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Roemmich, D, Gould WJ, Gilson J.  2012.  135 years of global ocean warming between the Challenger expedition and the Argo Programme. Nature Climate Change. 2:425-428.   10.1038/nclimate1461   AbstractWebsite

Changing temperature throughout the oceans is a key indicator of climate change. Since the 1960s about 90% of the excess heat added to the Earth's climate system has been stored in the oceans(1,2). The ocean's dominant role over the atmosphere, land, or cryosphere comes from its high heat capacity and ability to remove heat from the sea surface by currents and mixing. The longest interval over which instrumental records of subsurface global-scale temperature can be compared is the 135 years between the voyage of HMS Challenger(3) (1872-1876) and the modern data set of the Argo Programme(4) (2004-2010). Argo's unprecedented global coverage permits its comparison with any earlier measurements. This, the first global-scale comparison of Challenger and modern data, shows spatial mean warming at the surface of 0.59 degrees C +/- 0.12, consistent with previous estimates(5) of globally averaged sea surface temperature increase. Below the surface the mean warming decreases to 0.39 degrees C +/- 0.18 at 366m (200 fathoms) and 0.12 degrees C +/- 0.07 at 914 m (500 fathoms). The 0.33 degrees C +/- 0.14 average temperature difference from 0 to 700 m is twice the value observed globally in that depth range over the past 50 years(6), implying a centennial timescale for the present rate of global warming. Warming in the Atlantic Ocean is stronger than in the Pacific. Systematic errors in the Challenger data mean that these temperature changes are a lower bound on the actual values. This study underlines the scientific significance of the Challenger expedition and the modern Argo Programme and indicates that globally the oceans have been warming at least since the late-nineteenth or early-twentieth century.

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Roemmich, D, Gilson J.  2009.  The 2004-2008 mean and annual cycle of temperature, salinity, and steric height in the global ocean from the Argo Program. Progress in Oceanography. 82:81-100.   10.1016/j.pocean.2009.03.004   AbstractWebsite

The Argo Program has achieved 5 years of global coverage, growing from a very sparse global array of 1000 profiling floats in early 2004 to more than 3000 instruments from late 2007 to the present. Using nearly 350,000 temperature and salinity profiles, we constructed an upper-ocean climatology and monthly anomaly fields for the 5-year era, 2004-2008. A basic description of the modern upper ocean based entirely on Argo data is presented here, to provide a baseline for comparison with past datasets and with ongoing Argo data, to test the adequacy of Argo sampling of large-scale variability, and to examine the consistency of the Argo dataset with related ocean observations from other programs. The Argo 5-year mean is compared to the World Ocean Atlas, highlighting the middle and high latitudes of the southern hemisphere as a region of strong multi-decadal warming and freshening. Moreover the region is one where Argo data have contributed an enormous increment to historical sampling, and where more Argo floats are needed for documenting large-scale variability. Globally, the Argo-era ocean is warmer than the historical climatology at nearly all depths, by an increasing amount toward the sea surface; it is saltier in the surface layer and fresher at intermediate levels. Annual cycles in temperature and salinity are compared, again to WOA01, and to the National Oceanography Center air-sea flux climatology, the Reynolds SST product, and AVISO satellite altimetric height. These products are consistent with Argo data on hemispheric and global scales, but show regional differences that may either point to systematic errors in the datasets or their syntheses, to physical processes, or to temporal variability. The present work is viewed as an initial step toward integrating Argo and other climate-relevant global ocean datasets. (C) 2009 Elsevier Ltd. All rights reserved.

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Zhang, XB, Cornuelle B, Roemmich D.  2011.  Adjoint sensitivity of the Nino-3 surface temperature to wind forcing. Journal of Climate. 24:4480-4493.   10.1175/2011jcli3917.1   AbstractWebsite

