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Moore, AM, Arango HG, Di Lorenzo E, Miller AJ, Cornuelle BD.  2009.  An Adjoint Sensitivity Analysis of the Southern California Current Circulation and Ecosystem. Journal of Physical Oceanography. 39:702-720.   10.1175/2008jpo3740.1   AbstractWebsite

Adjoint methods of sensitivity analysis were applied to the California Current using the Regional Ocean Modeling Systems (ROMS) with medium resolution, aimed at diagnosing the circulation sensitivity to variations in surface forcing. The sensitivities of coastal variations in SST, eddy kinetic energy, and baroclinic instability of complex time-evolving flows were quantified. Each aspect of the circulation exhibits significant interannual and seasonal variations in sensitivity controlled by mesoscale circulation features. Central California SST is equally sensitive to wind stress and surface heat flux, but less so to wind stress curl, displaying the greatest sensitivity when upwelling-favorable winds are relaxing and the least sensitivity during the peak of upwelling. SST sensitivity is typically 2-4 times larger during summer than during spring, although larger variations occur during some years. The sensitivity of central coast eddy kinetic energy to surface forcing is constant on average throughout the year. Perturbations in the wind that align with mesoscale eddies to enhance the strength of the circulation by local Ekman pumping yield the greatest sensitivities. The sensitivity of the potential for baroclinic instability is greatest when nearshore horizontal temperature gradients are largest, and it is associated with variations in wind stress concentrated along the core of the California Current. The sensitivity varies by a factor of similar to 1.5 throughout the year. A new and important aspect of this work is identification of the complex flow dependence and seasonal dependence of the sensitivity of the ROMS California Current System (CCS) circulation to variations in surface forcing that was hitherto not previously appreciated.

Colosi, JA, Baggeroer AB, Cornuelle BD, Dzieciuch MA, Munk WH, Worcester PF, Dushaw BD, Howe BM, Mercer JA, Spindel RC, Birdsall TG, Metzger K, Forbes AMG.  2005.  Analysis of multipath acoustic, field variability and coherence in the finale of broadband basin-scale transmissions in the North Pacific Ocean. Journal of the Acoustical Society of America. 117:1538-1564.   10.1121/1.1854615   AbstractWebsite

The statistics of low-frequency, long-range acoustic transmissions in the North Pacific Ocean are presented. Broadband signals at center frequencies of 28, 75, and 84 Hz are analyzed at propagation ranges of 3252 to 5171 km, and transmissions were received on 700 and 1400 in long vertical receiver arrays with 35 in hydrophone spacing. In the analysis we focus on the energetic "finale" region of the broadband time front arrival pattern, where a multipath interference pattern exists. A Fourier analysis of 1 s regions in the finale provide narrowband data for examination as well. Two-dimensional (depth and time) phase unwrapping is employed to study separately the complex field phase and intensity. Because data sampling occured in 20 or 40 min intervals followed by long gaps, the acoustic fields are analyzed. in terms of these 20 and 40 min and multiday observation times. An analysis of phase, intensity, and complex envelope variability as a function of depth and time is presented in terms of mean fields, variances, probability density functions (PDFs), covariance, spectra, and coherence. Observations are compared to a random multipath model of frequency and vertical wave number spectra for phase and log intensity, and the observations are compared to a broadband multipath model of scintillation index and coherence. 2005 Acoustical Society of America.

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Dushaw, BD, Cornuelle BD, Worcester PF, Howe BM, Luther DS.  1995.  Barotropic and Baroclinic Tides in the Central North Pacific-Ocean Determined from Long-Range Reciprocal Acoustic Transmissions. Journal of Physical Oceanography. 25:631-647.   10.1175/1520-0485(1995)025<0631:babtit>2.0.co;2   AbstractWebsite

Travel times of reciprocal 1000-km range acoustic transmissions, determined from the 1987 Reciprocal Tomography Experiment, are used to study barotropic tidal currents and a large-scale, coherent baroclinic tide in the central North Pacific Ocean. The difference in reciprocal travel times determines the tidal currents, while the sum of reciprocal travel times determines the baroclinic tide displacement of isotachs (or equivalently, isotherms). The barotropic tidal current accounts for 90% of the observed differential travel time variance. The measured harmonic constants of the eight major tidal constituents of the barotropic tide and the constants determined from current meter measurements agree well with the empirical-numerical tidal models of Schwiderski and Cartwright et al. The amplitudes and phases of the first-mode baroclinic tide determined from sum travel times agree with those determined from moored thermistors and current meters. The baroclinic tidal signals are consistent with a large-scale, phase-locked internal tide, which apparently has propagated northward over 2000 km from the Hawaiian Ridge. The amplitude, phase, and polarization of the first-mode M(2) baroclinic tidal displacement and current are consistent with a northward propagating internal tide. The ratio of baroclinic energy to barotropic energy determined using the range-averaging acoustic transmissions is about 8%, while a ratio of 26% was determined from the point measurements. The large-scale, internal tide energy flux, presumed northward, is estimated to be about 180 W m(-1).

