41 research outputs found
Eulerian and Lagrangian correspondence of high-frequency radar and surface drifter data : effects of radar resolution and flow components
Author Posting. © American Meteorological Society, 2014. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 31 (2014): 945–966, doi:10.1175/JTECH-D-13-00146.1.This study investigated the correspondence between the near-surface drifters from a mass drifter deployment near Martha’s Vineyard, Massachusetts, and the surface current observations from a network of three high-resolution, high-frequency radars to understand the effects of the radar temporal and spatial resolution on the resulting Eulerian current velocities and Lagrangian trajectories and their predictability. The radar-based surface currents were found to be unbiased in direction but biased in magnitude with respect to drifter velocities. The radar systematically underestimated velocities by approximately 2 cm s−1 due to the smoothing effects of spatial and temporal averaging. The radar accuracy, quantified by the domain-averaged rms difference between instantaneous radar and drifter velocities, was found to be about 3.8 cm s−1. A Lagrangian comparison between the real and simulated drifters resulted in the separation distances of roughly 1 km over the course of 10 h, or an equivalent separation speed of approximately 2.8 cm s−1. The effects of the temporal and spatial radar resolution were examined by degrading the radar fields to coarser resolutions, revealing the existence of critical scales (1.5–2 km and 3 h) beyond which the ability of the radar to reproduce drifter trajectories decreased more rapidly. Finally, the importance of the different flow components present during the experiment—mean, tidal, locally wind-driven currents, and the residual velocities—was analyzed, finding that, during the study period, a combination of tidal, locally wind-driven, and mean currents were insufficient to reliably reproduce, with minimal degradation, the trajectories of real drifters. Instead, a minimum combination of the tidal and residual currents was required.I.R. was supported by the WHOI
Coastal Ocean Institute Project 27040148 and by the
WHOI Access to the Sea Program 27500036. I.R. and
A.K. acknowledge support fromthe NSF project 83264600.
A.K. acknowledges support from the Massachusetts
Clean Energy Center (MassCEC) via the New England
Marine Renewable Energy Center (MREC).2014-10-0
Wave-driven inner-shelf motions on the Oregon coast
Author Posting. © American Meteorological Society, 2009. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 39 (2009): 2942-2956, doi:10.1175/2009JPO4041.1.Recent work by S. Lentz et al. documents offshore transport in the inner shelf due to a wave-driven return flow associated with the Hasselmann wave stress (the Stokes–Coriolis force). This analysis is extended using observations from the central Oregon coast to identify the wave-driven return flow present and quantify the potential bias of wind-driven across-shelf exchange by unresolved wave-driven circulation. Using acoustic Doppler current profiler (ADCP) measurements at six stations, each in water depths of 13–15 m, observed depth-averaged, across-shelf velocities were generally correlated with theoretical estimates of the proposed return flow. During times of minimal wind forcing, across-shelf velocity profiles were vertically sheared, with stronger velocities near the top of the measured portion of the water column, and increased in magnitude with increasing significant wave height, consistent with circulation due to the Hasselmann wave stress. Yet velocity magnitudes and vertical shears were stronger than that predicted by linear wave theory, and more similar to the stratified “summer” velocity profiles described by S. Lentz et al. Additionally, substantial temporal and spatial variability of the wave-driven return flow was found, potentially due to changing wind and wave conditions as well as local bathymetric variability. Despite the wave-driven circulation found, subtracting estimates of the return flow from the observed across-shelf velocity had no significant effect on estimates of the across-shelf exchange due to along-shelf wind forcing at these water depths along the Oregon coast during summer.This work was performed with the