The evolution of sea surface temperature (SST) over the eastern equatorial Pacific plays a significant role in the intense tropical air-sea interaction there and is of central importance to the El Nino-Southern Oscillation (ENSO) phenomenon. Effects of atmospheric fields (especially wind stress) and ocean state on the eastern equatorial Pacific SST variations are investigated using the Massachusetts Institute of Technology general circulation model (MITgcm) and its adjoint model, which can calculate the sensitivities of a cost function (in this case the averaged 0-30-m temperature in the Nino-3 region during an ENSO event peak) to previous atmospheric forcing fields and ocean state going backward in time. The sensitivity of the Nino-3 surface temperature to monthly zonal wind stress in preceding months can be understood by invoking mixed layer heat balance, ocean dynamics, and especially linear equatorial wave dynamics. The maximum positive sensitivity of the Nino-3 surface temperature to local wind forcing usually happens similar to 1-2 months before the peak of the ENSO event and is hypothesized to be associated with the Ekman pumping mechanism. In model experiments, its magnitude is closely related to the subsurface vertical temperature gradient, exhibiting strong event-to-event differences with strong (weak) positive sensitivity during La Nina (strong El Nino) events. The adjoint sensitivity to remote wind forcing in the central and western equatorial Pacific is consistent with the standard hypothesis that the remote wind forcing affects the Nino-3 surface temperature indirectly by exciting equatorial Kelvin and Rossby waves and modulating thermocline depth in the Nino-3 region. The current adjoint sensitivity study is consistent with a previous regression-based sensitivity study derived from perturbation experiments. Finally, implication for ENSO monitoring and prediction is also discussed.

Roemmich, D, Wunsch C.  1984.  Apparent changes in the climatic state of the deep North Atlantic Ocean. Nature. 307:447-450.   10.1038/307447a0   AbstractWebsite

Determination of any long-term changes in the large-scale characteristics of the deep ocean circulation would be an important clue in understanding the climatic interactions of the ocean and atmosphere. In the summer of 1981, the RV Atlantis II reoccupied two transatlantic sections at nominal latitudes of 24°30′ N and 36°16′ N with a conductivity–temperature-depth instrument (CTD). One purpose of the work was to make a comparison with previous surveys conducted during the International Geophysical Year (IGY)1, when sections were obtained in October 1957 and April–May 1959. We report here that significant warming occurred in an ocean-wide band from 700 m to 3,000 m with a maximum temperature difference of 0.2 °C. These changes are sufficient to expand the water column by several centimetres. The historical temperature–salinity curve was apparently unchanged. Interannual changes in local water mass characteristics have been proposed previously2,3. Perhaps it would be most surprising if no changes were seen to occur. What remains obscure is the significance of these changes and the extent to which they represent long-term climate trends, or merely the minor and random fluctuations to be expected in any complex fluid system.

Holte, J, Talley LD, Gilson J, Roemmich D.  2017.  An Argo mixed layer climatology and database. Geophysical Research Letters. 44:5618-5626.   10.1002/2017gl073426   AbstractWebsite

A global climatology and database of mixed layer properties are computed from nearly 1,250,000 Argo profiles. The climatology is calculated with both a hybrid algorithm for detecting the mixed layer depth (MLD) and a standard threshold method. The climatology provides accurate information about the depth, properties, extent, and seasonal patterns of global mixed layers. The individual profile results in the database can be used to construct time series of mixed layer properties in specific regions of interest. The climatology and database are available online at . The MLDs calculated by the hybrid algorithm are shallower and generally more accurate than those of the threshold method, particularly in regions of deep winter mixed layers; the new climatology differs the most from existing mixed layer climatologies in these regions. Examples are presented from the Labrador and Irminger Seas, the Southern Ocean, and the North Atlantic Ocean near the Gulf Stream. In these regions the threshold method tends to overestimate winter MLDs by approximately 10% compared to the algorithm.

Cai, W, Pan A, Roemmich D, Cowan T, Guo X.  2009.  Argo profiles a rare occurrence of three consecutive positive Indian Ocean Dipole events, 2006-2008. Geophysical Research Letters. 36   10.1029/2008gl037038   Abstract

During 2006-2008, the Indian Ocean (IO) experienced a rare realization of three consecutive positive IO Dipoles (pIODs), including an unusual occurrence with a La Nina in 2007. Common to all three pIODs is an early excitation of equatorial easterly anomalies. Argo profiles reveal that for the 2008 and 2006 pIODs the wind anomalies are generated by the following process: upwelling Rossby waves propagating into the western IO and their subsequent reflection as equatorial upwelling Kelvin waves enhance the seasonal upwelling, changing sea surface temperature (SST) gradients. For the 2007 pIOD, coastal upwelling Kelvin waves off the Sumatra-Java coast associated with the 2006 pIOD/El Nino, radiate into the IO as upwelling Rossby waves. They curve sharply equatorward to arrive at the central equatorial IO, inducing easterly anomalies, upwelling Kelvin waves, and the unusual pIOD. Our results suggest that real-time Argo observations, when assimilated into predictive systems, will enhance IOD forecasting skills.

