Harley Hurlburt | Naval Research Lab (original) (raw)

Papers by Harley Hurlburt

Research paper thumbnail of Anomalous tropical ocean circulation associated with La Niña Modoki

ABSTRACT El Niño Modoki is a variant of El Niño characterized by warming around the dateline flan... more ABSTRACT El Niño Modoki is a variant of El Niño characterized by warming around the dateline flanked by anomalous cooling in the east and west. However, the opposite phase (La Niña Modoki) has received little attention because the prominent cooling of sea surface temperature (SST) during major La Niña events is observed in the central Pacific, and thus, it is difficult to define the two different types of cold events from the SST anomaly pattern. Here we demonstrate that cold events in 2000 and 2008 can be clearly distinguished from traditional La Niña events using surface currents derived from satellite observations. During 2000 and 2008, anomalous zonal currents in the equatorial Pacific demonstrate divergence, with westward currents west of the dateline and eastward currents east of it. These currents are opposite to the circulation pattern during the 2004 El Niño Modoki event. An empirical orthogonal function (EOF) analysis of surface currents for the period 1993-2009 shows a circulation anomaly pattern similar to that in 2000, 2004, and 2008 in the second EOF. The first EOF is consistent with traditional El Niño/La Niña events and does not exhibit a current reversal along the equator. Our results also indicate that strong cyclonic (anticyclonic) circulation anomalies occur in the tropical western Pacific around 5°N-15°N during the 2004 (2000 and 2008) El Niño (La Niña) Modoki events and during the strong traditional El Niño (La Niña) events of 1997 (1998). These circulation anomalies are related to an SST gradient in the western and central Pacific.

Research paper thumbnail of Multistatistics metric evaluation of ocean general circulation model sea surface temperature: Application to 0.08° Pacific Hybrid Coordinate Ocean Model simulations

Journal of Geophysical Research, 2008

The public reporting burden for this collection of information is estimated to average 1 hour per... more The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden, to the Department of Defense, Executive Services and Communications Directorate (0704-01881. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.

Research paper thumbnail of An optimal definition for ocean mixed layer depth

Journal of Geophysical Research, 2000

A new method is introduced for determining ocean isothermal layer depth (ILD) from temperature pr... more A new method is introduced for determining ocean isothermal layer depth (ILD) from temperature profiles and ocean mixed layer depth (MLD) from density profiles that can be applied in all regions of the world's oceans. This method can accommodate not only in situ data but also climatological data sets that typically have much lower vertical resolution. The sensitivity of the ILD and MLD to the temperature difference criteria used in the surface layer depth definition is discussed by using temperature and density data, respectively: (1) from 11 ocean weather stations in the northeast Pacific and (2) from the World Ocean Atlas 199•. Using these two data sets, a detailed statistical error analysis is presented for the ILD and MLD estimation by season. MLD variations with location due to temperature and salinity are properly accounted for in the defining density (Aat) criterion. Overall, the optimal estimate of turbulent mixing penetration is obtained using a MLD definition of AT=0.8øC, although in the northeast Pacific region the optimal MLD criterion is found to vary seasonally. The method is shown to produce layer depths that are accurate to within 20 m or better in 85% or more of the cases.

Research paper thumbnail of Mixed layer depth variability and barrier layer formation over the North Pacific Ocean

Journal of Geophysical Research, 2000

Seasonal variability in the isothermal and isopycnal surface mixed layers of the North Pacific Oc... more Seasonal variability in the isothermal and isopycnal surface mixed layers of the North Pacific Ocean is examined using the Naval Research Laboratory Ocean Mixed Layer Depth (NMLD) Climatology. A comparison with observations from 11 ocean weather stations in the northeast Pacific Ocean is performed that validates the NMLD climatology in this region. The general features of the isothermal layer depth (ILD) and mixed layer depth (MLD) obtained from these mixed layers are explained with wind stress, surface net heat flux, and freshwater flux climatologies, given guidance from a mixed layer model. Departures from a surface-forced interpretation of turbulent mixing are found near the Kuroshio, where horizontal heat transport is important. The much deeper ILD in the northeast Pacific in winter and spring relative to the MLD reveals a 50 m "barrier layer" between the bottom of the MLD and the top of the thermocline. A detailed analysis shows this barrier layer extends over most of the North Pacific subpolar gyre. It forms when the seasonal thermocline is deepened in winter by surface cooling, such that salinity stratification due to evaporation minus precipitation less than zero (E-P • 0) becomes important in the formation of the MLD. A shallower halocline forms over the subpolar gyre than in other regions of the North Pacific because of precipitation dominating over evaporation in the annual mean. A mechanism for maintaining the shallow halocline is provided by upward vertical motion driven by positive wind stress curl in the presence of diapycnal mixing. Numerical models show this as part of a shallow meridional overturning cell. stratification play a role? 16,783 16,784 KARA ET AL.: N. PACIFIC MLD VARIABILITY AND BL FORMATION Studies of the equatorial Pacific have revealed that surface freshwater fluxes (i.e., heavy rainfall with the effect of horizontal advection) and strong wind bursts are responsible for the formation of the equatorial barrier layer [Ando and McPhaden, 1997; Vialard and Delecluse, 1998; Godfrey and Lindstrom, 1989]. As described by Anderson et al. [1996], this barrier layer formation occurs because strong wind bursts deepen the surface mixed layer to the top of the thermocline and precipitation and surface heating increase the surface buoyancy, forming a relatively warm and fresh thin surface mixed layer. Are similar or different processes responsible for the North Pacific barrier layer at midlatitudes? Direct surface ventilation of the upper layers of the North Pacific is known to be quite shallow because of the relatively low density of the surface waters in winter and the presence of saline deep waters [e.g., Yuan and Talley, 1992]. Tsuchiya [1982] showed that the shallow salinity minima of the North Pacific can be related to the subduction (possibly when ILD < MLD) of surface waters. The formation of the North Pacific barrier layer can be answered by understanding the reasons for the seasonal variability in the ILD and MLD. Henceforth we shall use LD to denote ILD and MLD whenever the latter can be commonly referred to in the given context. A basin-scale study has been done on the seasonal changes in surface LD for the Pacific Ocean [Bathen, 1972], using an ILD definition applied to a monthly mean climatology constructed from observations. In that study the depth of mixing is defined using a temperature definition with a prescribed temperature gradient of 0.02 øC m -• because at the time the salinity observations needed were much less common for large regions of the world's oceans. With the present availability of higher-resolution global ocean climatologies for temperature [Levitus et al., 1994], salinity [Levitus and Boyer, 1994], wind stress, heat flux, and freshwater flux [e.g., da Silva et al., 1994], not only is investigating seasonal variability of isothermal and isopycnal mixed layers possible, but so is interpreting them in terms of surface-forced turbulent mixing [Price et al., 1986; Gordon and Corry, 1991], which can provide insight into the physical processes that are responsible for the formation of the winter barrier layer in the North Pacific. Given the known sensitivity of the LD to the criteria used to define them [Kava et al., this issue], be it a property gradient definition or a property change definition, appropriate care must be taken to apply an optimal definition. The major circulation systems in the North Pacific [e.g., Talley, 1993; Hurlbutt et al., 1996; $hriver and Hurlbutt, 1997] are found to influence the seasonal variability in LD in certain regions of the basin [Qiu and Joyce, 1995]. The surface circulation in the Pacific consists of the cyclonic subpolar gyve in the north, the anticyclonic North Pacific subtropical gyve, and the north Equatorial Counter current near the equator [e.g., Tal-ley, 1993]. Roden [1979] explained that a correlation exists between the positions of the North Pacific Current and the MLD variations. Monterey and Levitus [1997] noted a few small regions in the North Pacific where ILD is shallower than MLD, occurring inside the subtropical gyres during March and April. Differential radiative heating can sharpen or weaken existing temperature fronts in the North Pacific because radiative heat fluxes are effective in changing the temperature of the upper layer and in altering the hydrostatic stability [e.g., Roden, 1980; Dinniman and Rienecker, 1999]. Horizontal heat transport by advection and diffusion can alter local heat balances in the North Pacific [Gent, 1991; Qiu and Kelly, 1993], which in turn, diminish or enhance the KARA ET AL.: N. PACIFIC MLD VARIABILITY AND BL FORMATION 16,785 16,788 KARA ET AL.: N. PACIFIC MLD VARIABILITY AND BL FORMATION At midlatitudes, mean depths of more than 250 m occur for hoe(T) in the 40ø-55øN latitude band, while hoe(ert) reaches maximum depths of 175-225 m in the western mid-Pacific east of Japan. The deep winter structure

Research paper thumbnail of The contribution of the global thermohaline circulation to the Pacific to Indian Ocean Throughflow via Indonesia

