Velocity Time Series Research Articles

Climate-Induced Changes in River Hydrological and Thermal Conditions in a Large Basin: Implications for Diadromous Fish Migration

Climate-induced changes in river conditions, such as water temperature and current velocity, can disrupt species migration patterns by altering the conditions encountered during migration. We assessed these impacts across the Loire River basin in Europe by compiling long-term fish passage data for three diadromous fish species at fishways, alongside reconstructed time series of water temperature and current velocity. We considered both water temperature and current velocity on days when migration was observed as ''suitable conditions'' for the species' upstream migration. Our findings for the 1963–2019 period revealed that trends in the frequency of suitable conditions for upstream migration were species-specific. For Atlantic salmon, particularly fall migrants, the frequency of suitable conditions has declined over time in certain areas. In contrast, the frequency of suitable migration conditions for both allis shad and sea lamprey has shown an overall increase across the basin. This study offers policy-makers and environmental managers valuable insights for developing effective, spatially explicit strategies to preserve diadromous fish populations amid ongoing climate change.

A multi-technique detection of an eccentric giant planet around the accelerating star HD 57625

The synergy between different detection methods is a key asset in exoplanetology that allows the precise characterization of detected exoplanets and robust constraints even in the case of a non-detection. The interplay between imaging, radial velocities and astrometry has recently produced significant advancements in exoplanetary science. We report a first result of an ongoing survey performed with SHARK-NIR, the new high-contrast near-infrared imaging camera at the Large Binocular Telescope, in parallel with LBTI/LMIRCam in order to detect planetary companions around stars with a significant proper motion anomaly. We focus on HD\,57625, a F8 star for which we determine a $ Ga age, exhibiting significant astrometric acceleration and for which archival radial velocities indicate a previously undetected massive long-period companion. We analysed the imaging data we collected with SHARK-NIR and LMIRCam in synergy with the available public SOPHIE radial velocity time series and Hipparcos-Gaia proper motion anomaly. With this joint multi-technique analysis, we characterised the companion causing the astrometric and radial velocity signals. The imaging observations result in a non-detection, indicating the companion to be in the substellar regime. This is confirmed by the synergic analysis of archival radial velocity and astrometric measurements resulting in the detection of HD\,57625\,b, a planetary companion with an orbital separation of and an eccentricity of HD\,57625\,b joins the small but growing population of giant planets on outer orbits with a true mass determination provided by the synergic usage of multiple detection methods. This again proves the importance of a multi-technique analysis in providing a robust characterization of planetary companions.

From laminar to chaotic flow via stochastic resonance in viscoelastic channel flow

Recent research indicates that low-inertia viscoelastic channel flow experiences supercritical nonnormal mode elastic instability from laminar to sustained chaotic flow due to finite-size perturbations. The challenge of this paper is to elucidate a realization of such a pathway when the intensity of the elastic wave is too low to amplify vortex fluctuations above the instability onset. The study identifies two subregions in the transition flow regime at Weissenberg number Wi>Wic, the instability onset. In the lower subregion at Wic≤Wi≤300, we discover periodic spikes in the streamwise velocity time series u(t) that appear in the chaotic power spectrum as low-frequency, high-intensity peaks resembling stochastic resonance (SR). In contrast, the spanwise velocity power spectrum, Ew, remains flat and with low-intensity, noisy, and broad elastic wave peaks. The spikes significantly distort the probability density function of u and initiate and amplify random streaks and wall-normal vorticity fluctuations. The condition for the SR emergence is similar to that of a dynamical system where the presence of a chaotic attractor, limit cycle, and external white noise are necessary. This similarity is confirmed by presenting a phase portrait in two subregions of the transition regime. In the upper subregion at Wi>400, the periodic spikes disappear and Ew becomes chaotic with a large intensity elastic wave sufficient to self-organize and synchronize the streaks into cycles and to amplify the wall normal vorticity, according to a recently proposed mechanism of vortex-wave interactions. Published by the American Physical Society 2024