Roemmich, D, Johnson GC, Riser S, Davis R, Gilson J, Owens WB, Garzoli SL, Schmid C, Ignaszewski M.  2009.  The Argo Program: Observing the global ocean with profiling floats. Oceanography. 22:34-43.   10.5670/oceanog.2009.36   AbstractWebsite

The Argo Program has created the first global array for observing the subsurface ocean. Argo arose from a compelling scientific need for climate-relevant ocean data; it was made possible by technology development and implemented through international collaboration. The float program and its data management system began with regional arrays in 1999, scaled up to global deployments by 2004, and achieved its target of 3000 active instruments in 2007. US Argo, supported by the National Oceanic and Atmospheric Administration and the Navy through the National Oceanographic Partnership Program, provides half of the floats in the international array, plus leadership in float technology, data management, data quality control, international coordination, and outreach. All Argo data are freely available without restriction, in real time and in research-quality forms. Uses of Argo data range from oceanographic research, climate research, and education, to operational applications in ocean data assimilation and seasonal-to-decadal prediction. Argo's value grows as its data accumulate and their applications are better understood. Continuing advances in profiling float and sensor technologies open many exciting possibilities for Argo's future, including expanding sampling into high latitudes and the deep ocean, improving near-surface sampling, and adding biogeochemical parameters.

Jayne, SR, Roemmich DH, Zilberman NV, Riser SC, Johnson KS, Johnson GC, Piotrowicz SR.  2017.  The Argo Program: Present and future. Oceanography. 30:18-28.   10.5670/oceanog.2017.213   Abstract

The Argo Program has revolutionized large-scale physical oceanography through its contributions to basic research, national and international climate assessment, education, and ocean state estimation and forecasting. This article discusses the present status of Argo and enhancements that are underway. Extensions of the array into seasonally ice-covered regions and marginal seas as well as increased numbers of floats along the equator and around western boundary current extensions have been proposed. In addition, conventional Argo floats, with their 2,000 m sampling limit, currently observe only the upper half of the open ocean volume. Recent advances in profiling float technology and in the accuracy and stability of float-mounted conductivity-temperature-depth sensors make it practical to obtain measurements to 6,000 m. The Deep Argo array will help observe and constrain the global budgets of heat content, freshwater, and steric sea level, as well as the full-depth ocean circulation. Finally, another extension to the Argo Program is the addition of a diverse set of chemical sensors to profiling floats in order to build a Biogeochemical-Argo array to understand the carbon cycle, the biological pump, and ocean acidification.

Roemmich, D, Owens WB.  2000.  The Argo Project: Global ocean observations for understanding and prediction of climate variability. Oceanography. 13:45-50.   10.5670/oceanog.2000.33   Abstract

Oceanography is now engaged in the ambitious enterprise of designing and installing a global ocean observing system to provide unprecedented observation of seasonal to decadal variability (OCEANOBS99, 1999). This will enable major advances in understanding and prediction of climate along with other practical applications. The in situ backbone of the global system, indeed the only element that will produce a global subsurface dataset, is the Argo array of profiling floats (Argo Science Team, 1998, 1999a, 1999b).

Roemmich, DH, The ARGO Science Team.  1999.  Argo, the global array of profiling floats. OCEANOBS99 : International Conference on the Ocean Observing System for Climate, 18 - 22 October 1999, Saint-Raphael, France. ( Centre national d'Ètudes spatiales (Ocean Observations Panel for Climate) , Ed.). Abstract
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Roemmich, D, Argo Steering T.  2009.  Argo: the challenge of continuing 10 years of progress. Oceanography. 22:46-55.   10.5670/oceanog.2009.65   AbstractWebsite

