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21.
We examine the representation of the mean state and interannual variability of Antarctic sea ice in six simulations of the
twentieth century from coupled models participating in the Intergovernmental Panel on Climate Change fourth assessment report.
The simulations exhibit a largely seasonal southern hemisphere ice cover, as observed. There is a considerable scatter in
the monthly simulated climatological ice extent among different models, but no consistent bias when compared to observations.
The scatter in maximum winter ice extent among different models is correlated to the strength of the climatological zonal
winds suggesting that wind forced ice transport is responsible for much of this scatter. Observations show that the leading
mode of southern hemisphere ice variability exhibits a dipole structure with anomalies of one sign in the Atlantic sector
associated with anomalies of the opposite sign in the Pacific sector. The observed ice anomalies also exhibit eastward propagation
with the Antarctic circumpolar current, as part of the documented Antarctic circumpolar wave phenomenon. Many of the models
do simulate dipole-like behavior in sea ice anomalies as the leading mode of ice variability, but there is a large discrepancy
in the eastward propagation of these anomalies among the different models. Consistent with observations, the simulated Antarctic
dipole-like variations in the ice cover are led by sea-level pressure anomalies in the Amundsen/ Bellingshausen Sea. These
are associated, to different degrees in different models, with both the southern annular mode and the El Nino-Southern Oscillation
(ENSO). There are indications that the magnitude of the influence of ENSO on the southern hemisphere ice cover is related
to the strength of ENSO events simulated by the different models. 相似文献
22.
B. J. Haupt C. Schäfer-Neth K. Stattegger 《International Journal of Earth Sciences》1995,84(1):137-150
Modelling of Late Quaternary paleoceanography and sedimentation in the northern North Atlantic (NNA) is achieved by coupling the ocean general circulation model SCINNA (Sensitivity and Circulation In the NNA) to the sedimentation models SENNA (Sedimentation In the NNA) and PATRINNA (PArticle Tracing In the NNA).SCINNA is based on the primitive equations with conservation of mass, momentum, energy, heat and salt. SENNA and PATRINNA are driven by temperature, salinity and velocity fields derived from SCINNA. The modelling includes three-dimensional circulation of the ocean, sediment transport in the water column and two-dimensional sedimentary processes in a thin bottom layer. SENNA calculates the erosion, transport and deposition of sediments, resulting in sedimentation patterns for specific time intervals. PATRINNA models the transport paths of single sediment grains corresponding to the ocean circulation.The NNA reacts in a highly sensitive manner to small forcing changes, as shown by our sensitivity experiments. From these experiments it is possible to model specific circulation regimes for glacial and interglacial periods, for melt water events and for the onset of glaciation. The different climatic stages in the circulation model produce different sediment patterns in the sedimentation models, which correspond closely to the sedimentary record. 相似文献
23.
B. von Bodungen A. Antia E. Bauerfeind O. Haupt W. Koeve E. Machado I. Peeken R. Peinert S. Reitmeier C. Thomsen M. Voss M. Wunsch U. Zeller B. Zeitzschel 《International Journal of Earth Sciences》1995,84(1):11-27
Pelagic processes and their relation to vertical flux have been studied in the Norwegian and Greenland Seas since 1986. Results of long-term sediment trap deployments and adjoining process studies are presented, and the underlying methodological and conceptional background is discussed. Recent extension of these investigations at the Barents Sea continental slope are also presented. With similar conditions of input irradiation and nutrient conditions, the Norwegian and Greenland Seas exhibit comparable mean annual rates of new and total production. Major differences can be found between these regions, however, in the hydrographic conditions constraining primary production and in the composition and seasonal development of the plankton. This is reflected in differences in the temporal patterns of vertical particle flux in relation to new production in the euphotic zone, the composition of particles exported and in different processes leading to their modification in the mid-water layers.In the Norwegian Sea heavy grazing pressure during early spring retards the accumulation of phytoplankton stocks and thus a mass sedimentation of diatoms that is often associated with spring blooms. This, in conjunction with the further seasonal development of zooplankton populations, serves to delay the annual peak in sedimentation to summer or autumn. Carbonate sedimentation in the Norwegian Sea, however, is significantly higher than in the Greenland Sea, where physical factors exert a greater control on phytoplankton development and the sedimentation of opal is of greater importance. In addition to these comparative long-term studies a case study has been carried out at the continental slope of the Barents Sea, where an emphasis was laid on the influence of resuspension and across-slope lateral transport with an analysis of suspended and sedimented material. 相似文献
24.