Dushaw, BD, Worcester PF, Cornuelle BD, Howe BM.  1994.  Barotropic Currents and Vorticity in the Central North Pacific-Ocean During Summer 1987 Determined from Long-Range Reciprocal Acoustic Transmissions. Journal of Geophysical Research-Oceans. 99:3263-3272.   10.1029/93jc03335   AbstractWebsite

Large-scale depth-integrated currents and relative vorticity were measured in the central North Pacific Ocean during summer 1987 using long-range reciprocal acoustic transmissions between transceivers in a triangle approximately 1000 km on a side. Inverse techniques were used to estimate the depth-averaged (barotropic) current bihourly at 4-day intervals from differential travel times. Tidal constituent amplitudes and phases found from the acoustically determined currents agree with those found from current meters and with the tidal models of Schwiderski (1980) and Cartwright et al. (1992), providing confirmation that the tomographically derived barotropic currents are correct within the expected uncertainties. The estimated low-frequency, large-scale currents are compared with depth-averaged currents determined by point measurements using current meters and bottom-mounted electrometers. Meridional and zonal currents are calculated using the topographic Sverdrup balance with the Fleet Numerical Oceanography Center wind field. The measured time derivative of the areally averaged relative vorticity is shown to be insignificant to the Sverdrup balance. Currents and vorticity calculated using the Sverdrup balance are an order of magnitude smaller than the observations. The magnitude and variability of the large-scale currents and vorticity determined from the Semtner and Chervin (1988) eddy-resolving model of ocean circulation are similar to the direct measurements.

Miller, AJ, Neilson DJ, Luther DS, Hendershott MC, Cornuelle BD, Worcester PF, Dzieciuch MA, Dushaw BD, Howe BM, Levin JC, Arango HG, Haidvogel DB.  2007.  Barotropic Rossby wave radiation from a model Gulf Stream. Geophysical Research Letters. 34   10.1029/2007gl031937   AbstractWebsite

The barotropic Rossby wave field in the North Atlantic Ocean is studied in an eddy-resolving ocean model simulation. The meandering model Gulf Stream radiates barotropic Rossby waves southward through preferred corridors defined by topographic features. The smoother region between the Bermuda Rise and the mid-Atlantic Ridge is a particularly striking corridor of barotropic wave radiation in the 20-50 day period band. Barotropic Rossby waves are also preferentially excited at higher frequencies over the Bermuda Rise, suggesting resonant excitation of topographic Rossby normal modes. The prevalence of these radiated waves suggests that they may be an important energy sink for the equilibrium state of the Gulf Stream.

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Song, H, Miller AJ, Cornuelle BD, Di Lorenzo E.  2011.  Changes in upwelling and its water sources in the California Current System driven by different wind forcing. Dynamics of Atmospheres and Oceans. 52:170-191.   10.1016/j.dynatmoce.2011.03.001   AbstractWebsite

In the California Current System (CCS), upwelling is one of the most important features that enrich the coastal ecosystem. It is highly dependent on both wind stress and wind stress curl, because they contribute to the upwelling system through Ekman transport away from the coast and Ekman pumping as a result of the surface divergence, respectively. Various wind stress products are known to contain sharply different patterns of wind stress, and well-resolved wind forcing products have been shown to drive stronger upwelling due to their better-resolved wind stress curl in previous studies. However, sensitivities of upwelling to changes in wind stress patterns, and each of their control to the source waters and paths of the upwelling cells, are not yet well known for the CCS. Here we study these effects using the Regional Ocean Modeling System (ROMS) and its adjoint model under idealized wind stress forcing patterns representing three widely-used products in addition to a constant wind stress field (no curl): the NCEP/NCAR Reanalysis, the QuikSCAT satellite observations, and the Regional Spectral Model (RSM) downscaling. Changes in currents and isopycnal patterns during the upwelling season are first studied in ROMS under the four different wind stress fields. The model simulations show that the locations of the core of the equatorward flow and the gradient of the cross-shore isopycnals are controlled by the wind stress curl field. The core of the equatorward flow is found under negative wind stress curl, and a deeper upwelling cell is found as the gradient from positive and negative wind stress curl increases. Source waters for the upwelling in each of the four wind stress patterns are investigated using the ROMS adjoint model. The simulations follow a passive tracer backward in time and track the source waters for upwelling in two key areas of interest: inshore and offshore of the Point Sur region of California. The upwelling source waters depend strongly on the depth of the upwelling cell and the alongshore current location. We further relate these results to recent studies of the observed trends in upwelling favorable winds and consequent wind stress curl changes in the CCS. (C) 2011 Elsevier B.V. All rights reserved.

