Effects Of Tidal Forces Research Articles

Contaminant source characterization in a coastal aquifer influenced by tidal forces and density-driven flow

Contaminant source characterization (CSC) plays an important role in environmental forensics and pollution control. Past studies commonly solve the CSC problem in case studies where simple groundwater velocity fields (with e.g. parallel velocity vectors) prevail under steady state conditions. A few studies have addressed CSC in cases where the effect of heterogeneity or wells causes the velocity vectors to deviate from a parallel alignment. More complex transient velocity fields are yet to be addressed in groundwater CSC studies. One key example is coastal aquifers, where density-driven flow and the effect of oceanic forces (e.g. tides and waves) create complex transient velocity fields that lead to deformation of contaminant plumes and enhance mixing processes. The present paper aims to address this challenge by developing and validating a novel solution method for CSC in a coastal aquifer under the effect of tidal forces and density-driven flow. For this purpose, the study combines a numerical model of density-dependent flow and multiple-species solute transport, artificial neural networks, and a customized Kalman filtering technique, termed the ‘constrained restart dual ensemble Kalman filter’ (CRD-EnKF). In this approach, the time series of contaminant concentration downgradient of the source, and salinity concentrations in the transition zone between fresh and saline groundwater is employed for the estimation of contaminant source location and strength. We validated the proposed methodology by using a benchmark problem of a coastal aquifer with sloping beach and tide-induced pressure oscillation at the sea boundary.

Role of structure scalars on the evolution of compact objects in Palatini [formula omitted] gravity

The utmost concern of this article is the construction of modified scalar functions (structure scalars) by taking Palatini f(R) gravitational theory into account. At first, a general formalism is established in which we assess gravitational stellar equations by putting into use the Palatini’s technique. Later, from the perspective of tilted observer, we Lorentz boosted the components of energy-momentum tensor using relative velocity ω. To examine the physical as well as mathematical aspects of the fluid source, we carry out a detailed analysis of kinematical variables by evaluating shear tensor and scalar, four-acceleration and expansion scalar. For the fluid content inside our spherical star, we inferred the mass function (geometric mass) and the active gravitational mass. Raychaudhuri equation, Bianchi identities in addition to few other equations are worked out to discern the structure formation and analyze the object’s evolutionary stages. The Riemann tensor is then broken up orthogonally to set up few scalar functions connected with fundamental physical characteristics of the fluid source like energy density, effects of tidal forces and anisotropic stresses etc.

Effects of tidal forcing in an estuarine environment on high-frequency acoustics

Tidal forcing in rivers and estuaries has a large impact on the use high-frequency acoustics for bathymetric mapping. Changes in the sound speed profile due to changing salinity and temperature conditions affect acoustic propagation, and bubbles, entrained in the tidal flow, cause high backscattering and attenuation. In this study, a forward-looking, high-frequency bathymetric sonar was used to observe estuarine dynamics near the mouth of the Connecticut River in June 2017. The sonar was deployed on a REMUS 600 AUV under the fresh water plume near the river mouth during flood tide, in the lower estuary during ebb tide and in the upper estuary during slack tide. Backscattering from subducted bubbles was observed which was dependent on the propagation path through the fresh or salt water. The bubble backscatter over a 200-m swath at the front of the fresh water plume allowed the structure of the plume to be observed from beneath the surface. These data are compared with other measurements on site, including...

Underlining some aspects of the equivalence principle

We want to shed light on some discussed aspects of the principle of equivalence. We consider two different phases in the evolution of the principle. We pay attention to the fact that some textbooks do not dwell on the mathematical meaning of ‘locally flat spacetime’, which can confuse students and, occasionally, can also lead to misinterpretations. For example, the non-eliminability of tidal forces, not even locally, may suggest that the equivalence principle is wrong. By contrast, we want to show that this is in perfect agreement with the Einstein geometrical interpretation of spacetime. Finally, in order to check the approximations used in the Gedankenexperiment of an elevator, we estimate explicitly the magnitude of the deflection of light and the effects of tidal forces in a ‘real lift’.

