Combined Effects of Wind-Driven Upwelling and Internal Tide on the Continental Shelf

Internal tides on the continental shelf can be intermittent as a result of changing hydrographic conditions associated with wind-driven upwelling. In turn, the internal tide can affect transports associated with upwelling. To study these processes, simulations in an idealized, alongshore uniform setup are performed utilizing the hydrostatic Regional Ocean Modeling System (ROMS) with conditions corresponding, as closely as possible, to the central Oregon shelf. ‘‘Wind only’’ (WO), ‘‘tide only’’ (TO), and ‘‘tide and wind’’ (TW) solutions are compared, utilizing cases with constant upwelling-favorable wind stress as well as with timevariable observed stress. The tide is forced by applying cross-shore barotropic flow at the offshore boundary with intensity sufficient to generate an internal tide with horizontal velocity amplitudes near 0.15 m s21, corresponding to observed levels. The internal tide affects the subinertial circulation, mostly through the changes in the bottom boundary layer variability, resulting in a larger bottom stress and a weaker depthaveraged alongshore current in the TW case compared to WO. The spatial variability of the cross-shore and vertical volume transport is also affected. Divergence in the Reynolds stress associated with the baroclinic tidal flow contributes to the tidally averaged cross-shore momentum balance. Internal waves cause highfrequency variability in the turbulent kinetic energy in both the bottom and surface boundary layers, causing periodic restratification of the inner shelf in the area of the upwelling front. Increased vertical shear in the horizontal velocity resulting from the superposition of the upwelling jet and the internal tide results in intermittent patches of intensified turbulence in the mid–water column. Variability in stratification associated with upwelling can affect not only the propagation of the internal tide on the shelf, but also the barotropic-tobaroclinic energy conversion on the continental slope, in this case changing the classification of the slope from nearly critical to supercritical such that less barotropic tidal energy is converted to baroclinic and a larger fraction of the baroclinic energy is radiated into the open ocean

Spatial and Temporal Variability of the M2 Internal Tide Generation and Propagation on the Oregon Shelf

A 1-km-horizontal-resolution model based on the Regional Ocean Modeling System is implemented along the Oregon coast to study average characteristics and intermittency of the M₂ internal tide during summer upwelling. Wind-driven and tidally driven flows are simulated in combination, using realistic bathymetry, atmospheric forcing, and boundary conditions. The study period is April through August 2002, when mooring velocities are available for comparison. Modeled subtidal and tidal variability on the shelf are in good quantitative agreement with moored velocity time series observations. Depth-integrated baroclinic tidal energy flux (EF), its divergence, and topographic energy conversion (TEC) from the barotropic to baroclinic tide are computed from high-pass-filtered, harmonically analyzed model results in a series of 16-day time windows. Model results reveal several “hot spots” of intensive TEC on the slope. At these locations, TEC is well balanced by EF divergence. Changes in background stratification and currents associated with wind-driven upwelling and downwelling do not appreciably affect TEC hot spot locations but may affect intensity of internal tide generation at those locations. Relatively little internal tide is generated on the shelf. Areas of supercritical slope near the shelf break partially reflect baroclinic tidal energy to deeper water, contributing to spatial variability in seasonally averaged on-shelf EF. Despite significant temporal and spatial variability in the internal tide, the alongshore-integrated flux of internal tide energy onto the Oregon shelf, where it is dissipated, does not vary much with time. Approximately 65% of the M₂ baroclinic tidal energy generated on the slope is dissipated there, and the rest is radiated toward the shelf and interior ocean in roughly equal proportions. An experiment with smoother bathymetry reveals that slope-integrated TEC is more sensitive to bathymetric roughness than on-shelf EF.KEYWORDS: Continental shelf/slope, Tides, Internal waves, Hindcasts, North Pacific Ocean, Regional model

Volume, Heat and Salt Transport in the North-Eastern Bering Sea During 2007-2010 Derived Through the 4dvar Data Assimilation of In-Situ and Satellite Observations