Journal of Geophysical Research, 1997

World ocean simulations are used to investigate the pathways feeding the Indonesian throughflow a... more World ocean simulations are used to investigate the pathways feeding the Indonesian throughflow as a function of depth, including the role of the global thermohaline ("conveyor belt") circulation. The simulations use a horizontal resolution of 1/2 ø for each variable and the vertical resolution ranges from 1.5-layer reduced gravity to six layers with realistic bottom topography. They are forced by the Hellerman and monthly wind stress climatology. Contrary to the classical theory of Stommel and Arons [1960], the Naval Research Laboratory model shows the Antarctic Circumpolar Current (ACC) region as the main region of abyssal to upper ocean water upwelling which compensates for the deep water formation in the far North Atlantic, a result corroborated by recent observational evidence [Toggweiler and Samuels, 1993]. We examine the contribution of the global conveyor belt circulation to the throughflow by systematically varying the model dynamics (e.g., by disabling the far North Atlantic ports which parameterize deep water formation in that region). The model simulations show a global conveyor belt circulation contribution of 5.7 Sv to the throughflow, a contribution provided mainly by wind-driven upwelling in the Indo-Pacific ACC region. This is due to a cooperative interaction between the thermohaline and wind-driven circulations. The thermohaline circulation makes the throughflow more surface trapped and less subject to topographic blocking in the Indonesian passageways, while the wind-driven circulation provides the Indonesian throughflow pathway for the thermohaline flow upwelled in the ACC region. Mean layer transport fields, cross-layer mass transfer fields, and Lagrangian tracers are used to identify pathways feeding the Pacific to Indian Ocean throughflow via Indonesia. Starting from the ACC, Sverdrup flow shows a circuitous route that is northward in the eastern South Pacific, then westward in the South Equatorial Current (SEC). The SEC retroflects into the North Equatorial Countercurrent (NECC) followed by cyclonic flow around the Northern Tropical Gyre and into the North Equatorial Current (NEC), then into the Mindanao Current, the Sulawesi Sea, the Makassar Strait, and the Indian Ocean. The depth-integrated pathways from nonlinear simulations show the retroflection from the SEC into the NECC as a secondary route and retroflection into the Equatorial Undercurrent (EUC) as the primary route. The EUC connects with the NECC by westward and then northward flow on the northside of the EUC. The pathways as a function of depth can be presented in three layers: a surface layer, the layer containing the EUC, and layers below the EUC.

Research paper thumbnail of Comparison of Autonomous Lagrangian Circulation Explorer and fine resolution Antarctic model results in the South Atlantic

Journal of Geophysical Research, 1996

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Research paper thumbnail of An examination of the North Pacific Ocean in the spectral domain using Geosat altimeter data and a numerical ocean model

Journal of Geophysical Research, 1996

Research paper thumbnail of Dynamics of the Kuroshio/Oyashio current system using eddy-resolving models of the North Pacific Ocean

Journal of Geophysical Research, 1996

A set of numerical simulations is used to investigate the Pacific Ocean circulation north of 20øS... more A set of numerical simulations is used to investigate the Pacific Ocean circulation north of 20øS, with emphasis on the Kuroshio/Oyashio current system. The primitive equation models used for these simulations have a free surface and realistic geometry that includes the deep marginal seas such as the Sea of Japan. Most of the simulations have 1/8 ø resolution for each variable but range from 1/2 ø, 1.5-layer reduced gravity to 1/16 ø , six layer with realistic bottom topography. These are used to investigate the dynamics of the Kuroshio/Oyashio current system and to identify the processes that contribute most to the realism of the simulations. This is done by model-data comparisons, by using the modularity of layered ocean models to include/exclude certain dynamical processes, by varying the model geometry and bottom topography, and by varying model parameters such as horizontal grid resolution, layer structure, and eddy viscosity. In comparison with observational data the simulations show that the barotropic mode, at least one internal mode, nonlinearity, high "horizontal" resolution (1/8 ø or finer), the regional bottom topography, and the wind forcing are critical for realistic simulations. The first four are important for baroclinic instability (eddy-mean energetics actually show mixed barotropic-baroclinic instability), the wind curl pattern for the formation and basic placement of the current system, and the bottom topography for the distribution of the instability and for influences on the pathways of the mean flow. Both the Hellerman and Rosenstein (1983) (HR) monthly wind stress climatology and 1000-mbar winds from the European Centre for Medium-Range Weather Forecasts (ECMWF) have been used to drive the model. East of about 150øE, they give a mean latitude for the Kuroshio Extension that differs by about 3 ø, approximately 34øN for HR, 37øN for ECMWF, and 35øN observed. The subarctic front is the northern boundary of the subtropical gyre. It is associated with the annual and April-September mean zero wind stress curl lines (which are similar), while the Kuroshio Extension is associated with wintertime zero wind stress curl. This means that part of the flow from the Kuroshio must pass north of the Kuroshio Extension and connect with the Oyashio and subarctic front. Realistic routes for this connection are flow through the Sea of Japan, a nonlinear route separated from the east coast of Japan, and bifurcation of the Kuroshio at the Shatsky Rise. In addition, the sixlayer simulations show a 3-Sv meridional overturning cell with southward surface flow and northward return flow centered near 400 m depth. Baroclinic instability plays a critical role in coupling the shallow and abyssal layer circulations and in allowing the bottom topography to strongly influence the shallow circulation. By this means the Izu Ridge and Trench and seamounts upstream and downstream of these have profound influence on (1) the mean path of the Kuroshio and its mean meanders south and east of Japan and (2) on separating the northward flow connecting the Kuroshio and the Oyashio/subarctic front from the east coast of Japan. Without the topographic influence the models show an unrealistic northward current along the east coast of Japan. In essence, the topography regulates the location and strength of the baroclinic instability. The baroclinic instability gives eddy-driven deep mean flows that follow the f/h contours (where f is the Coriolis parameter and h is the depth of the water column) of the bottom topography. These abyssal currents then strongly influence the pathway for subtropical gyre flow north of the Kuroshio Extension and steer the mean meanders in the Kuroshio south and east of Japan. This is corroborated by current meter data from the Kuroshio Extension Regional Experiment (World Ocean Circulation Experiment line PCM 7). The meander path south Paper number 95JC01674. 0148-0227/96/95 J C-01674 $05.00 941 942 HURLBURT ET AL.' DYNAMICS OF THE KUROSHIO/OYASHIO CURRENT SYSTEM of Japan depends on the occurrence of baroclinic instability west of the Izu Ridge; otherwise, a straight path occurs. The pathway shows little sensitivity to the Tokara Strait transport over the range simulated (36-72 Sv in yearly means). However, interannual increases in wind forcing or Tokara Strait transport give rise to a predominant meander path, while decreases yield a predominant straight path. Resolution of 1/8 ø in an ocean model is comparable to the 2.5 ø resolution used in atmospheric forecast models in the early 1980s based on the first internal mode Rossby radius of deformation. Model comparisons at 1/8 ø and 1/16 ø resolution and comparisons with current meter data and Geosat altimeter data show that 1/16 ø resolution is needed for adequate eastward penetration of the high eddy kinetic energy associated with the Kuroshio Extension. 1. Introduction The dynamics of the Kuroshio/Oyashio current system are investigated by using several variations of an eddy-resolving numerical ocean model covering the Pacific Ocean north of 20øS and by model-data comparisons. The horizontal grid resolution of the principal simulations is 1/8 ø for each variable (1/8 ø in latitude by 45/256 ø in longitude), and the vertical structure ranges from 1.5-layer reduced gravity to six layers with realistic bottom topography. In addition, it was possible to extend one of the 1/8 ø simulations at 1/16 ø resolution and two different eddy viscosities. Simulations at 1/4 ø resolution and comparisons of 1/8 ø and 1/16 ø subtropical gyre simulations are also used. The subtropical gyre model treats that gyre in isolation by incorporating solid boundaries at 15øN, 48øN, 121øE, and 140øW. The basic model has a free surface, and all versions of the Pacific model include the deep marginal seas such as the Bering Sea, the Sea of Okhotsk, the Sea of Japan, the South China Sea, the Sulu Sea, and the Indonesian archipelago. The subtropical gyre model includes the Sea of Japan. These seas can play a significant role in the main basin dynamics. The Sea of Japan plays a role in the Kuroshio/Oyashio dynamics, which is discussed in the paper. The modularity of layered ocean models can be used to include or exclude certain features or dynamical processes. For example, a 1.5-layer reduced gravity model can allow barotropic instability but excludes baroclinic instability. This approach and comparisons with observations form the paradigm used to identify the essential model features and dynamical processes for realistic simulations. Section 2 covers the model design, and in section 3, simulations of the basic upper ocean features of the equatorial and North Pacific are discussed. Kuroshio/Oyashio current system dynamics are discussed in section 4. Topics include (1) the development of the basic current system including the roles of the wind curl, nonlinearity, bottom topography, and the Sea of Japan; (2) the essential model features and dynamics required for realistic simulation of the Kuroshio Extension; (3) how the Kuroshio feeds part of its transport north of the Kuroshio Extension and into the Oyashio/subarctic frontal region; and (4) the combined effects of baroclinic instability and bottom topography on the meandering of the Kuroshio/Kuroshio Extension mean path and in generating local maxima in variability. The dynamics of the meander path versus straight path for the Kuroshio south of Japan has been a topic of considerable debate (e.g., see Yoon and Yasuda [1987], who include a substantial review of the earlier literature, and Yamagata and Umatani [1989]). Section 5 discusses the eastward penetration of the Kuroshio Extension including model-data comparisons from the surface to 4000 m depth and the effects of model resolution (1/8 ø versus 1/16ø). Previous investigations of this topic for the Kuroshio and/or the Gulf Stream include those by Schmitz and Holland [1982, 1986], Holland and Schmitz [1985], Thompson and Schmitz [1989], Hogan et al. [1992], Marshall and Marshall [1992], and Schmitz and Thompson [1993]. Section 6 contains the summary and conclusions. Hurlburt et al. [1992] discuss an initial 1/8 ø six-layer Pacific simulation with realistic bottom topography. Hogan et al. [1992] include model-Geosat comparisons for a 1/8 ø two-layer version of the model. Jacobs et al. [this issue] and Mitchell et al. [this issue] investigate additional aspects of the dynamics and provide extensive comparisons between Geosat altimeter measurements and more recent simulations by improved versions of the 1/8 ø six-layer Pacific model run 1981-1993. These simulations are also used in model-data comparisons in section 5. 2. The Model The model is a primitive equation layered formulation where the model equations have been vertically integrated through each layer. It is a descendent of the semi-implicit free-surface model of Hurlburt and Thompson [1980] but with expanded capability [Wallcraft, 1991]. The equations for the n layer finite depth, hydrodynamic model are for layers k = looon OVa Ot --+ (V. Va + Va' V)va + fcx fVa = -ha E Gt,V(hl-Hi) + max (0, to0va+, /=1

