Lagrangian Drifters Research Articles

The impact of simulated super pressure balloon data on regional weather analyses and forecasts

This paper highlights results from a series of observing system simulation experiments (OSSEs) designed to assess the impact of assimilating data from a hypothetical network of constant density, super pressure balloons on regional weather analyses and forecasts over the continental U.S. These super pressure balloons would be carried passively by the wind at various levels in the atmosphere taking measurements of pressure, temperature, moisture, and wind velocity similar to other Lagrangian drifters that have been used in meteorology for nearly 50 years. The super pressure balloons or probes are envisioned to be the main component of a new observing system called Global Environmental Micro Sensors (GEMS). The novel aspect of the GEMS system is the integration of micro and eventually nanotechnology to develop probes with significantly lower mass, size, and cost. Given these attributes, thousands of probes could be deployed for research and operational missions thereby greatly expanding the amount of in situ observations, especially over data sparse oceanic regions.

Euphausiid transport in the Western Arctic Ocean

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 360:163-178 (2008) - DOI: https://doi.org/10.3354/meps07387 Euphausiid transport in the Western Arctic Ocean L. Berline1,*, Y. H. Spitz1, C. J. Ashjian2, R. G. Campbell3, W. Maslowski4, S. E. Moore5 1College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331-5503, USA 2Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA 3Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882-1197, USA 4Oceanography Department, Naval Postgraduate School, Monterey, California 93943-5122, USA 5NOAA/AFSC at APL-University of Washington, Seattle, Washington 98105, USA *Email: leo@coas.oregonstate.edu ABSTRACT: Euphausiids are commonly found in the stomachs of bowhead whales Balaena mysticetus hunted near Barrow, Alaska; however, no evidence exists of a self-sustaining population in this region. To explain euphausiid presence near Barrow, their transport from the northern Bering Sea was investigated through particle tracking experiments using velocity fields from an ocean general circulation model in 4 contrasted circulation scenarios (1997, 1998, 2002 and 2003). Euphausiids were released during their spawning season (April-June) in the bottom and surface layers in the northern Bering Sea, their endemic region, and tracked through the Chukchi-Beaufort Sea. Results show that both Anadyr Gulf and Shpanberg Strait are potential regions of origin for euphausiids. Topographically steered bottom particles have 4 to 5 times higher probability of reaching Barrow than surface particles (ca. 95% versus 20% of particles). As euphausiids are often found near the bottom on the northern Bering shelf, this suggests a very high probability of euphausiids reaching Barrow, making this location a privileged area for whale feeding. The main pathways to Barrow across the Chukchi Sea shelf are Central Valley (CV) and Herald Valley (HV). The transit to Barrow takes 4 to 20 mo. Arrivals at Barrow have 2 peaks at ca. 200 d (fall, CV particles) and 395 d after release (spring, mixed CV and HV) on average, because of the seasonal cycle of the Chukchi Sea currents. Elevated euphausiid abundance in the fall at Barrow is favored by a high Bering Strait northward transport and by southerly winds, driving organisms through CV rather than through the HV pathway. KEY WORDS: Euphausiid · Thysanoessa spp. · Bowhead whale · Balaena mysticetus · Western Arctic Ocean · Chukchi Sea · Lagrangian drifter · Zooplankton advection model Full text in pdf format PreviousNextCite this article as: Berline L, Spitz YH, Ashjian CJ, Campbell RG, Maslowski W, Moore SE (2008) Euphausiid transport in the Western Arctic Ocean. Mar Ecol Prog Ser 360:163-178. https://doi.org/10.3354/meps07387 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 360. Online publication date: May 22, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

Variations in the instantaneous mortality rate between larval patches of Pacific bluefin tuna Thunnus orientalis in the northwestern Pacific Ocean

We followed three patches of larval Pacific bluefin tuna ( Thunnus orientalis) using Lagrangian drifters in 2004 and 2005 from May to June and determined the age-specific larval instantaneous mortality rates, which were estimated to be between 0.06 and 2.75 day −1. The mortality rates differed significantly between patches and between ages within the same patch, which were higher than most of the estimations for other marine fish larvae. The results indicate that for the purpose of understanding the process of the larval survival, the use of larval patches is appropriate as a unit of observation. Evidence of the occurrence for net avoidance is presented and also it is concluded that net extrusion was observed for the larvae. Length-specific catch probability of the larvae was estimated to correct for length distribution biases derived from the net avoidance and net extrusion.