Dynamical evolution of globular clusters: Recent developments

We analyze structural parameters of the globular clusters belonging to the Milky Way system which were listed in the latest edition of the Harris Catalogue. We search for observational evidences of the effect of tidal forces induced by the Galaxy on the dynamical and thermodynamical evolution of a globular cluster. The behavior for the [Formula: see text] distribution exhibited by the globular cluster population seems to be in contrast with theoretical results in literature about gravothermal instability, and suggest a new limit value smaller than the previous one.

Weighing in on the masses of retired A stars with asteroseismology: K2 observations of the exoplanet-host star HD 212771

Doppler-based planet surveys point to an increasing occurrence rate of giant planets with stellar mass. Such surveys rely on evolved stars for a sample of intermediate-mass stars (so-called retired A stars), which are more amenable to Doppler observations than their main-sequence progenitors. However, it has been hypothesised that the masses of subgiant and low-luminosity red-giant stars targeted by these surveys --- typically derived from a combination of spectroscopy and isochrone fitting --- may be systematically overestimated. Here, we test this hypothesis for the particular case of the exoplanet-host star HD 212771 using K2 asteroseismology. The benchmark asteroseismic mass ($1.45^{+0.10}_{-0.09}\:\text{M}_{\odot}$) is significantly higher than the value reported in the discovery paper ($1.15\pm0.08\:\text{M}_{\odot}$), which has been used to inform the stellar mass-planet occurrence relation. This result, therefore, does not lend support to the above hypothesis. Implications for the fates of planetary systems are sensitively dependent on stellar mass. Based on the derived asteroseismic mass, we predict the post-main-sequence evolution of the Jovian planet orbiting HD 212771 under the effects of tidal forces and stellar mass loss.

Effects of tidal forcing, conductivity gradient, and active seeding on the climatology of equatorial spread F over Kwajalein

AbstractPlasma structure in nighttime equatorial F layer, referred to as equatorial spread F (ESF), displays climatology whose seasonal variation depends on longitude. At longitudes where ESF favors equinoxes, times when maxima occur can be predicted in terms of the day of year, when E region sunset is simultaneous in conjugate hemispheres (i.e., “sunset nodes”). Aside from occurrences around equinoxes, there are only three longitudes where ESF also occurs during a solstice; one is the central Pacific region. Here ESF activity is strong during the June solstice, when solar activity is high. To understand this puzzling behavior, ESF climatology over the Kwajalein Atoll was compared with properties of the postsunset rise (PSSR) of the F layer and seeding activity in the troposphere. The key findings are as follows: (1) Maxima in PSSR velocity (VPSSR) are better aligned with equinoxes than with sunset nodes; hence, seasonal pattern of VPSSR, not only sunset nodes, should be included in interpretation of ESF climatology. (2) The source of VPSSR during solstice appears to differ from that during equinoxes. (3) Equinoctial maxima in VPSSR could be related to a semiannual variation in equatorial electrojet strength and its contribution to polarization of the F region dynamo current. (4) Enhanced VPSSR during the June solstice is interpreted in terms of tidal forcing with a wave number of 2. (5) Displacements of maxima in ESF climatology from maxima in VPSSR are shown to be consistent with deep convective activity.

How much do tides affect the circulation of the Mediterranean Sea? From local processes in the Strait of Gibraltar to basin-scale effects

The effects of tidal forcing on the exchange flow through the Strait of Gibraltar and the circulation in the near-field region are revisited with a regional numerical model. Also a basin-scale model run is conducted in a first attempt to assess the impact of these local processes on the Western Mediterranean thermohaline circulation. In the Strait of Gibraltar, tides are found to (1) increase the exchange flow volume transport, (2) modify the hydrological properties of Atlantic inflowing waters through the enhancement of mixing, and (3) facilitate the drainage of Mediterranean deep water. In the far-field, the model reveals that these local processes can favor deep convection in the Gulf of Lion. Some thoughts are provided offering possible explanations.