In only 10 years, the Argo Program has grown from an idea into a functioning global observing system for the subsurface ocean. More than 3000 Argo floats now cover the world ocean. With these instruments operating on 10-day cycles, the array provides 9000 temperature/salinity/depth profiles every month that are quickly available via the Global Telecommunications System and the Internet. Argo is recognized as a major advance for oceanography, and a success for Argo's parent programs, the Global Ocean Data Assimilation Experiment and Climate Variability and Predictability, and for the Global Earth Observation System of Systems. The value of Argo data in ocean data assimilation (ODA) and other applications is being demonstrated, and will grow as the data set is extended in time and as experience in using the data set leads to new applications. The spatial coverage and quality of the Argo data set are improving, with consideration being given to sampling under seasonal ice at higher latitudes, in additional marginal seas, and to greater depths. Argo data products of value in ODA modeling are under development, and Argo data are being tested to confirm their consistency with related satellite and in situ data. Maintenance of the Argo Program for the next decade and longer is needed for a broad range of climate and oceanographic research and for many operational applications in ocean state estimation and prediction.

Gasparin, F, Roemmich D, Gilson J, Cornuelle B.  2015.  Assessment of the upper-ocean observing system in the equatorial Pacific: The role of Argo in resolving intraseasonal to interannual variability*. Journal of Atmospheric and Oceanic Technology. 32:1668-1688.   10.1175/jtech-d-14-00218.1   AbstractWebsite

Using more than 10 years of Argo temperature and salinity profiles (2004-14), a new optimal interpolation (OI) of the upper ocean in the equatorial Pacific is presented. Following Roemmich and Gilson's procedures, which were formulated for describing monthly large-scale anomalies, here every 5 days anomaly fields are constructed with improvements in the OI spatial covariance function and by including the time domain. The comparison of Argo maps with independent observations, from the TAO/TRITON array, and with satellite sea surface height (SSH), demonstrates that Argo is able to represent around 70%-80% of the variance at intraseasonal time scales (periods of 20-100 days) and more than 90% of the variance for the seasonal-to-longer-term variability. The RMS difference between Argo and TAO/TRITON temperatures is lower than 1 degrees C and is around 1.5 cm when the Argo steric height is compared to SSH. This study also assesses the efficacy of different observing system components and combinations, such as SSH, TAO/TRITON, and Argo, for estimating subsurface temperature. Salinity investigations demonstrate its critical importance for density near the surface in the western Pacific. Objective error estimates from the OI are used to evaluate different sampling strategies, such as the recent deployment of 41 Argo floats along the Pacific equator. Argo's high spatial resolution compared with that of the moored array makes it better suited for studying spatial patterns of variability and propagation on intraseasonal and longer periods, but it is less well suited for studying variability on periods shorter than 20 days at point locations. This work is a step toward better utilization of existing datasets, including Argo, and toward redesigning the Tropical Pacific Observing System.

Roemmich, D, Riser S, Davis R, Desaubies Y.  2004.  Autonomous profiling floats: Workhorse for broad-scale ocean observations. Marine Technology Society Journal. 38:21-29. AbstractWebsite

The autonomous profiling float has been a revolutionary development in oceanography enabling global broad-scale ocean observations of temperature, salinity, velocity, and additional variables. The Argo gloat array applies this new technology to provide unprecedented measurements of the global upper ocean in near real time, with no period of exclusive use. It builds on its predecessors, the upper ocean thermal networks of the 1970s to 1990s- extending the spatial domain and depth range, improving the accuracy, and adding salinity and velocity. Precision satellite measurements of sea surface height, as made by the Jason-1 altimeter, combine with Argo data in a dynamically complementary description of sea level variability and its subsurface causes. The broad-scale Argo float array is a central element in the international infrastructure for ocean research. A comprehensive ocean observing system can be constructed from floats, together with satellite measurements, improved measurements of air-sea fluxes, moored time-series in the tropics and other special locations, shipboard hydrography, and high resolution measurements in fronts, eddies and boundary currents from autonomous gliders. One of the primary objectives of the observing system is to close the oceanic budgets of momentum, heat, and freshwater on seasonal and longer time-scales in order to understand the role of the ocean in the climate system.

