North polar region of Mars: Advances in stratigraphy, structure, and erosional modification   总被引：1，自引：0，他引：1  

Kenneth L. Tanaka  J. Alexis P. Rodriguez  Mary C. Bourke  Kenneth E. Herkenhoff  Chris H. Okubo 《Icarus》2008,196(2):318-358

We have remapped the geology of the north polar plateau on Mars, Planum Boreum, and the surrounding plains of Vastitas Borealis using altimetry and image data along with thematic maps resulting from observations made by the Mars Global Surveyor, Mars Odyssey, Mars Express, and Mars Reconnaissance Orbiter spacecraft. New and revised geographic and geologic terminologies assist with effectively discussing the various features of this region. We identify 7 geologic units making up Planum Boreum and at least 3 for the circumpolar plains, which collectively span the entire Amazonian Period. The Planum Boreum units resolve at least 6 distinct depositional and 5 erosional episodes. The first major stage of activity includes the Early Amazonian (∼3 to 1 Ga) deposition (and subsequent erosion) of the thick (locally exceeding 1000 m) and evenly-layered Rupes Tenuis unit (Abrt), which ultimately formed approximately half of the base of Planum Boreum. As previously suggested, this unit may be sourced by materials derived from the nearby Scandia region, and we interpret that it may correlate with the deposits that regionally underlie pedestal craters in the surrounding lowland plains. The second major episode of activity during the Middle to Late Amazonian (1 Ga) began with a section of dark, sand-rich and light-toned ice-rich irregularly-bedded sequences (Planum Boreum cavi unit, Abb_c) along with deposition of evenly-bedded light-toned ice- and moderate-toned dust-rich layers (Planum Boreum 1 unit, Abb₁). These units have transgressive and gradational stratigraphic relationships. Materials in Olympia Planum underlying the dunes of Olympia Undae are interpreted to consist mostly of the Planum Boreum cavi unit (Abb_c). Planum Boreum materials were then deeply eroded to form spiral troughs, Chasma Boreale, and marginal scarps that define the major aspects of the polar plateau's current regional topography. Locally- to regionally-extensive (though vertically minor) episodes of deposition of evenly-bedded, light- and dark-toned layered materials and subsequent erosion of these materials persisted throughout the Late Amazonian. Sand saltation, including dune migration, is likely to account for much of the erosion of Planum Boreum, particularly at its margin, alluding to the lengthy sedimentological history of the circum-polar dune fields. Such erosion has been controlled largely by topographic effects on wind patterns and the variable resistance to erosion of materials (fresh and altered) and physiographic features. Some present-day dune fields may be hundreds of kilometers removed from possible sources along the margins of Planum Boreum, and dark materials, comprised of sand sheets, extend even farther downwind. These deposits also attest to the lengthy period of erosion following emplacement of the Planum Boreum 1 unit. We find no evidence for extensive glacial flow, topographic relaxation, or basal melting of Planum Boreum materials. However, minor development of normal faults and wrinkle ridges may suggest differential compaction of materials across buried scarps. Timing relations are poorly-defined mostly because resurfacing and other uncertainties prohibit precise determinations of surface impact crater densities. The majority of the stratigraphic record may predate the recent (<20 Ma) part of the orbitally-driven climate record that can be reliably calculated. Given the strong stratigraphic but loose temporal constraints of the north polar geologic record, a comparison of north and south polar stratigraphy permits a speculative scenario in which major Amazonian depositional and erosional episodes driven by global climate activity is plausible.  相似文献   

Testing the applicability of a kinematic wave-based distributed hydrological model in two climatically contrasting catchments     