Biogeochemical patterns in the Atlantic Inflow through the Strait of Gibraltar

The effects of tidal forcing on the biogeochemical patterns of surface water masses flowing through the Strait of Gibraltar are studied by monitoring the Atlantic Inflow (AI) during both spring and neap tides. Three main phenomena are defined depending on the strength of the outflowing phase predicted over the Camarinal Sill: non-wave events (a very frequent phenomenon during the whole year); type I Internal wave events (a very energetic event, occurring during spring tides); and type II Internal wave events (less intense, occurring during neap tides).During neap tides, a non-wave event comprising oligotrophic open-ocean water from the Gulf of Cádiz is the most frequent and clearly dominant flow through the Strait. In this tidal condition, the inflow of North Atlantic Central Water (NACW) provides the main nutrient input to the surface layer of the Alboran Sea, supplying almost 70% of total annual nitrate transport to the Mediterranean basin. A low percentage of active and large phytoplankton cells and low average concentrations of chlorophyll (0.3–0.4mgm−3) are found in this tidal phase. Around 50% of total annual phytoplankton biomass transport into the Mediterranean Sea through the Strait presents these oligotrophic characteristics.In contrast, during spring tides, patches of water with high chlorophyll levels (0.7–1mgm−3) arrive intermittently, and these are recorded concurrently with the passage of internal waves coming from the Camarinal Sill (type I internal wave events). When large internal waves are arrested over the Camarinal Sill this implies strong interfacial mixing and the probable concurrent injection of coastal waters into the main channel of the Strait. These processes result in a mixed water column in the AI and can account for around 30% of total annual nitrate transport into the Mediterranean basin. Associated with type I internal wave events there is a regular inflow of large and active phytoplankton cells, transported in waters with relatively high nutrient concentrations, which constitutes a significant supply of planktonic resources to the pelagic ecosystem of the Alboran Sea (almost 30% of total annual phytoplankton biomass transport).

Tidal and residual circulation in the St. Andrew Bay system, Florida

Two 24-h surveys were conducted in St. Andrew Bay, Florida, during spring and neap tides to describe the tidal and non-tidal circulation patterns and to determine the factors that affect these patterns. In particular, the effect of tidal forcing in modulating such circulation patterns was explored. Observed velocities were fitted to diurnal and semidiurnal harmonics separating tidal motions from sub-tidal motions. Residual flows were compared with an analytic model that allowed variations in the relative contributions from Coriolis acceleration and friction using the Ekman number. A solution with an Ekman number of 0.04 resembled the observations best and indicated that the hydrodynamics were governed by pressure gradient, Coriolis and friction. Locally, advective accelerations became important around headlands in sub-estuaries in the system. The consistency of the mean pattern from October to March suggests that tides play a minor role in modulating the exchange flow. Deviations from the long-term mean are mainly caused by wind-driven coastal setup and setdown.

Tidal corrections to gravity measurements

Methods taking into account the effect of tidal forces on gravity measurements are considered. Corrections for the effect of tidal forces can exceed 250 μGal. Only the structure of the Earth and positions of tide-generating celestial bodies are necessary for taking into account earth tides, while cotidal charts are additionally required for the correct incorporation of the effect of ocean tides. The effect can reach a few tens of μGal near shorelines. The modern accuracy of gravity measurements being 1–2 μGal, the ocean tide effect, together with other less significant factors, should be considered for the correct interpretation of gravity data.

The effect of tidal forcing on biogeochemical processes in intertidal salt marsh sediments.

