Stochastic analysis of bed-thickness distribution of sediments

On formation of a bed and distribution of bed thickness, A. N. Kolmogorov presented a mathematical explanation that if repetitive alternations of material accumulation and erosion form a sequence of beds, the resultant bed-thickness distribution curve takes a shape truncated by the ordinate at zero thickness. In this truncated distribution curve, its continuation and extension from positive to negative thickness represents the distribution of beds with negative thickness, that is, the depth of erosion. When a distribution curve, including both positive and negative parts, is expressed by a function f(x),the ratio \(\int_0^\infty {f(x)dx to} \int_{ - \infty }^\infty {f(x)dx} \) ,called Kolmogorov's coefficient and designated as p,is a parameter representing the degree of accumulation in the depositional environment. On the assumption that f(x)is described by the Gaussian distribution function, the coefficient pfor Permian and Pliocene sequences in central Japan was calculated. The coefficients also were obtained from published data for different types of sediments from other areas. It was determined that they are more or less different depending on their depositional environments. The calculated results are summarized as follows: $$\begin{gathered} p = 0.80 - 1.0for{\text{ }}alluvial{\text{ }}or{\text{ }}fluvial{\text{ }}deposits \hfill \\ p = 0.65 - 0.95for{\text{ }}nearshore{\text{ }}sediments \hfill \\ p = 0.55 - 0.95for{\text{ }}geosynclinal{\text{ }}sediments \hfill \\ p = 0.90 - 1.0for{\text{ }}varves \hfill \\ \end{gathered} $$ In addition, a ratio \(q = \int_0^\infty {xf(x)dx/} \int_{ - \infty }^\infty {|x|f(x)dx} \) ,called Kolmogorov's ratio in this paper, is introduced for estimating a degree of total thickness actually observed in the field relative to total thickness once present in a basin. The calculated results of Kolmogorov's ratio are as follows: $$\begin{gathered} q = 0.88 - 1.0for{\text{ }}alluvial{\text{ }}or{\text{ }}fluvial{\text{ }}deposits \hfill \\ q = 0.68 - 0.98for{\text{ }}nearshore{\text{ }}sediments \hfill \\ q = 0.55 - 0.96for{\text{ }}geosynclinal{\text{ }}sediments \hfill \\ q = 0.92 - 1.0for{\text{ }}varves \hfill \\ \end{gathered} $$ The sedimentological significance of these values is discussed.     

Lunar-A mission: Outline and current status

The scientific objective of the Lunar-A, Japanese Penetrator Mission, is to explore the lunar interior by seismic and heat-flow experiments. Two penetrators containing two seismometers (horizontal and vertical components) and heat-flow probes will be deployed from a spacecraft onto the lunar surface, one on the near-side and the other on the far-side of the moon. The data obtained by the penetrators will be transmitted to the earth station via the Lunar-A mother spacecraft orbiting at an altitude of about 200 km. The spacecraft of a cylindrical shape, 2.2 m in maximum diameter and 1.7 m in height, is designed to be spin-stabilized. The spacecraft will be inserted into an elliptic lunar orbit, after about a half-year cruise during which complex manoeuvering is made using the lunar-solar gravity assist. After lunar orbit insertion, two penetrators will be separated from the spacecraft near perilune, one by one, and will be landed on the lunar surface. The final impact velocity of the penetrator will be about 285 m/sec; it will encounter a shock of about 8000 G at impact on the lunar surface. According to numerous experimental impact tests using model penetrators and a lunar-regolith analog target, each penetrator is predicted to penetrate to a depth between l and 3 m, depending on the hardness and/or particle-size distribution of the lunar regolith. The penetration depth is important for ensuring the temperature stability of the instruments in the penetrator and heat flow measurements. According to the results of the Apollo heat flow experiment, an insulating regolith blanket of only 30 cm is sufficient to dampen out about 280 K lunar surface temperature fluctuation to < 3 K variation. The seismic observations are expected to provide key data on the size of the lunar core, as well as data on deep lunar mantle structure. The heat flow measurements at two penetrator-landing sites will also provide important data on the thermal structure and bulk concentrations of heat-generating elements in the Moon. These data will provide much stronger geophysical constraints on the origin and evolution of the Moon than has been obtained so far. Currently, the Lunar-A system is being reviewed and a more robust system for communication between the penetrators and spacecraft is being implemented according to the lessons learned from Beagle-2 and DS-2 failures. More impact tests for penetrators onto a lunar regolith analogue target will be undertaken before its launch.     