A Kinematic Approach for Rip Current Identification from ADCP Observation Data at Haeundae Beach, Korea

In May 2023, direct observations of rip currents were conducted at Haeundae Beach, Korea, over a two-day period at six different stations using upward-facing Acoustic Doppler Current Profilers (ADCPs). The depth-averaged cross-shore velocity data were low-pass filtered with a 30-s cutoff period to eliminate wave-related motions. By applying 15-min boxcar averages, correlation analyses were performed to examine the relationship between three types of flow (cross-shore, onshore, and offshore) and three environmental factors (tide, wave, and wind). The analysis revealed that only one (R2-3) of the six stations had a high likelihood of rip current occurrence. Rip currents were defined as regions of offshore flow within the low-pass filtered time series of cross-shore velocities. For each identified rip current, three key kinematic features—maximum speed, duration, and distance—were estimated. Using specific thresholds for these features, hazardous rip currents were determined. Station R2-3 was the only station where hazardous rip currents were observed, which is consistent with the findings of the correlation analysis. Additionally, swells with a 15-s period were detected exclusively at R2-3 during the period of the hazardous rip currents, suggesting their significant role in the development of the observed rip currents. Furthermore, both Rip Index from the Rip Current Monitoring and Warning System and the CCTV Score from the Rip Current Checklist exceeded threshold values during this period, reinforcing the reliability of the method used. The potential influence of bound infragravity waves on the duration and variability of these rip currents was discussed. The rip currents observed at Haeundae Beach could be categorized as the "focused" type.

Data Release 3: Spectroscopic binary-star orbital solution. The SB1 processing chain

The satellite constitutes one of ESA's cornerstone missions. Being primarily an astrometric space experiment measuring positions, proper motions, and parallaxes for a huge number of stars, it also performs photometric and spectrophotometric observations. operates a medium-dispersion spectrometer, known as Radial Velocity Spectrometer (RVS) which provides spectra and radial velocity (RV) time series. The paper is focussed on the analysis of the RV time series. We fit orbital and trend models, restricting our study to objects of spectral types F-G-K that are brighter than a magnitude of 12, presenting only one single spectrum (SB1). Suitable time series were processed and analysed on an object-per-object basis, providing orbital or trend solutions. The results of the various fits were further filtered internally on the basis of several quality measures to discard spurious solutions. The objects with solely a spectroscopic solution were classified in one of the three classes: SB1 (eccentric model) SB1C (circular model), or TrendSB1 (mere trend model). We detail the methods used in this work and describe the derived parameters and results. After a description of the models considered and the related quality tests of the fit, we detail the internal filtering process aimed at rejecting bad solutions. We also present a full validation of the pipeline. A description of the current content of the catalogue is also provided. We present the SB1 SB1C and TrendSB1 spectroscopic solutions contained in the SB subcatalogue, part of the DR3 catalogue. We deliver some 181\,327 orbital solutions in class SB1 202 in class SB1C and 56\,808 in the associated class TrendSB1 . This is a first release and the delivered SB subcatalogue could be further tuned and refined. However, the majority of the entries are correct. Thus, this data set constitutes by far the largest set of spectroscopic orbital solutions to be computed.

Turbulence statistics estimation across a step change in roughness via interpretable network-based modelling

Abstract This study proposes a data-driven methodology to complement existing time-series measurement tools for turbulent flows. Specifically, a cluster-based transition network model is employed for the estimation of velocity time traces and their corresponding statistics. The method is tested on a laboratory-modelled turbulent boundary layer over a step change in surface roughness, where velocity time series are recorded for training and validation purposes via Laser Doppler Anemometry. Results show that our approach can estimate velocity and momentum flux statistics within experimental uncertainty over a rough surface through an unsupervised approach, and across the step change in roughness through a semi-supervised variant. The friction velocity across the domain is also estimated with 10% relative error compared to the measured value. The proposed methodology is interpretable and robust against the main methodological parameters. A reliable data-driven framework is hence provided that can be integrated within existing laboratory setups to supplement or partially replace measurement systems, as well as to reduce wind tunnel running times.