Research paper thumbnail of Kuroshio Extension dynamics from satellite altimetry and a model simulation

Journal of Geophysical Research, 1996

Altimeter data from the Geosat Exact Repeat Mission (ERM) are analyzed with the aid of a simulati... more Altimeter data from the Geosat Exact Repeat Mission (ERM) are analyzed with the aid of a simulation from an eddy-resolving primitive equation model of the North Pacific basin in the region of the Kuroshio and Kuroshio Extension. The model domain covers the Pacific Ocean north of 20øS and has a resolution of 0.125 ø latitude and 0.176 ø longitude. The model is synoptically driven by daily 1000-mbar winds from the European Centre for Medium-Range Weather Forecasts (ECMWF) which encompass the Geosat time period. Model output is sampled along Geosat ground tracks for the period of the ERM. Additionally, the model and the Geosat data are compared with climatological hydrography and satellite IR frontal position analyses. Analyses compared include maps of sea surface height (SSH) mean and variability, eddy kinetic energy (EKE), seasonal transport anomaly, and time-longitude plots of SSH anomaly. The model simulation provides annual mean SSH fields for 1987 and 1988 which reproduce the four quasipermanent meanders seen in hydrographic climatology (cyclonic at 138øE and anticyclonic at 144øE, 150øE, and 160øE). These are linked to the bottom topography. In the model simulation, Geosat altimeter data, and climatology, we observe four peaks in SSH variability associated with meander activity and two peaks in EKE, with the strongest about 3200 cm 2 s -2 along the mean Kuroshio path in the Geosat data. The local maxima in SSH variability tend to occur where relatively strong, topographically steered meridional abyssal currents intersect the zonally oriented Kuroshio Extension. Westward propagation of SSH anomalies at phase speeds of 2 to 3 cm s -• in the region east of 155øE is observed in the model simulation and Geosat observations. A late summer maximum in the upper ocean transport anomaly of the Kuroshio Extension is inferred from changes in the crossstream differential in SSH from the simulation and Geosat observations.

Research paper thumbnail of Coupled dynamics of the South China Sea, the Sulu Sea, and the Pacific Ocean

Journal of Geophysical Research, 1996

The complex geometry, the seasonally reversing monsoon winds, and the connectivity with the Pacif... more The complex geometry, the seasonally reversing monsoon winds, and the connectivity with the Pacific Ocean all contribute to the coupled dynamics of the circulation in the South China Sea (SCS), the Sulu Sea, and the region around the Philippine Islands. The 1/2 ø, 1.5-layer global reduced gravity thermodynamic Navy layered ocean model (NLOM) is used to separate these components and to investigate the role of each one. When forced by the Hellerman and Rosenstein [1983] (Hit) monthly wind stress climatology, the basic features of the model solution compare well with observations, and with higher-resolution NLOM versions. The dynamics of the flow from the Pacific Ocean into the SCS via the Luzon Strait are emphasized. The effects of Ekman suction/pumping due to wind curl are examined by forming monthly spatial averages of the winds over the SCS/Sulu Sea basins. This maintains a monthly varying stress but with a region of zero curl. Forcing the model with these modified winds leaves the mean Luzon Strait transport unchanged, and the variability actually increases slightly. These results suggest that it is the pressure head created by the pileup of water from the monsoonal wind stress that controls the variability of the Luzon Strait transport. The forcing for wind stress pileup effects could be either internal or external to the SCS/Sulu Sea basin. The effects of internal forcing are studied by applying monthly winds within this basin but annual Hit winds outside the region. With this forcing the mean Luzon Strait transport is essentially unchanged, but the variability is only 44% of the standard case value. The external forcing is deftned as zero stress in the SCS/Sulu Sea basins and Hit monthly winds outside. Again, the mean Luzon Strait transport is unchanged, and here the variability is 60% of the standard case. The mean Luzon Strait transport is largely a function of the model geometry. When the Sulu archipelago is opened, a net cyclonic flow develops around the Philippines, which is essentially an extension of the northern tropical gyre. The bifurcation latitude of the North Equatorial Current (NEC) at the Philippine coast is also affected by the amount of transport through the Sulu archipelago. Opening this archipelago causes the NEC split point to move southward and increases the transport of the Kuroshio east of Luzon while decreasing the Mindanao Current. Opening or closing the Sunda Shelf/Java Sea or the Sulu archipelago does not affect the transport of the Pacific to Indian Ocean throughflow. South China Sea (SCS) via the wide and deep Luzon Strait. To the south, the waters are joined via the Sulu, Java, Sulawesi, Molucca, and Halmahera Seas as well as the interior passages of the Philippine Islands (Figure la). The seasonally reversing monsoon winds also play Copyright 1996 by the American Geophysical Union. Paper number 95JC03861. 0148-0227/96/95JC-03861 $09.00 an important role in determining the upper ocean circulation. This combination of geometry, connectivity with the Pacific Ocean, and strongly variable atmospheric forcing contributes to the complex dynamics of the flow around the Philippine Islands and Indonesia. Numerical ocean models can be important tools in helping to separate these dynamics, but only a few studies exist that are capable of adequately resolving the Indo-Pacific region. Among those which strive for a realistic representation of the geometry are by Hurlburr et al. [1989] and Masumoto and Yamagata [1991], who have focused on the current systems in the equatorial Pacific Ocean east of the Philippines. Metztier et al. [1991, 1992, 1994] have also looked at this region and compared upper layer currents and sea level 12,331 12,332 METZGER AND HURLBURT: SOUTH CHINA SEA-PACIFIC OCEAN COUPLING 25N 20N 15N 10N 5N

Research paper thumbnail of Bifurcation of the Kuroshio Extension at the Shatsky Rise

Journal of Geophysical Research, 1998

A 1/16 ø six-layer Pacific Ocean model north of 20øS is used to investigate the bifurcation of th... more A 1/16 ø six-layer Pacific Ocean model north of 20øS is used to investigate the bifurcation of the Kuroshio Extension at the main Shatsky Rise and the pathway of the northern branch from the bifurcation to the subarctic front. Upper ocean-topographic coupling via a mixed barotropic-baroclinic instability is essential to this bifurcation and to the formation and mean pathway of the northern branch as are several aspects of the Shatsky Rise complex of topography and the latitude of the Kuroshio Extension in relation to the topography. The flow instabilities transfer energy to the abyssal layer where it is constrained by geostrophic contours of the bottom topography. The topographically constrained abyssal currents in turn steer upper ocean currents, which do not directly impinge on the bottom topography. This includes steering of mean pathways. Obtaining sufficient coupling requires very fine resolution of mesoscale variability and sufficient eastward penetration of the Kuroshio as an unstable inertial jet. Resolution of 1/8 ø for each variable was not sufficient in this case. The latitudinal extent of the main Shatsky Rise (31øN-36øN) and the shape of the downward slope on the north side are crucial to the bifurcation at the main Shatsky Rise, with both branches passing north of the peak. The well-defined, relatively steep and straight eastern edge of the Shatsky Rise topographic complex (30øN-42øN) and the southwestward abyssal flow along it play a critical role in forming the rest of the Kuroshio northern branch which flows in the opposite direction. A deep pass between the main Shatsky Rise and the rest of the ridge to the northeast helps to link the northern fork of the bifurcation at the main rise to the rest of the northern branch. Two 1/16 ø "identical twin" interannual simulations forced by daily winds 1981-1995 show that the variability in this region is mostly nondeterministic on all timescales that could be examined (up to 7 years in these 15-year simulations). A comparison of climatologically forced and interannual simulations over the region 150øE -180øE, 29øN-47øN showed greatly enhanced abyssal and upper ocean eddy kinetic energy and much stronger mean abyssal currents east of the Emperor Seamount Chain (about 170øE) in the interannual simulations but little difference west of 170øE. This greatly enhanced the upper ocean-topographic coupling in the interannual simulations east of 170øE. This coupling affected the latitudinal positioning of the eastward

Research paper thumbnail of Mixed layer depth variability over the global ocean

Journal of Geophysical Research, 2003

The spatial and monthly variability of the climatological mixed layer depth (MLD) for the global ... more The spatial and monthly variability of the climatological mixed layer depth (MLD) for the global ocean is examined using the recently developed Naval Research Laboratory (NRL) Ocean Mixed Layer Depth (NMLD) climatologies. The MLD fields are constructed using the subsurface temperature and salinity data from the World Ocean Atlas 1994 [Levitus et al., 1994; Levitus and Boyer, 1994]. To minimize the limitations of these global data in the MLD determination, a simple mixing scheme is introduced to form a stable water column. Using these new data sets, global MLD characteristics are produced on the basis of an optimal definition that employs a density-based criterion having a fixed temperature difference of DeltaT = 0.8°C and variable salinity. Strong seasonality of MLD is found in the subtropical Pacific Ocean and at high latitudes, as well as a very deep mixed layer in the North Atlantic Ocean in winter and a very shallow mixed layer in the Antarctic in all months. Using the climatological monthly MLD and isothermal layer depth (ILD) fields from the NMLD climatologies, an annual mean DeltaT field is presented, providing criteria for determining an ILD that is approximately equivalent to the optimal MLD. This enables MLD to be determined in cases where salinity data are not available. The validity of the correspondence between ILD and MLD is demonstrated using daily averaged subsurface temperature and salinity from two moorings: a Tropical Atmosphere Ocean array mooring in the western equatorial Pacific warm pool, where salinity stratification is important, and a Woods Hole Oceanographic Institute (WHOI) mooring in the Arabian Sea, where strongly reversing seasonal monsoon winds prevail. In the western equatorial Pacific warm pool the use of ILD criterion with an annual mean DeltaT value of 0.3°C yields comparable results with the optimal MLD, while large DeltaT values yield an overestimated MLD. An analysis of ILD and MLD in the WHOI mooring show that use of an incorrect DeltaT criterion for the ILD may underestimate or overestimate the optimal MLD. Finally, use of the spatial annual mean DeltaT values constructed from the NMLD climatologies can be used to estimate the optimal MLD from only subsurface temperature data via an equivalent ILD for any location over the global ocean.

