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Hydrodynamics under regular plunging breaking waves over a fixed breaker bar were studied in a large-scale wave flume. A previous paper reported on the outer flow hydrodynamics; the present paper focuses on the turbulence dynamics near the bed (up to 0.10 m from the bed). Velocities were measured with high spatial and temporal resolution using a two component laser Doppler anemometer. The results show that even at close distance from the bed (1 mm), the turbulent kinetic energy (TKE) increases by a factor five between the shoaling, and breaking regions because of invasion of wave breaking turbulence. The sign and phase behavior of the time-dependent Reynolds shear stresses at elevations up to approximately 0.02 m from the bed (roughly twice the elevation of the boundary layer overshoot) are mainly controlled by local bed-shear-generated turbulence, but at higher elevations Reynolds stresses are controlled by wave breaking turbulence. The measurements are subsequently analyzed to investigate the TKE budget at wave-averaged and intrawave time scales. Horizontal and vertical turbulence advection, production, and dissipation are the major terms. A two-dimensional wave-averaged circulation drives advection of wave breaking turbulence through the near-bed layer, resulting in a net downward influx in the bar trough region, followed by seaward advection along the bar's shoreward slope, and an upward outflux above the bar crest. The strongly nonuniform flow across the bar combined with the presence of anisotropic turbulence enhances turbulent production rates near the bed.

Velocity bunching causes nonlinear modulations in synthetic aperture radar (SAR) images of oceanic scenes. SAR images for the azimuth waves exhibit destructive wavy patterns because of azimuthal distortion caused by velocity bunching. Meanwhile, velocity bunching creates constructive wavy patterns for long waves in certain cases. This paper aims to provide a simple indication for practical interpretation of plausible wavy patterns. A numerical simulation had been performed to address how velocity bunching forms a clear wave-like pattern caused by orbital motions of a long single swell under a certain condition. More specifically, when the azimuth shifts caused by the orbital motions of the azimuth wave concentrate in the wave trough or crest, the bunching causes a strong single peak in the SAR images. This paper explains the mechanism of displaying plausible wavy patterns from the viewpoint of the ocean wave spectra and this specific condition. First, the simulation was validated for irregular waves generated from ocean wave spectra matching actual buoy data from which SAR images were simultaneously obtained. The SAR image spectra showed longer waves than those of the ocean wave spectra estimated via buoy data. The simulated spectra exhibited a similar trend to the actual SAR image, thus validating the numerical simulation. Next, an additional numerical simulation was conducted for irregular waves under the specific condition. The simulated results suggest that if a significant wave height and wavelength match the specific condition, the long waves in SAR image spectra can be similar to the original ocean wave spectra.

In this paper, closed-form integral expressions are derived to describe how surface gravity waves (tsunamis) are generated when general asymmetric ground displacement (due to earthquake rupturing), involving both horizontal and vertical components of motion, occurs at arbitrary depth within the interior of an anisotropic sub-sea solid beneath the ocean. In addition, we compute the resultant hydrodynamic pressure within the seawater and the elastic wavefield within the seabed at any position. The method of potential functions and an integral transform approach, accompanied by a special contour integration scheme, are adopted to handle the equations of motion and produce the numerical results. The formulation accounts for any number of possible acoustic-gravity modes and is valid for both shallow and deep water situations as well as for any focal depth of the earthquake source. Phase and group velocity dispersion curves are developed for surface gravity (tsunami mode), acoustic-gravity, Rayleigh, and Scholte waves. Several asymptotic cases which arise from the general analysis are discussed and compared to existing solutions. The role of effective parameters such as hypocenter location and frequency of excitation are examined and illustrated through several figures which show the propagation pattern in the vertical and horizontal directions. Attention is directed to the unexpected contribution from the horizontal ground motion. The results have important application in several fields such as tsunami hazard prediction, marine seismology and offshore and coastal engineering. In a companion paper we examine the effect of ocean stratification on the appearance and character of internal and surface gravity waves. This article is protected by copyright. All rights reserved.

We are in an era of unprecedented data volumes generated from observations and model simulations. This is particularly true from satellite Earth Observations (EO) and global scale oceanographic models. This presents us with an opportunity to evaluate large scale oceanographic model outputs using EO data. Previous work on model skill evaluation has led to a plethora of metrics. The paper defines two new model skill evaluation metrics. The metrics are based on the theory of universal multifractals and their purpose is to measure the structural similarity between the model predictions and the EO data. The two metrics have the following advantages over the standard techniques: a) they are scale-free, b) they carry important part of information about how model represents different oceanographic drivers. Those two metrics are then used in the paper to evaluate the performance of the FVCOM model in the shelf seas around the south-west coast of the UK.

The classic theory for the interaction of surface gravity waves and the general ocean circulation entails the so-called wave radiation stress terms in the phase-averaged momentum equation. The equations of motion are for the combined Eulerian current and Stokes drift. On the other hand, a more recent approach includes the so-called vortex force term in the momentum equation wherein the only wave property is Stokes drift. The equations of motion are for the Eulerian current. The idea has gained traction in the ocean science community, a fact that motivates this paper. A question is: can both theories be correct? This paper answers the question in the negative and presents arguments in favor of the wave radiation theory. The vortex force approach stems from an interesting mathematical construct, but it does stand up to physical or mathematical scrutiny as described in this paper. Although not the primary focus of the paper, some discussion of Langmuir circulation is included since the vortex force was first introduced as the basis of this oceanic cellular phenomenon. Finaly the paper explains the difference in the derivation of the radiation stress theory and the vortex force theory: the later theory entails errors related to its use of curl and reverse-curl [or uncurl] processes.

In this paper, radar backscattering from a water surface in response to rainfall was studied. The paper consists of two parts. First, the spatial characteristics of raindrops in rain fields were analyzed based on published data and the response of a water surface to rainfall was experimentally studied in the laboratory. Rain-generated surface features including stalks, crowns, ring waves, and secondary drops were measured. It was found that stalks and crowns are dominant in terms of their height and energy. Second, the radar signatures of a rainfall event simultaneously observed by C band ENVISAT (European satellite), ASAR (Advanced Synthetic Aperture Radar), and ground-based weather radar in the Northwest Pacific were investigated. The relationship between the radar return intensity extracted from the C band ASAR image and the reflectivity factor (rain rate) obtained from ground-based weather radar was analyzed. For light/moderate rain (with low reflectivity factors), the radar backscattering intensity increases as the reflectivity factor increases. For heavy rain (with high reflectivity factors), the radar backscattering intensity decreases as the reflectivity factor increases. The maximum radar backscattering intensity occurs at a reflectivity factor of 45 dBZ (with rain rate of 24 mm/h). It was found that the spaceborne radar backscattering intensity strongly correlates with the average distance between the stalks on the water surface in the rain field in a nonlinear manner. The physics of the radar signatures of the rain event are explored.

