Slope instabilities in the central Southern Alps, New Zealand, are assessed in relation to their geological and topographic
distribution, with emphasis given to the spatial distribution of the most recent failures relative to zones of possible permafrost
degradation and glacial recession. Five hundred nine mostly late-Pleistocene- to Holocene-aged landslides have been identified,
affecting 2% of the study area. Rock avalanches were distinguished in the dataset, being the dominant failure type from Alpine
slopes about and east of the Main Divide of the Alps, while other landslide types occur more frequently at lower elevations
and from schist slopes closer to the Alpine Fault. The pre-1950 landslide record is incomplete, but mapped failures have prevailed
from slopes facing west–northwest, suggesting a structural control on slope failure distribution. Twenty rock avalanches and
large rockfalls are known to have fallen since 1950, predominating from extremely steep east–southeast facing slopes, mostly
from the hanging wall of the Main Divide Fault Zone. Nineteen occurred within 300 vertical metres above or below glacial ice;
13 have source areas within 300 vertical metres of the estimated lower permafrost boundary, where degrading permafrost is
expected. The prevalence of recent failures occurring from glacier-proximal slopes and from slopes near the lower permafrost
limit is demonstrably higher than from other slopes about the Main Divide. Many recent failures have been smaller than those
recorded pre-1950, and the influence of warming may be ephemeral and difficult to demonstrate relative to simultaneous effects
of weather, erosion, seismicity, and uplift along an active plate margin. 相似文献
Small amounts of oil that can persist for decades in the intertidal zone of coarse-sediment beaches have been documented in a few well-studied cases. Oil that survives attenuation over the short-term (weeks to months) will persist until there is a change in the environmental conditions, as might occur where there is a seasonal storm-wave climate or as a beach undergoes long-term (erosional) changes. Oil residues can persist on the beach surface as tar mats, asphalt-like pavements, or as veneers on sediment particles or hard surfaces. Subsurface oil residues can persist in similar forms or as fill or partial fill of the pore spaces between coarse-sediment particles. Oil penetrates until it reaches fine-grained sediment, the water table, bedrock, or other penetration-limiting layers. Amounts of persistent oil are very small fractions of the volumes that were originally stranded and these protected residues can continue to biodegrade as they become thinner and more discontinuous. 相似文献
This article introduces a type of DBMS called the Intentionally‐Linked Entities (ILE) DBMS for use as the basis for temporal and historical Geographical Information Systems. ILE represents each entity in a database only once, thereby mostly eliminating redundancy and fragmentation, two major problems in Relational and other database systems. These advantages of ILE are realized by using relationship objects and pointers to implement all of the relationships among data entities in a native fashion using dynamically‐allocated linked data structures. ILE can be considered to be a modern and extended implementation of the E/R data model. ILE also facilitates storage of things that are more faithful to the historical records, such as gazetteer entries of places with imprecisely known or unknown locations. This is difficult in Relational database systems but is a routine task using ILE because ILE is implemented using modern memory allocation techniques. We use the China Historical GIS (CHGIS) and other databases to illustrate the advantages of ILE. This is accomplished by modeling these databases in ILE and comparing them to the existing Relational implementations. 相似文献
The Soft X-ray Telescope (SXT) of the SOLAR-A mission is designed to produce X-ray movies of flares with excellent angular and time resolution as well as full-disk X-ray images for general studies. A selection of thin metal filters provide a measure of temperature discrimination and aid in obtaining the wide dynamic range required for solar observing. The co-aligned SXT aspect telescope will yield optical images for aspect reference, white-light flare and sunspot studies, and, possibly, helioseismology. This paper describes the capabilities and characteristics of the SXT for scientific observing.After the launch the name of SOLAR-A has been changed to YOHKOH. 相似文献
Multi-year nitrogen (N) and phosphorus (P) budgets were developed for the Patuxent River estuary, a seasonally stratified
and moderately eutrophic tributary of Chesapeake Bay. Major inputs (point, diffuse, septic, and direct atmospheric) were measured
for 13 years during which, large reductions in P and then lesser reductions in N-loading occurred due to wastewater treatment
plant improvements. Internal nutrient losses (denitrification and long-term burial of particulate N and P) were measured in
tidal marshes and sub-tidal sediments throughout the estuary as were nutrient storage in the water column, sediments, and
biota. Nutrient transport between the oligohaline and mesohaline zones and between the Patuxent and Chesapeake Bay was estimated
using a salt and water balance model. Several major nutrient recycling terms were directly and indirectly evaluated and compared
to new N and P inputs on seasonal and annual time-scales. Major findings included: (1) average terrestrial and atmospheric
inputs of N and P were very close to the sum of internal losses plus export, suggesting that dominant processes are captured
in these budgets; (2) both N and P export were a small fraction (13% and 28%, respectively) of inputs, about half of that
expected for N based on water residence times, and almost all exported N and P were in organic forms; (3) the tidal marsh-oligohaline
estuary, which by area comprised ~27% of the full estuarine system, removed about 46% and 74% of total annual upland N and
P inputs, respectively; (4) recycled N and P were much larger sources of inorganic nutrients than new inputs during warm seasons
and were similar in magnitude even during cold seasons; (5) there was clear evidence that major estuarine processes responded
rapidly to inter-annual nutrient input variations; (6) historical nutrient input data and nutrient budget data from drought
periods indicated that diffuse nutrient sources were dominant and that N loads need to be reduced by about 50% to restore