Gawarkiewicz, G, Jan S, Lermusiaux PFJ, McClean JL, Centurioni L, Taylor K, Cornuelle B, Duda TF, Wang J, Yang YJ, Sanford T, Lien RC, Lee C, Lee MA, Leslie W, Haley PJ, Niiler PP, Gopalakrishnan G, Velez-Belchi P, Lee DK, Kim YY.  2011.  Circulation and Intrusions Northeast of Taiwan: Chasing and Predicting Uncertainty in the Cold Dome. Oceanography. 24:110-121. AbstractWebsite

An important element of present oceanographic research is the assessment and quantification of uncertainty. These studies are challenging in the coastal ocean due to the wide variety of physical processes occurring on a broad range of spatial and temporal scales. In order to assess new methods for quantifying and predicting uncertainty, a joint Taiwan-US field program was undertaken in August/September 2009 to compare model forecasts of uncertainties in ocean circulation and acoustic propagation, with high-resolution in situ observations. The geographical setting was the continental shelf and slope northeast of Taiwan, where a feature called the "cold dome" frequently forms. Even though it is hypothesized that Kuroshio subsurface intrusions are the water sources for the cold dome, the dome's dynamics are highly uncertain, involving multiple scales and many interacting ocean features. During the experiment, a combination of near-surface and profiling drifters, broad-scale and high-resolution hydrography, mooring arrays, remote sensing, and regional ocean model forecasts of fields and uncertainties were used to assess mean fields and uncertainties in the region. River runoff from Typhoon Morakot, which hit Taiwan August 7-8, 2009, strongly affected shelf stratification. In addition to the river runoff, a cold cyclonic eddy advected into the region north of the Kuroshio, resulting in a cold dome formation event. Uncertainty forecasts were successfully employed to guide the hydrographic sampling plans. Measurements and forecasts also shed light on the evolution of cold dome waters, including the frequency of eddy shedding to the north-northeast, and interactions with the Kuroshio and tides. For the first time in such a complex region, comparisons between uncertainty forecasts and the model skill at measurement locations validated uncertainty forecasts. To complement the real-time model simulations, historical simulations with another model show that large Kuroshio intrusions were associated with low sea surface height anomalies east of Taiwan, suggesting that there may be some degree of predictability for Kuroshio intrusions.

Worcester, PF, Cornuelle BD, Hildebrand JA, Hodgkiss WS, Duda TF, Boyd J, Howe BM, Mercer JA, Spindel RC.  1994.  A Comparison of Measured and Predicted Broad-Band Acoustic Arrival Patterns in Travel Time-Depth Coordinates at 1000-Km Range. Journal of the Acoustical Society of America. 95:3118-3128.   10.1121/1.409977   AbstractWebsite

Broadband acoustic signals were transmitted from a moored 250-Hz source to a 3-km-long vertical line array of hydrophones 1000 km distant in the eastern North Pacific Ocean during July 1989. The sound-speed field along the great circle path connecting the source and receiver was measured directly by nearly 300 expendable bathythermograph (XBT), conductivity-temperature-depth (CTD), and air-launched expendable bathythermograph (AXBT) casts while the transmissions were in progress. This experiment is unique in combining a vertical receiving array that extends over much of the water column, extensive concurrent environmental measurements, and broadband signals designed to measure acoustic travel times with 1-ms precision. The time-mean travel times of the early raylike arrivals, which are evident as wave fronts sweeping across the receiving array, and the time-mean of the times at which the acoustic reception ends (the final cutoffs) for hydrophones near the sound channel axis, are consistent with ray predictions based on the direct measurements of temperature and salinity, within measurement uncertainty. The comparisons show that subinertial oceanic variability with horizontal wavelengths shorter than 50 km, which is not resolved by the direct measurements, significantly (25 ms peak-to-peak) affects the time-mean ray travel times. The final cutoffs occur significantly later than predicted using ray theory for hydrophones more than 100-200 m off the sound channel axis. Nongeometric effects, such as diffraction at caustics, partially account for this observation.

Colosi, JA, Scheer EK, Flatte SM, Cornuelle BD, Dzieciuch MA, Munk WH, Worcester PF, Howe BM, Mercer JA, Spindel RC, Metzger K, Birdsall TG, Baggeroer AB.  1999.  Comparisons of measured and predicted acoustic fluctuations for a 3250-km propagation experiment in the eastern North Pacific Ocean. Journal of the Acoustical Society of America. 105:3202-3218.   10.1121/1.424650   AbstractWebsite