This second paper of our set on short wind waves on the ocean utilizes the wavenumber-frequency spectrum of short wave heights, F(k,f), derived in our previous paper to investigate kinematic effects on the dependence of the frequency spectrum, F(f), and the wavenumber spectrum, F(k), on long-wave height. We show that the model predicts that neither F(f) nor F(k) are exactly power law functions of their independent variables and that F(f) varies with significant wave height much more than F(k) does. After calibrating the model against wave gauges, we also investigate the dependence of mean-square-slopes (mss), mean-square heights (msh) and root-mean-square orbital velocities (rmsv) of short ocean waves on wind speed and maximum frequency or wavenumber. We use data from the wire wave gauges on University of Miami's Air-Sea Interaction Spar (ASIS) buoy for calibration purposes. Frequency spectra from the wave gauges begin to be affected by noise at about 2.5 Hz. Therefore, above 1 Hz, we utilize F(f) from the modeled F(k,f) to extend the frequency dependence up to 180 Hz. We set modeled spectral densities by matching measured spectra at 1 Hz. Using the calibrated F(f,k), we are able to estimate the average value of the total mss, for long and short waves, and its upwind and crosswind components up to 180 Hz for a variety of wind speeds. The average mss values are in good agreement with the measurements of Cox and Munk [1954], although the upwind and crosswind components agree less well.

The Aquarius/SAC-D mission has been providing Sea Surface Salinity (SSS), globally over the ocean, for almost 3 years. As a member of the AQ/SAC-D Cal/Val team, the Central Florida Remote Sensing Laboratory has analyzed these salinity retrievals in the presence of rain and has noted the strong correlation between the spatial patterns of reduced SSS and the spatial distribution of rainfall. It was determined that this is the result of a cause and effect relationship, as opposed to SSS measurement errors. Hence, it is important to understand these SSS changes due to seawater dilution by rain and the associated near-surface salinity stratification. This paper addresses the effects of rainfall on the Aquarius (AQ) SSS retrieval using a macro-scale Rain Impact Model (RIM) in the region of high convective rain over the Inter-tropical Convergence Zone. This model, based on the superposition of a one-dimension eddy diffusion (turbulent diffusion) model, relates sea surface salinity to depth, rain accumulation and time since rainfall. For aiding in the identification of instantaneous and prior rainfall accumulations, an AQ Rain Accumulation product was developed. This product, based on the NOAA CMORPH rain data set, provides the rainfall history for 24 h prior to the observation time, which is integrated over each AQ SSS measurement cell. In this paper results of the RIM validation are presented by comparing AQ measured and RIM simulated SSS for several months of 2012. Results show the high cross correlation for these comparisons and also with the corresponding SSS anomalies relative to HYCOM.

[1] This paper reports the findings of a 2 week field campaign designed to study wave-induced flows within a meadow of Posidonia oceanica at water depth 9 m. Previous laboratory experiments suggest that waves induce a mean mass drift in the direction of wave propagation (“streaming”) through submerged canopies of vegetation. This paper provides the first field measurements of this wave-induced streaming. During periods of high wave activity, streaming flows with magnitudes as high as 20% of the near-bed oscillatory velocity were measured within the meadow. In addition to presenting field measurements of wave-induced streaming, this paper also considers the damping of wave-induced oscillatory flow within the seagrass meadow. Oscillatory velocities measured within the meadow were reduced by less than 30% relative to those above the meadow over the duration of the study. This is in agreement with previous laboratory and field measurements which show that oscillatory flows are damped less within submerged canopies compared to unidirectional flows. Existing analytical models underpredict the magnitude of the streaming flow and overpredict oscillatory velocity reductions. These discrepancies are thought to arise because the drag generated by flexible seagrasses moving with wave-induced flow is not well described.

Employing a linear shallow water equation (LSWE) model in the spherical coordinates, this paper investigates the tsunami waves generated by the atmospheric pressure shock waves due to the explosion of the submarine volcano Hunga Tonga-Hunga Ha'apai on January 15, 2022. Using the selected 59 atmospheric pressure records in the Pacific Ocean, an empirical atmospheric pressure model is first constructed. Applying the atmospheric pressure model and realistic bathymetric data in the LSWE model, tsunami generation and propagation are simulated in the Pacific Ocean. The numerical results show clearly the co-existence of the leading locked waves, propagating with the speed of the atmospheric pressure waves (~1,100 km/hr), and the trailing free waves, propagating with long gravity ocean wave celerity (~ 750 km/hr). During the event, tsunamis were reported by 41 DART buoys in the Pacific Ocean, which require corrections because of the occurrence of atmospheric pressure waves. The numerically simulated tsunami arrival time and the amplitudes of the wave crest and trough of the leading locked waves compare reasonably well with the corrected DART measurements. The comparisons for the trailing waves are less satisfactory, since free waves could also have been generated by other tsunami generation mechanisms, which have not been considered in the present model, and by the scattering of locked waves over changing bathymetry. In this regard, the numerical results show clearly that the deep Tonga trench (~ 10 km) amplifies the trailing waves in the Southeast part of the Pacific Ocean via the Proudman resonance condition.

This paper presents a new technique for estimating the wind friction velocity at the ocean surface from C-band radar scatterometer measurements. This technique uses physical models of ocean surface waves and electromagnetic backscattering from a rough surface at intermediate angles of incidence to generate predictions of the normalized radar cross section (NRCS, or σ 0 ) of the ocean surface for a given wind friction velocity and observational geometry. The ocean spectral model used in this technique has been developed specifically for this application. It combines in situ wave measurements at low wave numbers with the Phillips [1985] equilibrium spectral model. This choice of ocean wave model is supported by a set of open ocean wave measurements summarized in this paper. A suite of models, derived from both in situ and remote measurements of the sea surface, is used to characterize the directional spreading of ocean waves relative to the wind direction. The resulting two-dimensional ocean wave spectra are used with a composite surface model to predict radar backscattering from the ocean surface at C-band. These radar cross-section predictions are combined with ERS-1 scatterometer measurements in a cost function minimization scheme to yield estimates of the friction velocity vector at the ocean surface. We present examples of this technique and compare friction velocity retrievals obtained via this scheme with buoy-based measurements under a variety of wind and wave conditions. On the basis of the analysis of a limited number of cases, this technique yielded friction velocity estimates for which the magnitude was within 22% and the direction was within ±25°. Given that scientific applications require magnitude estimates within 10-15% and directional estimates within ±20° of in situ measurements, these preliminary results suggest that this is a promising approach to wind retrieval.

This paper is the third in a series of three that presents the results of experiments designed to verify the use of a single bottom roughness length scale for waves and currents over a rough bed. While the first two papers concentrated on the bottom roughnesses experienced by monochromatic wave and current boundary layer flows, this paper presents the results of additional experiments that investigate the use of an equivalent wave representation to extend these results to spectral wave and current boundary layer flows. Spectral waves, simulated by five components, and currents were generated in a 20-m-long wave flume with a fixed rippled bottom. Attenuation due to bottom friction is determined from total attenuation measurements for individual wave components by removing the effects of sidewall dissipation and wave-wave interactions. These attenuation estimates are used to establish representative friction factors, which are used in conjunction with an existing eddy viscosity model to determine bottom roughnesses. The bottom roughnesses experienced by spectral waves (in the presence and absence of a current) match the bottom roughnesses for monochromatic waves. When these experimentally determined bottom roughnesses are used in conjunction with the eddy viscosity model, predictions of attenuation for individual wave components closely match measurements. When the wave boundary layer thickness is defined to be the height at which the predicted velocity deficit in the wave boundary layer is within 5% of the free stream velocity, excellent agreement is obtained between predicted and measured velocity profiles for currents in the presence of codirectional waves. Therefore these experiments show that a single bottom roughness, when used in conjunction with an equivalent wave representation, adequately characterizes both monochromatic and spectral wave-current boundary layer flows over a fixed rippled bed.

