Tidal Shear Research Articles

Field-level inference of galaxy intrinsic alignment from the SDSS-III BOSS survey

As a large-scale overdensity collapses, it affects the orientation and shape of galaxies that form, by exerting tidal shear along their axes. Therefore, the shapes of elliptical galaxies align with the tidal field of cosmic structures. This intrinsic alignment provides insights into galaxy formation and the primordial universe, complements late-time cosmological probes and constitutes a significant systematic effect for weak gravitational lensing observations. In the present study, we provide constraints on the linear alignment model using a fully Bayesian field-level approach, using galaxy shape measurements from the SDSS-III BOSS LOWZ sample and three-dimensional tidal fields constrained with the LOWZ and CMASS galaxy samples of the SDSS-III BOSS survey. We find 4σ evidence of intrinsic alignment, with an amplitude of AI = 2.9 ± 0.7 at 20 Mpch.

Triggering and Relationship Between Mine Earthquake Activities and Stress of Earth Tides During Deep Mining

In the process of deep mining, the prevention and control of rock bursts, mine earthquakes, and other disasters are common problems. The stress of earth tides and its periodic actions should trigger mine earthquakes when the rock masses are in a critical state of rupture. In this study, the Yanbei coal mine was taken as the research background to explore the triggering effect of solid tides on mine earthquakes occurring in the floor. The relationship between the diurnal tidal stress phase and mine earthquakes was studied by statistically analyzing the mine earthquake frequency, and the triggering mechanism was also preliminarily discussed. It was found that the solid tide plays a significant role of trigger action in the occurrence of rock burst of the floor type. For different levels of mine earthquakes, the tidal stress triggering effect is different, but the overall trend is close. Compared with the components of tidal stress, vertical stress, north-south stress, and shear stress, rock burst occurred more at the stage close to 0° and ±180°. For different types of mine earthquakes, the triggered mechanics function of tidal stress is different. Mine earthquakes on the floor mainly include two kinds (the gravity control type and horizontal stress control type). The former easily occurs during the tidal stress vertical component of the maximum, while the latter easily occurs when the two horizontal components of the maximum are combined. The frequency of the former is larger than that of the latter. The results show that the floor seismic activity is correlated with the solid tidal activity of the earth’s crust, which provides a new idea for understanding the mechanism and trigger conditions of mine earthquakes.

Boosting riverine sediment by artificial flood in the Yellow River and the implication for delta restoration

Due to accelerated river-derived sediment deficits, global deltas are presently under an increasing risk of being submerged. To address the fundamental need to save Earth's deltas, boosting riverine sediment supply can be considered a reasonable option, but only if the new supply of sediment is prolonged and greater than the opposing forces: sea level rise, delta subsidence and compaction, and ocean energy. In July 2018, an artificial flood with a peak discharge of 3780 m3/s was released from the Xiaolangdi Reservoir, the last reservoir located on the mainstream of Yellow River, China. From July 03 to July 29, 412 million tons (Mt) of sediment was discharged out of the dam, including 240 Mt. that was previously sequestered within the reservoir. During this event, 140 Mt. of the escaped sediment directly reached the estuary. A total of 245 Mt. of sediment was deposited along the lower river channel bed, of which 83.6 Mt. was eroded once again and transported to the sea in the subsequent five months. This dam-released pulse, coupled with channel diversion and tidal shear fronts, nourished the deltaic area. New land was built, with the submarine offshore gaining up to 2.6 m in seafloor shoaling. Sediment impounded behind the dam, if properly released, could thus become a potential savior for sediment-starved deltas.

Cosmic Tidal Reconstruction with Halo Fields

Abstract The gravitational coupling between large-scale perturbations and small-scale perturbations leads to anisotropic distortions of the small-scale matter distribution. The measured local small-scale power spectrum can thus be used to infer the large-scale matter distribution. In this paper, we present a new tidal reconstruction algorithm for reconstructing large-scale modes using the full three-dimensional tidal shear information. We apply it to simulated dark matter halo fields and find the reconstructed large-scale density field correlates well with the original matter density field on large scales, improving upon the previous tidal reconstruction method, which only uses two transverse shear fields. This has profound implications for recovering lost 21 cm radial modes due to foreground subtraction and constraining primordial non-Gaussianity using the multitracer method with future cosmological surveys.