Ocean–Atmosphere Interaction over Agulhas Extension Meanders

AbstractMany years of high-resolution measurements by a number of space-based sensors and from Lagrangian drifters became available recently and are used to examine the persistent atmospheric imprints of the semipermanent meanders of the Agulhas Extension Current (AEC), where strong surface current and temperature gradients are found. The sea surface temperature (SST) measured by the Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) and the chlorophyll concentration measured by the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) support the identification of the meanders and related ocean circulation by the drifters. The collocation of high and low magnitudes of equivalent neutral wind (ENW) measured by Quick Scatterometer (QuikSCAT), which is uniquely related to surface stress by definition, illustrates not only the stability dependence of turbulent mixing but also the unique stress measuring capability of the scatterometer. The observed rotation of ENW in opposition to the rotation of the surface current clearly demonstrates that the scatterometer measures stress rather than winds. The clear differences between the distributions of wind and stress and the possible inadequacy of turbulent parameterization affirm the need of surface stress vector measurements, which were not available before the scatterometers. The opposite sign of the stress vorticity to current vorticity implies that the atmosphere spins down the current rotation through momentum transport. Coincident high SST and ENW over the southern extension of the meander enhance evaporation and latent heat flux, which cools the ocean. The atmosphere is found to provide negative feedback to ocean current and temperature gradients. Distribution of ENW convergence implies ascending motion on the downwind side of local SST maxima and descending air on the upwind side and acceleration of surface wind stress over warm water (deceleration over cool water); the convection may escalate the contrast of ENW over warm and cool water set up by the dependence of turbulent mixing on stability; this relation exerts a positive feedback to the ENW–SST relation. The temperature sounding measured by the Atmospheric Infrared Sounder (AIRS) is consistent with the spatial coherence between the cloud-top temperature provided by the International Satellite Cloud Climatology Project (ISCCP) and SST. Thus ocean mesoscale SST anomalies associated with the persistent meanders may have a long-term effect well above the midlatitude atmospheric boundary layer, an observation not addressed in the past.

Transport and survival of larvae of pelagic fishes in Kuroshio system region estimated with Lagrangian drifters

Transport and survival of larvae of pelagic fishes in the Kuroshio system region were studied using Lagrangian drifter data recorded from 1990 to 2003. A large portion of the drifters from the Kuroshio area south of Japan spread around the Kuroshio Extension up to 170°E, while some moved south to the offshore area of the Kuroshio because of a recirculation gyre. The monthly mean eastward movement from areas south of Japan was approximately 800-900 km, which was smaller than previous numerical estimates. The results of a survival model assuming optimal temperatures for larvae suggest that surface waters during the observation period were too warm for larval Japanese sardine, which has an optimal temperature of 16°C, and the adult abundances did not increase during the observation period. In contrast, the spawning ground temperatures and transport conditions from an area south-west of Japan in April-June matched the requirement for the larval Japanese anchovy, which has an optimal temperature of 22°C. The combined effects of temperature variations due to seasonality and water mass mixing are suggested to play an important role in determining the environmental temperatures that occur in an area.

Eddy statistics from Lagrangian drifters and hydrography for the northern Gulf of Mexico slope

Cyclones and anticyclones on the northern Gulf of Mexico slope have been statistically characterized using upper layer drifter orbits and repeated hydrographic surveys. A total of 243 slope eddy drifter orbits (151 cyclones and 92 anticyclones) were analyzed in terms of size (mean radius and eccentricity) and rotation period. Orbits in large Loop Current anticyclones were excluded. Eddies of both signs scale approximately as the baroclinic radius of deformation with relatively smaller radii on the upper slope, where water depths are less than 1000 m. The median radius for all eddies was ∼30 km, and median periods were 12 and 13.5 days for cyclones and anticyclones, respectively. Anticyclones also tend to be more circular than cyclones. Relative vorticity maps were constructed for seven hydrographic surveys, which mapped the slope at 4–5 month intervals. A total of 26 cyclones and 15 anticyclones had statistics that were consistent with drifter orbit analyses. The surveys indicate that at any one time, between 2 and 5 cyclones and 1 and 3 anticyclones may be present. Both drifters and surveys indicate that cyclones have a slight numerical dominance.