In the paper by Chu et al. [1997a] (hereinafter referred to as CETAL) we developed a thermal parametric model that was capable of estimating physical parameters from historical profile data. The output parameters included sea surface temperature (SST), mixed-layer depth (MLD), thermocline depth (THD), thermocline temperature difference (TTD), and deep layer stratification. On the basis of the U.S. Navy's Master Oceanographic Observation Data Set (MOODS) that was taken in the Yellow Sea (YS) from 1950 to 1988, we computed the thermal structure functions and spatial decorrelation scales of the water properties in the Yellow Sea [Chu et al., 1997b]. The results shown in our papers were derived from •35,658 profiles, which have provided us with the statistical seasonal variations of the thermal structure in this region. To our knowledge, these issues have not been addressed in previous observational and modeling studies in the Yellow Sea. We appreciate Lie's [1999] (hereinafter referred to as L99) comments on our two papers. The points he raised, to a certain extent, resulted from an unclear explanation of some aspects of our analysis and from a limitation on access to Asian (especially Korean and Chinese) journals. We were unaware of previous studies on the YS thermal features reported in the Asian literature, such as Kang [1985], Lie [1984], Lie et al. [1986], Nakao [1977], Seung et al. [1990], and Zhao [1989]. On the other hand, most previous work was based on individual hydrographic surveys. Those studies did provide some insights into the seasonal pattern of the thermal structure in the YS for particular years, but they lacked statistical meaning. MOODS has included more than 39 years of observational data in the YS, and our study was the first to provide a statistical pattern of the seasonal variation of the thermal structure in this region. Detailed responses and explanations to L99's comments are given as follows.

In low-saline estuaries, “juvenile freshwater,” that is, freshwater trapped by the seasonal thermal stratification, may be used as an almost neutrally buoyant natural tracer for dispersion studies. Most of the juvenile freshwater supplied to the Baltic proper enters the northern parts by runoff from rivers and outflow of low-saline water from the Bothnian Sea. The mean monthly spatial distribution of juvenile freshwater in the Baltic proper in the period April to August is studied using historical hydrographic data. Month-to-month changes of the distribution reveal a fast southward spreading that only partly can be explained by the quite slow mean circulation in the Baltic proper. Most of the spreading is probably due to currents forced by fluctuating winds. In early spring, when the surface temperature is around the temperature of maximal density, the spreading of juvenile freshwater may initiate the seasonal stratification, which in turn starts the spring bloom. The spreading route of juvenile freshwater in early spring, as deduced in this paper, is in qualitative agreement with the spatial progress of the observed time for the start of the spring bloom of phytoplankton. The use of juvenile freshwater as a tracer should help in the interpretation of the spreading of tracers (e.g., pollutants) from local sources, as well as helping to verify recipes for calculating the spread of tracer clouds by different mechanisms. The monthly averaged spatial distributions of juvenile freshwater in the Baltic proper presented in this paper should be useful for testing dispersion properties of state-of-the-art three-dimensional ocean circulation models.

Airborne sensors provide effective coverage of a broad region and are suitable for large-scale experiments. In this paper, two scanning sensors that use the direct ranging technique to measure surface wave displacement are described. On a NASA P-3 aircraft the sensors can complete one run across a 100-km continental shelf in 17 min. A case study is presented using radar-measured, two-dimensional surface topography to derive wave damping due to bottom friction. The results are in good agreement with an analytical model based on a quadratic formulation of bottom shear stress. This study demonstrates that remote sensing measurements can be used for rapid characterization of surface waves on the continental shelf and in coastal regions. Examples illustrated in this paper include the derivation of wavenumber spectra and estimation of the dissipation rate of shoaling ocean swell.

A major objective of modem biological oceanography is to quantify, model, and predict the downward flux of biogenic carbon. Previous papers have documented an empirical relationship between the sinking flux of particulate organic material from the euphotic zone (S) and phytoplankton biomass (B), in oceans, and suggested that S could be estimated directly from B. The present paper investigates, using a mathematical model and data from the literature, the relationship between S and B. Calculations show that S is determined mostly by B and also by p (instantaneous coefficient of net phytoplankton production minus euphotic zone heterotrophic community respiration and incorporation in the pelagic food web). The regression S = f(B) accounts for 90% of the variation in S. In remote sensing, B is derived from ocean color, phytoplankton production (P) is derived from B, and S is derived from P. Within that context, the biomass approach could be used as an additional means to constrain the estimates of S.

This paper is the first in a series of papers describing a fully nonlinear regional wave model for the Bight of Abaco, Bahamas. It discusses this model's hybrid representation for nonlinear transfer and the numerical errors associated with this representation. This discussion extends a number of results previously reported by Snyder et al. [1993], doubling both the Boltzmann integration resolution and the spectral resolution of the resulting nonlinear-transfer estimates and evaluating the errors associated with both resolutions. It also better resolves the structure of the negative midfrequency lobe of the nonlinear transfer for JONSWAP input [Hasselmann et al, 1973], evaluates the errors associated with the diagnostic range of the nonlinear-transfer computation, and extends the hybrid representation to various finite depths characteristic of the Abaco Bight. It also extends the previous discussion of truncations of the hybrid representation, defining some renormalized hybrid implementations of the discrete-interaction approximation [Hasselmann et al., 1985] and generalizing its selection algorithm to improve the accuracy of this approximation (at some cost in efficiency). Finally, it develops a systematic scheme for recursively selecting hybrid coefficients to define a family of recursively optimized renormalized hybrid truncations. Because this scheme selects coefficient groups (the interactions for which are scaled versions of one another or of mirror images of one another) rather than individual coefficients and because it optimizes over multiple spectral inputs, the resulting truncations perform well over a full range of peak frequency. The resulting truncations for a nominal spectral resolution of 16 prognostic and four diagnostic wave-number bands and 12 angle bands include some truncations that essentially trade a factor of 10 in efficiency for a factor of 10 in accuracy (relative to the discrete-interaction approximation). Other truncations, running only 600 times slower than the discrete-interaction approximation, give a very accurate representation of the full nonlinear transfer. These truncations, employed in sequential fashion and extended to multiple spectral resolution, enable a relatively accurate and efficient staged inverse modeling of the action-balance equation. By first inverse modeling to convergence at nominal spectral resolution, then inverse modeling to convergence at double spectral resolution (starting from the converged results for nominal spectral resolution), it should be possible to extrapolate the results of the inverse modeling with an error no worse than a few percent (assuming that the errors in the results of the inverse modeling generated by errors in the nonlinear-transfer computation are no worse than these generating errors and that the impact of other numerical errors can be similarly contained).

