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321.
ABSTRACTKnowledge of rainfall characteristics such as drop-size distribution is essential for the development of erosion-mitigation strategies and models. This research used an optical disdrometer to elucidate the relationships between raindrop-size distribution, median volume drop diameter (D50), kinetic energy and radar reflectivity (dBz) of simulated rainfall of different intensities. The D50 values were higher for the simulated rain than for natural rain at almost all rainfall intensities, perhaps due to variations in rainfall types and the turbulence in natural rain that breaks up large drops. The kinetic energy ranged from 26.67 to 5955.51 J m?2 h ?1, while the median volume drop diameter (D50) was in the range 1.94–7.25 mm, for intensities between 1.5 and 202.6 mm h?1. The relationship between radar reflectivity (Z) and the intensity (R) of the simulated rain was best described by a power law function (Z = aRb), with a and b coefficients in the ranges 162–706 and 0.94–2.46, respectively, throughout the range of rainfall intensities (1.5–202.6 mm h?1). 相似文献
322.
Atsushi Kubokawa 《地球物理与天体物理流体动力学》2013,107(1-4):223-257
Abstract The instability of a current with a geostrophic surface density front is investigated by means of a reduced gravity model having a velocity profile with nearly uniform potential vorticity. It is shown that currents are unstable when the mean potential vorticity decreases toward the surface front at the critical point of the frontal trapped waves investigated by Paldor (1983). This instability is identical with that demonstrated by Killworth (1983) in the longwave limit. The cross-stream component of mass flux and the rates of energy conversions among the five energy forms defined by Orlanski (1968) are also calculated. The main results are as follows, (a) The mass flux toward the surface front is positive near the front and negative around the critical point. The positive mass flux near the front does not vanish at the position of the undisturbed surface front, so that the mean position of the front moves outward and the region of the strong current spreads. (b) The potential energy of the mean flow integrated over the fluid is released through the work done by the force of the pressure gradient of the mean flow on the fluid, and is converted into the kinetic energy of the mean flow. (c) In the critical layer, the mean flow is rapidly accelerated with the growth of the unstable wave. This acceleration is caused by the rapid phase shift of the unstable wave in the critical layer. 相似文献
323.
M. Yagi Y. Nakamura M. Doi K. Shimasaku S. Okamura 《Monthly notices of the Royal Astronomical Society》2006,368(1):211-220
We investigate the behaviour of the asymmetry parameter A as a morphological parameter using a 'volume-limited' sample of 349 galaxies (distance ≤25 Mpc, MV ≤−18.5 mag) and a larger magnitude-limited sample of 707 nearby galaxies. We confirm the correlation of A with morphological type. The late-type galaxies (Sdm, Sm and Im) have larger A than early-type galaxies, and they tend to have larger A than spiral galaxies. We investigate the usefulness of the A versus concentration index C in diagram as a tool for the regular–irregular and early–late classification. The diagram is not very useful to the regular versus late-type irregular classification, as inferred previously, but it is found to be useful to the early–late classification. 相似文献
324.
325.
Kenya Ohgushi Yoshitaka Matsushita Nobuyoshi Miyajima Yoshio Katsuya Masahiko Tanaka Fujio Izumi Hirotada Gotou Yutaka Ueda Takehiko Yagi 《Physics and Chemistry of Minerals》2008,35(4):189-195
Structural, morphological, magnetic, and thermal properties have been investigated for a novel post-perovskite oxide CaPtO3 synthesized under high pressure. By comparing obtained structural parameters with those for known post-perovskite compounds,
we argue that the chemical bond has a strong covalent character. Precise measurements of the Langevin susceptibility χ
0
= −9.6 × 10−5 emu/mol and Debye temperature θ ∼ 470 K provide a good opportunity to confirm the reliability of first-principle calculations on predicting physical properties
of the Earth’s D” layer. 相似文献
326.
327.
Boundary-Layer Meteorology - We investigate the characteristics of a dust-devil-like vortex (DDLV) observed using thermal image velocimetry (TIV) at a sports ground in Tokyo. Thermal image... 相似文献
328.
