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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.

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.

Moore, AM, Martini MJ, Akella S, Arango HG, Balmaseda M, Bertino L, Ciavatta S, Cornuelle B, Cummings J, Frolov S, Lermusiaux P, Oddo P, Oke PR, Storto A, Teruzzi A, Vidard A, Weaver AT, Assimilation GOVD.  2019.  Synthesis of ocean observations using data assimilation for operational, real-time and reanalysis systems: A more complete picture of the state of the ocean. Frontiers in Marine Science. 6   10.3389/fmars.2019.00090   AbstractWebsite

Ocean data assimilation is increasingly recognized as crucial for the accuracy of real-time ocean prediction systems and historical re-analyses. The current status of ocean data assimilation in support of the operational demands of analysis, forecasting and reanalysis is reviewed, focusing on methods currently adopted in operational and real-time prediction systems. Significant challenges associated with the most commonly employed approaches are identified and discussed. Overarching issues faced by ocean data assimilation are also addressed, and important future directions in response to scientific advances, evolving and forthcoming ocean observing systems and the needs of stakeholders and downstream applications are discussed.

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.

Morawitz, WML, Cornuelle BD, Worcester PF.  1996.  A case study in three-dimensional inverse methods: Combining hydrographic, acoustic, and moored thermistor data in the Greenland sea. Journal of Atmospheric and Oceanic Technology. 13:659-679.   10.1175/1520-0426(1996)013<0659:acsitd>;2   AbstractWebsite

A variety of measurements, including acoustic travel times, moored thermistor time series, and hydrographic stations, were made in the Greenland Sea during 1988-89 to study the evolution of the temperature held throughout the year. This region is of intense oceanographic interest because it is one of the few areas in the world where open-ocean convection to great depths has been observed. This paper describes how the various data types were optimally combined using linear, weighted least squares inverse methods to provide significantly more information about the ocean than can be obtained from any single data type. The application of these methods requires construction of a reference state, a statistical model of ocean temperature variability relative to the reference state, and an analysis of the differing signal-to-noise ratios of each data type. A time-dependent reference state was constructed from all available hydrographic data, reflecting !he basic seasonal variability and keeping the perturbations sufficiently small so that linear inverse methods are applicable. Smoothed estimates of the vertical and horizontal covariances of the sound speed (temperature) variability were derived separately for summer and winter from all available hydrographic and moored thermistor data. The vertical covariances were normalized before bring decomposed into eigenvectors, so that eigenvectors were optimized to fit a fixed percentage of the variance at every depth. The 12 largest redimensionalized eigenvectors compose the vertical basis of the model. A spectral decomposition of a 40-km correlation scale Gaussian covariance is used as the horizontal basis. The uncertainty estimates provided by the inverse method illustrate the characteristics of each dataset in measuring large-scale features during a diversely sampled time period in the winter of 1989. The acoustic data alone resolve about 70% of the variance in the three-dimensional, 3-day average temperature field. The hydrographic data alone resolve approximately 65% of the variance during the selected period but are much less dense or absent over most of the year. The thermistor array alone resolves from 10% to 65% of the temperature variance, doing better near the surface where the most measurements were taken. The combination of the complete 1988-89 acoustic, hydrographic, and thermistor datasets give three-dimensional temperature and heat content estimates that resolve on average about 90% of the expected variance during this particularly densely sampled time period.

Morawitz, WML, Sutton PJ, Worcester PF, Cornuelle BD, Lynch JF, Pawlowicz R.  1996.  Three-dimensional observations of a deep convective chimney in the Greenland sea during Winter 1988/89. Journal of Physical Oceanography. 26:2316-2343.   10.1175/1520-0485(1996)026<2316:tdooad>;2   AbstractWebsite

