James Richman

• United States Naval Research Laboratory

The effects of horizontal resolution and wave drag damping on the semidiurnal M2 tidal energetics are studied for two realistically-forced global HYbrid Coordinate Ocean Model (HYCOM) simulations with 41 layers and horizontal resolutions of 8 km (1∕12.5∘; H12) and 4 km (1∕25∘; H25). In both simulations, the surface tidal error is minimized by tunin...

While westerly winds dominate the equatorial Indian Ocean and generate the well‐known eastward flowing Wyrtki Jets during boreal spring and fall, there is evidence of a strong westward surface jet during winter that is swifter than eastward currents during that season. A weaker westward jet is found in summer. In this study, we report the occurrenc...

Temperature variance and kinetic energy (KE) from two global simulations of the HYbrid Coordinate Ocean Model (HYCOM; 1/12° and 1/25°) and three global simulations of the Massachusetts Institute of Technology general circulation model (MITgcm; 1/12°, 1/24°, and 1/48°), all of which are forced by atmospheric fields and the astronomical tidal potenti...

Semidiurnal baroclinic tide sea surface height (SSH) variance and semidiurnal nonstationary variance fraction (SNVF) are compared between a hydrodynamic model and altimetry for the low‐ to middle‐latitude global ocean. Tidal frequencies are aliased by ∼10‐day altimeter sampling, which makes it impossible to unambiguously identify nonstationary tida...

This study examines the impact of turbulent mixing on horizontal density compensation in the upper ocean. A series of simulations model the role of mixing in scenarios initialized with geostrophically-adjusted compensated and uncompensated thermohaline gradients. Numerical experiments isolate the influence of mixing on these gradients using idealiz...

In global ocean simulations, forward (non-data-assimilative) tide models generally feature large sea-surface height errors near Hudson Strait in the North Atlantic Ocean with respect to altimetry-constrained tidal solutions. These errors may be associated with tidal resonances that are not well resolved by the complex coastal-shelf bathymetry in lo...

Tidal mixing fronts, which represent boundaries between stratified and tidally mixed waters, are locations of enhanced biological activity. They occur in summer shelf seas when, in the presence of strong tidal currents, mixing due to bottom friction balances buoyancy production due to seasonal heat flux. In this paper we examine the occurrence and...

https://deepblue.lib.umich.edu/bitstream/2027.42/146536/1/bookchapter_2018_arbicetal.pdf

The evidence for, baroclinic energetics of, and geographic distribution of parametric subharmonic instability (PSI) arising from both diurnal and semidiurnal tides in a global ocean general circulation model is investigated using 1/12.5° and 1/25° simulations that are forced by both atmospheric analysis fields and the astronomical tidal potential....

This letter investigates the relationship between wind, sea surface temperature (SST), and thermocline in the Seychelles-Chagos Thermocline Ridge (SCTR, 5°S-10°S, 50°E-80°E) using a combination of satellite data and a reanalysis version of the HYbrid Coordinate Ocean Model from 1993 to 2012. The asymmetry of this relationship during positive and ne...

Global maps of the mesoscale Eddy Available Potential Energy (EAPE) field at a depth of 500m are created using potential density anomalies in a high-resolution 112.5° global ocean model. Maps made from both a free-running simulation and a data-assimilative reanalysis of the HYbrid Coordinate Ocean Model (HYCOM) are compared with maps made by other...

Two global ocean models ranging in horizontal resolution from 1/12° to 1/48° are used to study the space- and time-scales of sea surface height (SSH) signals associated with internal gravity waves (IGWs). Frequency-horizontal wavenumber SSH spectral densities are computed over seven regions of the world ocean from three simulations of the HYbrid Co...

The jets in the equatorial Pacific Ocean of a realistically-forced global circulation model with a horizontal resolution of 1/12.5° cause a strong loss of phase coherence in semidiurnal internal tides that propagate equatorward from the French Polynesian Islands and Hawaii. This loss of coherence is quantified with a baroclinic energy analysis, in...