Plage areas and intensities derived from CaII K spectroheliograms are used as a proxy for the facular irradiance excess of solar active regions for the period 19 August to 4 September 1980. Using a calibration method proposed by Vrnak et al. (1991), the photospheric facular index (PFI) with constant facular contrastC
p
= 0.018 is replaced by a variableC
p
, depending on the plage brightness. A sgnificant increase ofC
p
from 0.015 to 0.025 is found for plage areas varying from a few to approx. 6 · 103 millionths hemispheres.Combining the facular irradiance excess with sunspot deficits (as determined for the same period by Steinegger et al. 1990) yields good aggrement with the irradiance variations measured by ACRIM I, using a center-to-limb variation ofC
p
according to Chapman and Meyer (1986). The ratio of facular excess to sunspot deficit (integrated over solid angle 2) decreases from values of 1.5 to 2 for regions with sunspot areas below 100 millionths hemispheres to 0.2 for sunspots of areas > 1000 millionths hemispheres, 相似文献
25.
Getchell Amy Ochoa-Cornejo Felipe Santagata Marika 《Geotechnical and Geological Engineering》2022,40(11):5307-5331
Geotechnical and Geological Engineering - Laponite—a synthetic nanoclay with (2:1) layer structure—has shown promise for the improvement of granular deposits susceptible to earthquake... 相似文献
26.
Dissolved organic matter dynamics during the spring snowmelt at a boreal river valley mire complex in Northwest Russia
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Armine Avagyan Benjamin R. K. Runkle Nina Hennings Hannes Haupt Tarmo Virtanen Lars Kutzbach 《水文研究》2016,30(11):1727-1741
Boreal mire landscapes are rich in soil carbon and significantly contribute to the carbon input of aquatic ecosystems. They are composed of different mesoscale ecohydrological subunits, whose individual contributions to the water and carbon export of mire catchments are not well understood. The spring snowmelt period is the major hydrological event in the annual water cycle of the boreal regions and strongly influences the carbon flux between the terrestrial and aquatic systems. The aim of this study was (1) to provide a conceptual understanding of the spatial and temporal dynamics of the surface water chemistry along a swamp forest‐fen‐bog gradient during the snowmelt period, (2) to quantify the exported dissolved organic carbon (DOC) content in the runoff and (3) to identify the ecohydrological landscape unit that contributes most to DOC export during the snowmelt period in a heterogeneous mire complex in Northwest Russia. The highest DOC concentrations were detected in the swamp forest, and the lowest concentrations were observed at the treeless bog by the end of the snowmelt period (swamp forest: 37–43 mg l?1, bog: 13–17 mg l?1). During the spring snowmelt period, a significant amount (~1.7 g C m?2) of DOC was transferred by the ~74 mm of runoff from the catchment into the river. Variability in the thawing periods led to differences in the relative contributions of each ecohydrological zone to the carbon export measured at a stream channel draining the studied part of the mire complex. An increased understanding of the variation in DOC concentrations and contributions from the mesoscale ecohydrological subunits to carbon export can help to predict the potential regional loss of DOC based on land cover type under climate change. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
27.
