高原大地形及海洋热力强迫对东亚及北半球环流和气候变化影响的观测研究     

罗会邦  陈蓉 《气象科学》1995,15(4):17-29

本文总结了“青藏高原大地形及西太平洋暖池势力强迫对东亚及全球气候变化的影响”专题五年来的主要研究工作。其中包括青世故高原东部大气热源的时间演变特征,夏半年高原热源异常对我国降水和北半球环流的影响;西沙海温变化特征及其与我南方降水的关系,北太平洋海温主因子特征及其与华南前汛期降水的变化。  相似文献   

Near-infrared imaging in H2 of molecular (CO) outflows from young stars     

Jochen Eislöffel  Christopher J. Davis 《Astrophysics and Space Science》1995,233(1-2):59-62

We have imaged several known molecular (CO) outflows in H₂ v=1-0 S(1) and wide-band K in order to identify the molecular shocks associated with the acceleration of ambient gas by outflows from young stars. We detected H₂ line emission in all the flows we observed: L 1157, VLA 1623, NGC 6334I, NGC 2264G, L 1641N and Haro 4-255. A comparison of the H₂ data with CO outflow maps strongly suggests that prompt entrainment near the head of a collimated jet probably is the dominant mechanism for producing the CO outflows in these sources.  相似文献   

Distribution and relations of 4- to 10-km-diameter craters to global geologic units of Mars     

Christopher D. Condit 《Icarus》1978,34(3):465-478

By correlating the 1:25,000,000 geologic map of Mars of Scott and Carr (1977) with 4- to 10-km-diameter crater density data from Mariner 9 images, the average crater density for 23 of the equatorial geologic-geomorphic units on Mars was computed. The correlation of these two data sets was accomplished by digitizing both the crater density data and geologic map at the same scale and by comparing them in a computer. This technique assigns the crater density value found in the corresponding location on the geologic data set to a discrete computer file assigned each of the 23 geologic units. By averaging the crater density values accumulated in each file, an “average” crater density for each geologic unit was obtained. Condit believes these average crater density values are accurate indicators of the relative age of the geologic units considered. The statistical validity of these average values is strongest for the geologic units of the largest areal extent. The relative ages as obtained from the average crater density values for the seven largest geologic units, from youngest to oldest, are: Tharsis volcanic material, 21 ± 4 craters/10⁶km²; smooth plains material, 57 ± 14 craters/10⁶km²; rolling plains material, 66 ± 16 craters/10⁶km²; plains materials, 80 ± 17 craters/10⁶km²; ridged plains material, 128 ± 25 craters/10⁶km²; hilly and cratered material, 137 ± 38 craters/10⁶km²; and cratered plateau material, 138 ± 27 craters/10⁶km².  相似文献   

Lapis Judaicus or the Jews' stone: the folklore of fossil echinoid spines     

Christopher J. Duffin 《Proceedings of the Geologists' Association. Geologists' Association》2006,117(3):265-275

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Magnetostratigraphic evidence from the Cold Creek bar for onset of ice-age cataclysmic floods in eastern Washington during the Early Pleistocene     

Christopher J. Pluhar  Bruce N. Bjornstad  Robert S. Coe 《Quaternary Research》2006,65(1):123-135

This study provides a detailed magnetostratigraphy of sediments composing the Cold Creek cataclysmic flood bar in the Pasco Basin, Washington. Our interpretation suggests onset of Missoula floods or similar events prior to 1.1 myr, later than previously suggested by Bjornstad et al. [Bjornstad, B.N., Fecht, K.R., Pluhar, C.J., 2001. Long history of pre-Wisconsin, Ice Age cataclysmic floods: evidence from southeastern Washington State. Journal of Geology 109 (6), 695-713]. Nonetheless these data suggest that Channeled Scabland features formed over a much longer timespan than commonly cited, that continental ice sheets of the early Pleistocene reached as far south as those of the late Pleistocene, and that similar physiography existed in eastern Washington and perhaps Montana to both generate and route Missoula-flood-like events. This study adds paleomagnetic polarity results from 213 new samples of silts and sands derived from nine new drill cores penetrating the Cold Creek cataclysmic flood bar to our previous database of 53 samples from four boreholes, resulting in a much more robust and detailed magnetostratigraphy. Rock magnetic studies on these sediments show pure magnetite to be the predominant remanence-carrying magnetic mineral, ruling out widespread remagnetization by secondary mineralization. The magnetostratigraphy at eastern Cold Creek bar is characterized by a normal polarity interval bracketed by reversed polarities. Equating the normal zone with the Jaramillo subchron (0.99-1.07 myr) affords the simplest correlation to the magnetic polarity timescale. Western Cold Creek bar was likely deposited during the Brunhes chron (0-0.78 myr) since it exhibits mainly normal polarities with only two thin reversed-polarity horizons that we interpret as magnetic excursions during the Brunhes.  相似文献   

Biofouling and the continuous monitoring of underwater light from a seagrass perspective     