We examine the temporal means and variability of the semidiurnal internal tide energy fluxes in 1/25° global simulations of the HYbrid Coordinate Ocean Model (HYCOM) and in a global archive of 79 historical moorings. Low-frequency flows, a major cause of internal tide variability, have comparable kinetic energies at the mooring sites in model and o...

https://deepblue.lib.umich.edu/bitstream/2027.42/152466/1/jpo_2017_bottomfrictionandtopography.pdf

The effects of a parameterized linear internal wave drag on the semidiurnal barotropic and baroclinic energetics of a realistically forced, three-dimensional global ocean model are analyzed. Although the main purpose of the parameterization is to improve the surface tides, it also influences the internal tides. The relatively coarse resolution of t...

A first order assessment of model skill in reproducing shelf sea tides for the 3-dimensional global HYCOM with embedded tides is presented. We compare HYCOM to the altimetry constrained model TPXO and also examine the ability of HYCOM to produce tidal mixing fronts in the North Sea.

The ocean tidal velocity and elevation can be estimated concurrently with the ocean circulation by adding the astronomical tidal forcing, parameterized topographic internal wave drag, and self-attraction and loading to the general circulation physics. However, the accuracy of these tidal estimates does not yet match accuracies in the best data-assi...

The impact of topographic internal lee wave drag (wave drag hereafter) on several aspects of the low-frequency circulation in a high-resolution global ocean model forced by winds and air-sea buoyancy fluxes is examined here. The HYbrid Coordinate Ocean Model (HYCOM) is run at two different horizontal resolutions (one nominally 1/12° and the other 1...

A global high-resolution ocean circulation model forced by atmospheric fields and the M2 tidal constituent is used to explore plausible scenarios for the damping of low-mode internal tides. The plausibility of different damping scenarios is tested by comparing the modeled barotropic tides with TPXO8, a highly accurate satellite-altimetry-constraine...

High-resolution global ocean models forced by atmospheric fields and tides are beginning to display realistic internal gravity wave spectra, especially as model resolution increases. This paper examines internal waves in global simulations with 0.08° and 0.04° (~8 and 4 km) horizontal resolutions, respectively. Frequency spectra of internal wave ho...

Based on observations and modeling studies we have evaluated the impact of submesoscale processes on the development and intensification of offshore narrow (5-10km wide) phytoplankton filaments during summer time in the Monterey Bay, CA. We have demonstrated that, submesoscale processes (surface frontogenesis and nonlinear Ekman transport) lead to...

High-resolution global ocean models forced by atmospheric fields and tides are beginning to display realistic internal gravity wave spectra, especially as model resolution increases. This paper examines internal waves in global simulations with 0.08° and 0.04° (~8 and 4 km) horizontal resolutions, respectively. Frequency spectra of internal wave ho...

The accuracy of state-of-the-art global barotropic tide models is assessed using bottom pressure data, coastal tide gauges, satellite altimetry, various geodetic data on Antarctic ice shelves, and independent tracked satellite orbit perturbations. Tide models under review include empirical, purely hydrodynamic (“forward”), and assimilative dynamica...

Motivated by the potential of oceanic mesoscale eddies to drive intrinsic low-frequency variability, this paper examines geostrophic turbulence in the frequency-wavenumber domain. Frequency-wavenumber spectra, spectral fluxes, and spectral transfers are computed from an idealized two-layer quasigeostrophic (QG) turbulence model, a realistic high-re...

Ocean mesoscale eddies are non-deterministic in that small errors grow in time so that accurate prediction is not possible without continual correction from observations. Ocean frontogenesis can be forced by mesoscale eddies through straining of buoyancy gradients, which produces filaments of surface divergence related to ageostrophic upwelling. Th...

We describe an approach to produce short-term (1-to 3-day) forecasts of bio-optical properties by coupling moderate-resolution imaging spectroradiometer satellite (MODIS) ocean color imagery with a hydrodynamic model. The bio-optical property (chlorophyll in this case) is treated as a conservative tracer; the satellite distribution is advected forw...

The stationarity of the internal tides generated in a global eddy-resolving ocean circulation model forced by realistic atmospheric fluxes and the luni-solar gravitational potential is explored. The root mean square (RMS) variability in the M2 internal tidal amplitude is approximately 2 mm or less over most of the ocean and exceeds 2 mm in regions...

[1] We apply several skill tests to assess tidal currents within a three-dimensional, eddy resolving, global ocean circulation model compared to over 5000 observational velocity records spanning 40 years. We examine the skill of the HYbrid Coordinate Ocean Model (HYCOM) on a regional, basin, and global scale and in deep versus shallow water. On a g...

