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141.
Yun Yuxing Liu Changhai Luo Yali Liang Xudong Huang Ling Chen Fei Rasmmusen Roy 《Climate Dynamics》2020,54(3):1469-1489
Climate Dynamics - Convection-permitting regional climate models have been shown to improve precipitation simulation in many aspects, such as the diurnal cycle, precipitation frequency, intensity... 相似文献
142.
In light of recent reductions in sulphur (S) and nitrogen (N) emissions mandated by Title IV of the Clean Air Act Amendments of 1990, temporal trends and trend coherence in precipitation (1984–2001 and 1992–2001) and surface water chemistry (1992–2001) were determined in two of the most acid‐sensitive regions of North America, i.e. the Catskill and Adirondack Mountains of New York. Precipitation chemistry data from six sites located near these regions showed decreasing sulphate (SO42?), nitrate (NO3?), and base cation (CB) concentrations and increasing pH during 1984–2001, but few significant trends during 1992–2001. Data from five Catskill streams and 12 Adirondack lakes showed decreasing trends in SO42? concentrations at all sites, and decreasing trends in NO3?, CB, and H+ concentrations and increasing trends in dissolved organic carbon at most sites. In contrast, acid‐neutralizing capacity (ANC) increased significantly at only about half the Adirondack lakes and in one of the Catskill streams. Flow correction prior to trend analysis did not change any trend directions and had little effect on SO42? trends, but it caused several significant non‐flow‐corrected trends in NO3? and ANC to become non‐significant, suggesting that trend results for flow‐sensitive constituents are affected by flow‐related climate variation. SO42? concentrations showed high temporal coherence in precipitation, surface waters, and in precipitation–surface water comparisons, reflecting a strong link between S emissions, precipitation SO42? concentrations, and the processes that affect S cycling within these regions. NO3? and H+ concentrations and ANC generally showed weak coherence, especially in surface waters and in precipitation–surface water comparisons, indicating that variation in local‐scale processes driven by factors such as climate are affecting trends in acid–base chemistry in these two regions. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
143.
It is shown that contortion and gravity are not interacting in the lowest possible order. The most convenient pairs of materials in the new Eötvös' experiments are also proposed. 相似文献
144.
145.
VOCs in Ground Water Influenced by Large Scale Withdrawals 总被引:1,自引:0,他引:1
146.
Jean L. Roy 《Precambrian Research》1983,19(4):319-348
More than half of the approximately 650 paleopoles reported from all Precambrian cratons have been obtained from North America. The observations have spurred a proliferation of apparent polar wander paths to support different hypotheses for the tectonic evolution of the continent. Many of the reasons for this development can be traced to the inadequacy of the data base with its average of only 1.6 poles 10 Ma?1 (as compared to 7 poles 10?1 Ma for the last 300 Ma). Even when it is assumed that a ·primary’ pole has been derived from each rock unit sampled, the total number of ·primary’ poles (excluding the 900–1200 Ma interval) yields an average of only 0.4 pole 10 Ma?1. An inspection of the data base shows a non-systematic sampling of a non-continuous (fragmented) paleomagnetic record with gaps as large as tens and even hundreds of Ma. More importantly, a search through the literature reveals that very few poles have an age known to better than 50 Ma and for many poles the age bracket could be as large as a few hundreds of Ma. This is partly owing to the fact that radiometric and paleomagnetic sites rarely originate from the same localities. It is shown that this limited data base with all its deficiencies and uncertainties cannot be used to support certain hypotheses, or for the drawing of a meaningful apparent polar path for the whole of the Precambrian. It appears that, because of the enormous time scale, Precambrian paleomagnetism should rather be directed towards the construction of segments of polar paths such as those in the 900–1200 Ma interval. Comparison of well dated contemporaneous segments from different parts (or structural provinces) could be used most effectively to delineate relative movements, if any, and reconstruct the mosaic of the past continent for certain time intervals. One of the recent developments of Precambrian paleomagnetism has been to show that the apparent pole did not remain constrained to the equatorial region, but made several excursions into high latitudes. 相似文献
147.
Spatially-flat cosmological models with interacting perfect fluid and zero-mass scalar field have been obtained under different equations of state and in presence of the scalar charge density associated with the Klein-Gordon equation assuming a special law of variation for the Hubble's parameter. 相似文献
148.