water quality conditions to pre-eutrophic levels. 相似文献
Heterogeneous coarse grained channels are often characterized by local transitions in bed surface roughness. Distinct spatial zones in terms of grain size have been reported, for example sand ribbons and bedload sheets. The transition from areas of finer to coarser grained surface sediment is often abrupt. However, the effects of these transitions on the shape of the velocity profile and associated shear velocity and roughness length estimates have not been investigated in detail in coarse grained channels. This paper therefore examines the combined effects of a sudden change in surface roughness and of superimposed scales of resistancé on the structure of the turbulent boundary layer. Measurements along roughness transitions from smooth to rough beds were conducted in a flume using artificial roughness features and in a natural gravel bed river. Immediately at the transition from a zone of close packed roughness to a rougher section dominated by obstacles superimposed on the more or less uniform roughness surface, boundary shear stress and roughness length increase considerably. Downstream from this transition, velocity profiles become concave upwards. Downstream and upstream sections show significant differences in terms of near bed velocities (deceleration downstream of the transition), velocity gradient and turbulence intensity of the streamwise velocity component. Comparing the mean velocity profiles corresponding to these two different roughness surfaces gives some indication of the proportion of total shear velocity (or shear stress) associated with the pressure drag produced by large and isolated obstacles. 相似文献
Time–distance helioseismology is a set of powerful tools to study localized features below the Sun’s surface. Inverse methods are needed to robustly interpret time–distance measurements, with many examples in the literature. However, techniques that utilize a more statistical approach to inferences, and that are broadly used in the astronomical community, are less-commonly found in helioseismology. This article aims to introduce a potentially powerful inversion scheme based on Bayesian probability theory and Monte Carlo sampling that is suitable for local helioseismology. We first describe the probabilistic method and how it is conceptually different from standard inversions used in local helioseismology. Several example calculations are carried out to compare and contrast the setup of the problems and the results that are obtained. The examples focus on two important phenomena that are currently outstanding issues in helioseismology: meridional circulation and supergranulation. Numerical models are used to compute synthetic observations, providing the added benefit of knowing the solution against which the results can be tested. For demonstration purposes, the problems are formulated in two and three dimensions, using both ray- and Born-theoretical approaches. The results seem to indicate that the probabilistic inversions not only find a better solution with much more realistic estimation of the uncertainties, but they also provide a broader view of the range of solutions possible for any given model, making the interpretation of the inversion more quantitative in nature. The probabilistic inversions are also easy to set up for a broad range of problems, and they can take advantage of software that is publicly available. Unlike the progress being made in fundamental measurement schemes in local helioseismology that image the far side of the Sun, or have detected signatures of global Rossby waves, among many others, inversions of those measurements have had significantly less success. Such statistical methods may help overcome some of these barriers to move the field forward.
Solar radiation variability spans a wide range in time, ranging from seconds to decadal and longer. The nearly 40 years of measurements of solar irradiance from space established that the total solar irradiance varies by \(\approx 0.1\%\) in phase with the Sun’s magnetic cycle. Specific intervals of the solar spectrum, e.g., ultraviolet (UV), vary by orders of magnitude more. These variations can affect the Earth’s climate in a complex non-linear way. Specifically, some of the processes of interaction between solar UV radiation and the Earth’s atmosphere involve threshold processes and do not require a detailed reconstruction of the solar spectrum. For this reason a spectral UV index based on the (FUV-MUV) color has been recently introduced. This color is calculated using SORCE SOLSTICE integrated fluxes in the FUV and MUV bands. We present in this work the reconstructions of the solar (FUV-MUV) color and Ca ii K and Mg ii indices, from 1749–2015, using a semi-empirical approach based on the reconstruction of the area coverage of different solar magnetic features, i.e., sunspot, faculae and network. We remark that our results are in noteworthy agreement with latest solar UV proxy reconstructions that exploit more sophisticated techniques requiring historical full-disk observations. This makes us confident that our technique can represent an alternative approach which can complement classical solar reconstruction efforts. Moreover, this technique, based on broad-band observations, can be utilized to estimate the activity on Sun-like stars, that cannot be resolved spatially, hosting extra-solar planetary systems.
Chesapeake Bay sediments were examined for biogeochemical evidence of eutrophication trends using two mesohaline sediment cores. Measurements of 210Pb geochronology and sediment profiles of organic carbon, nitrogen, organic phosphorus, inorganic phosphorus, and biogenis silica (BSi) were used used to develop temporal concentration trends. Recent sediments have 2–3 times as much organic carbon and nitrogen as sediments from 80 to 100 yr ago, but the increases result from both changes in organic matter deposition and time-dependent changes in organic matter decomposition rates. Despite increases in phosphorus loading, no major changes in phosphorus concentration were noted throughout most of the century; anthropogenic phosphorus deposition, though not evident in sulfidic mid-bay sediments, must occur in more oxidizing sediment environments in both the northern and southern bays. Temporal trends in BSi concentrations are much less evident and the lack of substantial increases in this century suggest that BSi inputs may be capped by late spring-summer Si limitation. 相似文献