Density compensation is the condition where temperature (T) and salinity (S) gradients counteract in their effect on density. Open ocean observations with SeaSoar tows and recent glider observations in the Gulf of Mexico reported in the scientific literature suggest that horizontal gradients in the surface mixed layer tend to be strongly density co...

Motivated by the recent interest in ocean energetics, the widespread use of horizontal eddy viscosity in models, and the promise of high horizontal resolution data from the planned wide-swath satellite altimeter, this paper explores the impacts of horizontal eddy viscosity and horizontal grid resolution on geostrophic turbulence, with a particular...

The slopes of the wavenumber spectra of sea surface height (SSH) and kinetic energy (KE) have been used to infer "interior" or surface quasi-geostrophic (QG or SQG) dynamics of the ocean. However, inspection of spectral slopes for altimeter SSH in the mesoscale band of 70 to 250 km shows much flatter slopes than the QG or SQG predictions over most...

We examine the impact of atmospheric correction, specifically aerosol model selection, on retrieval of bio-optical properties from satellite ocean color imagery. Uncertainties in retrievals of bio-optical properties (such as chlorophyll, absorption, and backscattering coefficients) from satellite ocean color imagery are related to a variety of fact...

Global comparisons of barotropic and internal tides generated in an eddy-resolving ocean circulation model are made with tidal estimates obtained from altimetric sea surface heights and an altimetry-constrained tide model. As far as we know, our Hybrid Coordinate Ocean Model (HYCOM) simulations shown here and in an earlier paper are the only publis...

Motivated by the ubiquity of time series in oceanic data, the relative lack of studies of geostrophic turbulence in the frequency domain, and the interest in quantifying the contributions of intrinsic nonlinearities to oceanic frequency spectra, this paper examines the spectra and spectral fluxes of surface oceanic geostrophic flows in the frequenc...

We present and apply several skill tests to assess tidal currents generated within a global ocean model compared to an archive of current meter records spanning 40 years. Within the North Atlantic we have identified over 1800 velocity records available for comparison to model output. The skill tests identify those regions where tidal ellipse parame...

Ocean tides, and the atmospherically forced oceanic generalcirculation and its associated mesoscale eddy field, have long been run separately in high-resolution global models. They are now being simulated concurrently in a high-resolution version of the HYbrid Coordinate Ocean Model (HYCOM). The incorporation of horizontally varying stratification...

We characterize the global ocean seasonal variability of the temperature versus salinity gradients in the transition layer just below the mixed layer using observations of conductivity temperature and depth and profiling float data from the National Ocean Data Center's World Ocean Data set. The balance of these gradients determines the temperature...

This paper examines the effect of "stencil width" on surface ocean geostrophic velocity and vorticity estimated from differentiating gridded satellite altimeter sea surface height products. In oceanographic applications, the value of the first derivative at a central grid point is generally obtained by differencing the sea surface heights at adjace...

We propose a methodology to quantify errors and produce uncertainty maps for satellite-derived ocean color bio-optical products using ensemble simulations. Ensemble techniques have been used by the environmental numerical modeling community to propagate initialization, forcing, and algorithm error sources through-out the full simulation process, bu...

We propose a methodology to quantify errors and produce uncertainty maps for satellite-derived ocean color bio-optical products using ensemble simulations. Ensemble techniques have been used by the environmental numerical modeling community to propagate initialization, forcing, and algorithm error sources through-out the full simulation process, bu...

We examine the impact of incorrect atmospheric correction, specifically incorrect aerosol model selection, on retrieval of bio-optical properties from satellite ocean color imagery. Uncertainties in retrievals of bio-optical properties (such as chlorophyll, absorption and backscattering coefficients) from satellite ocean color imagery are related t...

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September, 1976 The temporal and spatial variability of low frequency moored temperature and velocity observations, obtained as part of the Mid-Ocean Dynamics Experimen...

The relative influence of both temperature and salinity on the mixed layer depth (MLD) is evaluated using a relationship of binned regressions of MLD on vertical density compensation and isothermal layer depth (ILD) from a global set of in situ profile observations. Our approach is inspired by the observations of the difference between the MLD and...

In this paper, we study, in detail, one important aspect of our ongoing work on global ocean prediction. Modeling the behavior of western boundary currents, like the Gulf Stream, has been a long-standing issue. Recent modeling results suggest that the abyssal currents play an important role in determining the pathway of the Gulf Stream. The present...