Validation of large eddy simulations in urban wind studies using a new overall area metric

There is an increase in reliance on large-eddy simulations (LES) over traditional Reynolds-Averaged Navier–Stokes (RANS) simulations for conducting urban wind studies because of their potential to capture detailed flow characteristics and unsteady flow phenomena. Validation remains a crucial aspect of computational fluid dynamics (CFD) analysis. Yet, LES validation often relies on traditional RANS-based metrics that focus on mean quantities, despite LES providing richer flow details. With adequate LES validation guidelines lacking in the computational wind engineering literature, this paper introduces a new validation metric tailored for LES in urban wind studies. This study uses the ”Michelstadt” test case, a semi-idealized model of a generic European city, to demonstrate the metric’s evaluation. It begins by assessing the importance of mesh sensitivity and inflow generation techniques in achieving high-fidelity LES results. Then, the proposed metric, called the overall area metric (OAM), improves the evaluation of LES results by quantitatively comparing the cumulative density functions (CDFs) of the velocity time series of LES with experiments. The LES results for mean velocity and Reynolds stresses align well with the experimental data based on traditional hit rate and factor of two metrics both within and above the urban canopy layer (UCL). The OAM reveals poor results above the building compared to the results within the UCL for the mean streamwise velocity. Therefore, the OAM metric accurately represents velocity distributions, allowing validation of a wider range of wind speeds, unlike previous metrics. This is important in recent LES studies on rare high-wind events, such as gusts.

The curious case of 2MASS J15594729+4403595, an ultra-fast M2 dwarf with possible Rieger cycles

Context. RACE-OC (Rotation and ACtivity Evolution in Open Clusters) is a project aimed at characterising the rotational and magnetic activity properties of the late-type members of open clusters, stellar associations, and moving groups of different ages. The evolution in time of rotation and activity at different masses sheds light on the evolution of the stellar internal structure, on magneto-hydrodynamic processes operating in the stellar interior, and on the coupling and decoupling mechanisms between the radiative core and the external convective envelope. As part of this project, in the present paper we present the results of an investigation of a likely member of the AB Doradus association, the M-type star 2MASS J15594729+4403595. Aims. In the present study, we aim to reveal the real nature of our target, which turned out to be a hierarchical triple system, to derive the stellar rotation period and surface differential rotation, and to characterise its photospheric magnetic activity. Methods. We have collected radial velocity and photometric time series, complemented with archive data, to determine the orbital parameters and the rotation period and we have used the spot modelling technique to explore what causes its photometric variability. Results. We found 2MASS J15594729+4403595 to be a hierarchical triple system consisting of a dwarf, SB1 M2, and a companion, M8. The M2 star has a rotation period of P = 0.37 d, making it the fastest among M-type members of AB Dor. The most relevant result is the detection of a periodic variation in the spotted area on opposite stellar hemispheres, which resembles a sort of Rossby wave or Rieger-like cycles on an extremely short timescale. Another interesting result is the occurrence of a highly significant photometric periodicity, P = 0.443 d, which may be related to the stellar rotation in terms of either a Rossby wave or surface differential rotation. Conclusions. 2MASS J15594729+4403595 may be the prototype of a new class of extremely fast rotating stars exibiting short Rieger-like cycles. We shall further explore what may drive these short-duration cycles and we shall also search for similar stars to allow for a statistical analysis.