Partnership for Interdisciplinary Studies of Coastal
Oceans (PISCO), funded primarily by the Gordon and
Betty Moore Foundation and David and Lucile Packard
Foundation. SL acknowledges support
from NSF Ocean Science Grant #OCE-0548961. AK acknowledges
support from the WHOI Coastal Ocean
Institute Fellowship
Investigating the eddy diffusivity concept in the coastal ocean
Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 2201-2218, doi:10.1175/JPO-D-16-0020.1.This paper aims to test the validity, utility, and limitations of the lateral eddy diffusivity concept in a coastal environment through analyzing data from coupled drifter and dye releases within the footprint of a high-resolution (800 m) high-frequency radar south of Martha’s Vineyard, Massachusetts. Specifically, this study investigates how well a combination of radar-based velocities and drifter-derived diffusivities can reproduce observed dye spreading over an 8-h time interval. A drifter-based estimate of an anisotropic diffusivity tensor is used to parameterize small-scale motions that are unresolved and underresolved by the radar system. This leads to a significant improvement in the ability of the radar to reproduce the observed dye spreading.IR, AK, and SL were supported by the NSF OCE Grant 1332646. IR was also supported by NASA Grant NNX14AH29G.2016-12-2
OC449-09 Data Report : St. Thomas, USVI to Bermuda, December 1-10, 2008
Data collected during multiple surveys of hydrography, velocity, and biological quantities are presented
from a 9-day cruise aboard the R/V Oceanus near the island of St. Thomas, USVI and a subsequent transit
to Bermuda during December, 2008. This cruise (OC449-09) was undertaken primarily to field test a newly
acquired towed-undulating body, the Scanfish. The Scanfish and a second towed body, the Video Plankton
Recorder (VPR), were used to survey hydrographic, optical, and biological properties north and south of
St. Thomas. Conductivity-Temperature-Depth (CTD) casts and plankton net-tows were made at locations
along the survey transects for inter-comparison. The VPR was also used to profile conditions between St.
Thomas and Bermuda during transit. An overview of the cruise is given along with descriptions of the data
collection methods, processing steps taken, and data products available for distribution.Funding for this research was provided by the King Abdullah University of Science and Technology (KAUST)
under a cooperative research agreement with Woods Hole Oceanographic Institution
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Time-Varying Across-Shelf Ekman Transport and Vertical Eddy Viscosity on the Inner Shelf
The event-scale variability of across-shelf transport was investigated using observations made in 15 m of
water on the central Oregon inner shelf. In a study area with intermittently upwelling-favorable winds and
significant density stratification, hydrographic and velocity observations show rapid across-shelf movement of
water masses over event time scales of 2–7 days. To understand the time variability of across-shelf exchange,
an inverse calculation was used to estimate eddy viscosity and the vertical turbulent diffusion of momentum
from velocity profiles and wind forcing. Depth-averaged eddy viscosity varied over a large dynamic range,
but averaged 1.3 X 10⁻³ m² s⁻¹ during upwelling winds and 2.1 X 10⁻³ m² s⁻¹ during downwelling winds. The
fraction of full Ekman transport present in the surface layer, a measure of the efficiency of across-shelf
exchange at this water depth, was a strong function of eddy viscosity and wind forcing, but not stratification.
