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The physical processes associated with the clear-sky greenhouse effect in the presence of water vaporare examined by including surface emissivity in the greenhouse effect formulation, and by introducing anew way to partition physical processes of the greenhouse effect. In this new framework, it is found thatthe clear-sky greenhouse effect is governed by three physical processes associated with (1) the temperaturecontrast between the surface and the atmosphere, (2) the interaction between the surface emissivity andthe temperature contrast, and (3) the surface emissivity. The importance of the three physical processes isassessed by computing their vertical and spectral variations for the subarctic winter and summer standardatmosphere using the radiation model MODTRAN3 (Moderate Resolution Transmittance code Version3). The results show that the process associated with the temperature contrast between the surface andthe atmosphere dominates over the other two processes ill magnitude. The magnitude of this process hassubstantial variations in the spectral region of 1250 to 1880 cm 1 and in the far infrared region. Due tothe low-level temperature inversion over the subarctic winter, there exists a negative contribution to thegreenhouse trapping. The seasonal variations are, however, dominated by the processes associated with theinteraction between the surface emissivity and the temperature contrast as well as the surface emissivityitself. The magnitudes of these two physical processes contributing to the greenhouse trapping over thesubarctic winter are about 7 to 10 times of those over the subarctic summer, whereas the magnitude ofthe processes associated with the temperature contrast ill the subarctic summer is only about 2 times ofthat in the subarctic winter. 相似文献
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Abstract A connection between El Niño Southern Oscillation (ENSO) and weather phenomena in eastern Australia has been recognized for several decades. However, little work has been devoted to addressing how this correlation affects hydrological system behaviour within regional-scale catchments. In this study, spatially distributed ENSO effects are evaluated in terms of monthly rainfall, evaporation, streamflow and runoff characteristics for a 1300 km2 catchment. The catchment is located in southeastern Australia where previous studies have indicated only modest ENSO influences on rainfall variability. Spatial and temporal analysis indicates that strongest ENSO-induced rainfall variability occurs during summer months. Additionally, the strength of the relationship is variable in space indicating that topographic controls may affect ENSO influences on rainfall totals and intensities. However, analysis of runoff shows substantially magnified ENSO-induced variability in comparison to the induced variability in rainfall. This may be attributable to the nonlinearity of runoff generation. Differences in antecedent moisture storage conditions will exist but may also be enhanced by complementary ENSO influences on daily rainfall intensities and mean monthly evaporation and temperature totals. The degree of the nonlinearity displayed by the hydrometeorological processes presented demonstrates that the significance of ENSO forecasts for surface water resource management should be assessed with direct regard to streamflow generation rather than on the basis of rainfall totals alone. 相似文献
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Chris M DEBEER Howard S WHEATER William L QUINTON Sean K CAREY Ronald E STEWART Murray D MACKAY Philip MARSH 《中国科学:地球科学(英文版)》2015,(1):46-60
Climate change is causing rapid and severe changes to many Earth systems and processes,with widespread cryospheric,ecological,and hydrological impacts globally,and especially in high northern latitudes.This is of major societal concern and there is an urgent need for improved understanding and predictive tools for environmental management.The Changing Cold Regions Network(CCRN)is a Canadian research consortium with a focus to integrate existing and new experimental data with modelling and remote sensing products to understand,diagnose,and predict changing land,water,and climate,and their interactions and feedbacks over the geographic domain of the Mackenzie and Saskatchewan River Basins in Canada.The network operates a set of 14 unique and focused Water,Ecosystem,Cryosphere and Climate(WECC)observatories within this region,which provide opportunities to observe and understand processes and their interaction,as well as develop and test numerical simulation models,and provide validation data for remote sensing products.This paper describes this network and its observational,experimental,and modelling programme.An overview of many of the recent Earth system changes observed across the study region is provided,and some local insights from WECC observatories that may partly explain regional patterns and trends are described.Several of the model products being developed are discussed,and linkages with the local to international user community are reviewed—In particular,the use of WECC data towards model and remote sensing product calibration and validation is highlighted.Some future activities and prospects for the network are also presented at the end of the paper. 相似文献
