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Philip B. James 《Icarus》1985,64(2):249-264
The Martian CO2 cycle, which includes the seasonal condensation and subsequent sublimation of up to 30% of the planet's atmosphere, produces meridional winds due to the consequent mass flux of CO2. These winds currently display strong seasonal and hemispheric asymmetries due to the large asymmetries in the distribution of insolation on Mars. It is proposed that asymmetric meridional advection of water vapor on the planet due to these CO2 condensation winds is capable of explaining the observed dessication of Mars' south polar region at the current time. A simple model for water vapor transport is used to verify this hypothesis and to speculate on the effects of changes in orbital parameters on the seasonal water cycle. 相似文献
3.
Jonathan S. Price 《水文研究》1994,8(2):167-177
Over an oceanic peatland, the concentration of Na in fog averaged 38.1 mgl?1 compared with 1.8 mgl?1 in rain, resulting in a significant flux of mineral elements to the surface. Between 16 May and 20 June 1990 the average mass flux of Na to the bog surface by fog, rain, and dry deposition was 21.9, 10.4 and 7.0 mg m?2 d?1. There was little long-term storage of Na within the peatland system, where Na losses measured in stream runoff averaged 34.8 mg m2 d?1, and deep groundwater losses 4 mg m?2 d?1. Calcium and Mg were preferentially retained in the organic soil, whereas K was relatively mobile. Potassium tended to become concentrated in the unsaturated zone. Stream runoff had a consistently higher pH than groundwater, corresponding to higher Ca and Mg concentrations, which may have been from mineral sources in the headwater ponds. Otherwise, the stream water chemistry was closely related to groundwater in the upper layers of the peat deposit. 相似文献
4.
Jonathan Mackey Martin White Marc Kamionkowski 《Monthly notices of the Royal Astronomical Society》2002,332(4):788-798
It has recently been argued that the observed ellipticities of galaxies may be determined at least in part by the primordial tidal gravitational field in which the galaxy formed. Long-range correlations in the tidal field could thus lead to an ellipticity–ellipticity correlation for widely separated galaxies. We present a new model relating ellipticity to angular momentum, which can be calculated in linear theory. We use this model to calculate the angular power spectrum of intrinsic galaxy shape correlations. We show that, for low-redshift galaxy surveys, our model predicts that intrinsic correlations will dominate correlations induced by weak lensing, in good agreement with previous theoretical work and observations. We find that our model produces ' E -mode' correlations enhanced by a factor of 3.5 over B -modes on small scales, making it harder to disentangle intrinsic correlations from those induced by weak gravitational lensing. 相似文献
5.
Studies of soil productivity must compensate for the effects of temporal trends in order to examine the pattern of crop yields along spatial gradients. An analysis of the published yield estimates for 30 soils in 233 counties, however, did not find consistent yield increases over the past three decades. On the contrary, the yield estimates for many soils were markedly uniform since 1972. The uniformity appears to have two causes: the acknowledged difficulty of making yield estimates in a time of increasing variability in soil and crop management, both within and between regions, and surveyors' awareness of data stored in a national soils data base. The effect is to cast doubt on soil productivity data reported in county soil surveys published between 1973 and 1988. 相似文献
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Ralph D. Lorenz A. J. Timothy Jull Timothy D. Swindle Jonathan I. Lunine 《Meteoritics & planetary science》2002,37(6):867-874
Abstract— We explore the likely production and fate of 14C in the thick nitrogen atmosphere of Saturn's moon Titan and investigate the constraints that measurements of 14C might place on Titan's photochemical, atmospheric transport and surface‐atmosphere interaction processes. Titan's atmosphere is thick enough that cosmic‐ray flux limits the production of 14C: absence of a strong magnetic field and the increased distance from the Sun suggest production rates of ?9 atom/cm2/s, ?4x higher than Earth. The fate and detectability of 14C depends on the chemical species into which it is incorporated: as methane it would be hopelessly diluted even in only the atmosphere. However, in the more likely case that the 14C attaches to the haze that rains out onto the surface (as tholin, HCN or acetylene and their polymers), haze in the atmosphere or recently deposited on the surface would be quite radioactive. Such radioactivity may lead to a significant enhancement in the electrical conductivity of the atmosphere which will be measured by the Huygens probe. Measurements with simple detectors on future missions could place useful constraints on the mass deposition rates of photochemical material on the surface and identify locations where surface deposits of such material are “freshest”. 相似文献
9.
Jonathan D. Radley 《Geology Today》2009,25(4):140-144
The Hornton Stone is an unusually pure ooidal ironstone of the Lower Jurassic Marlstone Rock Formation, cropping out on the Edge Hill escarpment and adjacent ironstone plateau in central England. The stone has been quarried for building and ornamental purposes since Medieval times, and more recently as a source of iron ore. Local quarries and buildings provide excellent opportunities to appreciate its fossil content, sedimentary structures and origin. 相似文献
10.
The paper employs statistical hypothesis tests to explore the question of whether natural hazards (hail and tornadoes being considered here) are or are not intertemporally random. The answer to this question, at least for these two hazards, is surprising and has important policy implications: hazards appear to be more likely in year t if an event was experienced in year t?1: hence, apparent ‘Gambler's Fallacy’ behaviour on the part of farmers and others may indeed be rational. Should this result hold for a full range of climate-related hazard types. as we suspect, hundreds of millions of dollars of crop loss and other damages may be preventable (e.g., rotating to frost-resistant crops if past events suggest greater than usual likelihood of early or late frost). The degree of positive serial correlation is also seen to vary a great deal regionally, with individuals in some states being unable to benefit from knowledge of prior hazard occurrence. 相似文献