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Roemmich, D.  1983.  The balance of geostrophic and Ekman transports in the tropical Atlantic Ocean. Journal of Physical Oceanography. 13:1534-1539.   10.1175/1520-0485(1983)013<1534:tbogae>2.0.co;2   AbstractWebsite

Hydrographic station data from 24°N, 8°N, 8°S and 24°S in the Atlantic Ocean are used to calculate geostrophic transport in eight layers separated by isopycnal surfaces. In the upper ocean, the geostrophic transport is strongly northward across 8°S and strongly southward across 8°N resulting in a geostrophic convergence of 25 × 106 m2 s−1 in water of density less than ρ = 26.8. This is equal to the magnitude of the Ekman divergence calculated from observed wind. Similarly, geostrophic divergences of surface layers between 8°N and 24°N and between 8°S and 24°S are balanced by estimated Ekman convergences in those areas. The net upper-ocean transport across each latitude, given by the sum of Ekman transport plus upper ocean geostrophic transport, is 10 × 106 m3 s−1 northward. This transport is a component of the large-scale meridional cell which carries surface water and heat northward in both hemispheres of the Atlantic, with a return flow of cold water at depth.

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Auad, G, Roemmich D, Gilson J.  2011.  The California Current System in relation to the Northeast Pacific Ocean circulation. Progress in Oceanography. 91:576-592.   10.1016/j.pocean.2011.09.004   AbstractWebsite

The California Current System is described in its regional setting using two modern datasets. Argo provides a broadscale view of the entire eastern North Pacific Ocean for the period 2004-2010, and the High Resolution XBT Network includes transects from Honolulu to San Francisco (1991-2010) and to Los Angeles (2008-2010). Together these datasets describe a California Current of 500-800 km width extending along the coast from 43 degrees N to 23 degrees N. The mean southward transport of the California Current is about 5 Sv off Central and Southern California, with about 2.5 Sv of northward flow on its inshore side. Interannual variations are 50% or more of the mean transports. The salinity minimum in the core of the California Current is supplied by the North Pacific Current and by freshwater from the northern continental shelf and modified by alongshore geostrophic and across-shore Ekman advection as well as eddy fluxes and air-sea exchange. The heat and freshwater content of the California Current vary in response to the fluctuating strength of the alongshore geostrophic flow. On its offshore side, the California Current is influenced by North Pacific Intermediate Waters at its deepest levels and by Eastern Subtropical Mode Waters on shallower density surfaces. In total, the sources of the California Current, its alongshore advection, and its strong interactions with the inshore upwelling region and the offshore gyre interior combine to make this a rich and diverse ecosystem. The present work reviews previous contributions to the regional oceanography, and uses the new datasets to paint a spatially and temporally more comprehensive description than was possible previously. Published by Elsevier Ltd.

Sprintall, J, Roemmich D.  1999.  Characterizing the structure of the surface layer in the Pacific Ocean. Journal of Geophysical Research-Oceans. 104:23297-23311.   10.1029/1999jc900179   AbstractWebsite

The structure and statistics of the oceanic surface layer are characterized using quarterly surveyed, eddy-resolving expendable bathythermograph (XBT) and expendable conductivity-temperature-depth (XCTD) data collected along a number of routes spanning the Pacific Ocean. This data set consists of more than 18,000 temperature casts to 800 mi with station spacing of 10 to 40 km along transects between Auckland and Seattle (beginning in 1986), San Francisco and Taiwan (1991), Auckland and Valparaiso (1993), and Honolulu and Valdez (1993). The surface layer can assume many different shapes. It can include strongly stratified layers, actively mixed layers. salinity barrier layers, fossil mixed layers, and inversions. The spatial and temporal distribution of these features within the XBT and XCTD profiles is examined. Fossil layers are predominantly a springtime feature and are associated with regions of Subtropical Mode Water formation in the southwest Pacific (near New Zealand) and the northeast Pacific (near San Francisco). Inversions are less seasonally dependent and most commonly related to interleaving of different water masses in the high shear regions of the California Transition Zone and its counterpart eastern boundary systems in the far northeast and southeast Pacific and in the tropical zonal current system. The XCTD casts show a rich and varied surface layer structure in the equatorial and subpolar regions of the pacific Ocean chat is strongly influenced by the salinity stratification. This highlights the need for complementary salinity and density information in these areas to accurately categorize the true nature of the active mixed layer.

