A unified model for bedform development and equilibrium under unidirectional,oscillatory and combined‐flows

The development of bedforms under unidirectional, oscillatory and combined‐flows results from temporal changes in sediment transport, flow and morphological response. In such flows, the bedform characteristics (for example, height, wavelength and shape) change over time, from their initiation to equilibrium with the imposed conditions, even if the flow conditions remain unchanged. These variations in bedform morphology during development are reflected in the sedimentary structures preserved in the rock record. Hence, understanding the time and morphological development in which bedforms evolve to an equilibrium stage is critical for informed reconstruction of the ancient sedimentary record. This article presents results from a laboratory flume study on bedform development and equilibrium development time conducted under purely unidirectional, purely oscillatory and combined‐flow conditions, which aimed to test and extend an empirical model developed in past work solely for unidirectional ripples. The present results yield a unified model for bedform development and equilibrium under unidirectional, oscillatory and combined‐flows. The experimental results show that the processes of bedform genesis and growth are common to all types of flows, and can be characterized into four stages: (i) incipient bedforms; (ii) growing bedforms; (iii) stabilizing bedforms; and (iv) fully developed bedforms. Furthermore, the development path of bedform; growth exhibits the same general trend for different flow types (for example, unidirectional, oscillatory and combined‐flows), bedform size (for example, small versus large ripples), bedform shape (for example, symmetrical or rounded), bedform planform geometry (for example, two‐dimensional versus three‐dimensional), flow velocities and sediment grain sizes. The equilibrium time for a wide range of bed configurations was determined and found to be inversely proportional to the sediment transport flux occurring for that flow condition.     

Wide Field Imaging of Ion Tail of Comet C/Hale–Bopp

A sequential imaging observation of the ion tail of Comet C/Hale-Bopp 1995O1 was carried out in February–March 1997 with a wide-field CCD imaging camera using narrow band filters for two ion species; CO⁺ and H₂O⁺ along with those for blue and red continuum. From the surface photometry of the ion tail of two species, we derived a relationship between plasma density and distance from the nucleus. The local velocity of the ion flow as a function of the distance from the nucleus was also estimated on the basis of some assumptions. We report preliminary results of our analysis, and discuss some characteristics of cometary plasma and its interaction with interplanetary magnetic field (IMF). May the source be with you! This revised version was published online in July 2006 with corrections to the Cover Date.     

Radio imaging of the Subaru/XMM–Newton Deep Field – I. The 100-μJy catalogue, optical identifications, and the nature of the faint radio source population

We describe deep radio imaging at 1.4 GHz of the 1.3-deg² Subaru/ XMM–Newton Deep Field (SXDF), made with the Very Large Array in B and C configurations. We present a radio map of the entire field, and a catalogue of 505 sources covering 0.8 deg² to a peak flux density limit of 100 μJy. Robust optical identifications are provided for 90 per cent of the sources, and suggested identifications are presented for all but 14 (of which seven are optically blank, and seven are close to bright contaminating objects). We show that the optical properties of the radio sources do not change with flux density, suggesting that active galactic nuclei (AGN) continue to contribute significantly at faint flux densities. We test this assertion by cross-correlating our radio catalogue with the X-ray source catalogue and conclude that radio-quiet AGN become a significant population at flux densities below 300 μJy, and may dominate the population responsible for the flattening of the radio source counts if a significant fraction of them are Compton-thick.     

On the fissions of a solid body under influence of tidal force; with application to the problem of twin craters on the moon

The internal strain due to the tidal force in the proximity of a tide-generating body (in the present case, the Moon) is calculated according to the Lord Kelvin theory of Earth tides. The conditions for which uniform elastic sphere possessing a definite tensile strength is crushed near the surface of the Moon is investigated. The state of internal stress is almost independent of the value of elastic constants. Many lunar features, such as twin craters, craterous walled plains of irregular forms, compound craters, may be explained by fission of the meteoritic material before impact.     