Research paper thumbnail of Wind Stress Drag Coefficient over the Global Ocean*

Journal of Climate, 2007

... Oceanography Division, Naval Research Laboratory, Stennis Space Center, Mississippi.Chris W. ... more ... Oceanography Division, Naval Research Laboratory, Stennis Space Center, Mississippi.Chris W. Fairall Physical ... AB Kara, CN Barron. (2008) Comment on “Seasonal heat budgets of the Red and Black seas” by Matsoukas et al.. Journal ...

Research paper thumbnail of How Does Solar Attenuation Depth Affect the Ocean Mixed Layer? Water Turbidity and Atmospheric Forcing Impacts on the Simulation of Seasonal Mixed Layer Variability in the Turbid Black Sea*

Journal of Climate, 2005

A fine-resolution (ഠ3.2 km) Hybrid Coordinate Ocean Model (HYCOM) is used to investigate the impa... more A fine-resolution (ഠ3.2 km) Hybrid Coordinate Ocean Model (HYCOM) is used to investigate the impact of solar radiation attenuation with depth on the predictions of monthly mean sea surface height (SSH), mixed layer depth (MLD), buoyancy and heat fluxes, and near-sea surface circulation as well. The model uses spatially and temporally varying attenuation of photosynthetically available radiation (k PAR ) climatologies as processed from the remotely sensed Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) to take water turbidity into account in the Black Sea. An examination of the k PAR climatology reveals a strong seasonal cycle in the water turbidity, with a basin-averaged annual climatological mean value of 0.19 m Ϫ1 over the Black Sea. Climatologically forced HYCOM simulations demonstrate that shortwave radiation below the mixed layer can be quite different based on the water turbidity, thereby affecting prediction of upper-ocean quantities in the Black Sea. The clear water constant solar attenuation depth assumption results in relatively deeper MLD (e.g., ഠϩ15 m in winter) in comparison to standard simulations due to the unrealistically large amount of shortwave radiation below the mixed layer, up to 100 W m Ϫ2 during April to October. Such unrealistic sub-mixed layer heating causes weaker stratification at the base of the mixed layer. The buoyancy gain associated with high solar heating in summer effectively stabilizes the upper ocean producing shallow mixed layers and elevated SSH over the most of the Black Sea. In particular, the increased stability resulting from the water turbidity reduces vertical mixing in the upper ocean and causes changes in surface-layer currents, especially in the easternmost part of the Black Sea. Monthly mean SSH anomalies from the climatologically forced HYCOM simulations were evaluated against a monthly mean SSH anomaly climatology, which was constructed using satellite altimeter data from TOPEX/ Poseidon (T/P), Geosat Follow-On (GFO), and the Earth Remote Sensing Satellite-2 (ERS-2) over 1993-2002. Model-data comparisons show that the basin-averaged root-mean-square (rms) difference is ഠ4 cm between the satellite-based SSH climatology and that obtained from HYCOM simulations using spatial and temporal k PAR fields. In contrast, when all solar radiation is absorbed at the sea surface or clear water constant solar attenuation depth values of 16.7 m are used in the model simulations, the basin-averaged SSH rms difference with respect to the climatology is ഠ6 cm (ഠ50% more). This demonstrates positive impact from using monthly varying solar attenuation depths in simulating upper-ocean quantities in the Black Sea. The monthly mean k PAR and SSH anomaly climatologies presented in this paper can also be used for other Black Sea studies.

Research paper thumbnail of Black Sea Mixed Layer Sensitivity to Various Wind and Thermal Forcing Products on Climatological Time Scales*

Journal of Climate, 2005

This study describes atmospheric forcing parameters constructed from different global climatologi... more This study describes atmospheric forcing parameters constructed from different global climatologies, applied to the Black Sea, and investigates the sensitivity of Hybrid Coordinate Ocean Model (HYCOM) simulations to these products. Significant discussion is devoted to construction of these parameters before using them in the eddy-resolving (Ϸ3.2-km resolution) HYCOM simulations. The main goal is to answer how the model dynamics can be substantially affected by different atmospheric forcing products in the Black Sea. Eight wind forcing products are used: four obtained from observation-based climatologies, including one based on measurements from the SeaWinds scatterometer on the Quick Scatterometer (QuikSCAT) satellite, and the rest formed from operational model products. Thermal forcing parameters, including solar radiation, are formed from two operational models: the European Centre for Medium-Range Weather Forecasts (ECMWF) and the Fleet Numerical Meteorology and Oceanography Center (FNMOC) Navy Operational Global Atmospheric Prediction System (NOGAPS). Climatologically forced Black Sea HYCOM simulations (without ocean data assimilation) are then performed to assess the accuracy and sensitivity of the model sea surface temperature (SST) and sea surface circulation to these wind and thermal forcing products. Results demonstrate that the model-simulated SST structure is quite sensitive to the wind and thermal forcing products, especially near coastal regions. Despite this sensitivity, several robust features are found in the model SST in comparison to a monthly 9.3-km-resolution satellite-based Pathfinder SST climatology. Annual mean HYCOM SST usually agreed to within ϷϮ0.2°of the climatology in the interior of the Black Sea for any of the wind and thermal forcing products used. The fineresolution (0.25°ϫ 0.25°) wind forcing from the scatterometer data along with thermal forcing from NOGAPS gave the best SST simulation with a basin-averaged rms difference value of 1.21°C, especially improving model results near coastal regions. Specifically, atmospherically forced model simulations with no assimilation of any ocean data suggest that the basin-averaged rms SST differences with respect to the Pathfinder SST climatology can vary from 1.21°to 2.15°C depending on the wind and thermal forcing product. The latter rms SST difference value is obtained when using wind forcing from the National Centers for Environmental Prediction (NCEP), a product that has a too-coarse grid resolution of 1.875°ϫ 1.875°f or a small ocean basin such as the Black Sea. This paper also highlights the importance of using highfrequency (hybrid) wind forcing as opposed to monthly mean wind forcing in the model simulations. Finally, there are large variations in the annual mean surface circulation simulated using the different wind sets, with general agreement between those forced by the model-based products (vector correlation is usually Ͼ0.7). Three of the observation-based climatologies generally yield unrealistic circulation features and currents that are too weak.

Research paper thumbnail of Sea Surface Height Predictions from the Global Navy Coastal Ocean Model during 1998–2001*

Journal of Atmospheric and Oceanic Technology, 2004

... Received: September 9, 2003; Accepted: June 19, 2004. Corresponding author address: Charlie N... more ... Received: September 9, 2003; Accepted: June 19, 2004. Corresponding author address: Charlie N. Barron, Naval Research Laboratory, Code 7323, Bldg. ... Fox, DN, WJ Teague, CN Barron, MR Carnes, and CM Lee, 2002b: The Modular Ocean Data Analysis System (MODAS). ...

Research paper thumbnail of Climatological SST and MLD Predictions from a Global Layered Ocean Model with an Embedded Mixed Layer*

Journal of Atmospheric and Oceanic Technology, 2003

Research paper thumbnail of Efficient and Accurate Bulk Parameterizations of Air–Sea Fluxes for Use in General Circulation Models

Journal of Atmospheric and Oceanic Technology, 2000

... using the gas law. Note the mixing ratio values for air (q a at T a ) and sea (q s at T s ) a... more ... using the gas law. Note the mixing ratio values for air (q a at T a ) and sea (q s at T s ) are calculated using a simplified version of the original formulation for saturated vapor pressure (e s ) presented by Buck (1981). Similar to the ...

Research paper thumbnail of Stability-Dependent Exchange Coefficients for Air–Sea Fluxes*

Journal of Atmospheric and Oceanic Technology, 2005

... A. Birol Kara, Harley E. Hurlburt, and Alan J. Wallcraft ... 1998; Hare et al. 1999) into acc... more ... A. Birol Kara, Harley E. Hurlburt, and Alan J. Wallcraft ... 1998; Hare et al. 1999) into account, which suggests that a Charnock constant value of 0.011 (Smith 1988), used in the earlier COARE v2.5b algorithm, is too low for higher wind speeds. ...

Research paper thumbnail of The NRL Layered Global Ocean Model (NLOM) with an Embedded Mixed Layer Submodel: Formulation and Tuning

Journal of Atmospheric and Oceanic Technology, 2003

Abstract A bulk-type (modified Kraus-Turner) mixed layer model that is embedded within the Naval ... more Abstract A bulk-type (modified Kraus-Turner) mixed layer model that is embedded within the Naval Research Laboratory (NRL) Layered Ocean Model (NLOM) is introduced. It is an independent submodel loosely coupled to NLOM's dynamical core, requiring only near-...

