability in dust optical depth and atmospheric temperature. On the other hand, the aphelion season (Ls=0°-180°) is relatively cool, cloudy, free of dust, and shows a low degree of interannual variability. Water vapor abundance shows a moderate amount of interannual variability at all seasons, but the most in the perihelion season. Much of the small amount of interannual variability that is observed in the aphelion season appears to be caused by perihelion-season planet-encircling dust storms. These dust storms increase albedo through deposition of bright dust on the surface causing cooler daytime surface and atmospheric temperatures well after dust optical depth returns to prestorm values. 相似文献
11.
A method for separating the spectral signatures of the Martian surface and atmosphere was developed and is applied to multiple emission angle data returned from the MGS TES instrument. This method includes correlated-k and index gas removal algorithms that may be applied to all nadir-pointing TES data. Initial results have provided new and refined measurements of the spectral shapes of atmospheric dust and the Martian surface. Surface temperatures and atmospheric dust opacities are also retrieved with improved accuracy over single observation temperature and opacity retrievals. Low-albedo surfaces display absorptions consistent in both shape and depth with previous studies. These surfaces may be closely modeled using a combination of previously derived basalt, andesitic, and high-albedo surface spectral shapes. Short wavelengths display no significant absorptions, indicating both the coarse particulate nature of the surface and the lack of significant amounts of carbonate. Moderate- and high-albedo surfaces have spectral shapes distinctive of fine particulate silicate materials. No single material can match the entire high-albedo surface spectrum, though there are clear indications of a material that closely matches intermediate to calcic plagioclase and an emission peak at ∼1620 cm−1 due to bound water. The lack of residual restrahlen silicate absorptions indicates that minerals such as olivine or pyroxene are not present in high-albedo surfaces at significant (but unknown) abundances. High-albedo surface results presented here are in agreement with and complementary to shorter wavelength observations. The Martian dust is composed of both primary and secondary minerals. Either chemical weathering has not completely altered its source material or the soil is a mixture of altered and unaltered sources. Further laboratory studies are needed to better establish detection limits and behavior of mineral mixtures of fine particulates in the thermal infrared portion of the spectrum. 相似文献
12.
Owen B. Toon James B. Pollack William Ward Joseph A. Burns Kenneth Bilski 《Icarus》1980,44(3):552-607
We examine the response of Martian climate to changes in solar energy deposition caused by variations of the Martian orbit and obliquity. We systematically investigate the seasonal cycles of carbon dioxide, water, and dust to provide a complete picture of the climate for various orbital configurations. We find that at low obliquity (15°) the atmospheric pressure will fall below 1 mbar; dust storms will cease; thick permanent CO2 caps will form; the regolith will release CO2; and H2O polar ice sheets will develop as the permafrost boundaries move poleward. At high obliquity (35°) the annual average polar temperature will increase by about 10°K, slightly desorbing the polar regolith and causing the atmospheric pressure to increase by not more than 10 to 20 mbar. Summer polar ground temperatures as high as 273°K will occur. Water ice caps will be unstable and may disappear as the equilibrium permafrost boundary moves equatorward. However, at high eccentricity, polar ice sheets will be favored at one pole over the other. At high obliquity dust storms may occur during summers in both hemispheres, independent of the eccentricity cycle. Eccentricity and longitude of perihelion are most significant at modest obliquity (25°). At high eccentricity and when the longitude of perihelion is close to the location of solstice hemispherical asymmetry in dust-storm generation and in polar ice extent and albedo will occur.The systematic examination of the relation of climate and planetary orbit provides a new theory for the formation of the polar laminae. The terraced structure of the polar laminae originates when eccentricity and/or obliquity variations begin to drive water ice off the dusty permanent H2O polar caps. Then a thin (meters) layer of consolidated dust forms on top of a dirty, slightly thicker (tens of meters) ice sheet and the composite is preserved as a layer of laminae composed predominately of water ice. Because of insolation variation on slopes, a series of poleward- and equatorward-facing scarps are formed where the edges of the laminae are exposed. Independently of orbital variations, these scarps propagate poleward both by erosion of the equatorward slopes and by deposition on the poleward slopes. Scarp propagation resurfaces and recycles the laminae forming the distinctive spiral bands of terraces observed and provides a supply of water to form new permanent ice caps. The polar laminae boundary marks the furthest eqautorward extension of the permanent H2O caps as the orbit varies. The polar debris boundary marks the furthest equatorward extension of the annual CO2 caps as the orbit varies.The Martian regolith is now a significant geochemical sink for carbon dioxide. CO2 has been irreversibly removed from the atmosphere by carbonate formation. CO2 has also benn removed by regolith adsorption. Polar temperature increases caused by orbital variations are not great enough 相似文献
13.