A regional numerical ocean model of the circulation in the Bay of Biscay

The seasonal circulation along the northern Iberian Peninsula and in the Bay of Biscay is investigated by means of a regional ocean model. In particular, the modeled velocities and tracers are compared to available observations and used to hypothesize what the circulation may look like in areas where the density of observations is scarcer. Despite a few biases in the thermohaline properties of some water masses, the model is able to represent the various water masses present in the region in an acceptable way. In particular, the density and depth ranges of most water masses are in good agreement with observed ranges. Similarly, the circulation schemes compare generally well with observations, both in annual mean as for the seasonal features. The model simulates a baroclinic slope current system that extends within the upper 2000 m and is subject to a strong seasonal variability. As a result, these slope currents are seen to reverse seasonally at all depths. A numerical Lagrangian analysis indicates that water masses cannot be transported continuously within the slope currents in or out of the Bay of Biscay because of the flow reversals associated with this seasonality. Instead, this analysis highlights the numerous connections with the slope current system and the interior, in agreement with Lagrangian drifter data.

Wind induced oscillator dynamics in the Black Sea revealed by Lagrangian drifters

Lagrangian drifter observations of the Black Sea circulation between 2002 and 2003 show six transitions between two meta‐stable states representing single gyre structures centered in either the western or eastern sub‐basin of the Black Sea, respectively. The major mechanisms driving such an oscillator dynamics are Ekman pumping for the eastern sub‐basin, and most likely a resonance excitation for the western sub‐basin. The sea strongly amplifies the wind responses of 120‐day periodicity. Data analysis demonstrates that two‐gyre structure (“Knipovich spectacles”) was a transient between the states. Residence time for the sea to occupy either state is mainly determined by the instability of the gyres, wind variability and, probably, variations in the pycnocline. This behavior is a manifestation of a bimodal dynamical regime which affects the long‐term (climatic), large‐scale transport and mixing of bio‐geochemical substances.

Particle dispersion and deposition in ventilated rooms: Testing and evaluation of different Eulerian and Lagrangian models

Indoor particle dispersion in a three-dimensional ventilated room is simulated by a Lagrangian discrete random walk (DRW) model and two Eulerian models: drift flux model and mixture model. The simulated results are compared with the published measured data to check the performance of the three models for indoor particle dispersion simulation. The deposition velocity of the particles is also computed and compared with published data. The turbulent airflow is modeled with the renormalization group (RNG) k− ε and a zero equation turbulence model. Comparison of the calculated air velocities with measurement shows that both the two turbulence models can simulate the airflow well for the presented case. For the Lagrangian DRW model, a post-process program is used to state the particle trajectories and transfer the results to particle concentration distribution. For Eulerian models, the effect of particle deposition towards wall surfaces is incorporated with a semi-empirical particle deposition model. The comparison shows that both the Lagrangian DRW model and drift flux model yield satisfactory predictions, while the predicted results by the mixture model are not satisfied. The deposition velocity obtained by the three models match the experimental data well.

