Distribution of hydrate on Europa: Further evidence for sulfuric acid hydrate     

R.W. Carlson  M.S. Anderson  R.E. Johnson 《Icarus》2005,177(2):461-471

Sulfuric acid hydrate has been proposed as an important species on Europa's surface, the acid being produced by radiolysis of surficial sulfur compounds. We investigated the spectral properties of disordered and crystalline forms of sulfuric acid and suggest that the hydration properties of Europa's hypothesized sulfuric acid lie between two end members: liquid sulfuric acid and its higher crystalline hydrates. The spectra of these end members are similar except for spectral shifts at the band edges. We measured the optical constants of sulfuric acid octahydrate and used these with simple radiative transfer calculations to fit Europa spectra obtained by Galileo's Near Infrared Mapping Spectrometer (NIMS). The global distribution of the hydrate that we associate here with hydrated sulfuric acid shows a strong trailing-side enhancement with a maximum fractional hydrate abundance of 90% by volume, corresponding to a sulfur atom to water molecule ratio of 10%. The hydrate concentration spatially correlates with the ultraviolet and visible absorption of the surface and with the sulfur dioxide concentration. The asymmetric global distribution is consistent with Iogenic plasma ion implantation as the source of the sulfur, possibly modified by electron irradiation and sputtering effects. The variegated distribution also correlates with geologic forms. A high spatial resolution image shows resolved lineae with less hydrate appearing within the lineae than in nearby crustal material. The low concentration of hydrated material in these lineae argues against their conveying sulfurous material to the surface from the putative ocean.  相似文献   

Spatial pattern of recent sediment and diatom accumulation in a small,monomictic, eutrophic lake   总被引：1，自引：0，他引：1  

N. J. Anderson 《Journal of Paleolimnology》1990,3(2):143-160

Spatial variability of sediment and diatom deposition was assessed in a small monomictic, eutrophic lake in Northern Ireland (Lough Augher, Co. Tyrone) using measurements from 17 sediment cores. Loss-onignition profiles in water depths >6 m showed good repeatability, while littoral cores were more variable with localised profiles. Dry mass accumulation rates, derived by biostratigraphic correlation to a ²¹⁰Pb dated master core, were variable and not correlated with water depth. Basin mean dry mass accumulation rate was 0.068 g cm^-2 yr^-1 (range 0.036–0.09) prior to 1900, and 0.19 g cm^-2 yr^-1 (range 0.11–0.3) after 1974. Post-1940 cumulative fluxes were estimated for dry mass (range 3.49–916 g cm^-2) and diatoms (range 16.9–113.8×10⁷ frustules cm^-2). Cumulative dry mass was inversely correlated (r=–0.64) with distance from the inflow, indicating its localised influence. No variable was correlated with water depth except frustules of planktonic diatoms (r=0.66). However, high cumulative fluxes of diatoms and dry mass away from the inflow suggest that the expansion of the littoral macrophyte community may be responsible for decreased resuspension in shallow water, and together with increased sediment trapping, has enhanced sediment accumulation in shallow water over recent time periods.  相似文献   

The troposphere-stratosphere radiation field at twilight: A spherical model     

Donald E. Anderson Jr. 《Planetary and Space Science》1983,31(12):1517-1523

Time-dependent calculations of trace constituent distributions require as input the dissociating radiation field as a function of altitude and solar zenith angle. An isotropic, spherical, multiple scattering model of the radiation field has been developed to determine the radiation field at twilight. Comparison of the spherical model with a plane parallel model at twilight shows that: (1) for solar zenith angles less than 92°, plane parallel solutions for the source function are suitable if the initial deposition of solar energy is calculated for a spherical atmosphere; (2) for solar zenith angles greater than 92°, the plane parallel radiation field can be several orders of magnitude smaller than that calculated with the spherical model; (3) at altitudes above 40 km and at all solar zenith angles, the spherical model predicts 10–20% less radiation than the radiation field calculated with the plane parallel model. Calculations of the rate of photodissociation of NO₂ in the troposphere and stratosphere show that the spherical model yields significantly higher values at solar zenith angles greater than 92°.  相似文献   

Forecasting off-road trafficability     

Malcolm G. Anderson 《Applied geography (Sevenoaks, England)》1983,3(3):239-253

Forecasting off-road trafficability represents an interesting problem in the earth science field, since variables ranging from solar insolation to soil shear strength are involved. However, existing trafficability models do not include precipitation-soil moisture deterministic submodels. Instead, they frequently commence with soil moisture and invoke empirical relationships to predict trafficability. This investigation couples a deterministic soil moisture submodel to a principal empirical soil moisture-trafficability model. Sensitivity analysis shows the impact cloud cover, as well as other variables, can have on the trafficability of three soil types, and the complexity of the post-storm trafficability response.  相似文献   

Road-cut slope topography and stability relationships in St Lucia,West Indies     

Malcolm G. Anderson 《Applied geography (Sevenoaks, England)》1983,3(2):105-114

Slope topography is shown to be a significant factor in controlling the porewater pressures in road-cut slopes in the residual volcanic soils of St Lucia, West Indies. It is shown that this control diminishes as the permeability of the material decreases. This finding is confirmed by stability envelopes in which ‘stable’ and failed slopes are examined as a function of slope topography and material properties.  相似文献   