In the companion paper we have presented an improved composite surface model for the calculation of normalized radar backscattering cross sections (NRCS) of the ocean surface. The proposed model accounts for the impact of the full two-dimensional ocean wave spectrum on the radar backscatter and was shown to reproduce measured absolute NRCS values for a variety of radar configurations and wind speeds satisfactorily after some reasonable tuning of the input ocean wave spectrum. This paper focuses on the modulation of the NRCS in the presence of spatially varying surface currents. First, the sensitivity of the NRCS to intensity variations of different ocean wave spectral components is investigated. Then the hydrodynamic modulation of the wave spectrum over underwater bottom topography in tidal waters is computed in different ways, and the resulting radar signatures are discussed. The composite surface model yields comparable radar signatures at high (10 GHz, X band) and low (1 GHz, L band) radar frequencies, which is in much better agreement with experimental results than the predictions of a first-order Bragg scattering model. On the other hand, measured variations of the NRCS at high radar frequencies appear to be still underestimated in some cases, which may be due to shortcomings of our description of the wave-current interaction by conventional weak hydrodynamic interaction theory. Possible improvements of the theory are discussed, and requirements for future experiments are formulated.

A fast, recently developed, multiscale optimal interpolation algorithm has been adapted to the mapping of hydrographic and other oceanographic data. This algorithm produces solution and error estimates which are consistent with those obtained from exact least squares methods, but at a small fraction of the computational cost. Problems whose solution would be completely impractical using exact least squares, that is, problems with tens or hundreds of thousands of measurements and estimation grid points, can easily be solved on a small workstation using the multiscale algorithm. In contrast to methods previously proposed for solving large least squares problems, our approach provides estimation error statistics while permitting long-range correlations, using all measurements, and permitting arbitrary measurement locations. The multiscale algorithm itself, published elsewhere, is not the focus of this paper. However, the algorithm requires statistical models having a very particular multiscale structure; it is the development of a class of multiscale statistical models, appropriate for oceanographic mapping problems, with which we concern ourselves in this paper. The approach is illustrated by mapping temperature in the northeastern Pacific. The number of hydrographic stations is kept deliberately small to show that multiscale and exact least squares results are comparable. A portion of the data were not used in the analysis; these data serve to test the multiscale estimates. A major advantage of the present approach is the ability to repeat the estimation procedure a large number of times for sensitivity studies, parameter estimation, and model testing. We have made available by anonymous Ftp a set of MATLAB-callable routines which implement the multiscale algorithm and the statistical models developed in this paper.

In this paper we estimate the 18 coefficients of the CMOD4 σ0-to-wind transfer function using a maximum likelihood estimation (MLE) method in order to improve the prelaunch function. We show that a MLE method has to be used with caution when dealing with a nonlinear relationship or with measurement errors that depend on the measured values. In the transfer function estimation it is crucial to use the components of the wind, rather than wind speed and direction, to use σ0 in logarithmic units rather than physical ones, and to use well-sampled input data. In Stoffelen and Anderson [1997a] we showed that the triplets of measured backscatter are very coherent and, when plotted in a three-dimensional measurement space, they lie on a well-defined conical surface. Here we propose a strategy for validation of a transfer function, the first step of which is to test the ability of a transfer function to fit this conical surface. We derive an objective measure to compute the average fit of the transfer function surface to the distribution of measured σ0 triplets. The transfer function CMOD4, derived in the first part of this paper, is shown to fit the cone surface to within the observed scatter normal to the cone, i.e., within roughly 0.2 dB, equivalent to a root-mean-square wind vector error of ∼0.5 m s−1 The second step in the validation strategy is the verification of retrieved scatterometer winds at each position on the cone surface. Scatterometer winds computed from CMOD4 compare better to the European Centre for Medium-Range Weather Forecasts model winds than real-time conventional surface wind data (ship, buoy, or island reports) with the root-mean-square wind vector difference typically 3.0 m s−1. This surprising result can be explained by the so-called representativeness error. We further show that no significant spatial wind error correlation is present in scatterometer data and therefore conclude that the ERS 1 scatterometer provides winds useful for weather forecasting and climate studies.

This paper reports the findings of a 2 week field campaign designed to study wave-induced flows within a meadow of Posidonia oceanica at water depth 9 m. Previous laboratory experiments suggest that waves induce a mean mass drift in the direction of wave propagation (>streaming>) through submerged canopies of vegetation. This paper provides the first field measurements of this wave-induced streaming. During periods of high wave activity, streaming flows with magnitudes as high as 20% of the near-bed oscillatory velocity were measured within the meadow. In addition to presenting field measurements of wave-induced streaming, this paper also considers the damping of wave-induced oscillatory flow within the seagrass meadow. Oscillatory velocities measured within the meadow were reduced by less than 30% relative to those above the meadow over the duration of the study. This is in agreement with previous laboratory and field measurements which show that oscillatory flows are damped less within submerged canopies compared to unidirectional flows. Existing analytical models underpredict the magnitude of the streaming flow and overpredict oscillatory velocity reductions. These discrepancies are thought to arise because the drag generated by flexible seagrasses moving with wave-induced flow is not well described. Key Points We present field measurements of wave-induced flow through a seagrass meadow A mean current in the direction of wave propagation is generated within meadow Wave-induced oscillatory velocities are reduced by less than 30% within meadow ©2013. American Geophysical Union. All Rights Reserved., This study received support from the U.S. National Science Foundation under grant OCE 0751358. Any conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. Eduardo Infantes acknowledges financial support received from the Spanish Ministerio de Educacion y Ciencia, FPI scholarship program (BES-2006-12850). We thank the Club Nautico de Cala Bona, which made its harbor facilities available for the field campaign

The analysis of synthetic aperture radar observations over the ocean to derive the directional spectra of the waves is based upon a complex transfer function which is the sum of three terms : tilt modulation, hydrodynamic modulation, and velocity bunching effect. Both the hydrodynamic and the velocity bunching terms are still poorly known. Here we focus on the hydrodynamic part of the transfer function, from an experimental point of view. In this paper a new method is proposed to estimate the hydrodynamic modulation. The approach consists in analyzing observations obtained with an airborne real-aperture radar (called RESSAC). This radar (C band, HH polarized, broad beam of 14° × 3°) was used during the SEMAPHORE experiment, in two different modes. From the first mode (incidence angles from 7° to 21°) the directional spectra of the long waves are deduced under the assumption that the hydrodynamic modulation can be neglected (small incidence angles) and validated against in situ measurements. From the second mode (incidence angle from 27° to 41°) the amplitude and phase of the hydrodynamic modulation are deduced by combining the measured signal modulation spectrum at a mean incidence angle of 34° and the directional wave spectrum obtained from the first mode. The results, obtained in four different wind-wave cases of the SEMAPHORE experiment, show that the modulus of the hydrodynamic modulation is larger than that of the tilt modulation. Furthermore, we find that the modulus of the hydrodynamic transfer function is several times larger (by a factor 2-12) than the theoretical value proposed in previous works and 1.5-2.5 larger than experimental values reported in recent papers. The phase of the hydrodynamic modulation is found to be close to zero for waves propagating at an angle from the wind direction and between -20° and -40° for waves propagating along the wind direction. This indicates a significant influence of the wind-wave angle on the phase of the hydrodynamic modulation, in agreement with experimental results reported in recent papers.