During the Acoustic Engineering Test (AET) of the Acoustic Thermometry of Ocean Climate (ATOC) program, acoustic signals were transmitted from a broadband source with 75-Hz center frequency to a 700-m-long vertical array of 20 hydrophones at a distance of 3252 km receptions occurred over a period of-six days. Each received pulse showed early identifiable timefronts, followed by about 2 s of highly variable energy. For the identifiable timefronts, observations of travel-time variance, average pulse shape, and the probability density function (PDF) of intensity are presented, and calculations of internal-wave contributions to those fluctuations are compared to the observations. Individual timefronts have rms travel time fluctuations of 11 to 19 ms, with time scales of less than 2 h. The pulse time spreads are between 0 and 5.3 ms rms, which suggest that internal-wave-induced travel-time biases are of the same magnitude. The PDFs of intensity for individual ray arrivals are compared to log-normal and exponential distributions. The observed PDFs are closer to the log-normal distribution, and variances of log intensity are between (3.1 dB)(2) (with a scintillation index of 0.74) for late-arriving timefronts and (2.0 dB)(2) (with a scintillation index of 0.2) for the earliest timefronts. Fluctuations of the pulse termination time of the transmissions are observed to be 22 ms rms. The intensity PDF of nonidentified peaks in the pulse crescendo are closer to a log-normal distribution than an exponential distribution, but a Kolmogorov-Smimov test rejects both distributions. The variance of the nonidentified peaks is (3.5 dB)(2) land the-scintillation index is 0.92. As a group, the observations suggest that the propagation is on the border of the unsaturated and partially saturated regimes. After improving the specification of the. ray weighting function, predictions of travel-time variance using the Garrett-Munk (GM) internal-wave spectrum at one-half the reference energy are in good agreement with the observations, and the one-half GM energy level compares well with XBT data taken along the transmission path. Predictions of pulse spread and wave propagation regime are in strong disagreement with the observations. Pulse time spread estimates are nearly two orders of magnitude too large, and Lambda-Phi methods for predicting the wave propagation regime predict full saturation. (C) 1999 Acoustical Society of America. [S0001-4966(99)04606-8].

Moore, AM, Arango HG, Di Lorenzo E, Cornuelle BD, Miller AJ, Neilson DJ.  2004.  A comprehensive ocean prediction and analysis system based on the tangent linear and adjoint of a regional ocean model. Ocean Modelling. 7:227-258.   10.1016/j.ocemod.2003.11.001   AbstractWebsite

The regional ocean modelling system (ROMS) is a new generation ocean general circulation model that is rapidly gaining favour in the ocean modelling community. The tangent linear and adjoint versions of ROMS have recently been developed, and a new suite of tools that utilize these models for a variety of applications are now available to the ocean modelling community. In this paper we will describe the tangent linear and adjoint components of ROMS, and present examples from the tools that are currently available to ROMS users. In particular we will consider the finite time eigenmodes and the adjoint finite time eigenmodes of the tangent linear propagator, the singular vectors of the propagator, and its forcing singular vectors and stochastic optimals. The pseudospectra of the tangent linear resolvent matrix are also considered. Examples of each type of calculation will be presented for a time evolving double gyre ocean circulation in a rectangular ocean basin. (C) 2003 Elsevier Ltd. All rights reserved.

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Subramanian, AC, Miller AJ, Cornuelle BD, Di Lorenzo E, Weller RA, Straneo F.  2013.  A data assimilative perspective of oceanic mesoscale eddy evolution during VOCALS-REx. Atmospheric Chemistry and Physics. 13:3329-3344.   10.5194/acp-13-3329-2013   AbstractWebsite

Oceanic observations collected during the VOCALS-REx cruise time period, 1-30 November 2008, are assimilated into a regional ocean model (ROMS) using 4DVAR and then analyzed for their dynamics. Nonlinearities in the system prevent a complete 30-day fit, so two 15-day fits for 1-15 November and 16-30 November are executed using the available observations of hydrographic temperature and salinity, along with satellite fields of SST and sea-level height anomaly. The fits converge and reduce the cost function significantly, and the results indicated that ROMS is able to successfully reproduce both large-scale and smaller-scale features of the flows observed during the VOCALS-REx cruise. Particular attention is focused on an intensively studied eddy at 76 degrees W, 19 degrees S. The ROMS fits capture this eddy as an isolated rotating 3-D vortex with a strong subsurface signature in velocity, temperature and anomalously low salinity. The eddy has an average temperature anomaly of approximately -0.5 degrees C over a depth range from 50-600 m and features a cold anomaly of approximately -1 degrees C near 150 m depth. The eddy moves northwestward and elongates during the second 15-day fit. It exhibits a strong signature in the Okubo-Weiss parameter, which indicates significant non-linearity in its evolution. The heat balance for the period of the cruise from the ocean state estimate reveals that the horizontal advection and the vertical mixing processes are the dominant terms that balance the temperature tendency of the upper layer of the ocean locally in time and space. Areal averages around the eddies, for a 15-day period during the cruise, suggest that vertical mixing processes generally balance the surface heating. Although, this indicates only a small role for lateral advective processes in this region during this period, this quasi-instantaneous heat budget analysis cannot be extended to interpret the seasonal or long-term upper ocean heat budget in this region.