Surface circulation in the central Mediterranean Sea as deduced from Lagrangian drifters in the 1990s

The surface circulation in the central Mediterranean, including the Sicily Channel, the southern Tyrrhenian and western Ionian seas, is studied using the data of more than 150 satellite-tracked drifters for the period spanning 1990–99. Pseudo-Eulerian maps of mean flow, eddy variability and energy levels are produced using all the data, the data sorted by seasons and the data divided in major wind categories, to study the circulation variability at meso to seasonal scales, and in terms of the local wind forcing. In general, the new results revealed by the drifter data confirm the general characteristics of the surface circulation as detected in previous Eulerian investigations. However, they provide a new broad quantitative description of the central Mediterranean surface circulation and they shed light on the dynamics of the Channel at large, including the Tunisian shelf and the area south of Malta, which shows unexpected characteristics of the surface velocity field, sometimes stagnant or even directed the opposite way with respect to the currents flowing further to the north. In addition, the drifter dataset allows to underline the seasonal character of the surface circulation in the area, and to assess the importance of the wind forcing. It was found that when winds blow from the northwestern sector (like the Mistral) the surface eastward transport in the Sicily Channel is enhanced. In contrast, for opposing wind conditions (blowing from the southeastern sector), the transport trough the Channel is significantly reduced. The quasi-Lagrangian nature of the drifters is also exploited to estimate Lagrangian statistics, such as the auto-covariance, the horizontal diffusivity and the integral time and space scales. Diffusivities and scales ranging in 1–5×10 7 cm 2 s −1, 1–2 days and 10–30 km were found, respectively.

Comparison of model and observational ocean circulation climatologies for the New Zealand region

Primitive equation three‐dimensional regional models driven by global models can be used to generate climatologies of the ocean circulation. With 1/12° resolution, these model climatologies begin to resolve the coastal circulation and it is appropriate to ask whether they are adequate to replace observational climatologies. We compare circulation climatologies derived from a z coordinate 36 vertical layer model, run with three different diffusivities with an observational climatology (CSIRO Atlas of Regional Seas, CARS), and with surface velocities derived from Lagrangian drifters deployed under the Global Drifter Program (GDP). All the climatologies capture the major features in the mean circulation. South of the Chatham Rise, and east of New Zealand, the model climatologies agree better with GDP than does CARS. North of the Chatham Rise, the models overestimate the strength of the East Cape Eddy. Wave number spectra from the models suggest that instability processes which are important in the mean are captured with diffusion less than 25 m2 s−1. The model with lowest diffusion may be providing the best estimate of the mean circulation, but at the expense of numerical instability.

Vertical migration of the toxic dinoflagellate Karenia brevis and the impact on ocean optical properties

Vertical migration behavior is found in many harmful algal blooms; however, the corresponding impact on ocean optical properties has not been quantified. A near‐monospecific population of the dinoflagellate Karenia brevis was encountered off the west coast of Florida. The community was tracked for 24 hours by following a Lagrangian drifter deployed at the beginning of the experiment. A suite of inherent optical and cellular measurements was made. Over the 24 hour period, the K. brevis population increased during the day with concentrations peaking in the late afternoon (1600 local daylight time) in the upper 2 m of the water column. The increase in K. brevis in surface waters resulted in enhanced reflectance at the sea surface with distinct spectral changes. There was a 22% decrease in the relative amount of the green reflectance due to increased pigment absorption. There was enhanced red (35%) and infrared (75%) light reflectance due to the increased particle backscatter and chlorophyll a fluorescence; however, the relative impact of the fluorescence was relatively small despite high cell numbers due to the significant fluorescence quenching present in K. brevis. The relative change in the blue light reflectance was not as large as the change in green light reflectance, which is surprising given the pigment absorption in the blue wavelengths of light. The increased blue light pigment absorption was offset by a significant decrease in nonalgal particle absorption. The inverse relationship between K. brevis and nonalgal particles was robust. This relationship may reflect low grazing on K. brevis populations due to the neurotoxins associated with this dinoflagellate. The low‐grazing pressure may provide the mechanism by which this slow‐growing dinoflagellate can achieve high cell numbers in the ocean.

An experimental study of the surface drift currents in a wave flume

The Lagrangian surface drift current induced by surface gravity waves in a wave flume has been investigated experimentally by the particle tracking method. It was observed that in most regions of the flume, the time-mean surface drift current was in the opposite direction to that of the wave propagation. The secondary current in the form of a pair of longitudinal vortices caused by the lateral boundaries was analyzed. It is suggested that the convection of the vorticity generated by the wave-absorber and the lateral boundaries is an important factor in the determination of the time-mean drift in a wave flume.

