The orientation of the atmospheric angular momentum vector of Titan and its temporal variation predicted by a general circulation model are analysed and interpreted. The atmospheric angular momentum vector is tilted by a few degrees from the polar axis and the vector rotates (precesses) westward with a constant period of 1 Titan day. The fast westward rotation is likely to be caused by migrating diurnal thermal tides. The tilt is almost cancelled out in the troposphere by the wavenumber 2 pattern of Saturn's gravitational tide, but is more pronounced in the stratosphere, where thermal tides are significant. The predicted tilt angle and the equatorial angular momentum vary with season and maximize when the hemispheric asymmetry of the axial angular momentum or superrotation attains its peak. 相似文献
The paleomagnetic field intensity is estimated with the aid of the Koenigsberger-Thellier method for four ordinary chondrites and one carbonaceous chondrite by assuming that the stable NRM component of these meteorites is attributable to the TRM acquired in a low-temperature range (lower than about 400°C) during their extremely-slow cooling process. The results are summarized in Table IV, where the paleomagnetic field intensity ranges from 0.10 to 0.97 Oe.Possible effects of the extremely-slow cooling rate of meteorites and the secondary TRM acquisition of the surface fusion crust upon the original NRM of the meteorite interior are discussed. 相似文献
The ferromagnetism of irons, stony-irons, E-, H-, L- and LL-chondrites and achondrites is due to a metallic phase comprising mostly Fe and Ni and small amounts of Co and P. The ferromagnetic constituent in non-metamorphosed C-chondrites is magnetite, but some metamorphosed C-chondrites contain FeNi metallic grains too.
Among the stony meteorites, the content of metals as determined by their saturation magnetization (IS) sharply decreases in the order E → H → L → LL → achondrites, whereas the IS value for magnetite and additional metals in C-chondrites ranges from the IS value of achondrites to that of L-chondrites.
With an increase of Ni-content in the metallic phase in chondrites of the order E → H → L → LL → C, the relative amount of Ni-poor kamacite magnetization, IS(), in the total IS decreases in the same order, from IS()/IS 1 for E-chondrites to IS()/IS 0 for C-chondrites. Thus, E-, H-, L-, LL- and C-chondrites and achondrites are well separated in a diagram of IS()/IS versus I, which could be called a magnetic classification diagram for stony meteorites.
As the surface skin layer of all meteorites is anomalously magnetized, it must be removed and the natural remanent magnetization (NRM) of the unaltered interior only must be examined for the paleomagnetic study. The NMR of C-chondrites is highly stable and that of achondrites is reasonably stable against AF-demagnetization, whereas the NMR of E-chondrites and ordinary chondrites as well as stony-iron meteorites is not very stable in most cases. Although the NRM of iron meteorites is reasonably stable, it is not attributable to the extraterrestrial magnetic field.
The paleointensity for Allende C3-chondrite is estimated to be about 1.0 Oe assuming that its NRM is of TRM origin. The paleointensity for other reasonably reliable C-chondrites (Orgueil, Mighei, Leoville and Karoonda) is also around 1 Oe.
The paleointensity for two achondrites has been determined to be about 0.1 Oe. The NRM of other achondrites also suggests that their paleointensity is roughly 0.1 Oe.
The NRM of ordinary chondrites is less stable than that of C-chondrites and achondrites so that the estimated paleointensity for ordinary chondrites is less reliable. The paleointensity for comparatively reliable ordinary chondrites ranges from 0.1 to 0.4 Oe.