Dushaw, BD, Worcester PF, Munk WH, Spindel RC, Mercer JA, Howe BM, Metzger K, Birdsall TG, Andrew RK, Dzieciuch MA, Cornuelle BD, Menemenlis D.  2009.  A decade of acoustic thermometry in the North Pacific Ocean. Journal of Geophysical Research-Oceans. 114   10.1029/2008jc005124   AbstractWebsite

Over the decade 1996-2006, acoustic sources located off central California (1996 1999) and north of Kauai (1997-1999, 2002-2006) transmitted to receivers distributed throughout the northeast and north central Pacific. The acoustic travel times are inherently spatially integrating, which suppresses mesoscale variability and provides a precise measure of ray-averaged temperature. Daily average travel times at 4-day intervals provide excellent temporal resolution of the large-scale thermal field. The interannual, seasonal, and shorter-period variability is large, with substantial changes sometimes occurring in only a few weeks. Linear trends estimated over the decade are small compared to the interannual variability and inconsistent from path to path, with some acoustic paths warming slightly and others cooling slightly. The measured travel times are compared with travel times derived from four independent estimates of the North Pacific: (1) climatology, as represented by the World Ocean Atlas 2005 (WOA05); (2) objective analysis of the upper-ocean temperature field derived from satellite altimetry and in situ profiles; (3) an analysis provided by the Estimating the Circulation and Climate of the Ocean project, as implemented at the Jet Propulsion Laboratory (JPL-ECCO); and (4) simulation results from a high-resolution configuration of the Parallel Ocean Program (POP) model. The acoustic data show that WOA05 is a better estimate of the time mean hydrography than either the JPL-ECCO or the POP estimates, both of which proved incapable of reproducing the observed acoustic arrival patterns. The comparisons of time series provide a stringent test of the large-scale temperature variability in the models. The differences are sometimes substantial, indicating that acoustic thermometry data can provide significant additional constraints for numerical ocean models.

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Rasmussen, LL, Cornuelle BD, Levin LA, Largier JL, Di Lorenzo E.  2009.  Effects of small-scale features and local wind forcing on tracer dispersion and estimates of population connectivity in a regional scale circulation model. Journal of Geophysical Research-Oceans. 114   10.1029/2008jc004777   AbstractWebsite

A small-scale model of the Southern California-Northern Baja California coastline has been developed to explore dispersion over the continental shelf, with specific attention to physical parameters pertinent to simulations of larval dispersal and population connectivity. The ROMS simulation employs a nested grid system, with an inner domain resolution of 600 m and an outer domain resolution of 1.5 km. Realistic bathymetry and forcing were employed to investigate the effects of passive transport of tracers introduced at locations with known communities of mytilid mussels along the coastline. The effects of topographic resolution, boundary conditions, and choice of meteorological forcing products on dispersion rates, tracer trajectories, and the subsequent measures of population connectivity were examined. In particular, the choice of wind forcing product resulted in different circulation patterns and tracer trajectories and had especially important consequences on measures of larval connectivity such as self-seeding, potential for larval settlement ( import), and contribution to the pool of available larvae ( export). While some forcing products performed better when model data were compared to field measurements, no product was clearly superior. The uncertainty in results, which may appear minor in larger-scale temperature or surface velocity fields, is significant when examining a sensitive passive tracer. This modeling uncertainty needs to be addressed when interpreting connectivity results.

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Wiggins, SM, Dorman LRM, Cornuelle BD, Hildebrand JA.  1996.  Hess Deep rift valley structure from seismic tomography. Journal of Geophysical Research-Solid Earth. 101:22335-22353.   10.1029/96jb01230   AbstractWebsite

We present results from a seismic refraction experiment conducted across the Hess Deep rift valley in the equatorial east Pacific. P wave travel times between seafloor explosions and ocean bottom seismographs are analyzed using an iterative stochastic inverse method to produce a velocity model of the subsurface structure. The resulting velocity model differs from typical young, fast spreading, East Pacific Rise crust by approximately +/-1 km/s with slow velocities beneath the valley of the deep and a fast region forming the intrarift ridge. We interpret these velocity contrasts as lithologies originating at different depths and/or alteration of the preexisting rock units. We use our seismic model, along with petrologic and bathymetric data from previous studies, to produce a structural model. The model supports low-angle detachment faulting with serpentinization of peridotite as the preferred mechanism for creating the distribution and exposure of lower crustal and upper mantle rocks within Hess Deep.