This paper describes the results of the first quantitative comparison between high-resolution ocean surface current fields extracted from interferometric synthetic aperture radar (INSAR) measurements and those from a high-frequency (HF) ocean surface current radar (OSCR) system. Data from each of these radar systems along with supporting measurements from shipboard and buoy-mounted sensors were collected during the High-Resolution Remote Sensing Experiment (High-Res) on June 20, 1993, on the continental shelf off the coast of Cape Hatteras, North Carolina. Both components of the surface current were obtained from the INSAR system at roughly 10-m resolution from two orthogonal flight legs over the region separated in time by about 30 min. The OSCR system measured two-dimensional surface current vectors at about 1-km resolution over this same region, while the USNS Bartlett was collecting hydrographic samples and near-surface current measurements. Two-dimensional wave spectra as well as meteorological and additional current measurements were collected at two buoys within the experimental area. We discuss in the paper two techniques for eliminating the effect of surface wave motion on the INSAR current estimates. One method relies on some knowledge of the local wind and wave field and the use of a microwave scattering model. The other method makes use of a few in situ current measurements spaced at different range locations across the INSAR image. Using either of these techniques, we find that the agreement between the INSAR and OSCR current estimates is generally very good. Furthermore, the INSAR current and magnitude imagery show the presence of undulating surface features where abrupt changes in the current speed and direction occurred. The ship surveys indicate that these features were caused by the collision of water masses of different density. We show for the first time in this paper a high-resolution, area-extensive vector surface current map derived from the INSAR of the two-dimensional flow in the vicinity of these features. Our results demonstrate convincingly that high-resolution oceanic surface current vectors can be derived from INSAR current measurements and that these measurements may be very beneficial for detailed studies of the dynamics of small-scale surface features in regions of strong current divergences or shears.

The plasticity of the Arctic ice pack depends on its granular nature, in particular on the size and distribution of areas of thin ice and open water surrounding multiyear ice floes. The paper begins with construction of a mesoscale (10-100 km) granular model of the central Arctic ice pack. The mesoscale model is based on a dynamic particle simulation in which individual multiyear ice floes and surrounding parcels of first-year ice are explicitly modeled as discrete, convex polygons in a two-dimensional domain. Deformation of the domain produces areas of localized failure and areas of open water. The areas of localized failure are modeled as pressure ridging events using the results of numerical experiments performed with a computer simulation of the ridging process. The paper focuses on the results of numerical experiments performed with the mesoscale model. In the experiments the model ice pack is biaxially deformed at constant strain rates. The principal strain rates are varied to create deformation states ranging from pure shear to uniform compression. The results define the shape and magnitude of the plastic yield surface, the strain rate vectors associated with points on the yield surface, the partition of energy dissipation between ridging and in-plane sliding, and the changes in the ice thickness distribution associated with various deformation states.

This paper is the second of two papers which present the results of an experimental study to verify the use of a single bottom roughness length scale to characterize wave and current boundary layer flows over a rough bed. While the first paper [Mathisen and Madsen, this issue] included analysis of wave attenuation measurements to estimate the bottom roughness experienced by waves in the presence and absence of a current, this paper includes the analysis of time-averaged velocity profiles to estimate the bottom and apparent roughness experienced by a current in the presence of waves. In this paper, velocity profiles predicted by the Grant and Madsen [1986] model are compared with measured velocity profiles. Apparent hydraulic roughness predictions of the Grant and Madsen [1986] model are shown to underpredict the apparent hydraulic roughnesses experienced by the current. This difference is shown to be a result of an underprediction of the wave boundary layer thickness and of a steady streaming or mass transport which is induced by the wave motion within the wave boundary layer of the combined wave-current flow. By modifying the wave boundary layer thickness and estimating the wave-induced mass transport from pure wave experiments, the bottom roughness for pure current, pure wave, and combined wave-current boundary layer flows is shown to be characterized by a single roughness scale.

The shallowness of the Oresund prevents a continuous inflow of saline Kattegat water to the Baltic. Instead, the salt is exchanged largely by fluctuating barotropic transports. Buffer effects and temporal storage of low-salinity Baltic surface water complicate the exchange. The analysis of salt exchange through the Oresund requires use of a model of the stratification and baroclinically modified exchange processes. In this paper a three-layer model of the Oresund, forced by the exchange with the Kattegat and the Baltic, is formulated and calibrated. Frontal dynamics, necessary to explain the retreat of the uppermost layer, are included. The model is calibrated using genetic algorithms, which provide an efficient and robust optimization method for this kind of model. An analysis of the exchange in view of the model results is presented. The paper also gives estimates of typical mean quantities. For the analyzed period of 11 years (1977–1987) the mean salt outflow rate from the Baltic during outflows is 311,000 kg s−1, and the mean salt inflow rate to the Baltic during inflows is 500,000 kg s−1. The net salt outflow from the Baltic is estimated to 19,000 kg s−1. The mean frontal speed is estimated at 0.25 m s−1 and the typical required length of an inflow event for high-salinity Kattegat water to reach the Baltic is estimated at 4 days. Further results are also given. In addition, the baroclinic dynamics of the Oresund are discussed.

Several theoretical models have been advanced for turbulent boundary layers associated with wave and current flows over a rough bed. Although these models differ, particularly in the sophistication with which turbulence is modeled, they all share one common feature: the bottom roughness is characterized by a single roughness length scale kn. However, no experimental data have been presented which accurately characterize the bottom roughnesses for wave and current boundary layers such that this basic assumption can be considered verified. This paper and a companion paper [Mathisen and Madsen, this issue] present results of an experimental study to verify this basic assumption. In this paper, wave roughnesses (i.e., bottom roughnesses experienced by pure waves and waves in the presence of a current) are compared with the roughness experienced by a pure current. The roughnesses for pure currents and pure waves are shown to be the same if determination of the pure wave roughness from measurements of wave energy dissipation includes the phase difference between the near-bottom horizontal orbital velocity and bottom shear stress. When these analysis procedures are extended to combined wave-current flows, the roughness experienced by waves in the presence of a current is shown to be that obtained for pure waves.