All available temperature data, including moored thermistor. hydrographic, and tomographic measurements, have been combined using least-squares inverse methods to study the evolution of the three-dimensional temperature field in the Greenland Sea during winter 1988/89. The data are adequate to resolve features with spatial scares of about 40 km and larger. A chimney structure reaching depths in excess of 1000 m is observed to the southwest of the gyre center during March 1989. The chimney has a spatial scale of about 50 km, near the limit of the spatial resolution of the data, and a timescale of about 10 days, The chimney structure breaks up and disappears in only 3-6 days. A one-dimensional vertical heat balance adequately describes changes in total heat content in the chimney region from autumn 1988 until the time of chimney breakup, when horizontal advection becomes important. A simple one-dimensional mixed layer model is surprisingly successful in reproducing autumn to winter bulk temperature and salinity changes, as well as the observed evolution of the mixed layer to depths in excess of 1000 m. Uncertainties in surface freshwater fluxes make it difficult to determine whether net evaporation minus precipitation, or ice advection, is responsible for the observed depth-averaged salinity increase from autumn to winter in the chimney region. Rough estimates of the potential energy balance In the mixed laver suggest that potential energy changes are reasonably consistent with turbulent kinetic energy (TKE) production terms. Initially the TKE term parameterizing wind forcing and shear production is important, but as the mixed layer deepens the surface buoyancy production term dominates. The estimated average annual deep-water production rate in the Greenland Sea for 1988/89 is about 0.1 Sverdrups, comparable to production rates during the 1980s and early 1990s derived from tracer measurements. The location of the deep convection observed appears to be sensitively linked to the amount of Arctic Intermediate Water (AIW) present from autumn through spring. Although AIW is an important source of salt for the surface waters, too much AIW overstratifies the water column, preventing deep convection from occurring.

Morris, M, Roemmich D, Cornuelle B.  1996.  Observations of variability in the South Pacific subtropical gyre. Journal of Physical Oceanography. 26:2359-2380.   10.1175/1520-0485(1996)026<2359:oovits>;2   AbstractWebsite

Variability of the subtropical gyre in the South Pacific Ocean was investigated using high-resolution expendable bathythermograph sections along a repeated track between New Zealand and Hawaii. The southern part of the section sampled most of the zonal flow in the subtropical gyre with the eastward flowing branch between New Zealand and Fiji and the westward branch extending north of Fiji to approximately 10 degrees S. The time series began in September 1987 and extended through 1994, averaging four cruises every year. The geostrophic shear field was calculated, relative to 800 m, with the aid of a mean T-S relationship. Variability was present at a broad range of spatial and temporal scales but annual fluctuations were particularly prominent. The authors conclude that 30 snapshots of temperature, measured over a period of seven years, are sufficient to resolve the annual cycle of the gyre scale circulation along the transect. The shape and intensity of the gyre varied seasonally throughout the water column (0-800 m). Geostrophic transport was most intense (15 Sv, where Sv=10(6)m(3)s(-1)) in November. At this time, the northern edges of eastward dow at the surface and in the thermocline were closest together and the ratio of thermocline to surface transport was highest. Most intense flow occurred approximately two to three months after the basinwide seasonal peak in Ekman pumping. Transport was weakest(ll Sv) in May and was associated with an increase in the poleward slant of the gyre center with depth and a decrease in the ratio of thermocline to surface transport. Seasonal wind forcing was considered as a possible mechanism for the observed annual intensification of the gyre-scale circulation. A simple linear model of thermocline response to local changes in wind stress curl explained a significant fraction of the observed annual variability. Conservation of potential vorticity q yielded an estimate for the absolute mean how (-1 cm s(-1) at 800 m), consistent with direct measurements in the region. Interannual variability, possibly related to the El Nino-Southern Oscillation cycle, was observed. The cold event of 1988/89 appeared to be associated with relatively weak gyre-scale transport. After 1991, gyre-scale transport was more intense and a prominent change in the small-scale circulation occurred, with a shift in the alongtrack wavenumber spectral energy to higher wavenumbers.

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.

Orsi, AJ, Cornuelle BD, Severinghaus JP.  2014.  Magnitude and temporal evolution of Dansgaard-Oeschger event 8 abrupt temperature change inferred from nitrogen and argon isotopes in GISP2 ice using a new least-squares inversion. Earth and Planetary Science Letters. 395:81-90.   10.1016/j.epsl.2014.03.030   AbstractWebsite