Research paper thumbnail of Anomalous tropical ocean circulation associated with La Niña Modoki

ABSTRACT El Niño Modoki is a variant of El Niño characterized by warming around the dateline flan... more ABSTRACT El Niño Modoki is a variant of El Niño characterized by warming around the dateline flanked by anomalous cooling in the east and west. However, the opposite phase (La Niña Modoki) has received little attention because the prominent cooling of sea surface temperature (SST) during major La Niña events is observed in the central Pacific, and thus, it is difficult to define the two different types of cold events from the SST anomaly pattern. Here we demonstrate that cold events in 2000 and 2008 can be clearly distinguished from traditional La Niña events using surface currents derived from satellite observations. During 2000 and 2008, anomalous zonal currents in the equatorial Pacific demonstrate divergence, with westward currents west of the dateline and eastward currents east of it. These currents are opposite to the circulation pattern during the 2004 El Niño Modoki event. An empirical orthogonal function (EOF) analysis of surface currents for the period 1993-2009 shows a circulation anomaly pattern similar to that in 2000, 2004, and 2008 in the second EOF. The first EOF is consistent with traditional El Niño/La Niña events and does not exhibit a current reversal along the equator. Our results also indicate that strong cyclonic (anticyclonic) circulation anomalies occur in the tropical western Pacific around 5°N-15°N during the 2004 (2000 and 2008) El Niño (La Niña) Modoki events and during the strong traditional El Niño (La Niña) events of 1997 (1998). These circulation anomalies are related to an SST gradient in the western and central Pacific.

Research paper thumbnail of Multistatistics metric evaluation of ocean general circulation model sea surface temperature: Application to 0.08° Pacific Hybrid Coordinate Ocean Model simulations

Journal of Geophysical Research, 2008

The public reporting burden for this collection of information is estimated to average 1 hour per... more The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden, to the Department of Defense, Executive Services and Communications Directorate (0704-01881. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.

Research paper thumbnail of An optimal definition for ocean mixed layer depth

Journal of Geophysical Research, 2000

A new method is introduced for determining ocean isothermal layer depth (ILD) from temperature pr... more A new method is introduced for determining ocean isothermal layer depth (ILD) from temperature profiles and ocean mixed layer depth (MLD) from density profiles that can be applied in all regions of the world's oceans. This method can accommodate not only in situ data but also climatological data sets that typically have much lower vertical resolution. The sensitivity of the ILD and MLD to the temperature difference criteria used in the surface layer depth definition is discussed by using temperature and density data, respectively: (1) from 11 ocean weather stations in the northeast Pacific and (2) from the World Ocean Atlas 199•. Using these two data sets, a detailed statistical error analysis is presented for the ILD and MLD estimation by season. MLD variations with location due to temperature and salinity are properly accounted for in the defining density (Aat) criterion. Overall, the optimal estimate of turbulent mixing penetration is obtained using a MLD definition of AT=0.8øC, although in the northeast Pacific region the optimal MLD criterion is found to vary seasonally. The method is shown to produce layer depths that are accurate to within 20 m or better in 85% or more of the cases.

Research paper thumbnail of Mixed layer depth variability and barrier layer formation over the North Pacific Ocean

Journal of Geophysical Research, 2000

Seasonal variability in the isothermal and isopycnal surface mixed layers of the North Pacific Oc... more Seasonal variability in the isothermal and isopycnal surface mixed layers of the North Pacific Ocean is examined using the Naval Research Laboratory Ocean Mixed Layer Depth (NMLD) Climatology. A comparison with observations from 11 ocean weather stations in the northeast Pacific Ocean is performed that validates the NMLD climatology in this region. The general features of the isothermal layer depth (ILD) and mixed layer depth (MLD) obtained from these mixed layers are explained with wind stress, surface net heat flux, and freshwater flux climatologies, given guidance from a mixed layer model. Departures from a surface-forced interpretation of turbulent mixing are found near the Kuroshio, where horizontal heat transport is important. The much deeper ILD in the northeast Pacific in winter and spring relative to the MLD reveals a 50 m "barrier layer" between the bottom of the MLD and the top of the thermocline. A detailed analysis shows this barrier layer extends over most of the North Pacific subpolar gyre. It forms when the seasonal thermocline is deepened in winter by surface cooling, such that salinity stratification due to evaporation minus precipitation less than zero (E-P • 0) becomes important in the formation of the MLD. A shallower halocline forms over the subpolar gyre than in other regions of the North Pacific because of precipitation dominating over evaporation in the annual mean. A mechanism for maintaining the shallow halocline is provided by upward vertical motion driven by positive wind stress curl in the presence of diapycnal mixing. Numerical models show this as part of a shallow meridional overturning cell. stratification play a role? 16,783 16,784 KARA ET AL.: N. PACIFIC MLD VARIABILITY AND BL FORMATION Studies of the equatorial Pacific have revealed that surface freshwater fluxes (i.e., heavy rainfall with the effect of horizontal advection) and strong wind bursts are responsible for the formation of the equatorial barrier layer [Ando and McPhaden, 1997; Vialard and Delecluse, 1998; Godfrey and Lindstrom, 1989]. As described by Anderson et al. [1996], this barrier layer formation occurs because strong wind bursts deepen the surface mixed layer to the top of the thermocline and precipitation and surface heating increase the surface buoyancy, forming a relatively warm and fresh thin surface mixed layer. Are similar or different processes responsible for the North Pacific barrier layer at midlatitudes? Direct surface ventilation of the upper layers of the North Pacific is known to be quite shallow because of the relatively low density of the surface waters in winter and the presence of saline deep waters [e.g., Yuan and Talley, 1992]. Tsuchiya [1982] showed that the shallow salinity minima of the North Pacific can be related to the subduction (possibly when ILD < MLD) of surface waters. The formation of the North Pacific barrier layer can be answered by understanding the reasons for the seasonal variability in the ILD and MLD. Henceforth we shall use LD to denote ILD and MLD whenever the latter can be commonly referred to in the given context. A basin-scale study has been done on the seasonal changes in surface LD for the Pacific Ocean [Bathen, 1972], using an ILD definition applied to a monthly mean climatology constructed from observations. In that study the depth of mixing is defined using a temperature definition with a prescribed temperature gradient of 0.02 øC m -• because at the time the salinity observations needed were much less common for large regions of the world's oceans. With the present availability of higher-resolution global ocean climatologies for temperature [Levitus et al., 1994], salinity [Levitus and Boyer, 1994], wind stress, heat flux, and freshwater flux [e.g., da Silva et al., 1994], not only is investigating seasonal variability of isothermal and isopycnal mixed layers possible, but so is interpreting them in terms of surface-forced turbulent mixing [Price et al., 1986; Gordon and Corry, 1991], which can provide insight into the physical processes that are responsible for the formation of the winter barrier layer in the North Pacific. Given the known sensitivity of the LD to the criteria used to define them [Kava et al., this issue], be it a property gradient definition or a property change definition, appropriate care must be taken to apply an optimal definition. The major circulation systems in the North Pacific [e.g., Talley, 1993; Hurlbutt et al., 1996; $hriver and Hurlbutt, 1997] are found to influence the seasonal variability in LD in certain regions of the basin [Qiu and Joyce, 1995]. The surface circulation in the Pacific consists of the cyclonic subpolar gyve in the north, the anticyclonic North Pacific subtropical gyve, and the north Equatorial Counter current near the equator [e.g., Tal-ley, 1993]. Roden [1979] explained that a correlation exists between the positions of the North Pacific Current and the MLD variations. Monterey and Levitus [1997] noted a few small regions in the North Pacific where ILD is shallower than MLD, occurring inside the subtropical gyres during March and April. Differential radiative heating can sharpen or weaken existing temperature fronts in the North Pacific because radiative heat fluxes are effective in changing the temperature of the upper layer and in altering the hydrostatic stability [e.g., Roden, 1980; Dinniman and Rienecker, 1999]. Horizontal heat transport by advection and diffusion can alter local heat balances in the North Pacific [Gent, 1991; Qiu and Kelly, 1993], which in turn, diminish or enhance the KARA ET AL.: N. PACIFIC MLD VARIABILITY AND BL FORMATION 16,785 16,788 KARA ET AL.: N. PACIFIC MLD VARIABILITY AND BL FORMATION At midlatitudes, mean depths of more than 250 m occur for hoe(T) in the 40ø-55øN latitude band, while hoe(ert) reaches maximum depths of 175-225 m in the western mid-Pacific east of Japan. The deep winter structure

Research paper thumbnail of The contribution of the global thermohaline circulation to the Pacific to Indian Ocean Throughflow via Indonesia