T. Tanaka  Y. Tachikawa 《水文科学杂志》2015,60(7-8):1361-1373

Abstract

Steep mountainous areas account for 70% of all river catchments in Japan. To predict river discharge for the mountainous catchments, many studies have applied distributed hydrological models based on a kinematic wave approximation with surface and subsurface flow components (DHM-KWSS). These models reproduce observed river discharge of catchments in Japan well; however, the applicability of a DHM-KWSS to catchments with different geographical and climatic conditions has not been sufficiently examined. This research applied a DHM-KWSS to two river basins that have different climatic conditions from basins in Japan to examine the transferability of the DHM-KWSS model structure. Our results show that the DHM-KWSS model structure explained flow regimes for a wet river basin as well as a large flood event in an arid basin; however, it was unable to explain long-term flow regimes for the arid basin case study.  相似文献   

Cyclic behavior of soils and numerical analyses in cold regions and seismic zones     

Tadatsugu Tanaka 《寒旱区科学》2015,7(5):492-502

The solutions of boundary value problems involving strain-softening material property contain serious difficulties from both modeling of strain-localization and a viewpoint of numerical procedure. Mesh size-dependent hardening modulus is considered to alleviate the mesh size-dependency of the solution. The elasto-plastic soil model with kinematic hardening model considering the cumulative deformation by cyclic loading is developed. In finite element analyses, the dynamic relaxation method combined with the generalized return-mapping algorithm is applied to the static drained and un-drained tri-axial tests and plane strain tests. The cyclic behavior of retaining wall problems by freeze and thaw in cold regions is also analyzed. Finally the dynamic progressive failure analysis of rockfill dam is carried out.  相似文献   

Tsunami Bores in Kitakami River     

Elena Tolkova  Hitoshi Tanaka 《Pure and Applied Geophysics》2016,173(12):4039-4054

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Estimation of water requirement per unit carbon fixed by<Emphasis Type="Italic">Eucalyptus camaldulensis</Emphasis> in semi-arid land of Western Australia     

T. Kojima  Y. Tanaka  S. Katoh  K. Tahara  N. Takahashi  K. Yamada 《中国科学D辑(英文版)》2002,45(1):142-147

Afforestation in arid land is a promising method for carbon fixation, but the effective utilization of water is highly important and required. Thus, the evaluation of the amount of water per unit carbon fixed with the tree growth is required to minimize the amount of water supplied to the plants. In this research, a tree is regarded as a carbon fixation reactor with inflows of water and nutrients from roots, and CO₂ as the carbon source from leaves with outflow of water vapor from leaves and accumulation in the tree itself. In the process of photosynthesis and respiration nutritional elements are dissolved in water flow in trees. They do not flow out by these reactions, but are accumulated in trees. Thus, we have treated the behaviour of nutrients as a marker to evaluate the water/carbon ratio.Assuming that nutrient concentration is constant in sap, and the differences in the ratios of nutrient to carbon in living trees and dead (i.e. litter fall, etc.) are neglected, the ratio of the used water to fixed carbon is given as the ratio of nutrient to carbon in the tree body divided by the ratio of nutrient to water in sap. However, some nutrients are translocated and concentrated within the tree and some may be discarded through litter fall. Thus it is important to examine which nutrient element is the most suitable as the tracer.In this paper, the results of the above method applied toEucalyptus camaldulensis in semiarid land of Western Australia are shown. The value of water requirement per unit carbon fixation determined from potassium balance is between 421 kg-H₂O/kg-C for mature trees and 285 kg-H₂O/kg-C for young trees, while the values from calcium balance are much larger than these. The cause of the discrepancy between these values is discussed based on the measured element concentrations in sap and trees and the plant physiology. Finally, the actual average value through the life of a tree is suggested to fall between the two values.  相似文献   