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Dacite Genesis via both Slab Melting and Differentiation: Petrogenesis of La Yeguada Volcanic Complex, Panama 总被引：20，自引：2，他引：20
DEFANT MARC J.; RICHERSON PHIL M.; DE BOER JELLE Z.; STEWART ROBERT H.; MAURY REN? C.; BELLON HERV?; DRUMMOND MARK S.; FEIGENSON MARK D.; JACKSON THOMAS E. 《Journal of Petrology》1991,32(6):1101-1142
La Yeguada volcanioc complex (LYVC) is one of many major volcanoesthat represent the extension of the Central American arc inwestern Panama and that have resulted from current oblique subductionsouth of Panama. There are two major phases of calc-alkalinevolcanic activity at LYVC based on mapping and K-Ar radiometricdates. The first phase began at {small tilde} 13 Ma and ceasedat {small tilde} 7?5 Ma. This sequence, termed the old group,consists of basalts to rhyolites with typical arc mineralogies(OL, CPX, PL, MGT, and OPX). The samples have similar radiogenicSr and Nd values and appear to be related by fractional crystallizationwith assimilation and/or magma mixing involved in the differentiation.The parental basalts were probably derived from the metasomatizedmantle wedge via melting induced by fluids released from thesubducted lithosphere. There was an apparent period of minor volcanic activity from7–5 to 2–5 Ma (only one documented sample from thisperiod). The second phase (<2?5 Ma), termed the young group,consists only of dacites but with very different mineralogies(PL, MGT, AM, BI, with no PX) and geochemistries (e.g., highSr and low Y and HREE) compared with the old-group dacites (andandesites and rhyolites). The dacites cannot be related to theold group by various petrogenetic modeling techniques. Thesehigh-Al dacites have the characteristics of magmas derived fromthe partial melting of the subducted oceanic lithosphere witha hornblende eclogite residuum. This has been substantiatedby geochemical modeling. Samples similar to the young-group dacites in other arcs havebeen termed adakites and arc associated with the subductionof young hot crust which may explain why the slab melts. ThePanama basin has extremely high heat flow values, comparablewith those of the Galapagos ridge system. The change from normalarc volcanism to adakites suggests that the subducted oceaniccrust became hotter as time progressed. The subduction of anoceanic ridge or new ridge development along the Sandra Riftin the Panama basin can explain the change in volcanism withtime but more geophysical data are needed. 相似文献
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Compact micritic oncolites up to 8 cm in maximum diameter occur within Maestrichtian (Upper Cretaceous) Garumniense continental marls of Sierra del Montsec (Lerida Province) of north-eastern Spain. Synsedimentary development is documented by patches of terrigenous quartz that occur among oncolitic protuberances. Soluble nuclei (limestone fragments and bivalves) further suggest an origin through accretion, rather than that of soil pisolite. Similarities between the petrography and isotopic compositions of the oncolites and those of interbedded Garumniense limestones suggest similar sedimentary origins. However, these lacustrine oncolites, like modern counterparts described by others, probably developed through in situ metabolic precipitation of calcium carbonate. Evidence of this origin is their high degree of concentricity, which is unlikely to have developed through sedimentary accretion, inasmuch as the oncolites ‘float’ in quiet-water marls. 相似文献
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The estimation of the sensible heatflux from thermal infrared temperature requires anestimate of the excess resistance to be added to theaerodynamic resistance to the transfer of heat fromthe surface. This excess resistance can be expressedin terms of kB-1. An earlier studysuggested that the sensible heat flux over semi-aridregions could be derived from satellite thermalinfrared temperature using a value of kB-1= 7. Values of kB-1 were derived frommeasurements of sensible heat flux, radiometricsurface temperature, air temperature and wind speedtaken over millet, savannah and open forest sitesduring HAPEX-Sahel. These were comparable to valuesderived over similar sites during a previous study. Sensible and latent heat fluxes were estimated usingno excess resistance, kB-1 = 7 andkB-1 set to the values derived from theHAPEX-Sahel data set. There was an improvement on theestimated fluxes when an excess resistance wasincorporated. However, there was no apparentdifference between the errors in the estimated fluxeswith kB-1 set to either the derived orfixed values. This provides additional support forthe use of kB-1 = 7 in the derivation ofsurface fluxes from satellite data for sparsecanopies. 相似文献
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