Journal of Geophysical Research, 1997

World ocean simulations are used to investigate the pathways feeding the Indonesian throughflow a... more World ocean simulations are used to investigate the pathways feeding the Indonesian throughflow as a function of depth, including the role of the global thermohaline ("conveyor belt") circulation. The simulations use a horizontal resolution of 1/2 ø for each variable and the vertical resolution ranges from 1.5-layer reduced gravity to six layers with realistic bottom topography. They are forced by the Hellerman and monthly wind stress climatology. Contrary to the classical theory of Stommel and Arons [1960], the Naval Research Laboratory model shows the Antarctic Circumpolar Current (ACC) region as the main region of abyssal to upper ocean water upwelling which compensates for the deep water formation in the far North Atlantic, a result corroborated by recent observational evidence [Toggweiler and Samuels, 1993]. We examine the contribution of the global conveyor belt circulation to the throughflow by systematically varying the model dynamics (e.g., by disabling the far North Atlantic ports which parameterize deep water formation in that region). The model simulations show a global conveyor belt circulation contribution of 5.7 Sv to the throughflow, a contribution provided mainly by wind-driven upwelling in the Indo-Pacific ACC region. This is due to a cooperative interaction between the thermohaline and wind-driven circulations. The thermohaline circulation makes the throughflow more surface trapped and less subject to topographic blocking in the Indonesian passageways, while the wind-driven circulation provides the Indonesian throughflow pathway for the thermohaline flow upwelled in the ACC region. Mean layer transport fields, cross-layer mass transfer fields, and Lagrangian tracers are used to identify pathways feeding the Pacific to Indian Ocean throughflow via Indonesia. Starting from the ACC, Sverdrup flow shows a circuitous route that is northward in the eastern South Pacific, then westward in the South Equatorial Current (SEC). The SEC retroflects into the North Equatorial Countercurrent (NECC) followed by cyclonic flow around the Northern Tropical Gyre and into the North Equatorial Current (NEC), then into the Mindanao Current, the Sulawesi Sea, the Makassar Strait, and the Indian Ocean. The depth-integrated pathways from nonlinear simulations show the retroflection from the SEC into the NECC as a secondary route and retroflection into the Equatorial Undercurrent (EUC) as the primary route. The EUC connects with the NECC by westward and then northward flow on the northside of the EUC. The pathways as a function of depth can be presented in three layers: a surface layer, the layer containing the EUC, and layers below the EUC.

Research paper thumbnail of Comparison of Autonomous Lagrangian Circulation Explorer and fine resolution Antarctic model results in the South Atlantic

Journal of Geophysical Research, 1996

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Research paper thumbnail of An examination of the North Pacific Ocean in the spectral domain using Geosat altimeter data and a numerical ocean model

Journal of Geophysical Research, 1996

Research paper thumbnail of Dynamics of the Kuroshio/Oyashio current system using eddy-resolving models of the North Pacific Ocean

Journal of Geophysical Research, 1996

A set of numerical simulations is used to investigate the Pacific Ocean circulation north of 20øS... more A set of numerical simulations is used to investigate the Pacific Ocean circulation north of 20øS, with emphasis on the Kuroshio/Oyashio current system. The primitive equation models used for these simulations have a free surface and realistic geometry that includes the deep marginal seas such as the Sea of Japan. Most of the simulations have 1/8 ø resolution for each variable but range from 1/2 ø, 1.5-layer reduced gravity to 1/16 ø , six layer with realistic bottom topography. These are used to investigate the dynamics of the Kuroshio/Oyashio current system and to identify the processes that contribute most to the realism of the simulations. This is done by model-data comparisons, by using the modularity of layered ocean models to include/exclude certain dynamical processes, by varying the model geometry and bottom topography, and by varying model parameters such as horizontal grid resolution, layer structure, and eddy viscosity. In comparison with observational data the simulations show that the barotropic mode, at least one internal mode, nonlinearity, high "horizontal" resolution (1/8 ø or finer), the regional bottom topography, and the wind forcing are critical for realistic simulations. The first four are important for baroclinic instability (eddy-mean energetics actually show mixed barotropic-baroclinic instability), the wind curl pattern for the formation and basic placement of the current system, and the bottom topography for the distribution of the instability and for influences on the pathways of the mean flow. Both the Hellerman and Rosenstein (1983) (HR) monthly wind stress climatology and 1000-mbar winds from the European Centre for Medium-Range Weather Forecasts (ECMWF) have been used to drive the model. East of about 150øE, they give a mean latitude for the Kuroshio Extension that differs by about 3 ø, approximately 34øN for HR, 37øN for ECMWF, and 35øN observed. The subarctic front is the northern boundary of the subtropical gyre. It is associated with the annual and April-September mean zero wind stress curl lines (which are similar), while the Kuroshio Extension is associated with wintertime zero wind stress curl. This means that part of the flow from the Kuroshio must pass north of the Kuroshio Extension and connect with the Oyashio and subarctic front. Realistic routes for this connection are flow through the Sea of Japan, a nonlinear route separated from the east coast of Japan, and bifurcation of the Kuroshio at the Shatsky Rise. In addition, the sixlayer simulations show a 3-Sv meridional overturning cell with southward surface flow and northward return flow centered near 400 m depth. Baroclinic instability plays a critical role in coupling the shallow and abyssal layer circulations and in allowing the bottom topography to strongly influence the shallow circulation. By this means the Izu Ridge and Trench and seamounts upstream and downstream of these have profound influence on (1) the mean path of the Kuroshio and its mean meanders south and east of Japan and (2) on separating the northward flow connecting the Kuroshio and the Oyashio/subarctic front from the east coast of Japan. Without the topographic influence the models show an unrealistic northward current along the east coast of Japan. In essence, the topography regulates the location and strength of the baroclinic instability. The baroclinic instability gives eddy-driven deep mean flows that follow the f/h contours (where f is the Coriolis parameter and h is the depth of the water column) of the bottom topography. These abyssal currents then strongly influence the pathway for subtropical gyre flow north of the Kuroshio Extension and steer the mean meanders in the Kuroshio south and east of Japan. This is corroborated by current meter data from the Kuroshio Extension Regional Experiment (World Ocean Circulation Experiment line PCM 7). The meander path south Paper number 95JC01674. 0148-0227/96/95 J C-01674 $05.00 941 942 HURLBURT ET AL.' DYNAMICS OF THE KUROSHIO/OYASHIO CURRENT SYSTEM of Japan depends on the occurrence of baroclinic instability west of the Izu Ridge; otherwise, a straight path occurs. The pathway shows little sensitivity to the Tokara Strait transport over the range simulated (36-72 Sv in yearly means). However, interannual increases in wind forcing or Tokara Strait transport give rise to a predominant meander path, while decreases yield a predominant straight path. Resolution of 1/8 ø in an ocean model is comparable to the 2.5 ø resolution used in atmospheric forecast models in the early 1980s based on the first internal mode Rossby radius of deformation. Model comparisons at 1/8 ø and 1/16 ø resolution and comparisons with current meter data and Geosat altimeter data show that 1/16 ø resolution is needed for adequate eastward penetration of the high eddy kinetic energy associated with the Kuroshio Extension. 1. Introduction The dynamics of the Kuroshio/Oyashio current system are investigated by using several variations of an eddy-resolving numerical ocean model covering the Pacific Ocean north of 20øS and by model-data comparisons. The horizontal grid resolution of the principal simulations is 1/8 ø for each variable (1/8 ø in latitude by 45/256 ø in longitude), and the vertical structure ranges from 1.5-layer reduced gravity to six layers with realistic bottom topography. In addition, it was possible to extend one of the 1/8 ø simulations at 1/16 ø resolution and two different eddy viscosities. Simulations at 1/4 ø resolution and comparisons of 1/8 ø and 1/16 ø subtropical gyre simulations are also used. The subtropical gyre model treats that gyre in isolation by incorporating solid boundaries at 15øN, 48øN, 121øE, and 140øW. The basic model has a free surface, and all versions of the Pacific model include the deep marginal seas such as the Bering Sea, the Sea of Okhotsk, the Sea of Japan, the South China Sea, the Sulu Sea, and the Indonesian archipelago. The subtropical gyre model includes the Sea of Japan. These seas can play a significant role in the main basin dynamics. The Sea of Japan plays a role in the Kuroshio/Oyashio dynamics, which is discussed in the paper. The modularity of layered ocean models can be used to include or exclude certain features or dynamical processes. For example, a 1.5-layer reduced gravity model can allow barotropic instability but excludes baroclinic instability. This approach and comparisons with observations form the paradigm used to identify the essential model features and dynamical processes for realistic simulations. Section 2 covers the model design, and in section 3, simulations of the basic upper ocean features of the equatorial and North Pacific are discussed. Kuroshio/Oyashio current system dynamics are discussed in section 4. Topics include (1) the development of the basic current system including the roles of the wind curl, nonlinearity, bottom topography, and the Sea of Japan; (2) the essential model features and dynamics required for realistic simulation of the Kuroshio Extension; (3) how the Kuroshio feeds part of its transport north of the Kuroshio Extension and into the Oyashio/subarctic frontal region; and (4) the combined effects of baroclinic instability and bottom topography on the meandering of the Kuroshio/Kuroshio Extension mean path and in generating local maxima in variability. The dynamics of the meander path versus straight path for the Kuroshio south of Japan has been a topic of considerable debate (e.g., see Yoon and Yasuda [1987], who include a substantial review of the earlier literature, and Yamagata and Umatani [1989]). Section 5 discusses the eastward penetration of the Kuroshio Extension including model-data comparisons from the surface to 4000 m depth and the effects of model resolution (1/8 ø versus 1/16ø). Previous investigations of this topic for the Kuroshio and/or the Gulf Stream include those by Schmitz and Holland [1982, 1986], Holland and Schmitz [1985], Thompson and Schmitz [1989], Hogan et al. [1992], Marshall and Marshall [1992], and Schmitz and Thompson [1993]. Section 6 contains the summary and conclusions. Hurlburt et al. [1992] discuss an initial 1/8 ø six-layer Pacific simulation with realistic bottom topography. Hogan et al. [1992] include model-Geosat comparisons for a 1/8 ø two-layer version of the model. Jacobs et al. [this issue] and Mitchell et al. [this issue] investigate additional aspects of the dynamics and provide extensive comparisons between Geosat altimeter measurements and more recent simulations by improved versions of the 1/8 ø six-layer Pacific model run 1981-1993. These simulations are also used in model-data comparisons in section 5. 2. The Model The model is a primitive equation layered formulation where the model equations have been vertically integrated through each layer. It is a descendent of the semi-implicit free-surface model of Hurlburt and Thompson [1980] but with expanded capability [Wallcraft, 1991]. The equations for the n layer finite depth, hydrodynamic model are for layers k = looon OVa Ot --+ (V. Va + Va' V)va + fcx fVa = -ha E Gt,V(hl-Hi) + max (0, to0va+, /=1