Intrinsic alignments in IllustrisTNG and their implications for weak lensing: Tidal shearing and tidal torquing mechanisms put to the test

ABSTRACT Accurate measurements of the cosmic shear signal require a separation of the true weak gravitational lensing signal from intrinsic shape correlations of galaxies. These ‘intrinsic alignments’ of galaxies originate from galaxy formation processes and are expected to be correlated with the gravitational field through tidal processes affecting the galaxies, such as tidal shearing for elliptical galaxies and tidal torquing for spiral galaxies. In this study, we use morphologically selected samples of elliptical and spiral galaxies from the illustrisTNG simulation at z = 0 and z = 1 to test the commonly employed linear (tidal shearing) and quadratic (tidal torquing) models for intrinsic alignments. We obtain local measurements of the linear and quadratic alignment parameters, including corrections for large-scale anisotropies of the cosmologically small simulation volume, and study their dependence on galaxy and environmental properties. We find a significant alignment signal for elliptical galaxies (linear model), that increases with mass and redshift. Spiral galaxies (quadratic model), on the other hand, exhibit a significant signal only for the most massive objects at z = 1. We show the quadratic model for spiral galaxies to break down at its fundamental assumptions, and simultaneously obtain a significant signal of spiral galaxies to align according to the linear model. We use the derived alignment parameters to compute intrinsic alignment spectra and estimate the expected contamination in the weak lensing signal obtained by Euclid.

Tidal disruption events in post-starburst galaxies: the importance of a complete stellar mass function

ABSTRACT A tidal disruption event (TDE) occurs when a star is destroyed by the strong tidal shear of a massive black hole (MBH). The accumulation of TDE observations over the last years has revealed that post-starburst galaxies are significantly overrepresented in the sample of TDE hosts. Here we address the post-starburst preference by investigating the decline of TDE rates in a Milky-Way like nuclear stellar cluster featuring either a monochromatic (1 $\, \mathrm{M}{\odot {}}$) or a complete, evolved stellar mass function. In the former case, the decline of TDE rates with time is very mild, and generally up to a factor of a few in 10 Gyr. Conversely, if a complete mass function is considered, a strong TDE burst over the first 0.1–1 Gyr is followed by a considerable rate drop, by at least an order of magnitude over 10 Gyr. The decline starts after a mass segregation time-scale, and it is more pronounced assuming a more top-heavy initial mass function and/or an initially denser nucleus. Our results thus suggest that the post-starburst preference can be accounted for in realistic systems featuring a complete stellar mass function, even in moderately dense galactic nuclei. Overall, our findings support the idea that starbursting galactic nuclei are characterized by a top-heavy initial mass function; we speculate that accounting for this can reconcile the discrepancy between observed and theoretically predicted TDE rates even in quiescent galaxies.

The large-scale environment of thermonuclear and core-collapse supernovae

ABSTRACT The new generation of wide-field time-domain surveys has made it feasible to study the clustering of supernova (SN) host galaxies in the large-scale structure (LSS) for the first time. We investigate the LSS environment of SN populations, using 106 dark matter density realisations with a resolution of ∼3.8 Mpc, constrained by the 2M+ + galaxy survey. We limit our analysis to redshift z < 0.036, using samples of 498 thermonuclear and 782 core-collapse SNe from the Zwicky Transient Facility’s Bright Transient Survey and Census of the Local Universe catalogues. We detect clustering of SNe with high significance; the observed clustering of the two SNe populations is consistent with each other. Further, the clustering of SN hosts is consistent with that of the Sloan Digital Sky Survey (SDSS) Baryon Oscillation Spectroscopic Survey DR12 spectroscopic galaxy sample in the same redshift range. Using a tidal shear classifier, we classify the LSS into voids, sheets, filaments, and knots. We find that both SNe and SDSS galaxies are predominantly found in sheets and filaments. SNe are significantly under-represented in voids and over-represented in knots compared to the volume fraction in these structures. This work opens the potential for using forthcoming wide-field deep SN surveys as a complementary LSS probe.