Polar temperature is often inferred from water isotopes in ice cores. However, non-temperature effects on 3180 are important during the abrupt events of the last glacial period, such as changes in the seasonality of precipitation, the northward movement of the storm track, and the increase in accumulation. These effects complicate the interpretation of 8180 as a temperature proxy. Here, we present an independent surface temperature reconstruction, which allows us to test the relationship between delta O-18(ice) and temperature, during Dansgaard-Oeschger event 8, 38.2 thousand yrs ago using new delta N-15 and delta Ar-40 data from the GISP2 ice core in Greenland. This temperature reconstruction relies on a new inversion of inert gas isotope data using generalized least-squares, and includes a robust uncertainty estimation. We find that both temperature and delta O-18 increased in two steps of 20 and 140 yrs, with an overall amplitude of 11.80 +/- 1.8 degrees C between the stadial and interstadial centennial-mean temperature. The coefficient alpha = d delta O-18/dT changes with each time-segment, which shows that non-temperature sources of fractionation have a significant contribution to the delta O-18 signal. When measured on century-averaged values, we find that alpha = d delta O-18/dT = 0.32 +/- 0.06%(0)/degrees C, which is similar to the glacial/Holocene value of 0.328%(o)/degrees C. (C) 2014 Elsevier B.V. All rights reserved.

Orsi, AJ, Cornuelle BD, Severinghaus JP.  2012.  Little Ice Age cold interval in West Antarctica: Evidence from borehole temperature at the West Antarctic Ice Sheet (WAIS) Divide. Geophysical Research Letters. 39   10.1029/2012gl051260   AbstractWebsite

The largest climate anomaly of the last 1000 years in the Northern Hemisphere was the Little Ice Age (LIA) from 1400-1850 C. E., but little is known about the signature of this event in the Southern Hemisphere, especially in Antarctica. We present temperature data from a 300 m borehole at the West Antarctic Ice Sheet (WAIS) Divide. Results show that WAIS Divide was colder than the last 1000-year average from 1300 to 1800 C.E. The temperature in the time period 1400-1800 C.E. was on average 0.52 +/- 0.28 degrees C colder than the last 100-year average. This amplitude is about half of that seen at Greenland Summit (GRIP). This result is consistent with the idea that the LIA was a global event, probably caused by a change in solar and volcanic forcing, and was not simply a seesaw-type redistribution of heat between the hemispheres as would be predicted by some ocean-circulation hypotheses. The difference in the magnitude of the LIA between Greenland and West Antarctica suggests that the feedbacks amplifying the radiative forcing may not operate in the same way in both regions. Citation: Orsi, A. J., B. D. Cornuelle, and J. P. Severinghaus (2012), Little Ice Age cold interval in West Antarctica: Evidence from borehole temperature at the West Antarctic Ice Sheet (WAIS) Divide, Geophys. Res. Lett., 39, L09710, doi: 10.1029/2012GL051260.

Pinkel, R, Munk W, Worcester P, Cornuelle BD, Rudnick D, Sherman J, Filloux JH, Dushaw BD, Howe BM, Sanford TB, Lee CM, Kunze E, Gregg MC, Miller JB, Merrifield MA, Luther DS, Firing E, Brainard R, Flament PJ, Chave AD, Moum JM, Caldwell DR, Levine MD, Boyd T, Egbert GD.  2000.  Ocean mixing studied near Hawaiian Ridge. Eos, Transactions American Geophysical Union. 81:545-553.   10.1029/EO081i046p00545-02   AbstractWebsite

The Hawaii Ocean Mixing Experiment (HOME) is a grassroots program to study turbulent mixing processes near the Hawaiian Ridge. The HOME is motivated by the desire to understand diffusive aspects of the advective-diffusive balance that mediates the general circulation of the oceans. HOME is focused on tidally driven mixing, given the ubiquity of the tide as a deep-sea energy source. As the sea surface cools at high latitude, surface waters sink. Subsidence rate is sufficient to fill the worlds ocean with cold bottom water in approximately 3,000 years. Diffusive processes that transfer heat into the abyssal ocean are required to maintain a steady-state thermal structure. An effective eddy diffusivity of order Kp=10−4 m2 s−1, 700 times the molecular diffusivity of heat, is necessary [Munk, 1966]. Such a diffusivity might be supported by either mechanical mixing (turbulent transport) or thermodynamic (so-called doubly diffusive) processes.

