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741.
In this study, singular vector analysis was performed for the period from 1856 to 2003 using the latest Zebiak–Cane model
version LDEO5. The singular vector, representing the optimal growth pattern of initial perturbations/errors, was obtained
by perturbing the constructed tangent linear model of the Zebiak–Cane model. Variations in the singular vector and singular
value, as a function of initial time, season, ENSO states, and optimal period, were investigated. Emphasis was placed on exploring
relative roles of linear and nonlinear processes in the optimal perturbation growth of ENSO, and deriving statistically robust
conclusions using long-term singular vector analysis. It was found that the first singular vector is dominated by a west–east
dipole spanning most of the equatorial Pacific, with one center located in the east and the other in the central Pacific.
Singular vectors are less sensitive to initial conditions, i.e., independence of seasons and decades; while singular values
exhibit a strong sensitivity to initial conditions. The dynamical diagnosis shows that the total linear and nonlinear heating
terms play opposite roles in controlling the optimal perturbation growth, and that the linear optimal perturbation is more
than twice as large as the nonlinear one. The total linear heating causes a warming effect and controls two positive perturbation
growth regions: one in the central Pacific and the other in the eastern Pacific; whereas the total linearized nonlinear advection
brings a cooling effect controlling the negative perturbation growth in the central Pacific. 相似文献
742.
Summary This paper presents a comparison of column water vapor (CWV) information derived from both infrared measurements as part of the TIROS-N Operational Vertical Sounder (TOVS) and Special Sensor Microwave/Imager (SSM/I) in an attempt to assess the relative merits of each kind of data. From the analyses presented in this paper, it appears that both types of satellite data closely reproduce the bulk climatological relationships introduced in earlier studies using different data. This includes both the bulk relationship between CWV and the sea surface temperature and the annual variation of CWV over the world's oceans. The TOVS water vapor data tends to be systematically smaller than the SSM/I data and when averaged over the ocean covered regions of the globe this difference is between 2–3 kgm–2. Using a cloud liquid water threshold technique to establish clear sky values of SSM/I water vapor, we conclude that the differences between TOVS and SSM/I are largely a result of the clear sky bias in TOVS sampling except in the subsidence regions of the subtropics. The clear sky bias is considerably smaller than previously reported and we attribute this improvement to the new physical retrieval scheme implemented by NOAA NESDIS. While there is considerable agreement between the two types of satellite data, there are also important differences. In regions where there is drying associated with large scale subsidence of the atmosphere, the TOVS CWV's are too moist relative to both radiosonde and SSM/I data and this difference may exceed 10 kgm–2. The explanation for this difference lies in the limitations of infrared radiative transfer. By contrast, in regions of deep convection, such as in the ITCZ, TOVS CWV is systematically lower than the SSM/I CWV. Both TOVS and SSM/I data demonstrate similar kinds of gross effects of large scale circulation on the water vapor except in these subsidence regions where TOVS data leads to an under-prediction of the effects of subsidence drying.With 11 Figures 相似文献
743.
R. J. M. Farla H. Kokkonen J. D. Fitz Gerald A. Barnhoorn U. H. Faul I. Jackson 《Physics and Chemistry of Minerals》2011,38(5):363-377
The rate of static dislocation recovery in Fo90 olivine has been studied under conditions of high temperature and controlled atmosphere in compressively deformed polycrystals
hot-pressed from synthetic (sol–gel) and natural (San Carlos) precursor powders. The sol–gel olivine, containing a small fraction
of orthopyroxene, was deformed to a final strain of 19% with a maximum differential stress of 266 MPa whereas the San Carlos
specimen was deformed to 15% strain and 260 MPa differential stress. Small samples cut from these deformed materials were
annealed under high-temperature, controlled atmosphere conditions, for different durations to allow partial recovery of the
dislocation sub-structures. Oxidative-decoration of the microstructural features, followed by backscattered electron imaging
at 5 kV and image analysis, was used to determine dislocation density. The variation of dislocation density ρ with time t at absolute temperature T was fitted to a second-order rate equation, in integral form, 1/ρ(t) − 1/ρ(0) = kt with k = k
0 exp(−E
a/RT). The activation energy E
a of the recovery process is 240 ± 43 and 355 ± 81 kJ mol−1 for sol–gel and San Carlos olivine polycrystals, respectively. The measured rates are one to two orders of magnitude lower
than those reported in previous studies on natural single crystal olivine. The difference may be explained by several factors
such as high dislocation densities measurable from large areas at high magnification for the SEM and the technique used to
estimate dislocation densities. Comparison between fine-grained sol–gel olivine and the coarser-grained San Carlos olivine
aggregate did not indicate that grain boundaries play an important role in dislocation recovery, but the absence of grain
boundaries might also have contributed to the high dislocation recovery rates previously measured for single crystals. 相似文献
744.
M. Grégoire I. Jackson S. O'Reilly J. Cottin 《Contributions to Mineralogy and Petrology》2001,142(2):244-259
Deep-seated meta-igneous xenoliths brought to the surface by alkali basaltic magmas from the Kerguelen Islands reveal that basaltic magmas have intruded the upper mantle throughout their geological evolution. These xenoliths record volcanic activity associated with their early South East Indian Ridge location and subsequent translation to an intraplate setting over the Kerguelen Plume. The meta-igneous xenoliths sample two distinctive geochemical episodes: one is tholeiitic transitional and one is alkali basaltic. Geothermobarometry calculations provide a spatial context for the rock type sequence sampled and for interpreting petrophysical data. The garnet granulites equilibrated over a pressure range of 1.15 to 1.35 GPa and the garnet pyroxenite at 1.8 GPa. Ultrasonic measurements of compressional wave speed VP have been carried out at pressures up to 1 GPa, and densities measured for representative samples of meta-igneous xenoliths and for a harzburgite that represents the peridotitic mantle. VP and density have also been calculated using modal proportions of minerals and appropriate elastic properties for the constituent minerals. Calculated and measured VP agree well for rock types with microstructures not complicated by kelyphitic breakdown of garnet and/or pervasive grain-boundary cracking. Pyroxene granulites have measured and calculated VP within the range 7.37-7.52 km/s; calculated velocities for the garnet granulites and pyroxenites range from 7.69 to 7.99 km/s, whereas measured and calculated VP for a mantle harzburgite are 8.45 and 8.29 km/s respectively. The seismic structure observed beneath the Kerguelen Islands can be explained by (1) a mixture of underplated pyroxene granulites and ultramafic rocks responsible for the 2-3 km low velocity transitional zone below the oceanic layer 3, (2) varying proportions of granulites and pyroxenites in different regions within the upper mantle producing the lateral heterogeneities, and (3) intercalation of the granulites and pyroxenites throughout the entire upper mantle column, along with elevated temperatures, accounting for the relatively low mantle velocities (7.70-7.95 km/s). 相似文献
745.
We present a two-shell polarization model for the α-quartz and α-cristobalite structures. By allowing for polarization, we correct problems encountered in purely ionic bonding treatments of tetrahedrally coordinated silica phases. The shell model predicts zero pressure structures in very good agreement with experiment using no empirical parameters. The behavior of the shell model α-quartz lattice upon compression shows dramatic improvement over the distorted, rigid lattice given by the ionic model. 相似文献