The effect of groundwater on topographic changes in a gravel beach

In recent years, several attempts to stabilize the beach by control of the percolation of water have been proposed. However, morphodynamics in the surf zone is still not clear because of the complexity of wave actions and sediment transport. Especially, there is a little research on gravel beach morphodynamics including wave breaking in the surf zone. The present study investigates experimentally how groundwater level influences topographic changes in a gravel beach and simulates numerically the wave fields and flow patterns in the surf zone, considering the porosity of the media and the presence of groundwater. In experiments, water-level control tank was designed to control the simulated groundwater elevation and the wave flume was divided into two parts to maintain a constant mean water level. The experimental results show that the berm formed in the upper portion of the shoreline moves up the beach as the groundwater level falls and the lower the groundwater level, the steeper the beach surface. The numerical model was developed to clarify these features capable of simulating the difference of groundwater and mean water level. Numerical results showed different flow patterns due to the groundwater elevation; wave run-up weakens and wave run-down strengthens by the seaward currents caused by elevated groundwater. These deformations of the flow pattern explain well how the beach profile is affected by the groundwater elevation.     

A pair of Langmuir cells in a laboratory tank (I) wind-only experiment

Three velocity components of subsurface flow, observed in a rectangular tank under the action of a constant wind speed, are measured systematically at mesh points distributed uniformly over a vertical cross-section of the tank. Measurements are carried out for two cases: 1) reference wind speedU _r =7.5 m/s and fetchF=10 m; and 2)U _r =10 m/s andF=25 m. A pair of Langmuir cells is observed for both cases; downwelling zones are found along both of the sidewalls and an upwelling zone in the centre of the tank. Near the water surface, the vertical momentum flux is dominated by the Reynolds stress resulting from small-scale turbulence, while over the entire cross-section except near the surface, the Reynolds stress due to the Langmuir cells dominates the vertical momentum flux. As the result of the occurrence of this Langmuir cells, the vertical momentum flux, which consists of both mean advection and small-scale turbulence, is markedly inhomogeneous in the spanwise direction; for example, the largest vertical flux of the order of the wind stress is observed in the downwelling zone near one sidewall, while at the centre of the tank, the vertical momentum flux occupies only 30% of the wind stress. This indicates that a pair of Langmuir cells plays more important role than small-scale turbulence in the mixing process in a greater part of the wind-wave tank.Address after April 1, 1992: Department of Civil Engineering, Hiroshima Institute of Technology, Miyake 2-1-1, Saeki-ku, Hiroshima 731-51, Japan.     

Noctilucent cloud in the western Arctic in 2005: Simultaneous lidar and camera observations and analysis

We report observations of a noctilucent cloud (NLC) over central Alaska by a ground-based lidar and camera on the night of 9–10 August 2005. The lidar at Poker Flat Research Range (PFRR), Chatanika (65°N, 147°W) measured a maximum integrated backscatter coefficient of 2.4×10^?6 sr^?1 with a peak backscatter coefficient of 2.6×10^?9 m^?1 sr^?1 corresponding to an aerosol backscatter ratio of 120 at an altitude of 82.1 km. The camera at Donnelly Dome, 168 km southeast of PFRR, recorded an extensive NLC display across the sky with distinct filamentary features corresponding to wave structures measured by the lidar. The occurrence of the maximum integrated backscatter coefficient corresponded to the passage of a bright cloud band to the southwest over PFRR. The camera observations indicate that the cloud band had a horizontal width of 50 km and a length of 150 km. The horizontal scale of the cloud band was confirmed by medium-frequency radar wind measurements that reported mesopause region winds of 30 m/s to the southwest during the period when the cloud band passed over PFRR. Comparison of these measurements with current NLC microphysical models suggests a lower bound on the water vapor mixing ratio at 83 km of 7–9 ppmv and a cloud ice mass of 1.5–1.8×10³ kg. Satellite measurements show that this NLC display occurred during a burst of cloud activity that began on 5 August and lasted for 10 days. This cloud appeared 10 days after a launch of the space shuttle. We discuss the appearance of NLCs in August over several years at this lower polar latitude site in terms of planetary wave activity and space shuttle launches.     

Removal of Natural Free Estrogens and their Conjugates in a Municipal Wastewater Treatment Plant

Removal of natural free estrogens and estrogen conjugates in a municipal wastewater treatment plant (WWTP) was investigated and analyzed by GC‐MS, in which estrogen conjugates were first transformed to their corresponding free estrogens with an acid solvolysis procedure before their analysis. Natural free estrogens, E1‐3‐sulfate (E1‐3S), and E3‐3‐sulfate (E3‐3S) were detected with high concentrations in both the influent and effluent of the primary settling tank (PS), while no estrogen glucuronides were detected in any of the monitored wastewater samples. Regarding their removal efficiencies, all were almost completely removed, except for E1 with only a minor decrease. The estrogenic/androgenic removal of the same WWTP was also evaluated with estrogen receptor (androgen receptor) (ER (AR))‐binding assays, in which the removal efficiencies for E2 equivalents (EEQ) or testosterone equivalents (TEQ) were 68.5 and 72.2%. In addition, the chemically calculated EEQ from natural estrogens were about 20.6–39.3% that of the ER‐binding assay, in which E3 contributed the biggest proportion in both the influent and PS, while the calculated value of E1 increased from only 6.7% in the influent to as high as 20.6% in the effluent.     