Ponte, AL, Cornuelle BD.  2013.  Coastal numerical modelling of tides: Sensitivity to domain size and remotely generated internal tide. Ocean Modelling. 62:17-26.   10.1016/j.ocemod.2012.11.007   AbstractWebsite

The propagation of remotely generated superinertial internal tides constitutes a difficulty for the modelling of regional ocean tidal variability which we illustrate in several ways. First, the M2 tidal solution inside a control region located along the Southern California Bight coastline is monitored while the extent of the numerical domain is increased (up to 512 x 512 km). While the amplitude and phase of sea level averaged over the region is quasi-insensitive to domain size, a steady increase of kinetic energy, predominantly baroclinic, is observed with increasing domain size. The increasing flux of energy into the control region suggests that this trend is explained by the growing contribution from remote generation sites of internal tide which can propagate up to the control region. Increasing viscosities confirms this interpretation by lowering baroclinic energy levels and limiting their rate of increase with domain size. Doubling the grid spacing allows consideration of numerical domains 2 times larger. While the coarse grid has lower energy levels than the finer grid, the rate of energy increase with domain size appears to be slowing for the largest domain of the coarse grid simulations. Forcing the smallest domain with depth-varying tidal boundary conditions from the simulation in the largest domain produces energy levels inside the control region comparable to those in the control region for the largest domain, thereby confirming the feasibility of a nested approach. In contrast, simulations forced with a subinertial tidal constituent (K1) show that when the propagation of internal tide is limited, the control region kinetic energy is mostly barotropic and the magnitudes of variations of the kinetic energy with domain size are reduced. (C) 2012 Elsevier Ltd. All rights reserved.

Powell, BS, Kerry CG, Cornuelle BD.  2013.  Using a numerical model to understand the connection between the ocean and acoustic travel-time measurements. Journal of the Acoustical Society of America. 134:3211-3222.   10.1121/1.4818786   AbstractWebsite

Measurements of acoustic ray travel-times in the ocean provide synoptic integrals of the ocean state between source and receiver. It is known that the ray travel-time is sensitive to variations in the ocean at the transmission time, but the sensitivity of the travel-time to spatial variations in the ocean prior to the acoustic transmission have not been quantified. This study examines the sensitivity of ray travel-time to the temporally and spatially evolving ocean state in the Philippine Sea using the adjoint of a numerical model. A one year series of five day backward integrations of the adjoint model quantify the sensitivity of travel-times to varying dynamics that can alter the travel-time of a 611 km ray by 200 ms. The early evolution of the sensitivities reveals high-mode internal waves that dissipate quickly, leaving the lowest three modes, providing a connection to variations in the internal tide generation prior to the sample time. They are also strongly sensitive to advective effects that alter density along the ray path. These sensitivities reveal how travel-time measurements are affected by both nearby and distant waters. Temporal nonlinearity of the sensitivities suggests that prior knowledge of the ocean state is necessary to exploit the travel-time observations. (C) 2013 Acoustical Society of America.

Qiu, B, Rudnick DL, Cerovecki I, Cornuelle BD, Chen S, Schonau MC, McClean JL, Gopalakrishnan G.  2015.  The Pacific North Equatorial Current: New insights from the Origins of the Kuroshio and Mindanao Currents (OKMC) Project. Oceanography. 28:24-33.   10.5670/oceanog.2015.78   AbstractWebsite

Located at the crossroads of the tropical and subtropical circulations, the westward-flowing North Equatorial Current (NEC) and its subsequent bifurcation off the Philippine coast near 13 degrees N serve as important pathways for heat and water mass exchanges between the mid- and low-latitude North Pacific Ocean. Because the western Pacific warm pool, with sea surface temperatures > 28 degrees C, extends poleward of 17 degrees N in the western North Pacific, the bifurcation and transport partitioning of the NEC into the Kuroshio and Mindanao Currents are likely to affect the temporal evolution of the warm pool through lateral advection. In addition to its influence on physical conditions, NEC variability is also important to the regional biological properties and the fisheries along the Philippine coast and in the western Pacific Ocean. This article synthesizes our current understandings of the NEC, especially those garnered through the recent Origins of the Kuroshio and Mindanao Current (OKMC) project.