Transport fractions ranged from 60%, during times of weak or variable wind forcing and low eddy viscosity,
to 10%–20%, during times of strong downwelling and high eddy viscosity. The difference in eddy viscosities
between upwelling and downwelling led to varying across-shelf exchange efficiencies and, potentially,
increased net upwelling over time. These results quantify the variability of across-shelf transport efficiency
and have significant implications for ecological processes (e.g., larval transport) in the inner shelf
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Alongshelf Variability of Inner-Shelf Circulation along the Central Oregon Coast during Summer
The spatial and temporal variability of inner-shelf circulation along the central Oregon coast during the
2004 upwelling season is described using a 70-km-long array of moorings along the 15-m isobath. Circulation
at three stations located onshore of a submarine bank differed from that of a station north of the bank,
despite the relatively uniform wind forcing and inner-shelf bathymetry present. During upwelling-favorable
winds, strong southward alongshelf flow occurred north of the bank, no alongshelf flow occurred onshore of
the northern part of the bank, and increasing southward flow occurred onshore of the southern part of the
bank. During downwelling-favorable winds, strong northward flow occurred in the inner shelf onshore of the
bank while weak flow occurred north of the bank. These alongshelf differences in inner-shelf circulation were
due to the effects of the bank, which isolated the inner shelf onshore of the bank from the regional upwelling
circulation that was evident at the northernmost station. As a result, circulation onshore of the bank was
driven primarily by local wind forcing, while flow north of the bank was only partially driven by local winds.A
secondary mode of variability, attributed to the movement of the regional upwelling jet due to remote
forcings, contributed the bulk of the variability observed north of the bank. With the time-dependent wind
forcing present, acceleration was an important term in the depth-averaged alongshelf momentum equation at
all stations. During upwelling, bottom stress and acceleration opposed the wind stress north of the bank,
while bottom stress was weaker onshore of the bank where the across-shelf momentum flux and the
alongshelf pressure gradient balanced the residual of the acceleration and stresses. During downwelling,
waters onshore of the bank surged northward at magnitudes much larger than that found north of the bank.
These spatial variations developed as the season progressed and the regional upwelling circulation intensified,
explaining known variations in growth and recruitment of nearshore invertebrate species
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Wave-Driven Inner-Shelf Motions on the Oregon Coast*
Recent work by S. Lentz et al. documents offshore transport in the inner shelf due to a wave-driven return
flow associated with the Hasselmann wave stress (the Stokes–Coriolis force). This analysis is extended using
observations from the central Oregon coast to identify the wave-driven return flow present and quantify the
potential bias of wind-driven across-shelf exchange by unresolved wave-driven circulation. Using acoustic
Doppler current profiler (ADCP) measurements at six stations, each in water depths of 13–15 m, observed
depth-averaged, across-shelf velocities were generally correlated with theoretical estimates of the proposed
return flow. During times of minimal wind forcing, across-shelf velocity profiles were vertically sheared, with
stronger velocities near the top of the measured portion of the water column, and increased in magnitude with
increasing significant wave height, consistent with circulation due to the Hasselmann wave stress. Yet velocity
magnitudes and vertical shears were stronger than that predicted by linear wave theory, and more similar to
the stratified ‘‘summer’’ velocity profiles described by S. Lentz et al. Additionally, substantial temporal and
spatial variability of the wave-driven return flow was found, potentially due to changing wind and wave
conditions as well as local bathymetric variability. Despite the wave-driven circulation found, subtracting
estimates of the return flow from the observed across-shelf velocity had no significant effect on estimates of
the across-shelf exchange due to along-shelf wind forcing at these water depths along the Oregon coast during
summer
Northern Monterey Bay upwelling shadow front : observations of a coastally and surface-trapped buoyant plume
Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 114 (2009): C12013, doi:10.1029/2009JC005623.During the upwelling season in central California, northwesterly winds along the coast produce a strong upwelling jet that originates at Point Año Nuevo and flows southward across the mouth of Monterey Bay. A convergent front with a mean temperature change of 3.77 ± 0.29°C develops between the warm interior waters and the cold offshore upwelling jet. To examine the forcing mechanisms driving the location and movement of the upwelling shadow front and its effects on biological communities in northern Monterey Bay, oceanographic conditions were monitored using cross-shelf mooring arrays, drifters, and hydrographic surveys along a 20 km stretch of coast extending northwestward from Santa Cruz, California, during the upwelling season of 2007 (May–September). The alongshore location of the upwelling shadow front at the northern edge of the bay was driven by: regional wind forcing, through an alongshore pressure gradient; buoyancy forces due to the temperature change across the front; and local wind forcing (the diurnal sea breeze). The upwelling shadow front behaved as a surface-trapped buoyant current, which is superimposed on a poleward barotropic current, moving up and down the coast up to several kilometers each day. We surmise that the front is advected poleward by a preexisting northward barotropic current of 0.10 m s−1 that arises due to an alongshore pressure gradient caused by focused upwelling at Point Año Nuevo. The frontal circulation (onshore surface currents) breaks the typical two-dimensional wind-driven, cross-shelf circulation (offshore surface currents) and introduces another way for water, and the material it contains (e.g., pollutants, larvae), to go across the shelf toward shore.Funded primarily by the Gordon and Betty Moore Foundation and the David
and Lucile Packard Foundation
Gene expression profiling of the dorsolateral and medial orbitofrontal cortex in schizophrenia
Schizophrenia is a complex polygenic disorder of unknown etiology. Over 3,000 candidate genes associated with schizophrenia have been reported, most of which being mentioned only once. Alterations in cognitive processing - working memory, metacognition and mentalization - represent a core feature of schizophrenia, which indicates the involvement of the prefrontal cortex in the pathophysiology of this disorder. Hence we compared the gene expression in postmortem tissue from the left and right dorsolateral prefrontal cortex (DLPFC, Brodmann's area 46), and the medial part of the orbitofrontal cortex (MOFC, Brodmann's area 11/12), in six patients with schizophrenia and six control brains. Although in the past decade several studies performed transcriptome profiling in schizophrenia, this is the first study to investigate both hemispheres, providing new knowledge about possible brain asymmetry at the level of gene expression and its relation to schizophrenia. We found that in the left hemisphere, twelve genes from the DLPFC and eight genes from the MOFC were differentially expressed in patients with schizophrenia compared to controls. In the right hemisphere there was only one gene differentially expressed in the MOFC. We reproduce the involvement of previously reported genes TARDBP and HNRNPC in the pathogenesis of schizophrenia, and report seven novel genes: SART1, KAT7, C1D, NPM1, EVI2A, XGY2, and TTTY15. As the differentially expressed genes only partially overlap with previous studies that analyzed other brain regions, our findings indicate the importance of considering prefrontal cortical regions, especially those in the left hemisphere, for obtaining disease-relevant insights
Validation of turbulence intensity as simulated by the Weather Research and Forecasting model off the US northeast coast
Turbulence intensity (TI) is often used to quantify the strength of
turbulence in wind energy applications and serves as the basis of standards
in wind turbine design. Thus, accurately characterizing the spatiotemporal
variability in TI should lead to improved predictions of power production.
Nevertheless, turbulence measurements over the ocean are far less prevalent
than over land due to challenges in instrumental deployment, maintenance,
and operation. Atmospheric models such as mesoscale (weather prediction) and large-eddy simulation (LES) models are commonly used in the wind energy industry to assess the spatial variability of a given site. However, the TI derivation from atmospheric models has not been well examined. An algorithm is proposed in this study to realize online calculation of TI in the Weather Research and Forecasting (WRF) model. Simulated TI is divided into two components depending on scale, including sub-grid (parameterized based on turbulence kinetic energy (TKE)) and grid resolved. The sensitivity of sea surface temperature (SST) on simulated TI is also tested. An assessment is performed by using observations collected during a field campaign conducted from February to June 2020 near the Woods Hole Oceanographic Institution Martha's Vineyard Coastal Observatory. Results show that while simulated TKE is generally smaller than the lidar-observed value, wind speed bias is usually small. Overall, this leads to a slight underestimation in sub-grid-scale estimated TI. Improved SST representation subsequently reduces model biases in atmospheric stability as well as wind speed and sub-grid TI near the hub height. Large TI events in conjunction with mesoscale weather systems observed during the studied period pose a challenge to accurately estimating TI from models. Due to notable uncertainty in accurately simulating those events, this suggests summing up sub-grid and resolved TI may not be an ideal solution. Efforts in further improving skills in simulating mesoscale flow and cloud systems are necessary as the next steps.</p