Viral and bacterial assemblage covariance in oligotrophic waters of the West Florida Shelf (Gulf of Mexico)

Viruses are hypothesized to cause enhanced diversity in bacterial communities by regulating the outcome of intertaxon competition. However, concomitant documentation of viral and bacterial assemblage composition in oligotrophic waters are rare, particularly in situ over time, and there is almost no information on the temporal variability in virioplankton assemblage composition in oligotrophic water masses. Assemblage composition of viruses (via pulsed-field gel electrophoresis, PFGE) and bacteria (via automated rRNA intergenic spacer analysis, ARISA) was compared during surface lagrangian drifter deployments in the oligotrophic Gulf of Mexico during summer 2001, 2002, and 2003. In vertical profile, viruses and bacteria both had maximum abundances in surface waters, which decreased with depth; however, the richness of their assemblages was not significantly different between depths, suggesting independence of biomass and diversity. Viral assemblages changed rapidly (0.17–0.32 Jaccard index d−1), which was similar to the rate of change in bacterial assemblages reported in surface waters. Patterns of viral and bacterial assemblage composition were significantly related (P<0.001, r=0.58 between node ranks), and both assemblages clustered primarily by year and then by depth. These cultivation-independent observations demonstrate relationships between viral and bacterial assemblages, which are dynamic in patches of open ocean water. Even at the relatively low phylogenetic resolution of the ARISA and PFGE methods, the results support the idea that viruses may influence the species composition of host assemblages.

On the oscillatory and mean motions due to waves in a thin viscoelastic layer

A perturbation analysis based on equations of motion in Lagrangian form is presented for the oscillatory and mean motions induced by a forced periodic wave propagating in a thin layer of viscoelastic material. The material is assumed to be a Voigt body, for which the constitutive relation is a linear combination of viscous and elastic parts. In this work, the elastic part of the stress is assumed to be a linear function of the Lagrangian deformation tensor. The aim is to show a proper approach of carrying out the analysis to the second order in order to determine the mean deformation undergone by the material. This approach is in sharp contrast to the previous studies, which have mistakenly applied the complex viscoelastic parameter to the second order and assumed the mean motion to be a steady Lagrangian drift. It is shown here that for a sufficiently soft and viscous material the mean motion is actually a creeping motion that slowly dies out as a limit of finite deformation is approached. Numerical results are also generated to illustrate the combined effects due to viscous damping and elasticity on the first-order oscillatory and the second-order mean displacements of particles in the material.

A Method for Assimilating Lagrangian Data into a Shallow-Water-Equation Ocean Model

Abstract Lagrangian measurements provide a significant portion of the data collected in the ocean. Difficulties arise in their assimilation, however, since Lagrangian data are described in a moving frame of reference that does not correspond to the fixed grid locations used to forecast the prognostic flow variables. A new method is presented for assimilating Lagrangian data into models of the ocean that removes the need for any commonly used approximations. This is accomplished by augmenting the state vector of the prognostic variables with the Lagrangian drifter coordinates at assimilation. It is shown that this method is best formulated using the ensemble Kalman filter, resulting in an algorithm that is essentially transparent for assimilating Lagrangian data. The method is tested using a set of twin experiments on the shallow-water system of equations for an unsteady double-gyre flow configuration. Numerical simulations show that this method is capable of correcting the flow even if the assimilation time interval is of the order of the Lagrangian autocorrelation time scale (TL) of the flow. These results clearly demonstrate the benefits of this method over other techniques that require assimilation times of 20%–50% of TL, a direct consequence of the approximations introduced in assimilating their Lagrangian data. Detailed parametric studies show that this method is particularly effective if the classical ideas of localization developed for the ensemble Kalman filter are extended to the Lagrangian formulation used here. The method that has been developed, therefore, provides an approach that allows one to fully realize the potential of Lagrangian data for assimilation in more realistic ocean models.