Research paper thumbnail of Kuroshio Extension dynamics from satellite altimetry and a model simulation

Journal of Geophysical Research, 1996

Altimeter data from the Geosat Exact Repeat Mission (ERM) are analyzed with the aid of a simulati... more Altimeter data from the Geosat Exact Repeat Mission (ERM) are analyzed with the aid of a simulation from an eddy-resolving primitive equation model of the North Pacific basin in the region of the Kuroshio and Kuroshio Extension. The model domain covers the Pacific Ocean north of 20øS and has a resolution of 0.125 ø latitude and 0.176 ø longitude. The model is synoptically driven by daily 1000-mbar winds from the European Centre for Medium-Range Weather Forecasts (ECMWF) which encompass the Geosat time period. Model output is sampled along Geosat ground tracks for the period of the ERM. Additionally, the model and the Geosat data are compared with climatological hydrography and satellite IR frontal position analyses. Analyses compared include maps of sea surface height (SSH) mean and variability, eddy kinetic energy (EKE), seasonal transport anomaly, and time-longitude plots of SSH anomaly. The model simulation provides annual mean SSH fields for 1987 and 1988 which reproduce the four quasipermanent meanders seen in hydrographic climatology (cyclonic at 138øE and anticyclonic at 144øE, 150øE, and 160øE). These are linked to the bottom topography. In the model simulation, Geosat altimeter data, and climatology, we observe four peaks in SSH variability associated with meander activity and two peaks in EKE, with the strongest about 3200 cm 2 s -2 along the mean Kuroshio path in the Geosat data. The local maxima in SSH variability tend to occur where relatively strong, topographically steered meridional abyssal currents intersect the zonally oriented Kuroshio Extension. Westward propagation of SSH anomalies at phase speeds of 2 to 3 cm s -• in the region east of 155øE is observed in the model simulation and Geosat observations. A late summer maximum in the upper ocean transport anomaly of the Kuroshio Extension is inferred from changes in the crossstream differential in SSH from the simulation and Geosat observations.

Research paper thumbnail of Coupled dynamics of the South China Sea, the Sulu Sea, and the Pacific Ocean

Journal of Geophysical Research, 1996

The complex geometry, the seasonally reversing monsoon winds, and the connectivity with the Pacif... more The complex geometry, the seasonally reversing monsoon winds, and the connectivity with the Pacific Ocean all contribute to the coupled dynamics of the circulation in the South China Sea (SCS), the Sulu Sea, and the region around the Philippine Islands. The 1/2 ø, 1.5-layer global reduced gravity thermodynamic Navy layered ocean model (NLOM) is used to separate these components and to investigate the role of each one. When forced by the Hellerman and Rosenstein [1983] (Hit) monthly wind stress climatology, the basic features of the model solution compare well with observations, and with higher-resolution NLOM versions. The dynamics of the flow from the Pacific Ocean into the SCS via the Luzon Strait are emphasized. The effects of Ekman suction/pumping due to wind curl are examined by forming monthly spatial averages of the winds over the SCS/Sulu Sea basins. This maintains a monthly varying stress but with a region of zero curl. Forcing the model with these modified winds leaves the mean Luzon Strait transport unchanged, and the variability actually increases slightly. These results suggest that it is the pressure head created by the pileup of water from the monsoonal wind stress that controls the variability of the Luzon Strait transport. The forcing for wind stress pileup effects could be either internal or external to the SCS/Sulu Sea basin. The effects of internal forcing are studied by applying monthly winds within this basin but annual Hit winds outside the region. With this forcing the mean Luzon Strait transport is essentially unchanged, but the variability is only 44% of the standard case value. The external forcing is deftned as zero stress in the SCS/Sulu Sea basins and Hit monthly winds outside. Again, the mean Luzon Strait transport is unchanged, and here the variability is 60% of the standard case. The mean Luzon Strait transport is largely a function of the model geometry. When the Sulu archipelago is opened, a net cyclonic flow develops around the Philippines, which is essentially an extension of the northern tropical gyre. The bifurcation latitude of the North Equatorial Current (NEC) at the Philippine coast is also affected by the amount of transport through the Sulu archipelago. Opening this archipelago causes the NEC split point to move southward and increases the transport of the Kuroshio east of Luzon while decreasing the Mindanao Current. Opening or closing the Sunda Shelf/Java Sea or the Sulu archipelago does not affect the transport of the Pacific to Indian Ocean throughflow. South China Sea (SCS) via the wide and deep Luzon Strait. To the south, the waters are joined via the Sulu, Java, Sulawesi, Molucca, and Halmahera Seas as well as the interior passages of the Philippine Islands (Figure la). The seasonally reversing monsoon winds also play Copyright 1996 by the American Geophysical Union. Paper number 95JC03861. 0148-0227/96/95JC-03861 $09.00 an important role in determining the upper ocean circulation. This combination of geometry, connectivity with the Pacific Ocean, and strongly variable atmospheric forcing contributes to the complex dynamics of the flow around the Philippine Islands and Indonesia. Numerical ocean models can be important tools in helping to separate these dynamics, but only a few studies exist that are capable of adequately resolving the Indo-Pacific region. Among those which strive for a realistic representation of the geometry are by Hurlburr et al. [1989] and Masumoto and Yamagata [1991], who have focused on the current systems in the equatorial Pacific Ocean east of the Philippines. Metztier et al. [1991, 1992, 1994] have also looked at this region and compared upper layer currents and sea level 12,331 12,332 METZGER AND HURLBURT: SOUTH CHINA SEA-PACIFIC OCEAN COUPLING 25N 20N 15N 10N 5N

Research paper thumbnail of Bifurcation of the Kuroshio Extension at the Shatsky Rise

Journal of Geophysical Research, 1998

A 1/16 ø six-layer Pacific Ocean model north of 20øS is used to investigate the bifurcation of th... more A 1/16 ø six-layer Pacific Ocean model north of 20øS is used to investigate the bifurcation of the Kuroshio Extension at the main Shatsky Rise and the pathway of the northern branch from the bifurcation to the subarctic front. Upper ocean-topographic coupling via a mixed barotropic-baroclinic instability is essential to this bifurcation and to the formation and mean pathway of the northern branch as are several aspects of the Shatsky Rise complex of topography and the latitude of the Kuroshio Extension in relation to the topography. The flow instabilities transfer energy to the abyssal layer where it is constrained by geostrophic contours of the bottom topography. The topographically constrained abyssal currents in turn steer upper ocean currents, which do not directly impinge on the bottom topography. This includes steering of mean pathways. Obtaining sufficient coupling requires very fine resolution of mesoscale variability and sufficient eastward penetration of the Kuroshio as an unstable inertial jet. Resolution of 1/8 ø for each variable was not sufficient in this case. The latitudinal extent of the main Shatsky Rise (31øN-36øN) and the shape of the downward slope on the north side are crucial to the bifurcation at the main Shatsky Rise, with both branches passing north of the peak. The well-defined, relatively steep and straight eastern edge of the Shatsky Rise topographic complex (30øN-42øN) and the southwestward abyssal flow along it play a critical role in forming the rest of the Kuroshio northern branch which flows in the opposite direction. A deep pass between the main Shatsky Rise and the rest of the ridge to the northeast helps to link the northern fork of the bifurcation at the main rise to the rest of the northern branch. Two 1/16 ø "identical twin" interannual simulations forced by daily winds 1981-1995 show that the variability in this region is mostly nondeterministic on all timescales that could be examined (up to 7 years in these 15-year simulations). A comparison of climatologically forced and interannual simulations over the region 150øE -180øE, 29øN-47øN showed greatly enhanced abyssal and upper ocean eddy kinetic energy and much stronger mean abyssal currents east of the Emperor Seamount Chain (about 170øE) in the interannual simulations but little difference west of 170øE. This greatly enhanced the upper ocean-topographic coupling in the interannual simulations east of 170øE. This coupling affected the latitudinal positioning of the eastward

Research paper thumbnail of Mixed layer depth variability over the global ocean

Journal of Geophysical Research, 2003

The spatial and monthly variability of the climatological mixed layer depth (MLD) for the global ... more The spatial and monthly variability of the climatological mixed layer depth (MLD) for the global ocean is examined using the recently developed Naval Research Laboratory (NRL) Ocean Mixed Layer Depth (NMLD) climatologies. The MLD fields are constructed using the subsurface temperature and salinity data from the World Ocean Atlas 1994 [Levitus et al., 1994; Levitus and Boyer, 1994]. To minimize the limitations of these global data in the MLD determination, a simple mixing scheme is introduced to form a stable water column. Using these new data sets, global MLD characteristics are produced on the basis of an optimal definition that employs a density-based criterion having a fixed temperature difference of DeltaT = 0.8°C and variable salinity. Strong seasonality of MLD is found in the subtropical Pacific Ocean and at high latitudes, as well as a very deep mixed layer in the North Atlantic Ocean in winter and a very shallow mixed layer in the Antarctic in all months. Using the climatological monthly MLD and isothermal layer depth (ILD) fields from the NMLD climatologies, an annual mean DeltaT field is presented, providing criteria for determining an ILD that is approximately equivalent to the optimal MLD. This enables MLD to be determined in cases where salinity data are not available. The validity of the correspondence between ILD and MLD is demonstrated using daily averaged subsurface temperature and salinity from two moorings: a Tropical Atmosphere Ocean array mooring in the western equatorial Pacific warm pool, where salinity stratification is important, and a Woods Hole Oceanographic Institute (WHOI) mooring in the Arabian Sea, where strongly reversing seasonal monsoon winds prevail. In the western equatorial Pacific warm pool the use of ILD criterion with an annual mean DeltaT value of 0.3°C yields comparable results with the optimal MLD, while large DeltaT values yield an overestimated MLD. An analysis of ILD and MLD in the WHOI mooring show that use of an incorrect DeltaT criterion for the ILD may underestimate or overestimate the optimal MLD. Finally, use of the spatial annual mean DeltaT values constructed from the NMLD climatologies can be used to estimate the optimal MLD from only subsurface temperature data via an equivalent ILD for any location over the global ocean.