Tsunami Early Warning Using High-Frequency Ocean Radar System in the Kii Channel, Japan

Abstract The tsunami of the 2011 Tohoku earthquake was monitored by the high-frequency (HF) ocean radar system in the Kii Channel, Japan. In this study, we conducted a retrospective analysis of tsunami early warning based on HF radar observations. First, we synthesized the surface current velocity using observation data of two radar land stations: Minato and Saikazaki. After vector synthesis, the time series of current velocity showed high consistency with the results of forward simulation. Then, we used the time series starting from 08:00 (UTC), 11 March 2011, as the input for data assimilation, reconstructing the tsunami wavefield in the Kii Channel. Comparison with actual observations at Kobe showed that our approach can accurately forecast coastal tsunami waveforms at least 50 min prior to tsunami arrival. The normalized prediction error decreased over time, indicating a progressively improving forecast accuracy. This is the first study on tsunami data assimilation using HF radar for the early warning of an actual seismogenic tsunami. We also discussed the limitations of the current HF radar system in the Kii Channel and made suggestions regarding the deployment of future radar land stations.

The evolutionary history of GD 1400AB, a white dwarf–brown dwarf binary

ABSTRACT GD1400AB was one of the first known white dwarf $+$ brown dwarf binaries and is the only one of these systems where the white dwarf is a ZZ Ceti pulsator. Here, we present both radial velocity measurements and time-series photometry, analysing both the white dwarf pulsations and the effects of irradiation on the brown dwarf. We find that the brightness temperatures of 1760 $\pm $ 10 K for the nightside and 1860 $\pm$ 10 K for the dayside indicate that the brown dwarf is hotter than spectra have previously suggested, although brightness temperatures calculated using a larger radius for the brown dwarf are consistent with previously determined spectral types. We also discuss the likely evolutionary pathway of this binary and put its common envelope phase into context with the other known systems.

Long-range cross-correlations between center of pressure velocity and colored noises provided during quiet standing

Unperceivable electrical noise stimulation has been applied to improve postural control through the enhancement of somatosensory feedback. It has been observed that stimulation with a pink noise (1/f) structure is more effective than stimulation with other noise structures. In addition, the 1/f structure embedded in the postural control system may have a superior effect on postural control stabilization. However, the direct relationship between the long-range correlations of the pink-noise signal applied to somatosensory receptors and those of the postural control system has not been elucidated. Thus, we aimed to explore a common long-range correlation factor shared in the time series of the provided noise and foot center of pressure (CoP) during quiet standing. Sixteen young adults stood quietly on the force platform for 65 s. Four noise conditions (no stimulation and stimulation of knee joints with white-, pink-, and red-noise-like signals) were employed during the standing trials. The detrending moving-average cross-correlation analysis revealed that in each of the anteroposterior and mediolateral directions, the CoP velocity time series displayed significant long-range cross-correlations with the white and pink noise signals provided at that time, whereas such an effect was not observed in the red noise signal. This result indicates that pink and white noise signals would alter the temporal behavior of the CoP during quiet standing, although the mechanism remains to be elucidated.

Estimating the Purse Seine Net Geometry during a Hauling Operation Using a Data Assimilation Method

The dynamics of fishing nets can be estimated by modeling and numerically computing the forces acting on them. However, the dynamic models of fishing nets are highly nonlinear owing to the significant influence of hydrodynamic forces acting on the net. Therefore, if there are unknown parameters that define the state of motion in the model, it is often difficult to achieve high accuracy in the numerical simulations of fishing gear and evaluate its dynamics. To address this issue, a method is proposed for estimating these unknown parameters by integrating a nonlinear Kalman filter into a fishing net dynamics model. This study aimed to estimate the hauling velocity of large- and medium-sized purse seine fishing nets, which can be a challenging parameter to measure. The calculations are based on the data obtained from a research operation conducted by the Marine Fisheries Research and Development Center in 2019 using the purse seine fishing vessel “Taikei Maru No. 1”. The time series of the hauling-net velocity was estimated based on the results of the estimation experiment. These results allowed the estimation of the hauling velocity and calculation of the net dynamics during the hauling process. This shows that net dynamics simulation is possible even with unknown parameters.