The flares of August 1972     

Harold Zirin  Katsuo Tanaka 《Solar physics》1973,32(1):173-207

We present the analysis of observations of the August flares at Big Bear and Tel Aviv, involving monochromatic movies, magnetograms and spectra. In each flare the observations fit a model of particle acceleration in the chromosphere with emission produced by impact and by heating by the energetic electrons and protons. The region showed inverted polarity and high gradients from birth, and flares appear due to strong magnetic shears and gradients across the neutral line produced by sunspot motions. Post flare loops show a strong change from sheared, force-free fields parallel to potential-field-like loops, perpendicular to the neutral line above the surface.We detected fast (5 s duration) small (1') flashes in 3835 at the footpoints of flux loops in the August 2 impulsive flare at 1838 UT, which may be explained by dumping of > 50 keV electrons accelerated in individual flux loops. The flashes show excellent time and intensity agreement with > 45 keV X-rays. In the less impulsive 2000 UT flare a less impulsive wave of emission in 3835 moved with the separating footpoints. The thick target model of X-ray production gives a consistent model for X-ray, 3835 and microwave emission in the 18:38 UT event.Spectra of the August 7 flare show emission 12 Å FWHM in flare kernels, but only 1 to 2 Å wide in the rest of the flare. The kernels thus produce most of the H emission. The total emission in H in the August 4 and August 7 flares was about 2 × 10³⁰ erg. We belive this dependable value more accurate than previous larger estimates for great flares. The time dependence of total H emission agrees with radio and X-ray data much better than area measurements which depend on the weaker halo.Absorption line spectra show a large (6 km/s^-1) photospheric velocity discontinuity across the neutral line, corresponding to sheared flow across that line.This work has been supported by NASA under NGR 05 002 034, NSF Atmospheric Sciences program under GA 24015, and AFCRL under FI9628-73-C-0085.  相似文献   

Toyokawa Observatory     

H. Tanaka 《Solar physics》1967,1(2):295-300

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Diurnal variations in streamflow and water quality during the summer dry season     

Daiji Kobayashi  Yuji Kodama  Yoshiyuki Ishii  Yumiko Tanaka  Keisuke Suzuki 《水文研究》1995,9(7):833-841

In a headwater basin covered with boreal forest in northern Japan, the summer dry flow was monitored each summer from 1985 to 1993. Streamflow and specific electrical conductance fluctuated diurnally and these variations were attributed to daytime evapotranspiration. In 1989, the daytime reduction in streamflow and conductance were accompanied by a reduction in the HCO^?₃ concentration. The low flow hydrograph was separated into two components using HCO^?₃ and Cl^? concentrations in August 1989, assuming low flow to be a mixture of delayed subsurface flow and of quick shallow flow. The slight diurnal variation in the ratio of shallow flow to subsurface flow caused the diurnal variation in conductance by changing the HCO^?₃ concentration.  相似文献   

Coupled-oscillators     

Y. Tanaka 《Astrophysics and Space Science》1993,210(1-2):333-341

Modal coupling oscillation models for the stellar radial pulsation and coupled-oscillators are reviewed. Coupled-oscillators with the second-order and third-order terms seemed to behave non-systematically. Using the equation by Schwarzschild and Savedoff (1949) with the dissipation term of van del Pol's type which is third-order, we demonstrate the effect of each term. The effects can be understood by the terms of the nonlinear dynamics, which is recently developing, that is. phase-locking, quasi-periodicity, period doubling, and chaos. As the problem of stellar pulsation, especially of double-mode cepheids on the period-ratio, we examine the dependence on the stellar structure from which the coupling constants in the second-order terms are derived. Eigen functions for adiabatic pulsations had been used for the calculation of the constants. It is noted that only two set of the constants are available, that is, for the polytrope model withn = 3 and a cepheid model without convection. Some examples of nonlinear dynamical effects will be shown.It is shown that if the constants were suitable values, the period-ratio of double-mode cepheids is probably realized. The possibility is briefly suggested.  相似文献   

Polarization measurements using the Bragg crystal spectrometers on Hinotori     

Kyo Akita  Katsuo Tanaka  Tetsuya Watanabe 《Solar physics》1983,86(1-2):101-105

The two Bragg crystal spectrometers on board Hinotori provide a new technique for measuring linear polarization of the soft X-ray line emission from solar flares. The results of the measurements of large (X class) flares are given in this paper, and the polarization degree averaged over the soft X-ray maximum phases is estimated to be less than 4%.  相似文献