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21.
Side-scan sonar, seismic and core data are used to identify mega-flutes, transverse and ‘V’ shaped bedforms in turbidites around the Valencia channel mouth, north-west Mediterranean. Long-range side-scan sonar data reveal a broad, curved, asymmetric, channel, that widens and terminates downfan. The western channel bank near the channel mouth has been partly eroded by turbidity currents that spilled out of the channel. Transverse bedforms on the east of the channel floor are interpreted as antidunes and, if this interpretation is correct, they indicate that the flow was probably supercritical at least locally within the channel. Trains of mega-flutes, are incised into coarse-grained sediments of the channel floor near the channel mouth. The association of mega-flutes and antidunes is thought to be diagnostic of channel–lobe transitions on deep-sea fans. The mega-flutes pass downfan into an area of streaks that diverge at up to 45° and indicates flow expansion from the channel mouth. About 75 km downfan from the channel mouth, deep-towed side-scan data record transverse bedforms (interpreted as antidunes) passing downfan into an area covered by ‘V’ shaped bedforms with upflow pointing apices (named chevrons here). The chevrons are commonly c. 200 m from limb to limb and c. 2 m in amplitude with flow-parallel wavelengths of c. 400 m. We propose that chevrons were formed by a strong, probably supercritical (or near critical) turbidity current spreading from the channel mouth and flowing towards the Balearic Abyssal Plain. Thinning of the turbidity current, resulting from flow spreading would allow the Froude number to remain high up to 100 km from the channel mouth and could explain the observed reduction in antidune wavelength. 相似文献
22.
23.
P. D.Dobbie F.Kenyon R. F.Jameson S. T.Hodgkin 《Monthly notices of the Royal Astronomical Society》2002,331(2):445-452
We present both synthetic and observed I - Z colours for a sample of spectroscopically classified M and L dwarfs drawn primarily from recent wide-field infrared surveys. Our synthetic photometry does not reproduce the strong decrease in the I Harris - Z RGO natural colour beyond M9 to a minimum around L2.5 reported by Steele & Howells. However, it does support the result that the I Harris - Z RGO colour does not increase with spectral type between L0–L2.5 . Instead, the I Harris - Z RGO , i WFC - Z WFC , i SDSS - z SDSS and I C - Z RGO colours are shown to remain more or less constant before increasing once again for types later than L3–L4 . These results, which are supported by both previously published observations and new photometry obtained with the Isaac Newton Telescope (INT) and the Wide Field Camera (WFC), have implications for the interpretation of the recently publicly released Wide Field Survey Programme data covering the Pleiades cluster and surveys for late-type M and L dwarfs in general. 相似文献
24.
Dimension of the Earth's General Ellipsoid 总被引:1,自引:0,他引:1
Burša Milan Kenyon Steve Kouba Jan Raděj Karel Šíma Zdislav Vatrt Viliam Vojtíšková Marie 《Earth, Moon, and Planets》2002,91(1):31-41
The problem of specifying the Earth's mean (general)ellipsoid is discussed. This problem has been greatly simplified in the era of satellite altimetry, especially thanks to the adopted geoidal geopotential value, W0 = (62 636 856.0 ± 0.5) m2 s-2.Consequently, the semimajor axis a of the Earth's mean ellipsoid can be easily derived. However, an a priori condition must be posed first. Two such a priori conditions have been examined, namely an ellipsoid with the corresponding geopotential that fits best W0 in the least squares sense and an ellipsoid that has the global geopotential average equal to W0. It has been demonstrated that both a priori conditions yield ellipsoids of the same dimension, with a–values that are practically identical to the value corresponding to the Pizzetti theory of the level ellipsoid: a = (6 378 136.68 ± 0.06) m. 相似文献
25.
M. Burša S. Kenyon J. Kouba Z. Šíma V. Vatrt V. Vítek M. Vojtíšková 《Studia Geophysica et Geodaetica》2006,50(4):509-524
The long-term variations in the second degree sectorial Stokes parameters of the geopotential have been determined from TOPEX-POSEIDON
(T/P) satellite altimeter data, covering the period of January 1, 1993 to January 3, 2001 (T/P cycles 11-305). It is the first
attempt to determine the variations in the second sectorial harmonics in the Earth’s inertia tensor due to the ocean dynamics.
The variations amount to about 1 × 10−10 (J
2
(2)
≈ 1.6 × 10−6 and S
2
(2)
≈ −0.9 × 10−6). The variations are about 5% of the tidal effect. This corresponds to variations in the directions of the equatorial axes
of the Earth’s inertia ellipsoid of up to 10 arc-seconds. Consequently, the annual and semi-annual variations of the Earth’s
equatorial flattening is about 10−9; i.e. it corresponds to a change of 8 units of its denominator of 91 030. (The equatorial flattening ≈ 1/91 030).