Raghukumar, K, Cornuelle BD, Hodgkiss WS, Kuperman WA.  2008.  Pressure sensitivity kernels applied to time-reversal acoustics. Journal of the Acoustical Society of America. 124:98-112.   10.1121/1.2924130   AbstractWebsite

Sensitivity kernels for receptions of broadband sound transmissions are used to study the effect of the transmitted signal on the sensitivity of the reception to environmental perturbations. A first-order Born approximation is used to obtain the pressure sensitivity of the received signal to small changes in medium sound speed. The pressure perturbation to the received signal caused by medium sound speed changes is expressed as a linear combination of single-frequency sensitivity kernels weighted by the signal in the frequency domain. This formulation can be used to predict the response of a source transmission to sound speed perturbations. The stability of time-reversal is studied and compared to that of a one-way transmission using sensitivity kernels. In the absence of multipath, a reduction in pressure sensitivity using time reversal is only obtained with multiple sources. This can be attributed both to the presence of independent paths and to cancellations that occur due to the overlap of sensitivity kernels for different source-receiver paths. The sensitivity kernel is then optimized to give a new source transmission scheme that takes into account knowledge of the medium statistics and is related to the regularized inverse filter. (c) 2008 Acoustical Society of America.

Raghukumar, K, Cornuelle BD, Hodgkiss WS, Kuperman WA.  2010.  Experimental demonstration of the utility of pressure sensitivity kernels in time-reversal. Journal of the Acoustical Society of America. 128:989-1003.   10.1121/1.3466858   AbstractWebsite

Pressure sensitivity kernels were recently applied to time-reversal acoustics in an attempt to explain the enhanced stability of the time-reversal focal spot [Raghukumar et al., J. Acoust. Soc. Am. 124, 98-112 (2008)]. The theoretical framework developed was also used to derive optimized source functions, closely related to the inverse filter. The use of these optimized source functions results in an inverse filter-like focal spot which is more robust to medium sound speed fluctuations than both time-reversal and the inverse filter. In this paper the theory is applied to experimental data gathered during the Focused Acoustic Fields experiment, conducted in 2005, north of Elba Island in Italy. Sensitivity kernels are calculated using a range-independent sound-speed profile, for a geometry identical to that used in the experiment, and path sensitivities are identified with observed arrivals. The validity of the kernels in tracking time-evolving Green's functions is studied, along with limitations that result from a linearized analysis. An internal wave model is used to generate an ensemble of sound speed profiles, which are then used along with the calculated sensitivity kernels to derive optimized source functions. Focal spots obtained using the observed Green's functions with these optimized source functions are then compared to those obtained using time-reversal and the inverse-filter. It is shown that these functions are able to provide a focal spot superior to time-reversal while being more robust to sound speed fluctuations than the inverse filter or time-reversal. (C) 2010 Acoustical Society of America. [DOI: 10.1121/1.3466858]

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.

Roemmich, D, Cornuelle B.  1992.  The Subtropical Mode Waters of the South-Pacific Ocean. Journal of Physical Oceanography. 22:1178-1187.   10.1175/1520-0485(1992)022<1178:tsmwot>;2   AbstractWebsite

The subtropical mode waters (STMW) of the southwestern Pacific Ocean are described, including their physical characteristics, spatial distribution, and temporal variability. STMW is a thermostad, or minimum in stratification, having temperatures of about 15-degrees-19-degrees-C and vertical temperature gradient less than about 2-degrees-C per 100 m. Typical salinity is 35.5 psu at 16.5-degrees-C. The STMW layer is formed by deep mixing and cooling in the eastward-flowing waters of the separated East Australia Current. Surface mixed layers are observed as deep as 300 m north of New Zealand in winter, in the center of a recurring anticyclonic eddy. The STMW thermostad in the South Pacific is considerably weaker than its counterparts in the North Atlantic and North Pacific, a contrast that may help to discriminate between physical processes contributing to its formation. A quarterly time series of expendable bathythermograph transects between New Zealand and Fiji is used to study the temporal variability of STMW. Large fluctuations are observed at both annual and subannual periods. Based on the quarterly census of STMW volume, the lifetime of the thermostad is estimated to be of order 1 year. During the years 1986-91 wintertime sea surface and air temperature minima warmed by about 1.5-degrees-C. The volume of STMW decreased dramatically during that period, with the 1989-91 census showing only a small fraction of the 1986-87 STMW volume. The observed fluctuations may be due either to long-period change in air-sea heat exchange or to fluctuations in heat transport by ocean currents.

