We report and discuss solar systemNR abundances for nuclidesA>70, obtained as differences between measured solar system abundances and calculatedS-process contributions. The abundance peak atA163 in the rare Earth element region reveals properties which are similar to those of theR-process peaks corresponding to magic neutron numbersN=82 andN=126. We observe that systematic differences in theNR abundances of even-A and odd-A nuclides are restricted to specific mass regions. We discuss possible interpretations and conclude that these differences are most probably related to the properties of nuclear species during – to the stability valley.... A genesis of the elements such as is sketched out would not be confined to our little Solar System, but would probably follow the same general sequence of events in every center of energy now visible as a Star. Sir William Crookes (1886)Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988. 相似文献
Data collected every 20 minutes for 18 months by a meteorological buoy moored on Lake Sempach in Switzerland (maximum depth
86 m, surface area 14.1 km2) are used to calculate different processes contributing to the net heat flux between water and atmosphere. The processes
considered are shortwave and longwave radiation, evaporation/condensation and sensible heat transfer. The temporal resolution
of the measurements allows the evaluation of the processes occurring on three different time scales: diurnal variations, weather
events of a few days and yearly cycles. The heat content of the lake is calculated from quasi-continuous measurements of water
temperature at different depths. The yearly amplitude of the heat content is 1100·106 J/m2. Short-time variations of the heat flux determined from water temperature analysis agree well with the flux variations modeled
using meteorological data. However, the latter generally underestimates the measured net heat flux in the long term. Wind
measurements, together with the net heat flux, are used to calculate the Flux Richardson Number and the Monin-Obukov Length.
Examples are given to show the predominant influence of the wind on the stratification of the upper water column and thus
on the surface water temperature.
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The simulation of the mean seasonal cycle of sea surface temperature (SST) remains a challenge for coupled ocean–atmosphere
general circulation models (OAGCMs). Here we investigate how the numerical representation of clouds and convection affects
the simulation of the seasonal variations of tropical SST. For this purpose, we compare simulations performed with two versions
of the same OAGCM differing only by their convection and cloud schemes. Most of the atmospheric temperature and precipitation
differences between the two simulations reflect differences found in atmosphere-alone simulations. They affect the ocean interior
down to 1,000 m. Substantial differences are found between the two coupled simulations in the seasonal march of the Intertropical
Convergence Zone in the eastern part of the Pacific and Atlantic basins, where the equatorial upwelling develops. The results
confirm that the distribution of atmospheric convection between ocean and land during the American and African boreal summer
monsoons plays a key role in maintaining a cross equatorial flow and a strong windstress along the equator, and thereby the
equatorial upwelling. Feedbacks between convection, large-scale circulation, SST and clouds are highlighted from the differences
between the two simulations. In one case, these feedbacks maintain the ITCZ in a quite realistic position, whereas in the
other case the ITCZ is located too far south close to the equator. 相似文献
The low-frequency evolution of Indian rainfall mean-state and associated interannual-to-decadal variability is discussed for the last 6000 years from a multi-configuration ensemble of fully coupled global transient simulations. This period is marked by a shift of Indian Summer Monsoon Rainfall (ISMR) distribution towards drier conditions, including extremes, and a contraction of the rainy season. The drying is larger in simulations with higher horizontal resolution of the atmosphere and revised land surface hydrology. Vegetation–climate interactions and the way runoff is routed to ocean modulate the timing of the monsoon onset but have negligible effects on the evolution of seasonal rainfall amounts in our modeling framework in which carbon cycling is always active. This drying trend is accompanied by changes in ISMR interannual-to-decadal variability decreasing over north and south India but increasing over central India (20°–25° N). The ISMR interannual-to-decadal variability is decomposed into six physically consistent regimes using a clustering technique to further characterize its changes and associated teleconnections. From 6 to 3.8 kyr bp, the century-to-century modulations in the frequency of occurrence associated to the regimes are asynchronous between the simulations. Orbitally-driven trends can only be detected for two regimes over the whole 6–0 kyr bp period. These two regimes reflect increased influence of ENSO on both ISMR and Indian Ocean Dipole as the inter-hemispheric energy gradient weakens. Severe long-term droughts are also shown to be a combination of long-term drying and internally generated low-frequency modulations of the interannual-to-decadal variability.