Research paper thumbnail of Wind Stress Drag Coefficient over the Global Ocean*

Journal of Climate, 2007

... Oceanography Division, Naval Research Laboratory, Stennis Space Center, Mississippi.Chris W. ... more ... Oceanography Division, Naval Research Laboratory, Stennis Space Center, Mississippi.Chris W. Fairall Physical ... AB Kara, CN Barron. (2008) Comment on “Seasonal heat budgets of the Red and Black seas” by Matsoukas et al.. Journal ...

Research paper thumbnail of How Does Solar Attenuation Depth Affect the Ocean Mixed Layer? Water Turbidity and Atmospheric Forcing Impacts on the Simulation of Seasonal Mixed Layer Variability in the Turbid Black Sea*

Journal of Climate, 2005

A fine-resolution (ഠ3.2 km) Hybrid Coordinate Ocean Model (HYCOM) is used to investigate the impa... more A fine-resolution (ഠ3.2 km) Hybrid Coordinate Ocean Model (HYCOM) is used to investigate the impact of solar radiation attenuation with depth on the predictions of monthly mean sea surface height (SSH), mixed layer depth (MLD), buoyancy and heat fluxes, and near-sea surface circulation as well. The model uses spatially and temporally varying attenuation of photosynthetically available radiation (k PAR ) climatologies as processed from the remotely sensed Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) to take water turbidity into account in the Black Sea. An examination of the k PAR climatology reveals a strong seasonal cycle in the water turbidity, with a basin-averaged annual climatological mean value of 0.19 m Ϫ1 over the Black Sea. Climatologically forced HYCOM simulations demonstrate that shortwave radiation below the mixed layer can be quite different based on the water turbidity, thereby affecting prediction of upper-ocean quantities in the Black Sea. The clear water constant solar attenuation depth assumption results in relatively deeper MLD (e.g., ഠϩ15 m in winter) in comparison to standard simulations due to the unrealistically large amount of shortwave radiation below the mixed layer, up to 100 W m Ϫ2 during April to October. Such unrealistic sub-mixed layer heating causes weaker stratification at the base of the mixed layer. The buoyancy gain associated with high solar heating in summer effectively stabilizes the upper ocean producing shallow mixed layers and elevated SSH over the most of the Black Sea. In particular, the increased stability resulting from the water turbidity reduces vertical mixing in the upper ocean and causes changes in surface-layer currents, especially in the easternmost part of the Black Sea. Monthly mean SSH anomalies from the climatologically forced HYCOM simulations were evaluated against a monthly mean SSH anomaly climatology, which was constructed using satellite altimeter data from TOPEX/ Poseidon (T/P), Geosat Follow-On (GFO), and the Earth Remote Sensing Satellite-2 (ERS-2) over 1993-2002. Model-data comparisons show that the basin-averaged root-mean-square (rms) difference is ഠ4 cm between the satellite-based SSH climatology and that obtained from HYCOM simulations using spatial and temporal k PAR fields. In contrast, when all solar radiation is absorbed at the sea surface or clear water constant solar attenuation depth values of 16.7 m are used in the model simulations, the basin-averaged SSH rms difference with respect to the climatology is ഠ6 cm (ഠ50% more). This demonstrates positive impact from using monthly varying solar attenuation depths in simulating upper-ocean quantities in the Black Sea. The monthly mean k PAR and SSH anomaly climatologies presented in this paper can also be used for other Black Sea studies.

Research paper thumbnail of Black Sea Mixed Layer Sensitivity to Various Wind and Thermal Forcing Products on Climatological Time Scales*

Journal of Climate, 2005

This study describes atmospheric forcing parameters constructed from different global climatologi... more This study describes atmospheric forcing parameters constructed from different global climatologies, applied to the Black Sea, and investigates the sensitivity of Hybrid Coordinate Ocean Model (HYCOM) simulations to these products. Significant discussion is devoted to construction of these parameters before using them in the eddy-resolving (Ϸ3.2-km resolution) HYCOM simulations. The main goal is to answer how the model dynamics can be substantially affected by different atmospheric forcing products in the Black Sea. Eight wind forcing products are used: four obtained from observation-based climatologies, including one based on measurements from the SeaWinds scatterometer on the Quick Scatterometer (QuikSCAT) satellite, and the rest formed from operational model products. Thermal forcing parameters, including solar radiation, are formed from two operational models: the European Centre for Medium-Range Weather Forecasts (ECMWF) and the Fleet Numerical Meteorology and Oceanography Center (FNMOC) Navy Operational Global Atmospheric Prediction System (NOGAPS). Climatologically forced Black Sea HYCOM simulations (without ocean data assimilation) are then performed to assess the accuracy and sensitivity of the model sea surface temperature (SST) and sea surface circulation to these wind and thermal forcing products. Results demonstrate that the model-simulated SST structure is quite sensitive to the wind and thermal forcing products, especially near coastal regions. Despite this sensitivity, several robust features are found in the model SST in comparison to a monthly 9.3-km-resolution satellite-based Pathfinder SST climatology. Annual mean HYCOM SST usually agreed to within ϷϮ0.2°of the climatology in the interior of the Black Sea for any of the wind and thermal forcing products used. The fineresolution (0.25°ϫ 0.25°) wind forcing from the scatterometer data along with thermal forcing from NOGAPS gave the best SST simulation with a basin-averaged rms difference value of 1.21°C, especially improving model results near coastal regions. Specifically, atmospherically forced model simulations with no assimilation of any ocean data suggest that the basin-averaged rms SST differences with respect to the Pathfinder SST climatology can vary from 1.21°to 2.15°C depending on the wind and thermal forcing product. The latter rms SST difference value is obtained when using wind forcing from the National Centers for Environmental Prediction (NCEP), a product that has a too-coarse grid resolution of 1.875°ϫ 1.875°f or a small ocean basin such as the Black Sea. This paper also highlights the importance of using highfrequency (hybrid) wind forcing as opposed to monthly mean wind forcing in the model simulations. Finally, there are large variations in the annual mean surface circulation simulated using the different wind sets, with general agreement between those forced by the model-based products (vector correlation is usually Ͼ0.7). Three of the observation-based climatologies generally yield unrealistic circulation features and currents that are too weak.

Research paper thumbnail of Sea Surface Height Predictions from the Global Navy Coastal Ocean Model during 1998–2001*

Journal of Atmospheric and Oceanic Technology, 2004

... Received: September 9, 2003; Accepted: June 19, 2004. Corresponding author address: Charlie N... more ... Received: September 9, 2003; Accepted: June 19, 2004. Corresponding author address: Charlie N. Barron, Naval Research Laboratory, Code 7323, Bldg. ... Fox, DN, WJ Teague, CN Barron, MR Carnes, and CM Lee, 2002b: The Modular Ocean Data Analysis System (MODAS). ...

Research paper thumbnail of Climatological SST and MLD Predictions from a Global Layered Ocean Model with an Embedded Mixed Layer*

Journal of Atmospheric and Oceanic Technology, 2003

Research paper thumbnail of Efficient and Accurate Bulk Parameterizations of Air–Sea Fluxes for Use in General Circulation Models

Journal of Atmospheric and Oceanic Technology, 2000

... using the gas law. Note the mixing ratio values for air (q a at T a ) and sea (q s at T s ) a... more ... using the gas law. Note the mixing ratio values for air (q a at T a ) and sea (q s at T s ) are calculated using a simplified version of the original formulation for saturated vapor pressure (e s ) presented by Buck (1981). Similar to the ...

Research paper thumbnail of Stability-Dependent Exchange Coefficients for Air–Sea Fluxes*

Journal of Atmospheric and Oceanic Technology, 2005

... A. Birol Kara, Harley E. Hurlburt, and Alan J. Wallcraft ... 1998; Hare et al. 1999) into acc... more ... A. Birol Kara, Harley E. Hurlburt, and Alan J. Wallcraft ... 1998; Hare et al. 1999) into account, which suggests that a Charnock constant value of 0.011 (Smith 1988), used in the earlier COARE v2.5b algorithm, is too low for higher wind speeds. ...

Research paper thumbnail of The NRL Layered Global Ocean Model (NLOM) with an Embedded Mixed Layer Submodel: Formulation and Tuning

Journal of Atmospheric and Oceanic Technology, 2003

Abstract A bulk-type (modified Kraus-Turner) mixed layer model that is embedded within the Naval ... more Abstract A bulk-type (modified Kraus-Turner) mixed layer model that is embedded within the Naval Research Laboratory (NRL) Layered Ocean Model (NLOM) is introduced. It is an independent submodel loosely coupled to NLOM's dynamical core, requiring only near-...