The 𝒯ℛ𝒪𝒴 project

Context. Co-orbital objects, also known as trojans, are frequently found in simulations of planetary system formation. In these configurations, a planet shares its orbit with other massive bodies. It is still unclear why there have not been any co-orbitals discovered thus far in exoplanetary systems (exotrojans) or even pairs of planets found in such a 1:1 mean motion resonance. Reconciling observations and theory is an open subject in the field. Aims. The main objective of the 𝒯ℛ𝒪𝒴 project is to conduct an exhaustive search for exotrojans using diverse observational techniques. In this work, we analyze the radial velocity time series informed by transits, focusing the search around low-mass stars. Methods. We employed the α-test method on confirmed planets searching for shifts between spectral and photometric mid-transit times. This technique is sensitive to mass imbalances within the planetary orbit, allowing us to identify non-negligible co-orbital masses. Results. Among the 95 transiting planets examined, we find one robust exotrojan candidate with a significant 3-σ detection. Additionally, 25 exoplanets show compatibility with the presence of exotrojan companions at a 1-σ level, requiring further observations to better constrain their presence. For two of those weak candidates, we find dimmings in their light curves within the predicted Lagrangian region. We established upper limits on the co-orbital masses for either the candidates and null detections. Conclusions. Our analysis reveals that current high-resolution spectrographs effectively rule out co-orbitals more massive than Saturn around low-mass stars. This work points out to dozens of targets that have the potential to better constraint their exotrojan upper mass limit with dedicated radial velocity observations. We also explored the potential of observing the secondary eclipses of the confirmed exoplanets in our sample to enhance the exotrojan search, ultimately leading to a more accurate estimation of the occurrence rate of exotrojans.

Uncertainties in measurements of bubbly flows using phase-detection probes

The analysis of bubbly two-phase flows is challenging due to their turbulent nature and the need for intrusive phase-detection probes. However, accurately characterizing these flows is crucial for safely designing critical infrastructure such as dams and their appurtenant structures. The combination of dual-tip intrusive phase-detection probes with advanced signal processing algorithms enables the assessment of pseudo-instantaneous 1-D velocity time series; for which the limitations are not fully fathomed. In this investigation, we theoretically define four major sources of error, which we quantify using synthetically generated turbulent time series, coupled with the simulated response of a phase-detection probe. Based on the analysis of 1010 simulated bubble trajectories, our findings show that typical high-velocity flows in hydraulic structures hold up to 15% error in the mean velocity estimations and up to 35% error in the turbulence intensity estimations for the most critical conditions, typically occurring in the proximity of the wall. Based on thousands of simulations, our study provides a novel data-driven tool for the estimation of these baseline errors (bias and uncertainties) in real-word phase-detection probe measurements of bubbly flows (air concentrations c<40%).

Spatiotemporal variability in surface velocity of large tributary-bearing glaciers of the Indian Himalayas inferred from SAR polarimetry

ABSTRACT Glacier pattern changes directly indicate variability in local climatic circumstances. The present study dealt with the proposition and estimation of spatiotemporal glacier movement using a synthetic aperture radar-derived polarimetric tracking method which revealed improved estimates over four selected large tributary-bearing glaciers (Siachen, Bara Shigri, Gangotri, and Zemu) in the Indian Himalayas. The average estimated velocities in 2021–2022 for the four glaciers were 0.13, 0.06, 0.08 and 0.09 m/day. The thick debris cover hindered the movement temporally in the middle and lower reaches of the glaciers. The effect of meltwater influx along the tributary confluence zone was also witnessed over the glaciers. Comparison and validation with the US National Aeronautics and Space Administration (NASA) Inter-mission Time Series of Land Ice Velocity and Elevation (ITS_LIVE) products has shown the utility of the proposed method in studying the contributions of active feeding tributaries of the glaciers in the ablation zone.