Roemmich, D, Cornuelle B.  1990.  Observing the Fluctuations of Gyre-Scale Ocean Circulation - a Study of the Subtropical South-Pacific. Journal of Physical Oceanography. 20:1919-1934.   10.1175/1520-0485(1990)020<1919:otfogs>;2   AbstractWebsite

Seasonal and interannual variability of the subtropical gyre in the South Pacific Ocean are investigated by means of a time series of expendable bathythermograph (XBT) sections between New Zealand (36-degrees-S, 175-degrees-E) and Fiji (18-degrees-S, 178-degrees-E). The experiment spans much of the subtropical gyre and is a protype for future basin-scale observations. Eddy-resolving transects along the precisely repeating ship track, spanning four years, are used to estimate the mean field and fluctuations of temperature and geostrophic velocity. The mean field dominates on very large spatial scales while the fluctuations dominate on small scales. Mean and fluctuations have equal energy at a horizontal wavelength of about 2000 km. The study region contains three recurring small-scale features. These are the East Auckland Current, flowing eastward along the New Zealand continental slope, a front at about 29-degrees-S which is likely an extension of the Tasman Front, and a weaker feature, the Tropical Convergence at about 22-degrees-S. At lower latitudes in the study region, the entire thermocline migrates vertically at annual period. This annual oscillation ends near the front at 29-degrees-S. Farther poleward, the only substantial subsurface annual variation is in the strength of the East Auckland Current. Interannual variability of circulation during 1986-90 consisted of rapid transitions between two rather steady states. In one state, which persisted through 1987-88 and from mid-1989 to the present (mid-1990), the eastward flowing limb of the gyre was relatively strong and narrow, with a reversal in velocity at the ocean surface south of Fiji.

Roemmich, D, Cornuelle B.  1987.  Digitization and Calibration of the Expendable Bathythermograph. Deep-Sea Research Part a-Oceanographic Research Papers. 34:299-307.   10.1016/0198-0149(87)90088-4   AbstractWebsite

A study was undertaken of signal digitization and temperature calibration in expendable bathythermographs (XBT's) to learn how to minimize temperature errors in that system. An XBT digitizer was built into a PC-type microcomputer and used to calibrate 24 XBT probes at 5 temperature points, and later, to calibrate 72 probes at a single temperature. Twenty of the first set of probes were fastened rigidly in pairs and dropped in the ocean as a field test of the calibrations. Calibration of individual probes reduced the standard deviation of temperature calibration errors from around 0.05°C to <0.01°C. The calibration procedure is simple and nondestructive, so the probes can be used normally after calibration. Errors in the temperature digitizer can be held to about 0.01°C by periodic adjustment. An advantage of the PC-based digitizer is the ease with which the calibrations are accomplished and applied to the ocean tracers. Two substantial sources of transient systematic error in XBT temperatures are mentioned: an electronic transient lasting about 0.1 s occurs on entry of the probe into seawater, and a longer transient is due to the thermal mass of the XBT nose.

Roemmich, D, Gilson J, Cornuelle B, Weller R.  2001.  Mean and time-varying meridional transport of heat at the tropical subtropical boundary of the North Pacific Ocean. Journal of Geophysical Research-Oceans. 106:8957-8970.   10.1029/1999jc000150   AbstractWebsite

Ocean heat transport near the tropical/subtropical boundary of the North Pacific during 1993-1999 is described, including its mean and time variability. Twenty-eight trans-Pacific high-resolution expendable bathythermograph (XBT)/expendable conductivity-temperature-depth (XCTD) transects are used together with directly measured and operational wind estimates to calculate the geostrophic and Ekman transports. The mean heat transport across the XBT transect was 0.83 +/- 0.12 pW during the 7 year period. The large number of transects enables a stable estimate of the mean field to be made, with error bars based on the known variability. The North Pacific heat engine is a shallow meridional overturning circulation that includes warm Ekman and western boundary current components flowing northward, balanced by a southward flow of cool thermocline waters (including Subtropical Mode Waters). A near-balance of geostrophic and Ekman transports holds in an interannual sense as well as for the time mean. Interannual variability in geostrophic transport is strikingly similar to the pattern of central North Pacific sea level pressure variability (the North Pacific Index). The interannual range in heat transport was more than 0.4 pW during 1993-1999, with maximum northward values about 1 pW in early 1994 and early 1997. The ocean heat transport time series is similar to that of European Centre for Medium-Range Weather Forecasts air-sea heat flux integrated over the Pacific north of the XBT line. The repeating nature of the XBT/XCTD transects, with direct wind measurements, allows a substantial improvement over previous heat transport estimates based on one-time transects. A global system is envisioned for observing the time-varying ocean heat transport and its role in the Earth's heat budget and climate system.