Frequency dependence of Q in the mantle underlying the shield areas of Eurasia, Part I: analyses of short and intermediate period data   总被引：1，自引：0，他引：1  

Zoltan A. Der  Alison C. Lees  Vernon F. Cormier  Lisa M. Anderson 《Geophysical Journal International》1986,87(3):1057-1084

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Handling uncertainty in extreme or unrepeatable hydrological processes—the need for an alternative paradigm     

Jim Hall  Malcolm Anderson 《水文研究》2002,16(9):1867-1870

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Seismic scattering and shallow structure of the moon in oceanus procellarum   总被引：1，自引：0，他引：1  

Anton M. Dainty  M. Nafi Toksöz  Kenneth R. Anderson  P. Jacques Pines  Y. Nakamura  G. Latham 《Earth, Moon, and Planets》1974,9(1-2):11-29

Long, reverberating trains of seismic waves produced by impacts and moonquakes may be interpreted in terms of scattering in a surface layer overlying a non-scattering elastic medium. Model seismic experiments are used to qualitatively demonstrate the correctness of the interpretation. Three types of seismograms are found, near impact, far impact and moonquake. Only near impact and moonquake seismograms contain independent information. Details are given in the paper of the modelling of the scattering processes by the theory of diffusion.Interpretation of moonquake and artificial impact seismograms in two frequency bands from the Apollo 12 site indicates that the scattering layer is 25 km thick, with a Q of 5000. The mean distance between scatterers is approximately 5 km at 25 km depth and approximately 2 km at 14 km depth; the density of scatterers appears to be high near the surface, decreasing with depth. This may indicate that the scatterers are associated with cratering, or are cracks that anneal with depth. Most of the scattered energy is in the form of scattered surface waves.Communication presented at the Lunar Science Institute Conference on Geophysical and Geochemical Exploration of the Moon and Planets, January 10–12, 1973.  相似文献   

Lunar velocity structure and compositional and thermal inferences     

M. N. Toksöz  F. Press  A. M. Dainty  K. R. Anderson 《Earth, Moon, and Planets》1974,9(1-2):31-42

Seismic data from the Apollo Passive Seismic Network stations are analyzed to determine the velocity structure and to infer the composition and physical properties of the lunar interior. Data from artificial impacts (S-IVB booster and LM ascent stage) cover a distance range of 70–1100 km. Travel times and amplitudes, as well as theoretical seismograms, are used to derive a velocity model for the outer 150 km of the Moon. TheP wave velocity model confirms our earlier report of a lunar crust in the eastern part of Oceanus Procellarum.The crust is about 60 km thick and may consist of two layers in the mare regions. Possible values for theP-wave velocity in the uppermost mantle are between 7.7 km s^–1 and 9.0 km s^–1. The 9 km s^–1 velocity cannot extend below a depth of about 100 km and must decrease below this depth. The elastic properties of the deep interior as inferred from the seismograms of natural events (meteoroid impacts and moonquakes) occurring at great distance indicate that there is an increase in attenuation and a possible decrease of velocity at depths below about 1000 km. This verifies the high temperatures calculated for the deep lunar interior by thermal history models.Paper presented at the Lunar Science Institute Conference on Geophysical and Geochemical Exploration of the Moon and Planets, January 10–12, 1973.  相似文献   

Beta-dispersion of low-frequency Rossby waves     

Paul S. Schopf  David L.T. Anderson  Ronald Smith 《Dynamics of Atmospheres and Oceans》1981,5(3):187-214

An investigation is made into the dispersion of oceanic internal Rossby waves at annual and semi-annual frequencies. Turning of the group velocity vector due to latitudinal variations in the radius of deformation cannot be neglected, particularly in basins as large as the Pacific. This turning allows disturbances to propagate from high lattitudes into the equatorial zone and distorts the solutions in the western part of the basin. For no mean flow, and a coastline aligned north-south, an almost exact focus of wave energy is found very close to the equator at a distance of just under $\text{πc/4ω}$ from the eastern boundary, where $\text{c}$ is the eigenspeed of a high-frequency internal wave mode, and ω is the angular frequency of the low-frequency wave being studied. The focus depends on a long meridional wavelength excited at the coast, and a frequency small compared with $\text{c/a}$, where $\text{a}$ is the radius of the Earth. For the lowest baroclinic mode and waves of annual period, this distance is about 12 000 km. Equivalence of the ray theory and the theory of equatorial meridional modes is demonstrated for the simple cases where the latter applies.The effects of mean currents and irregular coastlines are examined. Barotropic mean currents may change the turning latitude and ray shapes, inducing critical layers and enhancing reflection. Baroclinic mean currents are seen to affect the rays by simply changing the speed in proportion to the depth of the thermocline. As long as the mean currents are geostrophically balanced, no “effective beta” term from variations in the thermocline depth appears, in contrast to the topographic Rossby wave problem.  相似文献