The paleointensity values of 1 Oe for C-chondrites and 0.1 Oe for achondrites may represent the early solar nebula magnetic field about 4.5 × 109 years ago. A possibility that the paleomagnetic field for achondrites was a magnetic field attributable to a dynamo within a metallic core of their parent planet may also not be rejected. 相似文献
This study investigates the convective boundary layer (CBL) that develops over anon-homogeneous surface under different thermal and dynamic conditions. Analysesare based on data obtained from a Russian research aircraft equipped with turbulentsensors during the GAME-Siberia experiment over Yakutsk in Siberia, from April to June 2000.Mesoscale thermal internal boundary layers (MTIBLs) that radically modified CBLdevelopment were observed under unstable atmospheric conditions. It was found thatMTIBLs strongly influenced the vertical and horizontal structures of virtual potentialtemperature, specific humidity and, most notably, the vertical sensible and latent heatfluxes. MTIBLs in the vicinity of the Lena River lowlands were confirmed by clouddistributions in satellite pictures.MTIBLs spread through the entire CBL and radically modify its structure if the CBL isunstable, and strong thermal features on the underlying surface have horizontal scalesexceeding 10 km. MTIBL detection is facilitated through the use of special parameterslinking shear stress and convective motion.The turbulent structure of the CBL with and without MTIBLs was scaled usingthe mosaic or flux aggregate approach. A non-dimensional parameterLRau/Lhetero (where LRau is Raupach's length and Lhetero is the horizontal scale of the surface heterogeneity)estimates the application limit of similarity and local similarity scaling models forthe mosaic parts over the surface. Normalized vertical profiles of wind speed, airtemperature, turbulent sensible and latent heat fluxes for the mosaic parts withLRauLhetero < 1 could be estimated by typical scalingcurves for the homogeneous CBL. Traditional similarity scaling models for the CBLcould not be applied for the mosaic parts with LRau/Lhetero > 1.For some horizontally non-homogeneous CBLs, horizontal sensible heat fluxes werecomparable with the vertical fluxes. The largest horizontal sensible heat fluxes occurred at the top of the surface layer and below the top of the CBL.Formerly affiliated to the Frontier Observational Research System for Global ChangeFormerly affiliated to the Frontier Observational Research System for Global Change 相似文献
An ore value-tonnage diagram has been proposed for assessing mineral resources. Diagrams of W+Mo, and Pb+Zn deposits show
a good linearity between ore value and logarithms of cumulative ore tonnage. Diagrams of the massive sulfide, orthomagmatic,
placer, porphyry, replacement, and stratabound types are also linear. It is assumed, therefore, that deposits of each of these
commodities and these types belong to a single population. In contrast, the ore value-tonnage relations of all the deposits
analyzed here is approximated by the combination of two exponential functions. The same feature is seen for deposits of the
Cu+W+Mo, Cu+Pb+Zn, and Au+Ag commodities, and of the vein and unconformity-related types. This suggests that deposits belonging
to each of such categories are divided into the high and low value groups. We can expect, accordingly, to find high value
deposits of such categories. 相似文献
Partitioning of elements between majorite garnet and ultrabasic melt has been studied at 16 GPa and 1950° C. Ca, Ti, La, Sm, Gd, Zr, Hf, Fe, Ni, Mn, K, and Na are enriched in the melt, whereas Al, Cr, V, Sc and Yb are concentrated in majorite garnet. Thus, majorite garnet fractionation by partial melting could produce chemical heterogeneities in these elements deviating from chondritic abundance. Using the partitioning behaviour of elements between majorite garnet and ultrabasic melt, the petrogenesis of komatiite is discussed. A simple model to explain the chemical varieties of komatiites is as follows. Aluminadepleted komatiite was generated by partial melting of the primitive mantle at 200–650 km depth, and alumina-enriched komatiite is the product of remelting of the residual solid at the same depths, whereas alumina-undepleted komatiite was formed by partial melting of the primitive upper mantle at depths shallower than 200 km. We suggest the possibility of large-scale chemical layering or heterogeneity in the early Archean upper mantle as an alternative model for komatiite genesis; shallower mantle depleted in majorite garnet and the underlying mantle enriched in majorite garnet. Alumina-depleted and alumina-enriched komatiites in the early Archean might be generated by a high degree of partial melting of the layered mantle. Such chemical layering could have been homogenized by the late Archean. This explains the observations that alumina-depleted and alumina-enriched komatiites were generally formed in the early Archean but alumina-undepleted komatiite was erupted in the late Archean. 相似文献
Unlike in the developed countries, Ethiopia does not have carbon inventories and databank to monitor and enhance carbon sequestration potential of different forests. Only small efforts have been made so far to assess the biomass and soil carbon sequestration at micro-level. This study was carried out to obtain sufficient information about the carbon stock potential of Gerba-Dima forest in south-western Ethiopia. A total of 90 sample plots were laid by employing stratified random sampling. Nested plots were used to collect data of the four carbon pools. For trees with a diameter range of 5 cm < diameter < 20 cm, the carbon stock was assessed from a plot size of 49 m2 (7 m * 7 m). For trees with a diameter range of 20 cm < diameter < 50 cm, the carbon stock was assessed from a plot size of 625 m2 (25 m * 25 m). For trees > 50 cm diameter, an additional larger sample of 35 * 35 m2 was used. Litter, herb and soil data were collected from 1 m2 subplot established at the center of each nested plot. To compute the above ground biomass carbon stock of trees and shrubs with DBH > 5 cm, their DBH and height were measured. The biomass carbon assessment of woody species having DBH < 5 cm, litter and herb were conducted by measuring their fresh weight in the field and dry weight in the laboratory.
Results
The mean total carbon stock density of Gerba-Dima forest was found to be 508.9 tons carbon ha−1, out of which 243.8, 45.97, 0.03 and 219.1 tons carbon ha−1 were stored in the above ground biomass, below ground biomass, litter biomass and soil organic carbon, respectively.
Conclusions
The existence of high carbon stock in the study forest shows the potential of the area for climate change mitigation. Thus, all stakeholders at the local and national level should work together to implement effective conservation measures and get benefit from the biocarbon fund.