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Muccino, JC, Arango HG, Bennett AF, Chua BS, Cornuelle BD, Di Lorenzo E, Egbert GD, Haidvogel D, Levin JC, Luo H, Miller AJ, Moore AA, Zaron ED.  2008.  The Inverse Ocean Modeling system. Part II: Applications. Journal of Atmospheric and Oceanic Technology. 25:1623-1637.   10.1175/2008jtecho522.1   AbstractWebsite

The Inverse Ocean Modeling (IOM) System is a modular system for constructing and running weak-constraint four-dimensional variational data assimilation (W4DVAR) for any linear or nonlinear functionally, smooth dynamical model and observing array. The IOM has been applied to four ocean models with widely varying characteristics. The Primitive Equations Z-coordinate-Harmonic Analysis of Tides (PEZ-HAT) and the Regional Ocean Modeling System (ROMS) are three-dimensional, primitive equations models while the Advanced Circulation model in 2D (ADCIRC-2D) and Spectral Element Ocean Model in 2D (SEOM-2D) are shallow-water models belonging to the general finite-element family. These models. in conjunction with the IOM, have been used to investigate a wide variety of scientific phenomena including tidal. mesoscale, and wind-driven circulation. In all cases, the assimilation of data using the IOM provides a better estimate of the ocean state than the model alone.

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Hammer, PTC, Dorman LM, Hildebrand JA, Cornuelle BD.  1994.  Jasper Seamount Structure - Seafloor Seismic Refraction Tomography. Journal of Geophysical Research-Solid Earth. 99:6731-6752.   10.1029/93jb02170   AbstractWebsite

The velocity structure of Jasper Seamount was modeled using one- and three-dimensional inversions of P wave travel times. The results represent the first detailed seismic images of a submerged, intraplate volcano. Two seismic refraction experiments were completed on Jasper Seamount, incorporating ocean bottom seismometers and navigated seafloor shots. The P wave travel times were first used to compute a one-dimensional velocity profile which served as a starting model for a three-dimensional tomographic inversion. The seamount P velocities are significantly slower than those observed in typical oceanic crust at equivalent subbasement depths. This suggests that Jasper Seamount is constructed predominantly of extrusive lavas with high average porosity. The velocity models confirm morphological predictions: Jasper Seamount is a shield volcano with rift zone development. High seismic velocities were detected beneath the large radial ridges while low velocities characterize the shallow summit and flanks. Comparisons between P velocity models of Jasper Seamount and the island of Hawaii reveal that these two shield volcanoes are not structurally proportional. Jasper Seamount is far smaller than Hawaii, yet both volcanoes exhibit an outer extrusive layer of similar thickness. This suggests that seamount size influences the intrusive/extrusive proportions; density equilibrium between melt and country rock may explain this behavior.

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Skarsoulis, EK, Cornuelle BD, Dzieciuch MA.  2013.  Long-range asymptotic behavior of vertical travel-time sensitivity kernels. Journal of the Acoustical Society of America. 134:3201-3210.   10.1121/1.4818785   AbstractWebsite

Vertical travel-time sensitivity kernels (VTSKs) describe the effect of horizontally uniform sound-speed changes on travel times in range-independent ocean environments. Wave-theoretic VTSKs can be obtained either analytically, through perturbation of the normal-mode representation, or numerically, as horizontal marginals of the corresponding two-dimensional and three-dimensional travel-time sensitivity kernels. In previous works, it has been observed that wave-theoretic finite-frequency VTSKs approach the corresponding ray-theoretic sensitivity kernels as the propagation range increases. The present work is an attempt to explain this behavior. A stationary-phase approach is used to obtain a long-range asymptotic expression for the wave-theoretic VTSKs. The resulting asymptotic VTSKs are very close to the corresponding ray-theoretic ones. The smoothness condition, required for the stationary-phase approximation to hold, is used to obtain an estimate for the range beyond which the asymptotic behavior sets in. (C) 2013 Acoustical Society of America.

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Duda, TF, Flatte SM, Colosi JA, Cornuelle BD, Hildebrand JA, Hodgkiss WS, Worcester PF, Howe BM, Mercer JA, Spindel RC.  1992.  Measured Wave-Front Fluctuations in 1000-Km Pulse-Propagation in the Pacific-Ocean. Journal of the Acoustical Society of America. 92:939-955.   10.1121/1.403964   AbstractWebsite

A 1000-km acoustical transmission experiment has been carried out in the North Pacific, with Pulses broadcast between a moored broadband source (250-Hz center frequency) and a moored sparse vertical line of receivers. Two data records are reported: a period of 9 days at a pulse rate of one per hour, and a 21 -h period on the seventh day at six per hour. Many wave-front segments were observed at each hydrophone depth, and arrival times were tracked and studied as functions of time and depth. Arrivals within the final section of the pulse are not trackable in time or space at the chosen sampling rates, however. Broadband fluctuations, which are uncorrelated over 10-min sampling and 60-m vertical spacing, are observed with about 40 (ms)2 variance. The variance of all other fluctuations (denoted as low-frequency) is comparable or smaller than the broadband value; this low-frequency variance can be separated into two parts: a wave-front segment displacement (with vertical correlation length greater than 1 km) that varies substantially between rays with different ray identifiers, and a distortion (with vertical correlation length between 60 m and 1 km) of about 2 (ms)2 variance. The low-frequency variance may be explained as the effect of internal waves, including internal tides. The variance of the broadband fluctuations is reduced somewhat but not eliminated if only high-intensity peaks are selected; this selection does not affect the statistics of the low-frequency fluctuations.