In a recent paper, Blayo et al. [1994] described the simulation of the North Atlantic general circulation during the period October 1992 to September 1993, as obtained from the assimilation of TOPEX/POSEIDON (T/P) altimeter data in a high-resolution, quasi-geostrophic model of the Atlantic basin between 20°N and 60°. In line with this paper, the purpose of the present study is to investigate the usefulness of the quasi-geostrophic model for predicting the time evolution of the mesoscale flow field from the perspective of operational oceanography. Forecast experiments have been conducted to address the following three questions: (1) how does the model with assimilation differ from a so-called “pure forecast” trajectory, as produced in the absence of altimeter data; (2) can the model evolution controlled with T/P altimetric residuals be considered as a decent description of the actual ocean evolution; (3) is the assimilation useful to predict the future of the system at short and medium ranges? The simulations consist of twin experiments obtained from the assimilation of subsets of the original T/P data set (covering, for instance, only part of the total duration of the reference experiment) or from the assimilation of synthetic altimeter data extracted from the reference simulation. In addition, predictability experiments have been carried out to determine the doubling timescale of small errors in the specification of the model initial conditions. The statistics derived from the simulations indicate that the assimilation of altimetry is efficient in reconstructing the past and the present state of the ocean on an operational basis. The procedure is shown to be able to recover both the surface and the deep flow during the assimilation period. The transport of the Gulf Stream is kept consistent with observational evidences as long as altimeter data are taken into account. However, forecasting mesoscale eddies is realistic only for a couple of weeks in advance. It is found that the averaged doubling time of initial errors is about 20 days, and credit of forecasts over more than 2 months in advance is questionable. As expected, predictions of the future are bounded by the predictability timescales inherent to the physical nature of the system.

International audience; This paper describes an interactive Eulerian-Lagrangian model of the turbulent transport of evaporating droplets. A k-ε (where k is turbulent kinetic energy and ε is its rate of dissipation) turbulence closure model is used to accurately simulate stable, near-neutral, and unstable boundary layers within the large air-sea interaction tunnel at the Institut de Mécanique Statistique de la Turbulence (IMST), Luminy, France. These results are then used with the Lagrangian model described in part 1 [Edson and Fairall, 1994]. The coupled model is shown to give excellent agreement with droplet dispersion measurements made during the 1988 Couche Limite Unidimensionelle Stationnaire d'Embrums (CLUSE, a French acronym that translates to one-dimensional stationary droplet boundary layer) campaign. Additionally, this paper describes how the coupled model can now be used to investigate the interaction between the evaporating droplets and the turbulent fields of temperature and humidity. The investigation shows that although the influence of the droplets is small under the conditions simulated at IMST, the potential for substantial modification of the surface energy budget exists for high-wind conditions over the ocean

An eddy-resolving primitive equation model was used to simulate circulation on the shelf in the western Gulf of Alaska. This paper describes the development and sensitivity analysis of the model, while a companion paper [Stabeno and Hermann, this issue] demonstrates correspondence with measured currents in specific years. The model is initialized with a salinity field derived from local conductivity-temperature-depth surveys and forced with an idealized alongshore wind stress pattern. Buoyancy forcing is achieved by freshening the salinity field along a portion of the coastal wall. The model exhibits many of the patterns evident in observations, including mean flows and mesoscale eddies associated with the Alaska Coastal Current (ACC). Sensitivity studies suggest a strong dependence of the barotropic flux of the ACC on local winds and weak dependence on upstream buoyancy forcing. Both wind and buoyancy forcing significantly affect the generation of eddies. Strong northeasterly winds enhance cross-shelf flow of the ACC to the west of Shelikof Strait, where isobaths veer southward. Strong buoyancy forcing also favors cross-shelf flow in that region and enhances the formation of eddies.

[1] This paper examines the effect of “stencil width” on surface ocean geostrophic velocity and vorticity estimated from differentiating gridded satellite altimeter sea surface height products. In oceanographic applications, the value of the first derivative at a central grid point is generally obtained by differencing the sea surface heights at adjacent grid points. This is called a “three-point stencil centered difference”. Here the stencil width is increased from three to five, seven, and nine points, using well-known formulae from the numerical analysis literature. The discrepancies between velocities computed with successive stencils decreases with increasing stencil width, suggesting that wide stencil results are more reliable. Significant speed-dependent biases (up to 10–20%) are found between results computed from three-point stencils versus those computed from wider stencils. The geostrophic velocity, and the variance of geostrophic velocity, are underestimated with thin stencils. Similar results are seen in geostrophic velocities computed from high-resolution model output. In contrast to the case when three-point stencils are used,wider stencils yield estimates of theanisotropy of velocity variance that are insensitive to the differences in grid spacing between two widely used altimeter products. Three-point stencils yield incorrect anisotropies on the 1/4 � anisotropic AVISO grid; we recommend the use of 7-point stencils. Despite the demonstrated inadequacies of the three-point stencils, the conclusions of earlier studies based on them, that the zonally averaged midlatitude eddy kinetic energy field is nearly isotropic, are found to pertain also with wider stencils. Finally, the paper also examines the strengths and limitations of applying noise-suppressing differentiators, versus classic centered differences, to altimeter data.

This study provides an intercomparison of two independent TB calibrations for the AMSR2 sensor. The Remote Sensing Systems (RSS) calibration is based on a radiative transfer model, a method used for all microwave sensors. The Japan Aerospace Exploration Agency (JAXA) calibration is based on pre-launch measurements of the sensor characteristics. Over the full range of TB, differences between the two calibrations are as large as 3-4 K and vary systematically with TB. This paper shows that the large TB differences are mostly due to large differences in the nonlinearity corrections used by RSS and JAXA, which are likely due to on-orbit versus pre-launch behavior. Despite the disagreement, both JAXA and RSS find nonlinearity corrections of 3 K or more. Such large nonlinearity complicates accurate intercalibration, and a major conclusion of this paper is that future radiometer designs should make strict nonlinearity requirements (0.1-0.2%) a primary design consideration. This article is protected by copyright. All rights reserved.

[1] A model that accurately simulates surf zone waves, mean currents, and low‐frequency eddies is required to diagnose the mechanisms of surf zone tracer transport and dispersion. In this paper, a wave‐resolving time‐dependent Boussinesq model is compared with waves and currents observed during five surf zone dye release experiments. In a companion paper, Clark et al. (2011) compare a coupled tracer model to the dye plume observations. The Boussinesq model uses observed bathymetry and incident random, directionally spread waves. For all five releases, the model generally reproduces the observed cross‐shore evolution of significant wave height, mean wave angle, bulk directional spread, mean alongshore current, and the frequency‐dependent sea surface elevation spectra and directional moments. The largest errors are near the shoreline where the bathymetry is most uncertain. The model also reproduces the observed cross‐shore structure of rotational velocities in the infragravity (0.004 < f < 0.03 Hz) and very low frequency (VLF) (0.001 < f < 0.004 Hz) bands, although the modeled VLF energy is 2–3 times too large. Similar to the observations, the dominant contributions to the modeled eddy‐induced momentum flux are in the VLF band. These eddies are elliptical near the shoreline and circular in the mid surf zone. The model‐data agreement for sea swell waves, low‐frequency eddies, and mean currents suggests that the model is appropriate for simulating surf zone tracer transport and dispersion.