Mixed Rossby Gravity Waves at Middepths of the Equatorial Indian Ocean

Abstract This study examines mixed Rossby gravity (MRG) waves at middepths (500–2000 m) of the Indian Ocean, using multiyear velocity time series obtained from current-meter moorings at 77°, 83°, and 93°E along the equator over the period 2000–19. These data are analyzed in combination with a high-resolution wind-forced ocean general circulation model. The spectrum of observed meridional velocity showed elevated energy over a wide range of periods from about 10 to 100 days with the spectral peak at a period of about 30 days. The model was able to simulate the characteristics of the observed spectrum. Further diagnostics determined that the detected variability is generally consistent with theoretical MRG waves in a resting ocean. Statistical analysis and a model sensitivity experiment identified distinct variations at three periods, where meridional velocity has sizable energy. The 14-day variability is wind driven and has a long zonal (∼3300 km) and vertical (∼4200 m) wavelength. The 28-day variability is excited by the dynamical instability of the background flow in the equatorial western Indian Ocean near the surface and propagates to the study area. It is characterized by a shorter zonal (∼1100 km) and vertical (∼2800 m) wavelength compared to 14-day variability. The 43-day variability has a zonal wavelength (∼820 km) comparable to the 28-day variability but does not show the tendency of propagation and is likely generated in situ through nonlinear interactions. These results show that various processes contribute to the excitation of MRG waves at middepths of the Indian Ocean. Significance Statement Mixed Rossby gravity (MRG) waves are a prominent mode of intraseasonal variability in tropical oceans. They are of climatic importance owing to their effects on turbulent mixing in the deep sea and how they affect the large-scale ocean circulation. This study examines MRG waves at the middepths of the equatorial Indian Ocean using a unique set of in situ current-meter measurements and a high-resolution ocean general circulation model. We describe characteristics such as horizontal and vertical wavelengths, frequency spectra, dispersion properties, and energy sources. Results show that wind forcing at the sea surface, dynamical instability of the background flow near the surface in the western Indian Ocean, and nonlinear interactions generate MRG waves at distinct periods and wavelengths.

Variability of saltwater flow in the Hoburg Channel, Baltic Sea: in situ measurements vs NEMO modelling

A half-year long time series of the bottom layer velocity measured in situ in the Hoburg Channel displayed seven-day oscillations of the saltwater flow. The flow was characterized by alterations of surges with the increase of northward velocity to approximately 0.2–0.3 m/s and blockages when the northward velocity vanishes or becomes small negative. The measured time series of the northward velocity component was surprisingly highly correlated with the simulation by NEMO reanalysis at the correlation coefficient of 0.82 and the 95 % confidence limits of 0.76–0.86. The seven-day oscillations were accompanied by almost synchronous oscillations of the southeast component of the wind vector. It can be considered convincing evidence that the seven-day oscillations in the saltwater flow were caused by wind forcing.

20-year permafrost evolution documented through petrophysical joint inversion, thermal and soil moisture data

This study investigates the ground characteristics of the high altitude (3410 m a.s.l.) permafrost site Stockhorn in the Swiss Alps using a combination of surface and subsurface temperature, soil moisture, electrical resistivity and P-wave velocity time series data including a novel approach to explicitly quantify changes in ground ice content. This study was motivated by the clear signal of permafrost degradation visible in the full dataset at this long-term monitoring site within the PERMOS (Permafrost Monitoring Switzerland) network. Firstly, we assess the spatio-temporal evolution of the ground ice and water content by a combined analysis of all available in situ thermal (borehole and ground surface temperature), hydrological (soil moisture) and geophysical (geoelectric and seismic refraction) data over two decades (2002–2022) regarding the driving factors for the spatially different warming. Secondly, we explicitly quantify the volumetric water and ice content and their changes in the subsurface from 2015 to 2022 using a time-consistent petrophysical joint inversion scheme within the open-source library pyGIMLi. The petrophysical joint inversion scheme has been improved by constraining the rock content to be constant in time for six subsequent inversions to obtain consistent changes in ice and water content over the monitoring period based on jointly inverted resistivity and traveltime data. All different data show a warming trend of the permafrost. The ice content modeled from the petrophysical joint inversion has decreased by about 15 vol.% between 2015 and 2022. Changes in ice content are first observed in the lower, south-facing part of the profile. As a result, resistivity and P-wave velocity have been decreasing significantly. Permafrost temperatures measured in the boreholes have increased between 0.5 °C and 1 °C in 20 years. Our study shows the high value of joint and quantitative analysis of datasets comprising complementary subsurface variables for long-term permafrost monitoring.