Strike-slip faulting on Titan: Modeling tidal stresses and shear failure conditions due to pore fluid interactions

Expressions of strike-slip faulting are well documented on multiple ocean worlds (e.g., Europa, Enceladus, and Ganymede) and the motion along these faults is thought to be driven by variations in diurnal tidal stresses. Titan exhibits a complex and dynamic geology with a varied surface morphology developed from fluvial, aeolian, and possible cryovolcanic and tectonic activity. However, observational data are currently limited and no clear strike-slip indicators have been identified so far. Nevertheless, the inferred presence of a porous ice layer saturated with liquid hydrocarbons in Titan's shallow subsurface provides a unique environment for studying zones of frictional weakness, shear heating, and the promotion of cryovolcanism. This study examines Titan's ability to host shear deformation mechanisms, including considerations for how the presence of near-surface liquid hydrocarbons and the crustal porosity of ice significantly reduce the resistance to shear failure of strike-slip faults in flexed areas under maximum diurnal tidal stresses. We conduct a sensitivity analysis of Titan's shear failure tendencies, given optimal failure conditions that may exist due to pore fluid interactions, and we examine the possibility for strike-slip tectonics guided by Coulomb failure laws and tidal stress mechanisms. Using the SatStress tidal stress model for a Titan-appropriate rheology, we compute the diurnal tidal stress tensor and resolve shear and normal stresses onto a suite of fault orientations. We adopt plausible coefficients of friction and include the effect of a hydrostatic pore fluid pressure gradient for Titan. At shallow fault depths (< 1 km) and for optimally oriented faults, this exploratory model suggests shear failure is achievable under diurnal tidal stress conditions subject to such pore fluid pressures, especially in the polar regions. Our results suggest that under these conditions, shear failure is not only possible, but may be an active deformation mechanism on the surface and in the subsurface of Titan, and could potentially serve as a pathway for the exchange of surface and subsurface materials through shear heating mechanisms. Moreover, the inference of conditions supporting strike-slip tectonism on Titan could have important implications for future Dragonfly observations and for future studies directed at better understanding the structural development of the surfaces of icy moons.

Precursory tidal triggering and b value variation before the 2011 Mw 5.1 and 5.0 Tengchong, China earthquakes

Recent studies have suggested that tidal triggering may preferentially occur when a region is critically stressed, and that tidal stresses provide a potential tool for forecasting earthquakes. Most tidally triggered precursors before large earthquakes are found in subduction zones. We examined tidal triggering of earthquakes near the intracontinental Gaoligong Shear Zone, which is also a geothermally active region. We observed statistically significant correlations between tidally induced stresses and earthquake times, which only appeared approximately two years before the 2011 Tengchong Mw 5.1 and 5.0 earthquakes. The Schuster spectrum shows two peaks at ∼0.5 and ∼1.0 days related to the tidal period. The tidal phase distribution in the pre-mainshock time period shows that most earthquakes occur during phases of positive tidal shear stress and dilatancy strain. Our findings provide a typical case of tidal triggering of earthquake precursors in a continental setting. The stress state can be inferred using the Gutenberg–Richter b value, which characterizes the relative proportion between small and large earthquakes and correlates negatively with differential stress. We investigated the temporal changes of the b value and found that it retains a long-term low value but has a prominent short-term decline prior to mainshocks. The coincidence of low Schuster probability ps with a low b value suggests that the crustal medium is near a critical state, making it more sensitive to external perturbations. The results of epidemic-type aftershock sequence (ETAS) modelling revealed that the seismic activity is affected by not only cascading earthquake triggering but also external forcing. Taking the collective results of the Schuster test, b value, ETAS modelling, and other evidence, we suggest that tidal triggering of earthquakes is likely when the fault is in a near-critical stress state, and geothermal fluid may play an important role in the triggering mechanism.

What Makes Quadruply Lensed Quasars Quadruple?

Abstract Among known strongly lensed quasar systems, ∼25% have gravitational potentials sufficiently flat (and sources sufficiently well aligned) to produce four images rather than two. The projected flattening of the lensing galaxy and tides from neighboring galaxies both contribute to the potential’s quadrupole. Witt’s hyperbola and Wynne’s ellipse permit determination of the overall quadrupole from the positions of the quasar images. The position of the lensing galaxy resolves the distinct contributions of intrinsic ellipticity and tidal shear to that quadrupole. Among 31 quadruply lensed quasars systems with statistically significant decompositions, 15 are either reliably (2σ) or provisionally (1σ) shear-dominated and 11 are either reliably or provisionally ellipticity-dominated. For the remaining eight, the two effects make roughly equal contributions to the combined cross section (newly derived here) for quadruple lensing. This observational result is strongly at variance with the ellipticity-dominated forecast of Oguri &amp; Marshall.