Roemmich, D.  1981.  Circulation of the Caribbean Sea: A well-resolved inverse problem. Journal of Geophysical Research-Oceans and Atmospheres. 86:7993-8005.   10.1029/JC086iC09p07993   AbstractWebsite

The Caribbean Sea is selected as a region where the large-scale circulation is well determined by historical hydrographic measurements through application of the inverse method. A simple example is used to illustrate the technique and to demonstrate how some physically relevant quantities may be well determined in the formally underdetermined inverse problem. The geostrophic flow field in the Caribbean is found by imposing mass and salt conservation constraints in seven layers separated by surfaces of constant potential density. An unsmoothed solution is displayed that has weak dependence on an initial choice of reference level. In addition, a unique smoothed solution is shown. Above σθ = 27.4, the total flow leaving the western Caribbean is estimated to be 29 × 106 m3 s−1, in agreement with direct measurements. This flow is made up of 22 × 106 m3 s−1 entering the Caribbean from the east and flowing across the southern half of the basin as the Caribbean Current, and 7 × 106 m3 s−1 entering from the north through Windward Passage. Both of these currents show small-scale variability that diminishes with distance from the respective passages. The deep flow has no net transport, as required by the shallow exit, but a well organized clockwise recirculation is found in the deep eastern Caribbean.

Roemmich, D, McGowan J.  1995.  Climatic warming and the decline of zooplankton in the California Current. Science. 267:1324-1326.   10.1126/science.267.5202.1324   AbstractWebsite

Since 1951, the biomass of macrozooplankton in waters off southern California has decreased by 80 percent. During the same period, the surface layer warmed-by more than 1.5 degrees C in some places-and the temperature difference across the thermocline increased. Increased stratification resulted in less lifting of the thermocline by wind-driven upwelling. A shallower source of upwelled waters provided less inorganic nutrient for new biological production and hence supported a smaller zooplankton population. Continued warming could lead to further decline of zooplankton.

Giglio, D, Roemmich D.  2014.  Climatological monthly heat and freshwater flux estimates on a global scale from Argo. Journal of Geophysical Research-Oceans. 119:6884-6899.   10.1002/2014jc010083   AbstractWebsite

The global pattern of climatological monthly heat and freshwater fluxes at the ocean surface is estimated using Argo temperature and salinity profile data for the period 2004-2013. Temperature or salinity changes are calculated in a volume of water above an isopycnal that is below the mixed layer and not subject to mixed-layer entrainment. Horizontal advection components from geostrophic velocity and from Ekman transport, based on wind stress, are also included. The climatological monthly heat or freshwater flux at the ocean surface is estimated as the sum of advective and time tendency contributions. The air-sea flux estimates from Argo are described in global maps and basin-wide integrals, in comparison to atmospheric reanalysis data and to air-sea flux products based on observations. This ocean-based estimate of surface fluxes is consistent with property variations in the subsurface ocean and indicates greater amplitude for the climatological monthly heat flux values in the subtropics compared to other products. Similarly, the combination of Argo freshwater flux and reanalysis evaporation, suggests greater amplitude for climatological monthly precipitation in the tropics.

Roemmich, D, Gilson J, Willis J, Sutton P, Ridgway K.  2005.  Closing the time-varying mass and heat budgets for large ocean areas: The Tasman Box. Journal of Climate. 18:2330-2343.   10.1175/jcli3409.1   AbstractWebsite