Confrontation between modelled solar integrated observables and direct observations

Context. Stellar variability strongly impacts the search for low-mass exoplanets with radial velocity techniques. Two types of planet-free time series can be used to quantify this impact: models and direct solar observations after a subtraction of the Solar System planetary contribution. Making a comparison among these approaches is necessary to improve the models, which can then be used for blind tests across a broad range of conditions. Aims. Our objective is therefore to validate the amplitude of the convective blueshift in plages used in our previous works, particularly in blind tests, with HARPS-N solar data. Methods. We applied our model to the structures observed at the time of HARPS-N observations and established a direct comparison between the radial velocity time series. To complete our diagnosis, we also studied the observed radial velocities separately for each diffraction order derived from the individual cross-correlation functions, as well as our line-by-line radial velocities. Results. We find that our previous model had been underestimating the amplitude of the convective blueshift inhibition by a factor of about 2. A direct estimation of the convective blueshift in the spectra, which is shown to be correlated with the plage filling factor, allows us to explain the difference with previous estimations obtained with MDI/SOHO Dopplergrams, based on the specific properties of the Ni line used in this mission. In addition, we identified several instrumental systematics, in particular, the presence of a 2 m s−1 peak-to-peak signal with a period of about 200 days in radial velocity and bisector. This signal could be due to periodic detector warmups, a systematic dependence of the long-term trend on wavelength that is possibly related to the variability of the continuum over time, and/or an offset in radial velocity after the interruption of several months in October 2017. Conclusions. A large amplitude in the convective blueshift inhibition of (360 ms−1, namely twice more than in our previous works) must be used when building synthetic times series for blind tests. The presence of instrumental systematics should also be taken into account when using sophisticated methods based on line properties to mitigate stellar activity when searching for very weak signals.

Internal Waves Force Elevated Turbulent Mixing at Barkley Canyon

AbstractSubmarine canyons are hot spots for topography‐internal wave interactions, with elevated mixing contributing to regional water mass transport and productivity. Two velocity time series compare and contrast internal waves deep inside Barkley Canyon to a nearby site on the shelf‐break slope of the Vancouver Island Continental Shelf. Elevation of internal wave energy occurs near topography, up to a factor of 10 above the slope and 100 in the canyon. All frequency bands display strong seasonal variability but weak interannual variability. Diurnal (K1) energy is sub‐inertial, trapped along topography, and forced locally through barotropic motions. Both sites have high near‐inertial (NI) energy linked to wind events, though fewer events are observed deep inside the canyon. At the slope site, near‐inertial energy is attenuated with depth, while in the canyon it is amplified near the bottom. Freely propagating semidiurnal (M2) energy appears focused near critical shelf‐break and canyon floor topography, due to local and remote baroclinic forcing. The high‐frequency internal wave continuum has enhanced near‐bottom energy at both sites (up to 7 × the Garrett‐Munk spectrum), and inferred dissipation rates, ɛ, reaching 10−7 W kg−1 near topography. Dissipation is most strongly correlated with semidiurnal energy variability at both sites, with secondary contributors that are site dependent. Forcing power law fits are on the slope, and NI0.2 in the canyon. There is also a build‐up of “shoulder” energy (PSh) near the buoyancy frequency, with a power law fit to dissipation of PSh ∼ ɛ0.3 at both sites.