Intrinsic and extrinsic correlations of galaxy shapes and sizes in weak lensing data

ABSTRACT The subject of this paper is to build a physical model describing shape and size correlations of galaxies due to weak gravitational lensing and due to direct tidal interaction of elliptical galaxies with gravitational fields sourced by the cosmic large-scale structure. Setting up a linear intrinsic alignment model for elliptical galaxies that parametrizes the reaction of the galaxy to an external tidal shear field is controlled by the velocity dispersion; we predict intrinsic correlations and cross-correlations with weak lensing for both shapes and sizes, juxtaposing both types of spectra with lensing. We quantify the observability of the intrinsic shape and size correlations and estimate with the Fisher formalism how well the alignment parameter can be determined from the Euclid weak lensing survey. Specifically, we find a contamination of the weak lensing convergence spectra with an intrinsic size correlation amounting to up to 10 per cent over a wide multipole range (ℓ = 100…300), with a corresponding cross-correlation exhibiting a sign change, similar to the cross-correlation between weak lensing shear and intrinsic shapes. A determination of the alignment parameter yields a precision of a few per cent forecasted for Euclid, and we show that all shape and many size correlations should be measurable with Euclid.

Cohesive Sediment Erosion in a Combined Wave‐Current Boundary Layer

AbstractWe conducted field work on the shoals of South San Francisco Bay to elucidate the mechanisms driving cohesive sediment erosion in a shallow, wave‐ and current‐driven flow. Compiling data from three deployments, including measurements taken within the combined wave‐current boundary layer, we found that wave shear stress was strongly correlated to turbulent sediment fluxes across all seasons and a range of deployment depths. Tidal turbulence was only correlated to turbulent sediment fluxes for larger relative depths, or when a wave‐driven sediment flux in the bottom boundary layer allowed the tidal shear stress to transport sediment into the overlying flow. Despite the dominance of waves in eroding sediment, we found favorable agreement between in situ boundary layer erosion measurements and laboratory erosion measurements conducted in a steady flume. Results were analyzed in the context of two benthic surveys which provided insight into the sediment bed properties.

Salt intrusion and its controls in the macro-tidal Oujiang River Estuary, China

The Oujiang River Estuary (ORE) is a macrotidal estuary in southeast Zhejiang Province of China. Although the economy has developed rapidly over the past two decades, few studies have been explored on the estuarine dynamics. Based on in situ measurements, we established a 3-D numerical model to investigate salt intrusion and its response to river discharge, tide, and the salinity at river mouth. We obtained following conclusions. (1) Although salt intrusion length followed a power law with respect to overall river discharge span capturing the fundamental trend, salt intrusion length should be analysed at different ranges of river runoff, as regression accuracy increased substantially at individual range. (2) Estuarine salt transport was dominated by two components of downstream Euler flux and upstream Stokes flux, while tidal shear effects and tidal pumping contributed less. (3) Salt intrusion length not only was a function of river runoff and tidal range but also influenced, with more indicating significance, by mouth salinity. Additionally, geometry effect and nonlinearity might amplify the strong dependences of salt intrusion on mouth salinity and tidal range. (4) Results from partial least squares revealed an approximately linear relation between salt intrusion length and the determining factors of tidal range, river runoff, and river mouth salinity. The hysteretic term was found to have most important influence on salt intrusion length. The response time of salt intrusion in ORE varied with runoff from ~ 2.5 days for medium discharge to ~ 1 day for large and small discharges.

Tidal effects on intra-continental earthquake initiation in the Tibetan Plateau and its adjacent areas*

To investigate the tidal effects on intra-continental earthquake initiation in the Tibetan Plateau and its surrounding areas, we selected over 1,500 focal mechanism solutions of inland earthquakes (epicenter locates at least 100 km to the coastlines) from Global Centroid Moment Tensor (GCMT) project and analyzed the p-values of tidal normal and shear stress as well as tidal Coulomb failure stress. For Coulomb failure stress calculation, we used Coulomb 3.40 software. We find that: (1) p-values of tidal stress change suggests a high tidal correlation of earthquake imitations with tidal normal stress change; (2) when tidal normal stress reached the local maximum values of compression and when tidal shear stress were closed to the positive peaks, earthquakes generated more frequently; (3) particular seismogenic environments such as strong continental plate interactions and the existence of fluids or rheologic substance possibly raise the tidal correlations and (4) higher sensitivity of earthquake initiation to earth tide presents along with higher seismicity, suggesting the rate of rain energy accumulation somehow has a dominating effect on the tidal correlation of earthquake initiation.