Ultraviolet spectral reflectance data obtained from the Mariner 9 during the 1971 Mars dust storm were analyzed at two wavelengths to deduce the complex index of refraction of Martian dust. Martian dust particles were considered to be irregularly shaped and randomly oriented nonspherical particles. The analysis shows that the Mariner 9 data are consistent with the scattering by irregular particles with an index of refraction m = 1.59 ? 0.0015i at λ = 0.305 μm and m = 1.55 ? 0.004i at λ = 0.268 μm. Both the real and the imaginary parts of refractive index found are considerably smaller than previously reported results using a spherical shape model for Martian dust particles. 相似文献
14.
Ai Inada Mark I. Richardson Timothy H. McConnochie Melissa J. Strausberg Huiqun Wang James F. Bell III 《Icarus》2007,192(2):378-395
High-resolution observations of atmospheric phenomena by the Mars Odyssey Thermal Emission Imaging System (THEMIS) during its first mapping year are presented. An atmospheric campaign was implemented on the basis of previous spacecraft imaging. This campaign, however, proved of limited success. This appears to be due to the late local time of the Odyssey orbit (the locations of activity at 4–6 p.m. appear to be different from those at 2 p.m.). Ironically, images targeting the surface were more useful for study of the atmosphere than those images specifically targeting atmospheric features. While many previously recognized features were found, novel THEMIS observations included persistent clouds in the southern polar layered deposits, dust or condensate plumes on the northern polar layered deposits, dust plumes as constituent parts of local dust storms, and mesospheric clouds. The former two features tend to be aligned parallel and normal to polar troughs, respectively, suggesting a wind system directed normal to troughs and radially outward from the center of the polar deposits. This is consistent with katabatic drainage of air off the polar deposits, analogous to flow off Antarctica. The observation of dust lifting plumes at unprecedented resolution associated with local dust storms not only demonstrates the importance of mean wind stresses (as opposed to dust devils) in initiation of dust storms, but is also seen to be morphologically identical to dust lifting in terrestrial dust storms. As Odyssey moves to earlier local times, we suggest that the atmospheric campaign from the first mapping year be repeated. 相似文献
15.
Rosenqvist J Drossart P Combes M Encrenaz T Lellouch E Bibring JP Erard S Langevin Y Chassefiere E 《Icarus》1992,98(2):254-270
Global Martian atmospheric results derived from the infrared imaging spectrometer ISM flown aboard the Phobos 2 Soviet spacecraft are presented. Over low altitude regions the expected CO mixing ratio of (8 +/- 3) x 10(-4) is measured. Variations of the 2.35-micrometers feature are inconsistent with this value over the Great Martian Volcanoes. If the 2.35-micrometers band is entirely attributable to carbon monoxide, the CO mixing ratio is typically depleted by a factor of 3 over these high altitude areas. Orography should play a major role in the existence of this CO "hole." If, however, these spectral variations at 2.35 micrometers are due to the surface composition, the fraction of the surface covered by the responsible mineral must smoothly decrease as the surface elevation decreases. This phenomenon implies a strong interaction between the surface and the atmosphere for the Great Martian Volcanoes. Diurnal behavior and latitudinal variations of water vapor are globally consistent with Viking measurements. During the Phobos observations, the water vapor amounts over the bright equatorial regions range around 11 pr-micrometers during the day. These amounts are slightly larger than those inferred from 1976 to 1979. The lack of global dust storms during 1988-1989 could explain the enhancement of H2O in the atmosphere. 相似文献
16.