Miller, AJ, Di Lorenzo E, Neilson DJ, Cornuelle BD, Moisan JR.  2000.  Modeling CalCOFI observations during El Nino: Fitting physics and biology. California Cooperative Oceanic Fisheries Investigations Reports. 41:87-97. AbstractWebsite

Surveys of temperature, salinity, and velocity from CalCOFI, altimetric measurements of sea level, and drifter observations of temperature and velocity during the 1997-98 El Nino are now being fit with an eddy-resolving ocean model of the Southern California Eight region to obtain dynamically consistent estimates of eddy variability. Skill is evaluated by the model-data mismatch (rms error) during the fitting interval and eventually by forecasting independent data. Preliminary results of fitting July 1997 physical fields are discussed. The physical fields are used to drive a three-dimensional NPZD-type model to be fit to subsurface chlorophyll a (chl a), nitrate, and bulk zooplankton from CalCOFI surveys, and surface chi a from SeaWiFS. Preliminary results of testing the ecosystem model in one-dimensional and three-dimensional form are discussed.

Di Lorenzo, E, Miller AJ, Neilson DJ, Cornuelle BD, Moisan JR.  2004.  Modelling observed California Current mesoscale eddies and the ecosystem response. International Journal of Remote Sensing. 25:1307-1312.   10.1080/01431160310001592229   AbstractWebsite

Satellite and in situ observations are used to test model dynamics for the California Current System (CCS). The model and data are combined to reconstruct the mesoscale ocean structure during a given three-week period. The resulting physical flow field is used to drive a 3D ecosystem model to interpret SeaWiFS and in situ chlorophyll-a (chl-a) variations. With this approach a more complete and consistent picture of the physical and ecosystem processes of the CCS is obtained, providing the basis for addressing fundamental questions about dynamics and predictability of the coastal ocean.

Dushaw, BD, Howe BM, Mercer JA, Spindel RC, Baggeroer AB, Menemenlis D, Wunsch C, Birdsall TG, Clark KMC, Colosi JA, Cornuelle BD, Dzieciuch M, Munk W.  1999.  Multimegameter-Range Acoustic Data Obtained by Bottom-Mounted Hydrophone Arrays for Measurement of Ocean Temperature. Ieee Journal of Oceanic Engineering. 24:202-214.   10.1109/48.757271   AbstractWebsite

Acoustic signals transmitted from the ATOC source on Pioneer Seamount off the coast of California have been received at various sites around the Pacific Basin since January 1996. We describe data obtained using bottom-mounted receivers, including U.S. Navy Sound Surveillance System arrays, at ranges up to 5 Mm from the Pioneer Seamount source. Stable identifiable ray arrivals are observed in several cases, but some receiving arrays are not well suited to detecting the direct ray arrivals. At 5-Mm range, travel-time variations at tidal frequencies (about 50 ms peak to peak) agree well with predicted values, providing verification of the acoustic measurements as well as the tidal model. On the longest and northernmost acoustic paths, the time series of resolved ray travel times show an annual cycle peak-to-peak variation of about 1 s and other fluctuations caused by natural oceanic variability. An annual cycle is not evident in travel times from shorter acoustic paths in the eastern Pacific, though only one realization of the annual cycle is available. The low-pass-filtered travel times are estimated to an accuracy of about 10 ms. This travel-time uncertainty corresponds to errors in range- and depth-averaged temperature of only a few millidegrees, while the annual peak-to-peak variation in temperature averaged horizontally over the acoustic path and vertically over the upper 1 km of ocean is up to 0.5 degree C.

