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991.
Andreas Dittrich Annette Schulte-Rentrop Michael Marek Volker Späth 《Acta Geophysica》2007,55(1):33-46
Flow in rivers and on floodplains is complex as it is affected by several interconnected factors such as topography, sediment
transport and vegetation characteristics. The resulting processes are explained by the measure “Hartheim” planned for retention
purposes at the Upper Rhine river. On the basis of existing formulas and instruments it is demonstrated that a good estimation
of the development of the measure is possible. The proposed procedure is a useful tool for estimating morphological developments
of restored river sections. 相似文献
992.
Adrien Oth Friedemann Wenzel Hillel Wust-Bloch Ellen Gottschämmer Zvi Ben-Avraham 《Pure and Applied Geophysics》2007,164(1):23-37
3-D simulations of elastic wave propagation generated by earthquakes with magnitudes between 5.5 and 7.0 are used to parameterize
strong ground motion attenuation relations for the Dead Sea Rift (DSR) graben structure. The results show that standard attenuation
relations with an isotropic distance parameter are inadequate for a graben structure with a deep sedimentary trough. A new
strategy is devised for the parameterization of attenuation relations in graben structures by looking at the statistical properties
of 53 simulated earthquakes of variable magnitudes located at various sites along the western boundary fault of the DSR graben.
An exemplary attenuation relation is designed from the synthetics for the 1 Hz spectral acceleration, modifying the Joyner-Boore-type
parametrization by adding coefficients suited for three different source-to-sensor configurations: within the graben, beyond
the graben and path unaffected by the graben structure. 相似文献
993.
Coupling of groundwater and surface water at Lake Willersinnweiher: Groundwater modeling and tracer studies 总被引:1,自引:0,他引:1
994.
995.
F. W. Jäger 《Solar physics》1972,27(2):481-488
It is shown in detail in which way magnetographic measurements may be affected by instrumental polarization. To eliminate this influence we propose a combined method of partial compensation and computation practicable successfully with only a moderate expenditure of calculations and instrumental equipment. 相似文献
996.
Lauri Ryynänen 《Astrophysics and Space Science》1970,8(3):497-501
Pulsars at different galactic latitudes have different periods. It seems possible that there are two different types of pulsars. 相似文献
997.
Spatial And Temporal Variability Of Mixed-Layer Depth And Entrainment Zone Thickness 总被引:4,自引:1,他引:3
Mixed-layer depth and entrainment zone thickness areextracted from two large lidar data sets with arecently developed technique. The entrainment fluxratio (which is often used to model entrainment inatmospheric boundary-layer models) can be calculatedfrom these two quantities. This ratio is generallybelieved to be in the range of 0.1 and 0.4. Aqualitative analysis of time series (MERMOZ II dataset) confirms this range of values under equilibriumconditions (afternoon hours), but also shows that itclearly underestimates the importance of entrainmentduring the morning hours when the mixed layer isgrowing most rapidly. An examination of the spatialdistribution of the entrainment flux ratio (Pacific'93 data set) shows that this parameter is spatiallyhighly variable, even during equilibrium hours inthe afternoon. In regions where the boundary layerhas to adjust to new boundary conditions at theground, values much larger than 0.4 can be observed. Although these results can only be interpretedqualitatively, they suggest that currently usedentrainment parameterisations in boundary-layer modelsare not sufficient to capture the entrainment processproperly. 相似文献
998.
Temporary enhancements of the coronal emission measure in a quiet region have been shown to constitute a significant energy input. Here some relatively large events are studied for simultaneous brightenings in transition region lines and in radio emission. Associated emissions are discussed and tested for characteristics known from full-sized impulsive flares in active regions. Heating events and flares are found to have many properties in common, including (i) associated polarized radio emission, which usually precedes the emission measure peak (Neupert effect) and sometimes has a non-thermal spectrum, and (ii) associated and often preceding peaks in Ov and Hei emission. On the other hand, heating events also differ from impulsive flares: (i) In half of the cases, their radio emission at centimeter waves shows a spectrum consistent with thermal radiation, (ii) the ratio of the gyro-synchrotron emission to the estimated thermal soft X-ray emission is smaller than in flares, and (iii) the associated emission in the Ov transition region line shows red shifts and blue shifts, indicating upflows in the rise phase and downflows in the decay phase, respectively. Nevertheless, the differences seem to be mainly quantitative, and the analyzed heating events with thermal energies around 1026 erg may in principle be considered as microflares or large nanoflares, thus small versions of regular flares. 相似文献
999.