Ocean models run with atmospheric forcing but without ocean data assimilation are useful in studies of ocean model dynamics and simulation skill. Models that give realistic simulations with accurate dynamics, when run without data assimilation, are essential for eddy-resolving ocean prediction because of the multiple roles that ocean models must pl...

Estimating the errors in the data and model are critical aspects of data assimilation. In this paper we present a reduced state space optimal interpolation scheme to assimilate satellite remotely sensed sea surface temperature into a coarse resolution general circulation model of the North Pacific. Using statistical tests on the principal component...

The Southern Ocean is the largest high-nutrient, low-chlorophyll region in the world's ocean and a potentially important site for the sequestration of carbon. We present a one-dimensional physical/biogeochemical model that integrates biogeochemical measurements obtained during the AESOPS (U.S. JGOFS) study in the southwest Pacific sector to elucida...

Paleoceanographic evidence points to the Southern Ocean as a strong sink for atmospheric CO 2 during the Last Glacial Maximum (LGM), but no consensus about the responsible mechanism has yet been reached. Martin (Paleoceanography 5 (1990) 1) postulated that greater iron input during the LGM could have stimulated phytoplankton to consume the surface...

The Antarctic Polar Front is a complex set of meandering jets, which appear to support enhanced primary productivity. The US Joint Global Ocean Flux Study conducted a series of survey and process studies in part to study the processes regulating primary productivity in this high nutrient, low chlorophyll region. We deployed a set of surface velocit...

The US Joint Global Ocean Flux Study (JGOFS) conducted a series of survey and process studies in part to understand the processes regulating primary productivity and carbon flux in the APFZ, which is a high-nutrient, low-chlorophyll (HNLC) region. We deployed a high-resolution array of 12 moorings (average horizontal spacing 30 km) equipped with bi...

copyrighted by American Geophysical Union

SeaWiFS estimates of surface chlorophyll. concentrations are reported for the region of the U.S. JGOFS study in the Southern Ocean (∼ 170 °W, 60 °S). Elevated chlorophyll was observed at the Southern Ocean fronts, near the edge of the seasonal ice sheet, and above the Pacific-Antarctic Ridge. The elevated chlorophyll levels associated with the Paci...

copyrighted by American Geophysical Union The location of the Antarctic Polar Front (PF) was mapped over a 7-year period (1987-1993) within images of satellite-deprived sea surface temperature. The mean path of the PF is strongly steered by the topographic features of the Southern Ocean. The topography places vorticity constraints on the dynamics o...

Variations in the spectral shape of underwater irradiance at a fixed depth can be used to describe changes in water column constituents, such as chlorophyll concentration. However, random fluctuations of the depth of the monitoring sensor, caused by current variations, makes interpretation more challenging. Even in homogeneous water, the spectral u...

Copyrighted by American Geophysical Union. The path of the Antarctic Polar Front (PF) is mapped using satellite sea surface temperature data from the NOAA/NASA Pathfinder program. The mean path and variability of the PF are strongly influenced by bathymetry. Meandering intensity is weaker where the bathymetry is steeply sloped and increases in area...

Four years of ocean vector wind data are used to evaluate statistics of wind stress over the ocean. Raw swath wind stresses derived from the Quick Scatterometer (QuikSCAT) are compared with five different global gridded wind products, including products based on scatterometer observations, meteorological analysis winds from the European Centre for...

Using Geosat altimeter data for 26 months from November 1986 to December 1988 and a newly developed technique for the analysis of height data, the variability of the sea level and the surface geostrophic currents in the Southern Ocean is investigated. The processed Geosat data are used to examine the relationship between the mesoscale variability a...

Copyrighted by American Geophysical Union. Several methods are developed for analyzing data containing a highly variable internal tide. In particular, the methods are aimed at the analysis of moored observations with relatively few measurements in the vertical. The analysis depends upon an "elliptical decomposition" that is a generalization of the...

Deep fluctuations in current along the equator in the Central Pacific are dominated by coherent structures which correspond closely to narrow-band (in wave number) propagating equatorial waves. Currents were measured roughly at 1500 and 3000 m depths at 5 moorings between 144 and 148°W from January 1981 to March 1983 as part of the Pacific Equatori...