Christopher P. Onuf 《Estuaries and Coasts》2006,29(3):511-518

For more than a decade, inexpensive electronic instruments have made continuous underwater light monitoring an integral part of many seagrass studies. Although biofouling, if not controlled, compromises the utility of the record. A year-long assessment of the time course of sensor fouling, in the Laguna Madre of Texas established that light transmitted through the fouling layer after 2 wk of exposure exceeded 90% except for a 6–8 wk period in May and June. On that basis, a 2-wk interval was chosen for routine servicing. Subsequent monitoring proved this choice to be grossly in error. The period of sub-90% transmittance after 2 wk extended to 4–6 mo annually over the next 3 yr. Fouling was strongly correlated with temperature, ambient light, and year. Since an algal bloom of 7-yr duration finally waned during this study, increased ambient light seemed most likely to explain increased fouling later in the study. The explanatory value of light was less than temperature or year in multiple regression, requiring some other explanation of the date effect than change in ambient light. Allelopathic and suspension-feeding depressant effects of the brown tide are offered as the most likely cause of unusually low fouling in the first year. Biofouling was so unpredictable and rapid in this study that at least weekly maintenance would be required to assure reliability of the light monitoring record.  相似文献   

THE AMERICAN GEOGRAPHICAL SOCIETY LIBRARY: A TREASURE TROVE FOR TWENTY–FIRST–CENTURY GEOGRAPHICAL SCHOLARSHIP*     

Christopher Baruth 《Geographical review》2006,96(3):459-472

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Comparison of methods to model the gravitational gradients from topographic data bases   总被引：7，自引：0，他引：7  

Christopher Jekeli  Lizhi Zhu 《Geophysical Journal International》2006,166(3):999-1014

A number of methods have been developed over the last few decades to model the gravitational gradients using digital elevation data. All methods are based on second-order derivatives of the Newtonian mass integral for the gravitational potential. Foremost are algorithms that divide the topographic masses into prisms or more general polyhedra and sum the corresponding gradient contributions. Other methods are designed for computational speed and make use of the fast Fourier transform (FFT), require a regular rectangular grid of data, and yield gradients on the entire grid, but only at constant altitude. We add to these the ordinary numerical integration (in horizontal coordinates) of the gradient integrals. In total we compare two prism, two FFT and two ordinary numerical integration methods using 1" elevation data in two topographic regimes (rough and moderate terrain). Prism methods depend on the type of finite elements that are generated with the elevation data; in particular, alternative triangulations can yield significant differences in the gradients (up to tens of Eötvös). The FFT methods depend on a series development of the topographic heights, requiring terms up to 14th order in rough terrain; and, one popular method has significant bias errors (e.g. 13 Eötvös in the vertical–vertical gradient) embedded in its practical realization. The straightforward numerical integrations, whether on a rectangular or triangulated grid, yield sub-Eötvös differences in the gradients when compared to the other methods (except near the edges of the integration area) and they are as efficient computationally as the finite element methods.  相似文献   

Subsidence in the super-deep Pattani and Malay basins of Southeast Asia: a coupled model incorporating lower-crustal flow in response to post-rift sediment loading   总被引：8，自引：0，他引：8  

Christopher K. Morley  Rob Westaway†‡ 《Basin Research》2006,18(1):51-84

Two Early Cenozoic rifts in Southeast Asia (beneath the Pattani and Malay basins) experienced only limited upper-crustal extension (β≤1.5); yet very thick post-rift sequences are present, with 6–12 km of Late Cenozoic terrestrial and shallow-marine sediment derived from adjacent sources. Conventional post-rift backstripping requires depth-dependent lithospheric thinning by β=2–4 to explain these tremendous thicknesses. We assess an alternative explanation for this post-rift subsidence, involving lower-crustal flow from beneath these basins in response to lateral pressure-gradients induced by the sediment loads and the negative loads arising from the erosion of their sediment sources. We calculate that increased rates of erosion in western Thailand in the Early Miocene placed the crust in a non-steady thermal state, such that the depth (and thus, the pressure) at the base of the brittle upper crust subsequently varied over time. Following such a perturbation, thermal and mass-flux steady-state conditions took millions of years to re-establish. In the meantime, the lateral pressure-gradient caused net outflow of lower crust, thinning the crust beneath the depocentre by several kilometres (mimicking the isostatic effect of greater crustal extension having occurred beforehand) and thickening it beneath the sediment source region. The local combination of hot crust and high rates of surface processes, causing lower-crustal flow to be particularly vigorous and thus making its effects more readily identifiable, means that the Pattani and Malay basins represent a set of conditions different from basins in many other regions. However, lower-crustal flow induced by surface processes will also occur to some extent, but less recognisably, in many other continental crustal provinces, but its effects may be mistaken for those of other processes, such as larger-magnitude stretching and/or depth-dependent stretching.  相似文献   

Relationship of Uncertainty and Line Segment for Between Polygon Segment Spatial Data in GIS     

LIU Chun TONG Xiaohua 《地球空间信息科学学报》2005,8(3):183-188

The mathematic theory for uncertainty model of line segment are summed up to achieve a general conception, and the line error hand model of εσ is a basic uncertainty model that can depict the line accuracy and quality efficiently while the model of εm and error entropy can be regarded as the supplement of it. The error band model will reflect and describe the influence of line uncertainty on polygon uncertainty. Therefore, the statistical characteristic of the line error is studied deeply by analyzing the probability that the line error falls into a certain range. Moreover, the theory accordance is achieved in the selecting the error buffer for line feature and the error indicator. The relationship of the accuracy of area for a polygon with the error loop for a polygon boundary is deduced and computed.  相似文献