Daisuke Nishio-Hamane Asa Shimizu Ritsuko Nakahira Ken Niwa Asami Sano-Furukawa Taku Okada Takehiko Yagi Takumi Kikegawa 《Physics and Chemistry of Minerals》2010,37(3):129-136
The stability and equation of state for the cotunnite phase in TiO2 were investigated up to a pressure of about 70 GPa by high-pressure in situ X-ray diffraction measurements using a laser-heated
diamond anvil cell. The transition sequence under high pressure was rutile → α-PbO2 phase → baddeleyite phase → OI phase → cotunnite phase with increasing pressure. The cotunnite phase was the most stable
phase at pressures from 40 GPa to at least 70 GPa. The equation of state parameters for the cotunnite phase were established
on the platinum scale using the volume data at pressures of 37–68 GPa after laser annealing, in which the St value, an indicator of the magnitude of the uniaxial stress component in the samples, indicates that these measurements were
performed under quasi-hydrostatic conditions. The third-order Birch-Murnaghan equation of state at K
0′ = 4.25 yields V
0 = 15.14(5) cm3/mol and K
0 = 294(9), and the second-order Birch-Murnaghan equation of state yields V
0 = 15.11(5) cm3/mol and K
0 = 306(9). Therefore, we conclude that the bulk modulus for the cotunnite phase is not comparable to that of diamond. 相似文献
329.
Atsushi Inagaki Marieta Cristina L. Castillo Yoshimi Yamashita Manabu Kanda Hiroshi Takimoto 《Boundary-Layer Meteorology》2012,142(2):207-222
Instantaneous flow structures “within” a cubical canopy are investigated via large-eddy simulation. The main topics of interest
are, (1) large-scale coherent flow structures within a cubical canopy, (2) how the structures are coupled with the turbulent
organized structures (TOS) above them, and (3) the classification and quantification of representative instantaneous flow
patterns within a street canyon in relation to the coherent structures. We use a large numerical domain (2,560 m × 2,560 m ×
1,710 m) with a fine spatial resolution (2.5 m), thereby simulating a complete daytime atmospheric boundary layer (ABL), as
well as explicitly resolving a regular array of cubes (40 m in height) at the surface. A typical urban ABL is numerically
modelled. In this situation, the constant heat supply from roof and floor surfaces sustains a convective mixed layer as a
whole, but strong wind shear near the canopy top maintains the surface layer nearly neutral. The results reveal large coherent
structures in both the velocity and temperature fields “within” the canopy layer. These structures are much larger than the
cubes, and their shapes and locations are shown to be closely related to the TOS above them. We classify the instantaneous
flow patterns in a cavity, specifically focusing on two characteristic flow patterns: flushing and cavity-eddy events. Flushing
indicates a strong upward motion, while a cavity eddy is characterized by a dominant vortical motion within a single cavity.
Flushing is clearly correlated with the TOS above, occurring frequently beneath low-momentum streaks. The instantaneous momentum
and heat transport within and above a cavity due to flushing and cavity-eddy events are also quantified. 相似文献
330.
Organized Structure of Active Turbulence Over an Array of Cubes within the Logarithmic Layer of Atmospheric Flow 总被引:2,自引:2,他引:0
We investigate the coherent structure of atmosphere turbulence over very large roughness within a fully rough, high Reynolds number turbulent flow. The horizontal distributions of coherent turbulence were determined by multipoint measurements of velocity fluctuations using sonic anemometers in a comprehensive outdoor scale model experiment for urban climate (COSMO). COSMO is made up of 512 cubical obstacles, each 1.5 m on a side, arranged in a rectangular pattern on a flat 50 m × 100 m concrete plate. A total of 15 sets of sonic anemometers were aligned horizontally within the logarithmic layer above this site. The velocity fluctuations observed in COSMO were decomposed into active and inactive contributions by applying a spatial-filtering method, and which used a simple moving average along the spanwise direction of the predominant flow as a filter function. The size of the filter should be between the sizes of the active and inactive fluctuations. This method potentially eliminates the considerable portion of low frequency modes included in the horizontal velocity fluctuation, while preserving well the Reynolds stress. The structural characteristics of the active turbulence were qualitatively similar to those measured over various surface configurations. Overall, the observed structures of the active turbulence are composed of very large streaks of low momentum fluid elongated in the streamwise direction with some sub-structures included in the streaks. The sub-structures were the main cause of the ejections, which accompany horizontal vortices. The active motion, including the streaky structures, did not reproduce the lower frequency peak of the bi-modal distribution of the horizontal velocity spectra, but reproduced the higher frequency mode that robustly follows inner-layer similarity (i.e. Monin–Obukhov similarity). 相似文献