Storm-induced hydrodynamic changes and seabed erosion in the littoral area of Yellow River Delta: A model-guided mechanism study

Morphological evolution of large river deltas is highly vulnerable to extreme storm events due to insufficient sediment supply. As an abandoned delta lobe, the coasts along the northern Yellow River Delta (YRD) and Gudong Oil Field have recently suffered serious erosion due to extreme storm events and become increasingly vulnerable. In this study, a well validated and tested Delft 3D module by the observing hydrodynamic and sediment data to simulate the hydrodynamics and seabed erosion during a storm event in the littoral area of YRD. Observed wave, current and sediment data under both fair-weather and storm conditions were collected in the study area and used to validate the model. The results indicated that the model can reproduce well the hydrodynamic and sediment transport processes. A series of numerical experiments were carried out to examine the hydrodynamic changes and sediment transports. In the numerical experiment of normal condition, there is hardly any sediment transport off the YRD. The numerical experiment of storm condition showed that storms enhanced tidal residual currents, weakened tidal shear front, and significant wave heights up to 2 m, considerably intensified the sediment resuspension and dispersal. The local sediment resuspension due to the increased wave-induced bottom stress promoted the sediment plume to expand to the central area of Laizhou Bay, which seemed to provide sediment source for offshore and southward transport. During the storm, the active nearshore sediment resuspension provided sediment source for offshore and southward transport. The intensive dynamics and sediment transport under storm conditions caused significant changes in seabed erosion and siltation. The main erosion occurred off the Gudong and northern YRD, while the main siltation appeared in the central area of Laizhou Bay. No significant recovery after a storm and frequent strong winds have an accumulative effect on the erosion, which is very likely to dominate the erosive states of the YRD coast in the future.

Flocculation under the control of shear, concentration and stratification during tidal cycles

Tide-dominated estuaries are often characterized by a high variability of turbulent shear, suspended particulate matter (SPM) concentration and salinity, which poses challenges for a comprehensive understanding of its mass transport including cohesive sediment dynamics. Here, a combined in situ and numerical study was undertaken to investigate the mechanism of flocculation during tidal cycles, with the aim to disentangle the impacts of turbulent shear, SPM concentration and salinity on flocs. Results show that microflocs (20–200 μm) dominate in the Pearl River Estuary and floc size variation is caused primarily by exchange between flocculi (4–20 μm) and microflocs. We also identified a critical shear rate (G* ≈ 5/s) below which floc exchange occurs slowly. Above the threshold, the particle size distribution is left-skewed and clustered below 60 μm. Evolutions of flocs with different initial sizes synchronize gradually to adapt to the local hydrological environment. The trends of floc size evolution and absolute net flocculation rates are similar among diverse tidal shear cycles. The reason can be attributed to the turbulent shear which enhances both aggregation and breakup processes, thereby limiting the floc size in a certain range. The higher the concentration, the larger both the particle size and the range of variation. In addition, results of numerical modelling reveal that the flocculation time for primary particles is inversely proportional to shear and concentration. A critical concentration (C* ≈ 50 mg/L), below which the impact of concentration on the equilibrium diameter of flocs is more than twice as strong as shear, whilst above which the equilibrium diameter is inversely proportional to the Kolmogorov microscale and weakly correlated to concentration, was also identified. Furthermore, halocline was found to increase vertical variation of flocs size, suggesting co-existence of different flocculation mechanisms across this layer.

Statistical separation of weak gravitational lensing and intrinsic ellipticities based on galaxy colour information

ABSTRACT Intrinsic alignments of galaxies are recognized as one of the most important systematic in weak lensing surveys on small angular scales. In this paper, we investigate ellipticity correlation functions that are measured separately on elliptical and spiral galaxies, for which we assume the generic alignment mechanisms based on tidal shearing and tidal torquing, respectively. Including morphological information allows to find linear combinations of measured ellipticity correlation functions that suppress the gravitational lensing signal completely or which show a strongly boosted gravitational lensing signal relative to intrinsic alignments. Specifically, we find that (i) intrinsic alignment spectra can be measured in a model-independent way at a significance of Σ ≃ 60 with a wide-angle tomographic survey such as Euclid’s, (ii) the underlying intrinsic alignment model parameters can be determined at per cent-level precision, (iii) this measurement is not impeded by misclassifying galaxies and assuming a wrong alignment model, (iv) parameter estimation from a cleaned weak lensing spectrum is possible with almost no bias, and (v) the misclassification would not strongly impact parameter estimation from the boosted weak lensing spectrum.