The role of oceanic advection in seasonal-to-interannual balances of mass and heat is studied using a 12-yr time series of quarterly eddy-resolving expendable bathythermograph (XBT) surveys around the perimeter of a region the authors call the Tasman Box in the southwestern Pacific. The region contains the South Pacific's subtropical western boundary current system and associated strong mesoscale variability. Mean geostrophic transport in the warm upper ocean (temperature greater than 12 degrees C) is about 3.8 Sv (1 Sv equivalent to 10(6) m(3) s(-1)) southward into the box across the Brisbane, Australia-Fiji northern edge. Net outflows are 3.3 Sv eastward across the Auckland, New Zealand-Fiji edge, and 2.7 Sv southward across Sydney, Australia-Wellington, New Zealand. Mean Ekman convergence of 2.2 Sv closes the mass budget. Net water mass conversions in the upper ocean consist of inflow of waters averaging about 26 degrees C and 35.4 psu balanced by outflow at about 18 degrees C and 35.7 psu, and reflect the net evaporation and heat loss in the formation of South Pacific Subtropical Mode Water. The mean heat balance shows good agreement between ocean heat flux convergence (42.3 W m(-2)), heat loss to the atmosphere from the NCEP-NCAR reanalysis (39.2 W m(-2)), and heat storage calculated from data in the box interior (1.3 W m(-2)). On interannual time scales, volume transport through the box ranges from about I to 9 Sv, with heat flux convergence ranging from about 20 to 60 W m(-2). An interannual balance in the heat budget of the warm layer is achieved to within about 10 W m(-2) (or 6 W m(-2) for the upper 100 m alone). Maxima in the advective heat flux convergence occurred in 1993, 1,997, and 1999-2000, and corresponded to maxima in air-sea heat loss. The evolution of surface-layer temperature in the region is the residual of nearly equal and opposing effects of ocean heat flux convergence and air-sea exchange. Hence, ocean circulation is a key element in the interannual heat budget of the air-sea climate system in the western boundary current region.

Willis, JK, Roemmich D, Cornuelle B.  2003.  Combining altimetric height with broadscale profile data to estimate steric height, heat storage, subsurface temperature, and sea-surface temperature variability. Journal of Geophysical Research-Oceans. 108   10.1029/2002jc001755   AbstractWebsite

A new technique is demonstrated for combining altimetric height (AH) and sea-surface temperature (SST) with in situ data to produce improved estimates of 0/800 m steric height (SH), heat content, and temperature variability. The technique uses a linear regression onto AH to construct an initial guess for the subsurface quantity. This guess is then corrected toward the in situ data creating an estimate with substantially less error than could be achieved using either data set alone. Inclusion of the SST data further improves the estimates and illustrates how the procedure can be generalized to allow inclusion of additional data sets. The technique is demonstrated over a region in the southwestern Pacific enclosing the Tasman Sea. Nine-year time series of heat storage and temperature variability, averaged over 4degrees latitude and longitude and 1 year in time, are calculated. The estimates have RMS errors of approximately 4.6 W/m(2) in heat storage, 0.10degreesC in subsurface temperature and 0.11degreesC in surface temperature, and fractional errors of 20, 28, and 18%, respectively, relative to the total variance overall spatial and temporal scales considered. These represent significant improvements over previous estimates of these quantities. All the time series show strong interannual variability including the El Nino event of 1997. Application of these techniques on a global scale could provide new insight into the variability of the general circulation and heat budget of the upper ocean.

Chereskin, TK, Roemmich D.  1991.  A comparison of measured and wind-derived Ekman transport at 11°N in the Atlantic-Ocean. Journal of Physical Oceanography. 21:869-878.   10.1175/1520-0485(1991)021<0869:acomaw>2.0.co;2   AbstractWebsite

A comparison of measured and wind-derived ageostrophic transport is presented from a zonal transect spanning the Atlantic Ocean along 11-degrees-N. The transport per unit depth shows a striking surface maximum that decays to nearly zero at a depth of approximately 100 m. We identify this flow in the upper 100 m as the Ekman transport. The sustained values of wind stress and the penetration depth of the Ekman transport reported here are considerably greater than in previous observations, which were made in conditions of light winds. The transport of 12.0 +/- 5.5 x 10(6) m3 s-1, calculated from the difference of geostrophic shear and shear measured by an acoustic Doppler current profiler, is in good agreement with that estimated from the shipboard winds, 8.8 +/- 1.9 x 10(6) m3 s-1, and from climatology, 13.5 +/- 0.3 x 10(6) m3 s-1. Qualitatively, the horizontal distribution of the wind-driven flow was best predicted by the shipboard winds. The cumulative transport increased linearly over the western three-fourths of the basin, where the winds were large and spatially uniform, and remained constant over the eastern fourth where the easterly stress was uncharacteristically low. The mean depth of the Ekman transport extended below the mixed layer depth, which varied from 25 to 90 m. The profile of ageostrophic transport does not appear consonant with slablike behavior in the mixed layer, even when spatial variations in mixed layer depth are taken into account.