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Colosi, JA, Van Uffelen LJ, Cornuelle BD, Dzieciuch MA, Worcester PF, Dushaw BD, Ramp SR.  2013.  Observations of sound-speed fluctuations in the western Philippine Sea in the spring of 2009. Journal of the Acoustical Society of America. 134:3185-3200.   10.1121/1.4818784   AbstractWebsite

As an aid to understanding long-range acoustic propagation in the Philippine Sea, statistical and phenomenological descriptions of sound-speed variations were developed. Two moorings of oceanographic sensors located in the western Philippine Sea in the spring of 2009 were used to track constant potential-density surfaces (isopycnals) and constant potential-temperature surfaces (isotherms) in the depth range 120-2000 m. The vertical displacements of these surfaces are used to estimate sound-speed fluctuations from internal waves, while temperature/salinity variability along isopycnals are used to estimate sound-speed fluctuations from intrusive structure often termed spice. Frequency spectra and vertical covariance functions are used to describe the space-time scales of the displacements and spiciness. Internal-wave contributions from diurnal and semi-diurnal internal tides and the diffuse internal-wave field [related to the Garrett-Munk (GM) spectrum] are found to dominate the sound-speed variability. Spice fluctuations are weak in comparison. The internal wave and spice frequency spectra have similar form in the upper ocean but are markedly different below 170-m depth. Diffuse internal-wave mode spectra show a form similar to the GM model, while internal-tide mode spectra scale as mode number to the minus two power. Spice decorrelates rapidly with depth, with a typical correlation scale of tens of meters.

Colosi, JA, Duda TF, Lin YT, Lynch JF, Newhall AE, Cornuelle BD.  2012.  Observations of sound-speed fluctuations on the New Jersey continental shelf in the summer of 2006. Journal of the Acoustical Society of America. 131:1733-1748.   10.1121/1.3666014   AbstractWebsite

Environmental sensors moored on the New Jersey continental shelf tracked constant density surfaces (isopycnals) for 35 days in the summer of 2006. Sound-speed fluctuations from internal-wave vertical isopycnal displacements and from temperature/salinity variability along isopycnals (spiciness) are analyzed using frequency spectra and vertical covariance functions. Three varieties of internal waves are studied: Diffuse broadband internal waves (akin to waves fitting the deep water Garrett/Munk spectrum), internal tides, and, to a lesser extent, nonlinear internal waves. These internal-wave contributions are approximately distinct in the frequency domain. It is found that in the main thermocline spicy thermohaline structure dominates the root mean square sound-speed variability, with smaller contributions coming from (in order) nonlinear internal waves, diffuse internal waves, and internal tides. The frequency spectra of internal-wave displacements and of spiciness have similar form, likely due to the advection of variable-spiciness water masses by horizontal internal-wave currents, although there are technical limitations to the observations at high frequency. In the low-frequency, internal-wave band the internal-wave spectrum follows frequency to the -1.81 power, whereas the spice spectrum shows a -1.73 power. Mode spectra estimated via covariance methods show that the diffuse internal-wave spectrum has a smaller mode bandwidth than Garrett/Munk and that the internal tide has significant energy in modes one through three. (C) 2012 Acoustical Society of America. [DOI: 10.1121/1.3666014]

Dushaw, B, Bold G, Chiu CS, Colosi J, Cornuelle B, Desaubies Y, Dzieciuch M, Forbes A, Gaillard F, Gavrilov A, Gould J, Howe BM, Lawrence M, Lynch J, Menemenlis D, Mercer J, Mikhalevsky PN, Munk W, Nakano I, Schott F, Send U, Spindel R, Terre T, Worcester P, Wunsch C.  2001.  Observing the ocean in the 2000's: A strategy for the role of acoustic tomography in ocean climate observation. Observing the Oceans in the 21st Century. ( Koblinsky C, Smith NR, Eds.).:391-418., Melbourne: Bureau of Meteorology Abstract
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Cornuelle, BD, Worcester PF, Hildebrand JA, Hodgkiss WS, Duda TF, Boyd J, Howe BM, Mercer JA, Spindel RC.  1993.  Ocean Acoustic Tomography at 1000-Km Range Using Wave-Fronts Measured with a Large-Aperture Vertical Array. Journal of Geophysical Research-Oceans. 98:16365-16377.   10.1029/93jc01246   AbstractWebsite

Broadband acoustic signals transmitted from a moored 250-Hz source to a 3-km-long vertical line array of hydrophones 1000 km distant in the north central Pacific Ocean were used to determine the amount of information available from tomographic techniques used in the vertical plane connecting a source-receiver pair. A range-independent, pure acoustic inverse to obtain the sound speed field using travel time data from the array is shown to be possible by iterating from climatological data without using any information from concurrent environmental measurements. Range-dependent inversions indicate resolution of components of oceanic variability with horizontal wavelengths shorter than 50 km, although the limited spatial resolution of concurrent direct measurements does not provide a strong cross-validation, since the typical cast spacing of 20-25 km gives a Nyquist wavelength of 40-50 km. The small travel time signals associated with high-wavenumber ocean variability place stringent but achievable requirements on travel time measurement precision. The forward problem for the high-wavenumber components of the model is found to be subject to relatively large linearization errors, however, unless the sound speed field at wavelengths greater than about 50 km is known from other measurements or from a two-dimensional tomographic array. The high-ocean-wavenumber resolution that is in principle available from tomographic measurements is therefore achievable only under restricted conditions.