Sebastian Wagner Martin Widmann Julie Jones Torsten Haberzettl Andreas Lücke Christoph Mayr Christian Ohlendorf Frank Schäbitz Bernd Zolitschka 《Climate Dynamics》2007,29(4):333-355
This study investigates the atmospheric circulation in transient climate simulations with a coupled atmosphere–ocean general
circulation model (GCM) for the mid-Holocene (MH) period 7–4.5 ka BP driven with combinations of orbital, solar and greenhouse
gas forcings. The focus is on southern South America. Statistical downscaling models are derived from observational data and
applied to the simulations to estimate precipitation in south-eastern Patagonia during the MH. These estimates are compared
with lake level estimates for Laguna Potrok Aike (LPA) from sediments. Relative to pre-industrial conditions (i.e. 1550–1850),
which show extraordinarily high lake levels, the proxy-based reconstructed lake levels during the MH are lower. The downscaled
simulated circulation differences indicate higher LPA precipitation during the MH from March to August, higher annual means,
and reduced precipitation from September to February. Thus the reconstructed lower LPA lake levels can not be explained solely
by the simulated precipitation changes. Possible reasons for this discrepancy are discussed. Based on proxy data from southern
South America hypotheses have also been proposed on the latitudinal position of the southern hemispheric westerlies (SHWs).
In agreement with some of these hypotheses our simulations show an increased seasonal cycle of the latitudinal position of
the SHWs during the MH, which can be explained by the orbital forcing. The simulations also show stronger SHWs over southern
Patagonia during austral summer and weaker SHWs during winter. The downscaling model associates weaker SHWs with increased
precipitation in the LPA region. However, this relationship is only moderate, and therefore the downscaling model does not
support the assumption of a strong link between mean SHWs and precipitation over south-eastern Patagonia, which is the basis
of many proxy-based hypotheses about the SHWs. 相似文献
1000.
Assessments of the impacts of global change on carbon stocks in mountain regions have received little attention to date, in
spite of the considerable role of these areas for the global carbon cycle. We used the regional hydro-ecological simulation
system RHESSys in five case study catchments from different climatic zones in the European Alps to investigate the behavior
of the carbon cycle under changing climatic and land cover conditions derived from the SRES scenarios of the IPCC. The focus
of this study was on analyzing the differences in carbon cycling across various climatic zones of the Alps, and to explore
the differences between the impacts of various SRES scenarios (A1FI, A2, B1, B2), and between several global circulation models
(GCMs, i.e., HadCM3, CGCM2, CSIRO2, PCM). The simulation results indicate that the warming trend generally enhances carbon
sequestration in these catchments over the first half of the twenty-first century, particularly in forests just below treeline.
Thereafter, forests at low elevations increasingly release carbon as a consequence of the changed balance between growth and
respiration processes, resulting in a net carbon source at the catchment scale. Land cover changes have a strong modifying
effect on these climate-induced patterns. While the simulated temporal pattern of carbon cycling is qualitatively similar
across the five catchments, quantitative differences exist due to the regional differences of the climate and land cover scenarios,
with land cover exerting a stronger influence. The differences in the simulations with scenarios derived from several GCMs
under one SRES scenario are of the same magnitude as the differences between various SRES scenarios derived from one single
GCM, suggesting that the uncertainty in climate model projections needs to be narrowed before accurate impact assessments
under the various SRES scenarios can be made at the local to regional scale. We conclude that the carbon balance of the European
Alps is likely to shift strongly in the future, driven mainly by land cover changes, but also by changes of the climate. We
recommend that assessments of carbon cycling at regional to continental scales should make sure to adequately include sub-regional
differences of changes in climate and land cover, particularly in areas with a complex topography. 相似文献