On the possible amplitudes of the moon's free libration

The relations between probable amplitude of the Moon's free libration and its exciting action are obtained using a theory of the stochastic process. Among the three modes of the free libration, the one in longitude is most prominent if the exciting effect is isotropic. If the excitations are caused by crater-producing meteoritic impacts, it is very probable that the free librations in longitude exist whose semi-amplitude exceeds 1.     

Observed and simulated sensitivities of summertime urban surface air temperatures to anthropogenic heat in downtown areas of two Japanese Major Cities,Tokyo and Osaka

In this study, the sensitivities of surface air temperatures to anthropogenic heat (AH) were investigated in downtowns of the two Japanese major cities, Tokyo and Osaka. First, meteorological measurements were made with the simultaneous monitoring of electricity demand in a contrastive couple of a downtown commercial area (C-area) and a residential area (R-area) within each city in summer 2007. From the measurements, the areal-mean surface air temperatures were obtained as \( {\overline{T}}_{\mathrm{C}} \) and \( {\overline{T}}_{\mathrm{R}} \) for each of the C-area and R-area, respectively. Using the actual electricity demand and the estimated motor fuels consumption, their areal total was evaluated as the energy-consumption-basis AH. The estimated C-areas' AH indicated greater values up to 220 W/m² on weekdays and remarkable decrease about by half on weekends, whereas that in the R-areas showed less values of 10–20 W/m² stably. Then, \( {\overline{T}}_{\mathrm{C}}-{\overline{T}}_{\mathrm{R}} \) on calm and fine days were found to be systematically decreased from weekdays to weekends in both cities roughly indicating a proportional relationship with the reductions in the C-areas' AH on weekends. The result suggested a common afternoon sensitivity for both C-areas of around 1.0°C/100 W/m², which indicated an intensity of the AH impact on surface air temperature there. Next, to simulate the observed AH impact, the authors' CM-BEM (a multilayer urban canopy model coupled with a building energy model) was newly implemented in the mesoscale Weather Research and Forecasting (WMF) model. This new system, WRF-CM-BEM, was applied to Tokyo and almost reasonably validated from the aspects of the reproducibility of urban surface air temperature and electricity demand in the observation areas. The simulations also suggested that WRF-CM-BEM underestimated the observed air temperature sensitivity to AH in the Tokyo C-area roughly by half but still in the same order of magnitude.     

Rocket observations of atomic oxygen density and airglow emission rate in the WAVE2000 campaign

Atomic oxygen density and airglow volume emission rate profiles measured in the rocket experiment S-310-29 carried out as a part of the Waves in Airglow Structures Experiment over Kagoshima in 2000 (WAVE2000) campaign are presented, and the excitation processes of the atomic oxygen 557.7 nm line and the molecular oxygen atmospheric band airglow emissions are discussed. The volume emission rate profiles calculated from the measured atomic oxygen densities using the methods and parameters proposed by the ETON campaign (EATON model) are found to well represent the shapes of measured twin-peak emission rate profiles seen during this campaign suggesting that the EATON model is valid for a perturbed atmosphere. There is some discrepancy in the modeled absolute values for the emissions. Applying the model to the current O density measurements results in predicted emission rates that are a factor of 3.2 and 1.5 too high for the 557.7 nm line and Atmospheric band, respectively. This suggests either that the atomic oxygen densities of the present campaign are too large by a factor of 1.2 (=1.5^1/2) to 1.5 (=3.2^1/3), or that those of the ETON campaign were too small by the same factor or that the combined errors in both campaigns can account for the discrepancy (the modeled volume emission rates of the 557.7 nm line and atmospheric band are roughly in proportion to [O]³ and [O]², respectively). Our present data findings do not favor the 2-step more than the 1-step excitation process for the atmospheric band because a calculation of the quantum efficiency based on the observed O density does not show a steep gradient around 100 km.