Drift and mixing under the ocean surface: A coherent one‐dimensional description with application to unstratified conditions

Waves have many effects on near‐surface dynamics: Breaking waves enhance mixing, waves are associated with a Lagrangian mean drift (the Stokes drift), waves act on the mean flow by creating Langmuir circulations and a return flow opposite to the Stokes drift, and, last but not least, waves modify the atmospheric surface roughness. A realistic ocean model is proposed to embrace all these aspects, focusing on near‐surface mixing and surface drift associated with the wind and generated waves. The model is based on the generalized Lagrangian mean that separates the momentum into a wave pseudomomentum and a quasi‐Eulerian momentum. A wave spectrum with a reasonably high frequency range is used to compute the Stokes drift. A turbulent closure scheme based on a single evolution equation for the turbulent kinetic energy includes the mixing due to breaking wave effects and wave‐turbulence interactions. The roughness length of the closure scheme is adjusted using observations of turbulent kinetic energy near the surface. The model is applied to unstratified and horizontally uniform conditions, showing good agreement with observations of strongly mixed quasi‐Eulerian currents near the surface when waves are developed. Model results suggest that a strong surface shear persists in the drift current because of the Stokes drift contribution. In the present model the surface drift only reaches 1.5% of the wind speed. It is argued that stratification and the properties of drifting objects may lead to a supplementary drift as large as 1% of the wind speed.

On upscaling operator-stable Lévy motions in fractal porous media

The dynamics of motile particles, such as microbes, in random porous media are modeled with a hierarchical set of stochastic differential equations which correspond to micro, meso and macro scales. On the microscale the motile particle is modeled as an operator stable Lévy process with stationary, ergodic, Markov drift. The micro to meso and meso to macro scale homogenization is handled with generalized central limit theorems. On the mesoscale the Lagrangian drift (or the Lagrangian acceleration) is assumed Lévy to account for the fractal character of many natural porous systems. Diffusion on the mesoscale is a result of the microscale asymptotics while diffusion on the macroscale results from the mesoscale asymptotics. Renormalized Fokker–Planck equations with time dependent dispersion tensors and fractional derivatives are presented at the macro scale.

Note on the induced Lagrangian drift and added-mass of a vortex

Darwin (1953) introduced a simple heuristic that relates the Lagrangian fluid drift induced by a solid body propagating in irrotational flow to its virtual- or added-mass. The force required to accelerate the solid body must also overcome this added-mass. An extension of Darwin's (1953) method to the case of vortices propagating in a real fluid is described here. Experiments are conducted to demonstrate the existence of an added-mass effect during uni-directional vortex motion, which is analogous to the effect of solid bodies in potential flow. The definition of the vortex added-mass coefficient is modified from the solid body case to account for entrainment of ambient fluid by the vortex. This modified coefficient for propagating vortices is shown to be equal in magnitude to the classical coefficient for a solid body of equivalent boundary geometry. An implication of these results is that the vortex added-mass concept can be used as a surrogate for the velocity potential, in order to facilitate calculations of the pressure contribution to forces required to set fluid into unsteady vortical motion. Application of these results to unsteady wake analyses and fluid–structure interactions such as vortex-induced vibrations is suggested.

Mean drift velocity in viscous flow over a corrugated bottom

The mean, steady-state particle velocity in pressure-driven viscous flow in a horizontal channel with a sinusoidal bottom and a plane top is computed using a Lagrangian description of motion. The bottom corrugations are longitudinal, i.e., having crests aligned along the basic flow. At the bottom a no-slip condition is applied. At the upper boundary two different cases are considered: one stress free and one no slip. The nonlinear interaction between the basic Poiseuille flow and the bottom corrugations yields a mean Lagrangian drift velocity that is directed along the basic flow for small nondimensional wave numbers, and against the basic flow for larger wave numbers. More specifically, the entire mean drift velocity is negative for stress-free and no-slip upper boundaries when the wave number for the two cases exceeds 1.35 and 2.28, respectively. It is demonstrated that the total nonlinear wall drag is zero for both these cases. The results for longitudinal corrugations are compared with earlier calculations for bottom corrugations that are transverse to the basic flow. In that case the nonlinear mean drift current is always directed against the basic flow. It is found that for the same wave number, transverse corrugations induce a stronger negative mean drift velocity than do longitudinal corrugations.