Roux, P, Kuperman WA, Cornuelle BD, Aulanier F, Hodgkiss WS, Song HC.  2013.  Analyzing sound speed fluctuations in shallow water from group-velocity versus phase-velocity data representation. Journal of the Acoustical Society of America. 133:1945-1952.   10.1121/1.4792354   AbstractWebsite

Data collected over more than eight consecutive hours between two source-receiver arrays in a shallow water environment are analyzed through the physics of the waveguide invariant. In particular, the use of vertical arrays on both the source and receiver sides provides source and receiver angles in addition to travel-times associated with a set of eigenray paths in the waveguide. From the travel-times and the source-receiver angles, the eigenrays are projected into a group-velocity versus phase-velocity (Vg-Vp) plot for each acquisition. The time evolution of the Vg-Vp representation over the 8.5-h long experiment is discussed. Group speed fluctuations observed for a set of eigenrays with turning points at different depths in the water column are compared to the Brunt-Vaisala frequency. (C) 2013 Acoustical Society of America.

Roux, P, Cornuelle BD, Kuperman WA, Hodgkiss WS.  2008.  The structure of raylike arrivals in a shallow-water waveguide. Journal of the Acoustical Society of America. 124:3430-3439.   10.1121/1.2996330   AbstractWebsite

Acoustic remote sensing of the oceans requires a detailed understanding of the acoustic forward problem. The results of a shallow-water transmission experiment between a vertical array of sources and a vertical array of receivers are reported. The source array is used to provide additional degrees of freedom to isolate and track raylike arrivals by beamforming over both source and receiver arrays. The coordinated source-receiver array processing procedure is presented and its effectiveness in an example of tracking raylike arrivals in a fluctuating ocean environment is shown. Many of these arrivals can be tracked over an hour or more and show slowly varying amplitude and phase. The use of a double-beamforming algorithm lays the foundation for shallow-water acoustic remote sensing using travel time and source and receive angles of selected eigenrays. (C) 2008 Acoustical Society of America. [DOI: 10.1121/1.2996330]

Rudnick, DL, Gopalakrishnan G, Cornuelle BD.  2015.  Cyclonic eddies in the Gulf of Mexico: Observations by underwater gliders and simulations by numerical model. Journal of Physical Oceanography. 45:313-326.   10.1175/jpo-d-14-0138.1   AbstractWebsite

Circulation in the Gulf of Mexico (GoM) is dominated by the Loop Current (LC) and by Loop Current eddies (LCEs) that form at irregular multimonth intervals by separation from the LC. Comparatively small cyclonic eddies (CEs) are thought to have a controlling influence on the LCE, including its separation from the LC. Because the CEs are so dynamic and short-lived, lasting only a few weeks, they have proved a challenge to observe. This study addresses that challenge using underwater gliders. These gliders' data and satellite sea surface height (SSH) are used in a four-dimensional variational (4DVAR) assimilation in the Massachusetts Institute of Technology (MIT) general circulation model (MITgcm). The model serves two purposes: first, the model's estimate of ocean state allows the analysis of four-dimensional fields, and second, the model forecasts are examined to determine the value of glider data. CEs have a Rossby number of about 0.2, implying that the effects of flow curvature, cyclostrophy, to modify the geostrophic momentum balance are slight. The velocity field in CEs is nearly depth independent, while LCEs are more baroclinic, consistent with the CEs origin on the less stratified, dense side of the LCE. CEs are formed from water in the GoM, rather than the Atlantic water that distinguishes the LCE. Model forecasts are improved by glider data, using a quality metric based on satellite SSH, with the best 2-month GoM forecast rivaling the accuracy of a global hindcast.

Sabra, KG, Cornuelle B, Kuperman WA.  2016.  Sensing deep-ocean temperatures. Physics Today. 69:32-38. AbstractWebsite

Though not yet widely implemented, the technique of monitoring the ocean's warming via changes in the speed of sound through the water is a powerful complement to the more common tools available: free-floating thermometers and altimetry satellites.