Recently, a number of authors have used global particle tracking simulations to identify the effect that different surface currents have on marine litter accumulation, including the role of surface waves through the Stokes drift. However, in the upper-ocean boundary layer and in the presence of the Coriolis force, a wave-driven Eulerian flow forms that must be superimposed onto the Stokes drift in order to obtain the correct Lagrangian velocity. Taking into account both the Coriolis–Stokes force and the surface wave stress, Higgins et al. (2020), https://doi.org/10.1029/2020GL089189 derived an expression for this unsteady wave-driven Eulerian-mean flow in the form of a convolution between the Stokes drift and the so-called Ekman–Stokes kernel. In this paper, we apply this Ekman–Stokes kernel to generate a 12-year global hindcast of the wave-driven Eulerian current and show that its inclusion in particle tracking simulations has a significant effect on the distribution of small floating marine litter, such as microplastics. Using Lagrangian simulations, we find that the wave-driven Eulerian current is sensitive to the value of viscosity but generally opposes the dispersive behavior of the Stokes drift, reducing the amount of cross-Equator particle transport and transport to the polar regions, resulting in closer agreement between modeled and observed microplastic distributions.

This paper presents a critique of experimental data and papers by Martin et al. (1989, 1990), who suggested that the phytoplankton growth is iron-limited and that, small additions of iron to large subarctic ocean areas might be a way of removing significant amounts of atmospheric CO2 by increasing phytoplancton growth. Data are presented to show that, in the summer of 1987, the phytoplankton assemblage as a whole was not iron limited, as measured by the bulk removal of nitrate or by the increase of chlorophyll. It is suggested that grazing normally prevents the phytoplankton from reaching concentrations that reduce the iron (and nitrate) to levels that depress division rates drastically.

[1] This paper uses the results from two multiseason numerical model simulations of Lake Michigan hydrodynamics to examine the relative effects of wind stress curl, topography, and stratification on large-scale circulation. The multiseason simulations provide a period long enough to encompass the full range of atmospheric and thermal conditions that can occur in the lake. The purpose of this paper is to diagnose the relative importance of various mechanisms responsible for the large-scale circulation patterns by analyzing the vorticity balance in the lake on a monthly timescale. Five different model scenarios are used to isolate the predominant mechanisms: (1) baroclinic lake, spatially variable wind stress; (2) barotropic lake, spatially variable wind stress; (3) baroclinic lake, spatially uniform wind stress; (4) barotropic lake, spatially uniform wind stress; and (5) barotropic lake, linearized equations, spatially uniform wind stress. By comparing the results of these five model scenarios it is shown that the cyclonic wind stress curl in the winter and the effect of baroclinicity in the summer are primarily responsible for the predominantly cyclonic flow in the lake. Topographic effects are also important but are not as significant as wind stress curl and baroclinic effects. Nonlinear effects are much smaller.

The tropical Pacific Ocean is a globally significant region of climate‐driven biogeochemical variability. Satellite ocean color algorithms have been used for over 20 years, providing a substantial historical record of global ocean chlorophyll‐a variability. Current chlorophyll algorithms perform better in the tropical Pacific than for the globe. Nevertheless, improvements can be made to produce a robust historical record of chlorophyll variability, which is essential to accurately identify ocean‐atmosphere carbon fluxes and long‐term trends in ocean productivity. We use a large in situ chlorophyll database to tune empirical ocean color algorithms to reduce bias in the equatorial Pacific. Traditional band ratio chlorophyll algorithms (OCx) perform adequately but exhibit errors at low chlorophyll concentrations. A new algorithm, the Ocean Color Index (OCI; Hu et al., 2012, https://doi.org/10.1029/2011JC007395), is more effective at calculating low chlorophyll concentrations in the mesotrophic tropical Pacific Ocean. Existing ocean color algorithms underestimate tropical Pacific chlorophyll by 5.8%, 14%, and 2% for three satellite ocean color sensors: SeaWiFS, MODIS‐Aqua, and MERIS. In this paper, we develop regionally tuned sensor‐specific coefficients and blending windows between the OCI to OCx algorithms to reduce systematic biases in the tropical Pacific. We assess cross‐sensor consistency to produce robust 21‐year time series trends. These updated estimates increase chlorophyll concentrations in open water and decrease around island and warm‐pool regions, with implications for our understanding of El Nino‐Southern Oscillation driven carbon fluxes and net primary productivity.

This paper describes an integrated climatological-hydrodynamic method that couples probabilistic hurricane model, storm surge model, inundation model, coastal protection data, and sea level rise projections to estimate tropical cyclone-induced coastal flood inundation hazard in a coastal megacity-Shanghai, China. We identify three “worst-case” scenarios (extracted from over 5,000 synthetic storms) that generate unprecedentedly high flood levels in Shanghai. Nevertheless, we find that the mainland Shanghai is relatively safe from coastal flooding under the current climate, thanks to its high-standard seawall protection. However, the city is expected to be increasingly at risk due to future sea level rise, with inundation two times and 20 times more likely to occur by mid- and late-21st century, respectively, and inundation depth and area to greatly increase (e.g., 60%–1,360% increase in the inundation area for the “worst cases” by 2,100). The low-lying and poorly protected area (e.g., Chongming Island) is likely to be moderately affected by flood events with long return periods at the current state but could be largely inundated in future sea-level-rise situations.

The Indo-Australian Basin (IAB) constitutes a crucial water route for the global ocean's circulation between the Pacific and Indian Oceans. Locally generated eddies contribute to the continued westward transport of water away from the IAB. In this paper, results from the first comprehensive regional ocean eddy census are discussed. A hybrid eddy census and tracking algorithm is used to analyze satellite altimetry data from 1993 to 2018. A total of 2,792 eddies were identified and tracked. Cyclonic eddies and anticyclonic eddies exhibit geographical segregation in terms of their dynamic characteristics. Larger amplitudes, radii, and absolute vorticities are associated with high eddy kinetic energy regions located in the vicinity of the South Java Current, South Equatorial Current, and Indonesian Throughflow. The eddies are grouped into three duration-based classifications providing the first systematic insight into understanding their physical characteristics, formation, and distribution in the IAB.

The 2D‐parametric model suggested in the companion paper is used to simulate waves under Tropical Cyclones (TCs). Set of equations describing both wind waves and swell evolution in space and time, is solved using the method of characteristics. Wave‐ray patterns efficiently chart on how wave trains develop and travel through the TC varying wind field, to leave the storm area as swell systems. Depending on TC main characteristics, ‐ maximal wind speed (um), radius (Rm), and translation velocity (V), wave‐train rays superpose to exhibit particular coherent spatial patterns of significant wave height, peak wavelength and direction. Group velocity resonance leads to the appearance of waves with abnormally high energy, further outrunning as long swell systems through the TC front sector. Yet, when the TC translation velocity exceeds a threshold value, waves cannot reach group velocity resonance, and travel backwards, to form a wake of swell systems trailing the forward moving TC. Importantly, the model solutions for TC 2D‐wave fields can be parameterized using 2D self‐similar universal functions. Comparisons between self‐similar solutions and measurements, demonstrate a reasonable agreement to warrant scientific and practical applications. Self‐similar solutions provide immediate estimates of azimuthal‐radial distributions of wave parameters under TCs, solely characterized by arbitrary sets of um, Rm and V conditions. Self‐similar solutions clearly divide TCs between slow TCs, fulfilling conditions Rm/Lcr>1, and fast TCs corresponding to Rm/Lcr