Since the coverage of the Earth’s ocean surface is not worldwide, and the inclination of T/P is i = 66°, it is only 58.2%
(min. depth of the ocean 2 000 m) of the Earth’s surface which is processed, the torque, resulting from the seasonal transfer
of masses within a sea surface layer, is not zero. It amounts up to 1016 kg m2s−2, which is comparable to the total indirect tidal torque due to the Moon and the Sun, ∼ 3.9 × 1016 kg m2s−2. However, the above estimate strongly depends on the adopted thickness of the sea surface layer, ΔR = 50 m. For a larger
thickness of ΔR = 100 m, the seasonal torque amounts to about ∼ 2.3 × 1016 kg m2s−2. 相似文献
26.
Kern E. Kenyon 《Journal of Oceanography》1991,47(2):45-48
The cyclostrophic balance (pressure forcevs. force centrifugal force) is shown to be satisfied for all fluid particles in surface gravity waves with sinusoidal form and
circular particle orbits. Consequences of the cyclostrophic balance are 1) that the normal dispersion relation for deep water
hold and 2) that the orbital radius decrease with increasing depth at the usual exponential rate, from which it follows that
the wave pressure and particle speed also decrease with depth exponentially. In addition, the cyclostrophic and hydrostatic
balances together predict wave breaking at the crests for amplitudes exceeding one divided by the wave number. In contrast
to the traditional perturbation method, based on irrotational flow, the cyclostrophic method does not demand that the amplitude
be much less than a wave length and does not require an infinite wave train. 相似文献
27.
Neil H. Kenyon 《Geo-Marine Letters》1992,12(1):24-32
Published analyses of 61 piston cores, bottom photographs, and dredge samples provide ground truth for 6.5 kHz GLORIA side-scan sonar records of the Mississippi and De Soto fans. GLORIA sound appears to have penetrated through up to 4 m of foraminiferal ooze and terrigenous mud to reach sandy sediments. Possible primary geological causes of high backscatter include slump structures at various scales (1->1,000 cm), possible debris flow fabrics (roughness 1–100 cm) in sandy (5–21%) sediments, and thin ironstone crusts with a roughness of tens of centimeters. 相似文献
28.
A. Elverhøi H. Norem E. S. Andersen J. A. Dowdeswell I. Fossen H. Haflidason N. H. Kenyon J. S. Laberg E. L. King H. P. Sejrup A. Solheim T. Vorren 《Geo-Marine Letters》1997,17(2):119-125
Debris lobes with characteristic lengths, widths, and thickness of 30–200 km, 2–10 km, and 10–50 m, respectively, represent
the main building blocks of deep-sea fans along the Norwegian–Barents Sea continental margin. Their formation is closely related
to the input of clay-rich sediments to the upper continental slope by glaciers during periods of maximum ice advance. It is
likely that slide release was a consequence of an instability arising from high sedimentation rates on the upper continental
slope. The flow behavior of the debris lobes can be described by a Bingham flow model.
Received: 17 November 1995 / Revision received: 24 June 1996 相似文献
29.
Kern E. Kenyon 《Journal of Oceanography》1978,34(6):288-294
East-west vertical sections centered on Kinmei Seamount (35N, 172E) of potential temperature, salinity, and oxygen, based on recent standard hydrographic measurements, and vertical profiles ofin situ temperature and density (
4) east of the seamount, based on STD data, show contrasting variability in the deep water characteristics east and west of the seamount. These data are consistent with horizontal variations in water mass properties (temperature-salinity and temperature-oxygen curves) east of the seamount between 2,600–3,900 m but not west of the seamount. East of the seamount on surfaces of constant potential temperature (or density) salinity and oxygen are higher at a station 200 km from the seamount than at stations on either side. From these relations and from known deep water properties of the North Pacific, it is suggested that east of the seamount, between 2,600–3,900 m, the observations are consistent with northward flow, which is interpreted to be a western boundary current with an east-west scale of about 300 km. 相似文献
30.
Kern E. Kenyon 《Journal of Oceanography》1998,54(4):343-346
The central physics of capillary waves (or ripples) can be understood by an elementary method which makes use of the balance
of static and dynamic pressure differences along the surface streamline between crest and trough, in the steady reference
frame, and conservation of mass through vertical cross-sections beneath crest and trough. Basically Einstein’s (1916) model
of surface gravity waves is adapted for the purpose of explaining the existence of capillary waves of infinitesimal amplitude.
One product of the physical understanding, the phase speed of capillary waves, is derived as a function of the wave length
and surface tension and the result agrees exactly with that obtained by the classical mathematical procedure. In the elementary
method it is not necessary to assume irrotational flow, upon which the classical theory is founded, nor are perturbation expansions
of the nonlinear fluid equations employed. The extension to capillary-gravity waves, by including the acceleration of gravity
in the physical model, is straightforward, and the calculated phase speed of these waves is identical to what is found in
the text books as well. 相似文献