The rich collection of BEST-BSIERP observations and other sources of data provide an excellent opportunity for synthesis through modeling and data assimilation to improve our understanding of changes in physical forcings of the Bering ecosystem in response to climate change. Assimilating data of different origins, which may be sparse in space and time, is difficult using simple algorithms (traditional optimal interpolation, correlation analysis etc.). The 4Dvar approach is effective for performing spatiotemporal interpolation of sparse data via interpolation (covariance) functions with scales based on ocean dynamics (Bennett, 2002).NSF Arctic Progra

Intensified Diurnal Tides along the Oregon Coast

Intensified diurnal tides are found along portions of the Oregon shelf (U.S. West Coast) based on analyses of high-frequency (HF) radar surface current data and outputs of a 1-km resolution ocean circulation model. The K₁ tidal currents with magnitudes near 0.07 m s⁻¹ over a wider part of the shelf (Heceta Bank complex; 44°–44.5°N), previously predicted by Erofeeva et al., are confirmed here by newly available HF radar data. Intensified diurnal tides are also found along the narrow shelf south of Heceta Bank. In the close vicinity of Cape Blanco (42.8°N), diurnal tidal currents (K₁ and O₁ constituents combined) may reach 0.3 m s⁻¹. Appreciable differences in diurnal tide intensity are found depending on whether the model is forced with tides and winds (TW) or only tides. Also, diurnal variability in wind forcing is found to affect diurnal surface velocities. For the case forced by tides alone, results strongly depend on whether the model ocean is stratified [tides only, stratified (TOS)] or not [tides only, no stratification (TONS)]. In case TONS, coastal-trapped waves at diurnal frequencies do not occur over the narrow shelf south of 43.5°N, consistent with the dispersion analysis of a linear shallow-water model. However, in case TOS, diurnal tides are intensified in that area, associated with the presence of coastal-trapped waves. Case TW produces the strongest modeled diurnal tidal motions over the entire Oregon shelf, partially due to cross-shore tidal displacement (advection) of alongshore subinertial currents. At Cape Blanco, diurnal tidal variability dominates the modeled relative vorticity spectrum, suggesting that tides may influence the separation of the alongshore coastal jet at that location.Keywords: Boundary currents, Dynamics, Topographic effects, Currents, Ocean dynamics, Fronts, Circulation/ Dynamic

Model-data synthesis and high resolution simulation of the Bering Sea

The Bering Sea is the source of over 50% of the total US fish catch and the home to immense populations of birds and marine mammals. This extraordinarily productive ecosystem is vulnerable to climate regime shifts that have occurred over the past decades. These regime shifts are closely linked to warming and cooling of the atmosphere and ocean, and the coincident retreat or expansion of the sea ice cover with strong interannual and decadal variability. Here we investigate changes in the Bering ice/ocean system in recent years. One of key tools for this investigation is the Bering Ecosystem STudy ice-ocean Modeling and Assimilation System (BESTMAS) for synthesis and modeling of the Bering ice/ocean system

Modeling Bottom Mixed Layer Variability on the Mid-Oregon Shelf during Summer Upwelling

Results from a model of wind-driven circulation are analyzed to study spatial and temporal variability in the bottom mixed layer (BML) on the mid-Oregon shelf in summer 2001. The model assimilates acoustic Doppler profiler velocities from two cross-shore lines of moorings 90 km apart to provide improved accuracy of near-bottom velocities and turbulence variables in the area between the mooring lines. Model results suggest that the response of the BML thickness to upwelling- and downwelling-favorable winds differs qualitatively between an area of “simple” bathymetric slope at 45°N and a wider shelf area east of Stonewall Bank (44.5°N). At 45°N, the BML grows in response to downwelling-favorable conditions, in agreement with known theories. East of Stonewall Bank, the BML thickness is increased following upwelling events. In this area, the southward upwelling jet detaches from the coast and flows over a wider part of the Oregon shelf, creating conditions for Ekman pumping near the bottom. Based on computations of bottom stress curl, the vertical pumping velocity in this area may reach 15 m day⁻¹ following periods of intensified upwelling-favorable winds. A column of denser, near-bottom water upwelled over the Ekman flow convergence area is tilted as a result of vertical shear in horizontal velocities, causing unstable stratification and convective overturning. As a result of this process, BML thickness values east of Stonewall Bank can be in excess of 20 m following upwelling, comparable to maximum values at 45°N following downwelling