This work was completed during a visit in 2016 by KRR to Townsville within the AIMS Capability Development Fund's Visiting AIMS fellowship program. The glider deployments were made by the ANFOG (Australian National Facility for Ocean Gliders), which is a facility of the Integrated Marine Observing System (IMOS). IMOS is a national collaborative research infrastructure, supported by the Australian Government. The Lizard Island mooring deployments were completed by AIMS through the IMOS Australian National Mooring Network Facility. We acknowledge the skipper and crew of the R/V Cape Ferguson and the technicians and scientific seagoing staff involved in these deployments. Salinity from CTD data were provided from the archives of the AIMS in the AIMS Data Catalog (https://data.aims.gov.au) and the CSIRO, Oceans and Atmosphere Data Centre (http://www.cmar.csiro.au/datacentre/).Surface salinity data, within the Great Barrier Reef, derive from underway systems on the R/V Cape Ferguson and the R/V Solander. Processed glider, underway, and mooring data and the CSIRO Atlas of Regional Seas (CARS2009) were obtained from the Australian Ocean Data Network (AODN) Portal (https://portal.aodn.org.au).These observations also contribute to the international research program SPICE (Southwest Pacific Ocean Circulation and Climate Experiment). The Bluelink ocean data products (OFAM) were provided by CSIRO, and these data are publically available on the National Computational Infrastructure THREDDS server (http://dap.nci.org.au/thredds/catalog.html).Bluelink is a collaboration involving the Commonwealth Bureau of Meteorology, the CSIRO, and the Royal Australian Navy. Thanks to two reviewers who made suggestions that improved the paper.

Antarctic sea ice trends have to date been linked to surface winds, through sea ice motion and atmospheric thermal advection. This paper analyzes sea ice volume in 10 CMIP5 model configurations under pre-industrial and historical climate forcings, to compare the relative importance of ice motion and thermodynamic processes. We find that the models’ responses to historical forcings is dependent on their sea ice motion formulation; models with low-magnitude sea ice motion tend to have historical trends that are dominated by thermodynamic processes, whilst sea ice models with higher-magnitude motion have more spatially variable relative contributions from dynamic and thermodynamic processes. Trends at the sea ice edge during the season of sea ice advance are generally dominated by dynamic processes, whereas during retreat thermodynamic trends dominate. The models show more disagreement in the sea ice interior. This analysis highlights the different estimates and patterns of sea ice volume among global climate models and offers insight into the drivers of sea ice volume change as well as the subsequent implications for simulated atmosphere-sea ice-ocean interactions.

This paper investigates turbulent exchange processes in a droplet-laden air flow over a waved water surface by performing direct numerical simulation (DNS). Turbulent Couette flow is considered in DNS as a model of a constant-flux layer in the marine atmospheric surface layer. Two-dimensional stationary waves at the water surface are prescribed and assumed to be unaffected by the airflow and/or droplets. Evaporating droplets of different sizes are injected into the air in the vicinity of wave crests with initial velocities and temperatures of water, and thus mimicking spume sea-spray droplets. Evolution equations of the airflow velocity, temperature, and humidity are solved in a Eulerian framework simultaneously with the equations of individual droplets coordinates and velocities, temperatures, and masses tracked in a Lagrangian framework. The momentum (Q(m)) and sensible (Q(S)) and latent (Q(L)) heat fluxes from the droplets to air are evaluated both as phase-averaged Eulerian fields and as fluxes integrated over time along Lagrangian droplets trajectories. The results show that droplets extract momentum from the surrounding air (Q(m)0 and increases with droplet diameter, d, whereas Q(S)0 vanishes for droplets with diameters d

The authors gratefully acknowledge the NASA Goddard Space Flight Center, Ocean Ecology Laboratory, Ocean Biology Processing Group for remote sensing data and the Copernicus website for the SLA data used in this study. Datasets from ocean color and SLA are freely accessible online on their official websites (https://oceancolor.gsfc.nasa.gov/) and (https://resources.marine.copernicus.eu/?option=com_csw&view=details&product_id=SEALEVEL_GLO_PHY_L4_REP_OBSERVATIONS_008_047). The glider data that support the study are available at 10.6084/m9.figshare.13670125. The authors are grateful to the KAUST Coastal Marine Resources Core Lab (CMRCL) for their engineering and field support during the glider operations. Particular thanks go to Sebastian Steinke, Brian Hession, Samer Mahmoud and Lloyd Smith for their help with the glider deployments. We thank Ian Walsh and an anonymous reviewer for evaluating the paper and providing insightful suggestions. Funding from King Abdullah University of Science and Technology (KAUST) supported the research in this publication

Our ability to predict the future of Arctic sea ice is limited by ice's sensitivity to detailed surface conditions such as the distribution of snow and melt ponds. Snow on top of the ice decreases ice's thermal conductivity, increases its reflectivity (albedo), and provides a source of meltwater for melt ponds during summer that decrease the ice's albedo. In this paper, we develop a simple model of pre-melt snow topography that accurately describes snow cover of flat, undeformed Arctic sea ice on several study sites for which data was available. The model considers a surface that is a sum of randomly sized and placed "snow dunes" represented as Gaussian mounds. This model generalizes the "void model" of Popovi\'c et al. (2018) and, as such, accurately describes the statistics of melt pond geometry. We test this model against detailed LiDAR measurements of the pre-melt snow topography. We show that the model snow-depth distribution is statistically indistinguishable from the measurements on flat ice, while small disagreement exists if the ice is deformed. We then use this model to determine analytic expressions for the conductive heat flux through the ice and for melt pond coverage evolution during an early stage of pond formation. We also formulate a criterion for ice to remain pond-free throughout the summer. Results from our model could be directly included in large-scale models, thereby improving our understanding of energy balance on sea ice and allowing for more reliable predictions of Arctic sea ice in a future climate.

The accurate modeling of the landslide?generated tsunami characteristics in the so-called near-field is crucial for many practical applications. In this paper, we present a new full-3-D numerical method for modeling tsunamis generated by rigid and impermeable landslides in OpenFOAM® based on the overset mesh technique. The approach has been successfully validated through the numerical reproduction of past experiments for landslide?generated tsunamis triggered by a rigid and impermeable wedge at a sloping coast. The method has been applied to perform a detailed numerical study of the near-field wave features induced by submerged landslides. A parametric analysis has been carried out to explore the importance of the landslide's initial acceleration, directly related to the landslide-triggering mechanisms, on the tsunami generation process and on the related wave properties. Near-field analysis of the numerical results confirms that the influence of the initial acceleration on the tsunami wave properties is significant, affecting wave height, wave period, and wave celerity. Furthermore, it is found that the tsunami generation mechanism experiences a saturation effect for increasing landslide's initial acceleration, confirming and extending previous studies. Moreover, the resulting extended database, composed of previous experimental data and new numerical ones, spanning a wider range of governing parameters, has been represented in the form of a “nondimensional wavemaker curve,” and a new relationship for predicting the wave properties in the near-field as a function of the Hammack number is proposed.

This paper describes laboratory experiments (using a high-speed wind-wave flume) of the effects of water waves on heat and momentum exchange in the near-water atmospheric boundary layer at high win...