This paper presents the method to develop response surface diagrams (RSD) suitable to evaluate the impacts of climate change on potential crop production and crop area. The diagrams depict the response of different agricultural crops to average long-term changes in ambient temperature and precipitation on a country basis. They take into account the spatial and seasonal variability of climate, and differences in the climate response of important crops. RSDs for Germany and the Democratic Republic of Congo illustrate that countries and crop types differ greatly in their sensitivity to unit changes in long-term average climate. In comparing the area-weighted RSDs for Germany and Democratic Republic of Congo, it was found that the potential production in Germany of a weighted aggregation of crops is mainly sensitive to changes in temperature, whereas the potential crop production in the Democratic Republic of Congo mainly responds to changes in precipitation (over the specified ranges of climate variables). The RSDs can provide a visual overview of these varying sensitivities, and are a convenient and simple-to-understand method to summarize crop responses to climate change in a particular country. 相似文献
28.
According to the current paradigm of modern climatology and oceanography, the global ocean thermohaline circulation works as the so-called “global ocean salinity conveyor belt” – a system of currents connecting different ocean basins and most notably – the northern North Atlantic and northern North Pacific Oceans – the most distant regions of the world ocean. It is shown here that a slight disparity in freshwater redistribution between the Atlantic and Pacific oceans can be sufficient for building up and maintaining a global conveyor-type ocean thermohaline circulation. On the other hand, relatively small changes in this disparity leading to change in sea surface salinity contrasts between and in the north-south within the northern parts of these two oceans can easily change the conveyor. 相似文献
29.
The ability of five, global coupled climate models to simulate important atmospheric circulation characteristics in the Southern
Hemisphere for the period 1960–1999 is assessed. The circulation features examined are the Southern Hemisphere annular mode
(SAM), the semi-annual oscillation (SAO) and the quasi-stationary zonal wave 3 (ZW3). The models assessed are the National
Center for Atmospheric Research Community Climate System Model Version 3 (CCSM3), the Commonwealth Scientific and Industrial
Research Organisation Mark 3, the Geophysical Fluid Dynamics Laboratory Model, the Goddard Institute for Space Studies Model
ER (GISS-ER) and the UK Meteorological Office Hadley Center Coupled Model Version 3. The simulations were compared to the
NCAR–NCEP reanalyses. The models simulate a SAO which differs spatially from the observed over the Pacific and Indian oceans.
The amplitudes are too high over the southern ocean and too low over the midlatitudes. These differences are attributed to
a circumpolar trough which is too deep and extends too far north, and to the inability of the models to simulate the middle
to high latitude temperature gradient. The SAM is well-represented spatially by most models but there are important differences
which may influence the flow over the Pacific and in the region extending from the Ross to Weddell Seas. The observed trend
towards positive polarity in the SAM is apparent in the ensemble averages of the GISS-ER and CCSM3 simulations, suggesting
that the trend is due to external forcing by changes in the concentration of ozone and greenhouse gases. ZW3 is well-represented
by the models but the observed trend towards positive phases of ZW3 is not apparent in the simulations suggesting that the
observed trend may be due to natural variability, not external forcing. 相似文献
30.
The sensitivity of the ocean circulation to changes in North Atlantic surface fluxes has become a major factor in explaining climate variability. The role of the Antarctic Bottom Water in modulating this variability has received much less attention, limiting the development of a complete understanding of decadal to millennial time-scale climate change. New analyses indicate that the southern deepwater source may change dramatically (e.g., experience a decrease of as much as two thirds during last 800 years). Such change can substantially alter the ocean circulation patterns of the last millennium. Additional analyses indicate that the Southern Hemisphere led the Northern Hemisphere changes in some of the glacial cycles of Pleistocene, implying a seesaw-type oscillation of the global ocean conveyor. The potential for melting of sea ice and ice sheets in the Antarctica associated with global warming can cause a further slowdown of the southern deepwater source. These results demand an assessment of the role of the Southern Ocean in driving changes of the global ocean circulation and climate. Systematic model simulation targeting the ocean circulation response to changes in surface salinity in the high latitudes of both Northern and Southern Hemispheres demonstrate that meltwater impacts in one hemisphere may lead to a strengthening of the thermohaline conveyor driven by the source in the opposite hemisphere. This, in turn, leads to significant changes in poleward heat transport. Further, meltwater events can lead to deep-sea warming and thermal expansion of abyssal water, that in turn cause a substantial sea-level change even without a major ice sheet melting. 相似文献