Variational assimilation of satellite observations in a coastal ocean model off Oregon

Satellite along-track sea surface height (SSH) and multisatellite sea surface temperature (SST) maps are assimilated in a coastal ocean circulation model off Oregon. The study period is June–October 2005, featuring intensive separation of the coastal upwelling jets in the eddy-dominated coastal transition zone (CTZ). The data assimilation (DA) system combines the nonlinear Regional Ocean Modeling System (ROMS) and the Advanced Variational Regional Ocean Representer Analyzer (AVRORA) tangent linear and adjoint codes developed by our group. The variational representer DA method is implemented in a series of 6 day time windows, with initial conditions corrected at the beginning of each window. To avoid the problem of matching the model and observed SSH mean levels, the observed SSH slope has been assimilated. Location, timing, and intensity of jets and eddies in the CTZ are constrained, to improve accuracy of nonlinear model analyses and forecasts. In the case assimilating SSH alone, the geometry of the SST front is improved. SSH assimilation results in the cross-shore transport more uniformly distributed along the coast than in the free run model. An outer front is identified in the DA analyses at a distance of 200 km from the coast. A strong subsurface horizontal temperature gradient across this front influences the depth of the thermocline in an area between the front and the continental slope. The DA correction term is comparable in magnitude to dominant terms in the volume-integrated heat equation. The time-averaged DA correction term in the volume-integrated heat balance is closer to 0 in the combined SSH-SST assimilation case, than in the case assimilating SSH alone.This is the publisher's final pdf. The published article is copyrighted by American Geophysical Union and can be found at: http://www.agu.org/journals/jc/index.shtm

Towards an integrated observation and modeling system in the New York Bight using variational methods. Part I : 4DVAR data assimilation

Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Ocean Modelling 35 (2010): 119-133, doi:10.1016/j.ocemod.2010.08.003.Four-dimensional Variational data assimilation (4DVAR) in the Regional Ocean Modeling System (ROMS) is used to produce a best-estimate analysis of ocean circulation in the New York Bight during spring 2006 by assimilating observations collected by a variety of instruments during an intensive field program. An incremental approach is applied in an overlapped cycling system with 3-day data assimilation window to adjust model initial conditions. The model-observation mismatch for all observed variables is reduced substantially. Comparisons between model forecast and independent observations show improved forecast skill for about 15 days for temperature and salinity, and 2 to 3 days for velocity. Tests assimilating only certain subsets of the data indicate that assimilating satellite sea surface temperature improves the forecast of surface and subsurface temperature but worsens the salinity forecast. Assimilating in situ temperature and salinity from gliders improves the salinity forecast but has little effect on temperature. Assimilating HF-radar surface current data improves the velocity forecast by 1-2 days yet worsens the forecast of subsurface temperature. During some time periods the convergence for velocity is poor as a result of the data assimilation system being unable to reduce errors in the applied winds because surface forcing is not among the control variables. This study demonstrates the capability of 4DVAR data assimilation system to reduce model-observation mismatch and improve forecasts in the coastal ocean, and highlights the value of accurate meteorological forcing.This work was funded by National Science Foundation grant OCE-0238957

Physical synthesis of iron oxide nanoparticles and their biological activity in vivo

The physical synthesis of iron oxide nanoparticles obtained from the vapor phase using the electron beam physical vapor deposition method is considered. The results of studying the structure of porous condensates of iron-sodium chloride compound, chemical and phase compositions, as well as nanoparticles size are presented. With a rapid removal from vacuum, iron nanoparticles are oxidized in the air to magnetite. In the initial state, they have signi¬cant sorption capacity with respect to oxygen and moisture, therefore, with further heating in the air, the porous condensate mass decreases up to the temperature 650°C, primarily due to the desorption of physically sorbed moisture. Physically adsorbed oxygen participates in oxidation of Fe3O4–Fe2O3 in the range of 380–650°C. An increase in condensation temperature is accompanied by an increase of nanoparticle size, as a result of which the total surface area of nanoparticles is signicantly reduced, and, consequently, their sorption capacity is decreased. Even without stabilization, such nanoparticles studied as ex tempore prepared aqueous dispersion have characteristic anti-anemic effect in the laboratory animals that can be used in medicine