Longitudinal profile evolution of valleys on coastal terraces under the compound influence of eustasy, tectonism and marine erosion

On the coast of Tosa Bay, Southwestern Japan, there is a wide coastal terrace which was formed in the Last Interglacial and has been uplifted to altitudes of 150–200 m above the present sea level by crustal movement. Many valleys dissect the terrace surface with upwardly convex profiles in downstream reaches. Numerical simulations were conducted to investigate the development of longitudinal profiles of the valleys under the influence of baselevel change and marine erosion. The basic equation used for the calculation had been derived theoretically from the hydraulic mechanism of river erosion. The independent variables are the gradient and curvature of the valley floor and the distance from the divide (drainage area per unit basin width). The parameter in the sediment transport equation is determined based on the results of laboratory experiments. A time sequence of seashore migration which has been caused by marine erosion and relative sea level change due to crustal uplift and glacial eustasy since the Last Interglacial was given as a boundary condition. Numerical calculations were conducted using a finite difference method, starting from 125000 years ago when the shoreline was located at the upper end of the terrace surface, and progressive changes in the valley profiles over time were simulated. The present profiles obtained from the calculation fit quite closely to actual valley profiles, which demonstrates the validity of the equation, and at the same time suggests a formation process for wide coastal terraces.     

Kinematics of overturning solitary waves and their relations to breaker types

Numerical simulations using a full-nonlinear BIM (Boundary Integral Method) potential-theory wave model are carried out to study the internal velocity and acceleration fields of an solitary wave overturning on a reef with vertical face (submerged breakwater) and their relation to breaker type. The simulations make it clear that the jet size normalized by the incident wave height is uniquely governed by the crown height of the reef, while the jet shape is similar and independent of the size. Further, they reveal that the overall internal kinematics of overturning waves is clearly related to the jet size. As the jet size increases and the breaker type changes from spilling to plunging, the kinematics thus become increasingly different from those of steady waves. Water particles with the greatest velocities or accelerations within the wave converge towards the jet. After the breaking, both of the velocities and accelerations almost simultaneously reach extreme values near locations beneath the jet. Some of the extreme values are closely related to the breaker type and can be uniquely determined by substituting the breaker type index into the regression equations suggested here.     

Sand suction mechanism in artificial beach composed of rubble mound breakwater and reclaimed sand area

An artificial beach has been constructed compensating for losing of the natural one caused by the development of coastal area. In this paper, the hydraulic model tests are carried out to investigate the suction phenomenon on the artificial beach constituted of rubble mound breakwater with gravel and the reclaimed sand area. In addition, the numerical model for waves, structures and seabed interaction as well as the numerical method based on the u–p approximation of the Biot equations is developed for investigation of suction mechanism. After verification of the numerical models by comparing numerical results with experimental data, the numerical models are further used to clarify the detailed suction mechanism of the reclaimed sand. The factors that affect the suction phenomenon are examined experimentally and their critical values are presented. Also, it can be pointed out that the vertical discharge velocity as well as the volumetric strain around the still water level of the boundary between the breakwater and the beach gets up to the critical value, the reclaimed sand starts to flow out to the offshore, and it finally leads to caves and cave-ins in the reclaimed zone.     

Seasonal variation of land–atmosphere coupling strength over the West African monsoon region in an atmospheric general circulation model

Abstract

The seasonal variation of land–atmosphere coupling strength has been examined using an extended series of atmospheric general circulation model (AGCM) simulations. In the Western Sahel of Africa, strong coupling strength for precipitation is found in April and May, just prior to and at the beginning of the monsoon season. At this time, heat and water fluxes from the surface are strongly controlled by land conditions, and the unstable conditions in the lower level of the troposphere, as induced by local land state, allow the surface fluxes to influence the variability of convective precipitation—and thus the timing of monsoon onset.

Editor Z. W. Kundzewicz

Citation Yamada, T.J., Kanae, S., Oki, T., and Koster, R.D., 2013. Seasonal variation of land–atmosphere coupling strength over the West African monsoon region in an atmospheric general circulation model. Hydrological Sciences Journal, 58 (6), 1276–1286.