E. van Hemelrijck 《Earth, Moon, and Planets》1985,33(2):157-162
In this paper, we compare changes in the mean seasonal daily insolations at the Martian surface caused by global dust storms characterized by various atmospheric optical thickness (). The calculations, made for optical depths equal to 0, 0.1, 0.5, 1.0, 2.0, and 3.0, are based on the assumption of planet encircling storms lasting one season or one year. The variations in the latitudinal and seasonal surface insolation distributions are important, mainly at the poles where e.g. the mean annual and summer daily insolations decrease by nearly a factor of 3000 as goes from 0 to 3.0. At equatorial latitudes the corresponding loss is much smaller, reaching a value of approximately 40. Concerning the mean wintertime solar radiations it is found that the decrease is even more spectacular, especially at high latitudes. 相似文献
17.
P. Nørnberg H.P. Gunnlaugsson J.P. Merrison A.L. Vendelboe 《Planetary and Space Science》2009,57(5-6):628-631
A fine grained magnetic iron oxide precipitate found in Denmark has been studied with regard to grain size, magnetic properties, aerosol transport, grain electrification, aggregation and optical reflectance. It has shown itself to be a good Martian dust analogue. The fraction of the Salten Skov I soil sample <63 μm was separated from the natural sample by dry sieving. This fraction could be dispersed by ultrasonic treatment into grains of diameter ～1 μm, in reasonable agreement with suspended dust grains in the Martian atmosphere estimated from the Viking, Pathfinder and Mars Exploration Rover missions. Though mineralogical and chemical differences exist between this analogue and Martian dust material, in wind tunnel experiments many of the physical properties of the atmospheric dust aerosol are reproduced. 相似文献
18.
Bruce A. Cantor 《Icarus》2007,186(1):60-96
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 (Ls=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 (Ls=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 Ls=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 τdust∼5.0. By Ls=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 Ls∼200.4° with atmospheric dust concentrations returning to nominal seasonal low-levels at Ls∼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. 相似文献
19.
W.A. Baum 《Planetary and Space Science》1973,21(9):1511-1519
Day-to-day and hour-to-hour changes in the large-scale atmospheric and surface features of the planets can now be studied more effectively than previously possible. Since 1969 a network of observatories has obtained almost uninterrupted photographic coverage during all apparitions of Jupiter and Mars, plus some of Venus. Patrol films and catalogues are available to the scientific community. Recent or current analyses include the distribution and motion of clouds on Mars, the development and decay of Martian dust storms, the seasonal, diurnal and random fluctuations in contrast between adjacent light and dark regions on Mars, the detection of vertical shear in the Jovian atmosphere, the longitudinal oscillation of the Red Spot, the dependence of rotation period on xenographic latitude and on time, the eruption and spread of SEB disturbances, and the retrograde circulation of the Venus cloud deck. 相似文献
20.
J.P. Merrison H.P. Gunnlaugsson J. Jensen K. Kinch P. Nørnberg K.R. Rasmussen 《Planetary and Space Science》2004,52(13):1177-1186
Suspended dust is a dominant component of the Martian environment. It has a major influence on atmospheric circulation and it is deposited widely over the planetary surface causing a serious hazard to instrumentation. In order to study dust transport, quantification of the wind flow and dust concentration are vital. A simple laser-based anemometer system is presented that is able to measure suspended dust grain velocity and turbulence from a landed spacecraft. This system has advantages over other techniques of wind speed determination in being insensitive to contamination or atmospheric conditions such as temperature, pressure or composition. For the first time it would allow direct measurement of the suspended dust concentration on Mars. A prototype instrument has been constructed and successfully tested in a wind tunnel facility under simulated Martian conditions. The optics are simple in design, light weight and the instrument has low power consumption. It is also robust and the output signal is easily interpreted, producing only a small data volume. Future improvements will be discussed, specifically modification to measure wind direction, the possibility of obtaining information about dust grain size and the construction of a flight model. 相似文献