Magnetic remanence acquisition in Finnish lake sediments 总被引:2,自引:0,他引:2
Summary. Magnetic studies have been carried out on organic sediments from five Finnish lakes to determine the carrier(s) of the stable NRM and to find how the remanence is acquired. Single or pseudo-single domain 'magnetite' is thought to carry the NRM. It was found that drying and cooling sediment samples resulted in a loss of NRM which was attributed to the misalignment of small magnetic particles. Low-field experiments were carried out on sediment samples in different physical states and from the results of these investigations it was concluded that post-depositional processes are important in the acquisition of an NRM. Stabilization of magnetic grains is thought to be due to the growth of gels in the organic sediment rather than to dewatering. 相似文献
149.
150.
The middle Pleistocene transition: characteristics, mechanisms, and implications for long-term changes in atmospheric pCO2 总被引:1,自引:0,他引:1
Peter U. Clark David Archer David Pollard Joel D. Blum Jose A. Rial Victor Brovkin Alan C. Mix Nicklas G. Pisias Martin Roy 《Quaternary Science Reviews》2006,25(23-24):3150
The emergence of low-frequency, high-amplitude, quasi-periodic (100-kyr) glacial variability during the middle Pleistocene in the absence of any significant change in orbital forcing indicates a fundamental change internal to the climate system. This middle Pleistocene transition (MPT) began 1250 ka and was complete by 700 ka. Its onset was accompanied by decreases in sea surface temperatures (SSTs) in the North Atlantic and tropical-ocean upwelling regions and by an increase in African and Asian aridity and monsoonal intensity. During the MPT, long-term average ice volume gradually increased by 50 m sea-level equivalent, whereas low-frequency ice-volume variability experienced a 100-kyr lull centered on 1000 ka followed by its reappearance 900 ka, although as a broad band of power rather than a narrow, persistent 100-kyr cycle. Additional changes at 900 ka indicate this to be an important time during the MPT, beginning with an 80-kyr event of extreme SST cooling followed by the partial recovery and subsequent stabilization of long-term North Atlantic and tropical ocean SSTs, increasing Southern Ocean SST variability primarily associated with warmer interglacials, the loss of permanent subpolar sea-ice cover, and the emergence of low-frequency variability in Pacific SSTs and global deep-ocean circulation. Since 900 ka, ice sheets have been the only component of the climate system to exhibit consistent low-frequency variability. With the exception of a near-universal organization of low-frequency power associated with marine isotope stages 11 and 12, all other components show an inconsistent distribution of power in frequency-time space, suggesting a highly nonlinear system response to orbital and ice-sheet forcing.Most hypotheses for the origin of the MPT invoke a response to a long-term cooling, possibly induced by decreasing atmospheric pCO2. None of these hypotheses, however, accounts for the geological constraint that the earliest Northern Hemisphere ice sheets covered a similar or larger area than those that followed the MPT. Given that the MPT was associated with an increase in ice volume, this constraint requires that post-MPT ice sheets were substantially thicker than pre-MPT ice sheets, indicating a change in subglacial conditions that influence ice dynamics. We review evidence in support of the hypothesis that such an increase in ice thickness occurred as crystalline Precambrian Shield bedrock became exposed by glacial erosion of a thick mantle of regolith. This exposure of a high-friction substrate caused thicker ice sheets, with an attendant change in their response to the orbital forcing. Marine carbon isotope data indicate a rapid transfer of organic carbon to inorganic carbon in the ocean system during the MPT. If this carbon came from terrigenous sources, an increase in atmospheric pCO2 would be likely, which is inconsistent with evidence for widespread cooling, Apparently rapid carbon transfer from terrestrial sources is difficult to reconcile with gradual erosion of regolith. A more likely source of organic carbon and nutrients (which would mitigate pCO2 rise) is from shelf and upper slope marine sediments, which were fully exposed for the first time in millions of years in response to thickening ice sheets and falling sealevels during the MPT. Modeling indicates that regolith erosion and resulting exposure of crystalline bedrock would cause an increase in long-term silicate weathering rates, in good agreement with marine Sr and Os isotopic records. We use a carbon cycle model to show that a post-MPT increase in silicate weathering rates would lower atmospheric pCO2 by 7–12 ppm, suggesting that the attendant cooling may have been an important feedback in causing the MPT. 相似文献