We have developed a new method to accelerate tracer simulations to steady-state in a 3-D global ocean model, run off-line.
Using this technique, our simulations for natural 14C ran 17 times faster when compared to those made with the standard non-accelerated approach. For maximum acceleration we
wish to initialize the model with tracer fields that are as close as possible to the final equilibrium solution. Our initial
tracer fields were derived by judiciously constructing a much faster, lower-resolution (degraded), off-line model from advective
and turbulent fields predicted from the parent on-line model, an ocean general circulation model (OGCM). No on-line version
of the degraded model exists; it is based entirely on results from the parent OGCM. Degradation was made horizontally over
sets of four adjacent grid-cell squares for each vertical layer of the parent model. However, final resolution did not suffer
because as a second step, after allowing the degraded model to reach equilibrium, we used its tracer output to re-initialize
the parent model (at the original resolution). After re-initialization, the parent model must then be integrated only to a
few hundred years before reaching equilibrium. To validate our degradation-integration technique (DEGINT), we compared 14C results from runs with and without this approach. Differences are less than 10‰ throughout 98.5% of the ocean volume. Predicted
natural 14C appears reasonable over most of the ocean. In the Atlantic, modeled Δ14C indicates that as observed, the North Atlantic Deep Water (NADW) fills the deep North Atlantic, and Antartic Intermediate
Water (AAIW) infiltrates northward; conversely, simulated Antarctic Bottom Water (AABW) does not penetrate northward beyond
the equator as it should. In the Pacific, in surface eastern equatorial waters, the model produces a north–south assymetry
similar to that observed; other global ocean models do not, because their resolution is inadequate to resolve equatorial dynamics
properly, particularly the intense equatorial undercurrent. The model’s oldest water in the deep Pacific (at −239‰) is close
to that observed (−248‰), but is too deep. Surface waters in the Southern Ocean are too rich in natural 14C due to inadequacies in the OGCM’s thermohaline forcing.
Received: 18 March 1997 / Accepted: 27 July 1997 相似文献
Fossil particle tracks and spallation-produced He and Ne in the Kenna ureilite indicate that it existed in space as a small object for 23 m.y. In our study of Kenna, we found no evidence of trapped He or Ne. Large amounts of heavy rare gases occur in Kenna in concentrations typical of ureilites. In a step-wise release of gases, the isotopic compositions of Kr and Xe were found to be constant above 600°C, revealing the presence of a single retentively sited component. The Xe isotopic abundances are characterized by 124:126:128:129:130:131:132:134:136 = 0.471:0.414:8.280:103.61: 16.296:81.92:100:37.70:31.23. This isotopic composition is distinct from AVCC (average carbonaceous chondritic), but similar to compositions known for some time in certain temperature fractions of Renazzo, Murray and Murchison. Kenna-type Xe appears to be one of the several components found in carbonaceous chondrites.
Binz et al. (Geochim. Cosmochim. Acta 39, 1576–1579, 1975) have recently found that many volatile trace elements are strongly depleted in ureilites. Thus, the relatively large amounts of heavy rare gases present in ureilites did not result from a mixture of a volatile-rich component with the ureilite host. It appears that some material rich in carbon and heavy rare gases was incorporated into a differentiated ureilite host. All current hypotheses which purport to explain the origin of trapped gases in meteorites encounter difficulty in accounting for trapped gases in ureilites in a straightforward manner. 相似文献
Abstract— We report on studies of the concentrations of cosmogenic nuclides in the magnetic fraction of cosmic dust particles recovered from the South Pole Water Well (SPWW) and from Greenland. Our results confirm that cosmic dust material from these locations contains measurable amounts of cosmogenic nuclides. The Antarctic particles (and possibly those from Greenland as well) also contain minor amounts of solar Ne. Concentrations of cosmogenic nuclides are consistent with irradiation of this material as small objects in space, with exposure ages similar to the expected Poynting‐Robertson (P‐R) lifetimes of 50–200 kyr for particles 25–100 μm in size. 相似文献