Relationships Between Chlorophyll‐a and Suspended Sediment Concentration in a High‐Nutrient Load Estuary: An Observational and Idealized Modeling Approach

AbstractThe Guadalquivir estuary is a high‐nutrient load environment, yet it has a reduced primary production because the high suspended sediment concentration (SSC) causes light attenuation. High‐resolution observations revealed relationships between the SSC and Chlorophyll‐a (Chla) concentration from seasonal to intratidal time scales. Local maxima of time‐averaged Chla levels occurred at locations with relatively low SSC. In the upper (lower) part of the estuary, larger Chla concentrations were observed during the wet (dry) season. In contrast to longer time scales, SSC and Chla exhibited in‐phase oscillations during the spring‐neap cycle. Both SSC and Chla were found to peak at maximum ebb and flood. There was no positive correlation at certain apogean neap tides, and instead, Chla exhibited daily variations. An idealized model was developed, which mimicked and helped to explain SSC‐Chla relationships at different time scales. The model accounts for the vertical advection of Chla and SSC, tidal resuspension, radiation‐mediated growth, and effects of the change in stratification stemming from tides and SSC. The specific growth rate of the Chla biomass is inhibited due to high SSC throughout the year. The in‐phase relationship at spring‐neap and tidal scales seems to be due to resuspension of algal microorganisms attached to sediments. Daily variability of Chla during apogean neap tides emerges because tidal shear stress is low and the strong decline in the suspended particulate matter reduces the light attenuation. The light‐mediated growth of part of the biomass, still remaining in the upper layers of the water column, is then driven by the day‐night cycle.

The morphodynamic difference in the western and southern coasts of Laizhou Bay: Responses to the Yellow River Estuary evolution in the recent 60 years

Abstract The Yellow River Estuary (YRE), which is famous for its abundant sediment, rapid accretion, and frequent migration, has experienced a remarkable decrease of sediment transported by the Yellow River (YR) during the past 60 years. By taking the west coast (Yellow River Delta, YRD) and the south coast of Laizhou Bay (LZB) as a unified coastal unit, this paper has analyzed the evolution of shorelines, isobaths, and geomorphic erosion/accretion during the last 60 years based on the remote sensing images and nautical charts; these data were also used to reveal the depositional dynamic mechanisms controlling the coastal geomorphic responses to YRE evolution in a hydrodynamic numerical simulation. Then, the coastal dynamics, subaqueous slope accretion, and geomorphic evolution were integrated spatially. Finally, the impacts of YRE evolution, including changes of the position and amount of sediment loading into the sea, on the coastal geomorphic evolution of western–southern LZB during the recent 60 year period were elucidated. Results showed that outside of the YRE delta lobes, there has always been an arc high-velocity zone, outside of which there has existed a northeast arc tidal shear frontal zone during the last 60 years. As the estuary delta lobes extended into the sea, the high-velocity zone moved toward the southeast, where its range and velocity also increased. As an overall trend, the duration of the tidal shear frontal zone (TSFZ) has grown longer and longer over a whole tidal cycle, while the interval time has grown shorter and shorter; moreover, the span between the southern and northern endpoints has grown larger and larger, while the southern end always remained confined to a fixed position in the northeast sea area of Qingtuozi. Under the control of TSFZ, the suspended sediment of the Yellow River deposits nearly entirely in the arc area in the vicinity of the estuary delta lobes on the west coast, and thus, the sediment cannot cross TSFZ and move into southern LZB. As a result, the western and southern coasts of LZB have shown significant differences in the evolution of shorelines, isobaths, and geomorphic erosion/accretion during the last 60 years. That is, these features have changed dramatically in the west coast but have remained relatively stable in the southern coast, and sediment deposition is now greatly reduced in the southern LZB. Therefore, the YRE evolution had a significant geomorphic impact on the coast of western LZB where the YRD is located, while it had only a slight impact on southern LZB.

Observational Evidence of Surface Wave‐Generated Strong Ocean Turbulence

AbstractBy using an acoustic Doppler velocimeter mounted on the seabed of the continental shelf of the northern South China Sea, high frequency velocity fluctuations were measured for 4.5 days. The turbulent kinetic energy dissipation rate was estimated. During the observation, the strong ocean response to Typhoon Rammasun was recorded to compare the turbulent characteristics before and during the typhoon. The results show that the turbulence near the seabed is mainly generated by the tidal current shear and exhibits a quarter diurnal variation during the period before the typhoon. During the typhoon period, the dissipation rate ε dramatically increased from 1 × 10−6 to 1 × 10−2 m2 s−3 within a short time, and the significant wave height and the surface wave orbital velocity showed the same tendency. This finding suggests that the turbulence is dominantly generated by the surface waves near the seabed.