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Le Traon, PY, Larnicol G, Guinehut S, Pouliquen S, Bentamy A, Roemmich D, Donlon C, Roquet H, Jacobs G, Griffin D, Bonjean F, Hoepffner N, Breivik LA.  2009.  Data assembly and processing for operational oceanography: 10 years of achievements. Oceanography. 22:56-69.   10.5670/oceanog.2009.66   AbstractWebsite

Data assembly and processing centers are essential elements of the operational oceanography infrastructure. They provide data and products needed by modeling and data assimilation systems; they also provide products directly usable for applications. This paper discusses the role and functions of the data centers for operational oceanography. It describes some of the main data assembly centers (Argo and in situ data, altimetry, sea surface temperature) developed during the Global Ocean Data Assimilation Experiment. An overview of other data centers (wind and fluxes, ocean color, sea ice) is also given. Much progress has been achieved over the past 10 years to validate, intercalibrate, and merge altimeter data from multiple satellites. Accuracy and timeliness of products have been improved, and new products have been developed. The same is true for sea surface temperature data through the Global High-Resolution Sea Surface Temperature Pilot Project. A breakthrough in processing, quality control, and assembly for in situ data has also been achieved through the development of the real-time and delayed-mode Argo data system. In situ and remote-sensing data are now systematically and jointly used to calibrate, validate, and monitor over the long term the quality and consistency of the global ocean observing system. Main results are illustrated. There is also a review of the development and use of products that merge in situ and remote-sensing data. Future issues and main prospects are discussed in the conclusion.

Douglass, E, Roemmich D, Stammer D.  2009.  Data Sensitivity of the ECCO State Estimate in a Regional Setting. Journal of Atmospheric and Oceanic Technology. 26:2420-2443.   10.1175/2009jtecho641.1   AbstractWebsite

The Estimating the Circulation and Climate of the Ocean (ECCO) consortium provides a framework in which the adjoint method of data assimilation is applied to a general circulation model to provide a dynamically self-consistent estimate of the time-varying ocean state, which is constrained by observations. In this study, the sensitivity of the solution to the constraints provided by various datasets is investigated in a regional setting in the North Pacific. Four assimilation experiments are performed, which vary by the data used as constraints and the relative weights associated with these data. The resulting estimates are compared to two of the assimilated datasets as well as to data from two time series stations not used as constraints. These comparisons demonstrate that increasing the weights of the subsurface data provides overall improvement in the model-data consistency of the estimate of the state of the North Pacific Ocean. However, some elements of the solution are degraded. This could result from incompatibility between datasets, possibly because of hidden biases, or from errors in the model physics made more evident by the increased weight on subsurface data. The adjustments to the control parameters of surface forcing and initial conditions necessary to obtain the more accurate fit to the data are found to be within prior error bars.

Roemmich, D, Gilson J, Davis R, Sutton P, Wijffels S, Riser S.  2007.  Decadal spinup of the South Pacific subtropical gyre. Journal of Physical Oceanography. 37:162-173.   10.1175/jpo3004.1   AbstractWebsite

An increase in the circulation of the South Pacific Ocean subtropical gyre, extending from the sea surface to middepth, is observed over 12 years. Datasets used to quantify the decadal gyre spinup include satellite altimetric height, the World Ocean Circulation Experiment ( WOCE) hydrographic and float survey of the South Pacific, a repeated hydrographic transect along 170 W, and profiling float data from the global Argo array. The signal in sea surface height is a 12-cm increase between 1993 and 2004, on large spatial scale centered at about 40 S, 170 W. The subsurface datasets show that this signal is predominantly due to density variations in the water column, that is, to deepening of isopycnal surfaces, extending to depths of at least 1800 m. The maximum increase in dynamic height is collocated with the deep center of the subtropical gyre, and the signal represents an increase in the total counterclockwise geostrophic circulation of the gyre, by at least 20% at 1000 m. A comparison of WOCE and Argo float trajectories at 1000 m confirms the gyre spinup during the 1990s. The signals in sea surface height, dynamic height, and velocity all peaked around 2003 and subsequently began to decline. The 1990s increase in wind-driven circulation resulted from decadal intensification of wind stress curl east of New Zealand - variability associated with an increase in the atmosphere's Southern Hemisphere annular mode. It is suggested ( based on altimetric height) that midlatitude gyres in all of the oceans have been affected by variability in the atmospheric annular modes on decadal time scales.