BackgroundEarly diagenetic processes involved in natural organic matter (NOM) oxidation in marine sediments have been for the most part characterized after collecting sediment cores and extracting porewaters. These techniques have proven useful for deep-sea sediments where biogeochemical processes are limited to aerobic respiration, denitrification, and manganese reduction and span over several centimeters. In coastal marine sediments, however, the concentration of NOM is so high that the spatial resolution needed to characterize these processes cannot be achieved with conventional sampling techniques. In addition, coastal sediments are influenced by tidal forcing that likely affects the processes involved in carbon oxidation.ResultsIn this study, we used in situ voltammetry to determine the role of tidal forcing on early diagenetic processes in intertidal salt marsh sediments. We compare ex situ measurements collected seasonally, in situ profiling measurements, and in situ time series collected at several depths in the sediment during tidal cycles at two distinct stations, a small perennial creek and a mud flat. Our results indicate that the tides coupled to the salt marsh topography drastically influence the distribution of redox geochemical species and may be responsible for local differences noted year-round in the same sediments. Monitoring wells deployed to observe the effects of the tides on the vertical component of porewater transport reveal that creek sediments, because of their confinements, are exposed to much higher hydrostatic pressure gradients than mud flats.ConclusionOur study indicates that iron reduction can be sustained in intertidal creek sediments by a combination of physical forcing and chemical oxidation, while intertidal mud flat sediments are mainly subject to sulfate reduction. These processes likely allow microbial iron reduction to be an important terminal electron accepting process in intertidal coastal sediments.

Effect of tidal forcing on a subterranean estuary

Groundwater flow and chemical transport in subterranean estuaries are poorly understood despite their potentially important implications for chemical fluxes from aquifers to coastal waters. Here, a numerical study of the dynamics in a subterranean estuary subject to tidal forcing is presented. Simulations show that salt transport associated with tidally driven seawater recirculation leads to the formation of an upper saline plume in the intertidal region. Computed transit times and flow velocities indicate that this plume represents a more active zone for mixing and reaction than the dispersion zone of the lower, classical salt wedge. Proper conceptualisation of this surficial mixing zone extends our understanding of processes within the subterranean estuary. Numerical tracer simulations reveal that tidal forcing may reduce the threat of a land-derived contaminant discharging to the marine environment by modifying the subsurface transport pathway and local geochemical conditions. Mixing and stratification in the subterranean estuary are strongly affected by both inland and tidal forcing. Based on the estuarine analogy we present a systematic classification of subterranean estuaries.

SIMULATION OF SEA WATER INTRUSION AND TIDAL INFLUENCE

ABSTRACT Coastal zones contain some of the most densely populated areas in the world as they generally present the best conditions for productivity. However, these regions face many hydrological problems like flooding due to cyclones and wave surge and drinking fresh water scarcity due to salt water intrusion. This paper presents the simulation of sea water intrusion in Nauru Island through Saturated-Unsaturated TRAnsport (SUTRA) model and examine the effect of tidal forcing on the fresh water resources.

The effects of tidal forces on an elastic satellite in a closed orbit

An evaluation is presented of the impact of tidal forces on both the secular changes in the orbital elements and the material stability, using an elastic deformation model for the satellite. The analysis of the material stability yields an estimate of the elasto-gravitational Roche limit. The critical semilatus rectum has been obtained for both circular orbits and for elliptical orbits with small eccentricity. The secular orbital variation due to tidal forces manifests itself predominantly in terms of the precession of the perihelion for orbits with a non-zero eccentricity. The effect is small compared with the general relativistic effect for the Sun/Mercury system. The effect is large for the Earth/Moon system.

A geophysical note on man's free‐running circadian rhythm

Abstract In consideration of the possibility that the close correspondence between the lunar day and the reported average length of man's free‐running circadian rhythm is not, from an evolutionary point of view, entirely coincidental (even though the moon does not appear to function as Zeitgeber to subjects in temporal isolation), the present article calculates the length of the lunar and solar days back to some 1.3·109 years ago. While it is shown that on the average the lunar day in absolute, atomic clock hours decreases roughly 40 min for every 108 years we trace it back, it is also shown that the lunar day has in every epoch been approx. 31/2% longer than the solar day: roughly the same value by which the average length of man's free‐running circadian rhythms presently exceeds the solar day. Possible evolutionary effects of tidal forces to account for the 3 1/4% correspondence are briefly considered.

The Effects of Tidal Forces on the Stability and Dispersal Rates of a Protoplanet

The Effects of Tidal Forces on the Stability and Dispersal Rates of a Protoplanet