177 research outputs found
Horizontal and vertical structure of velocity, potential vorticity and energy in the Gulf Stream
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 February 1985From October, 1982 to October, 1983 a current meter mooring reaching
from the bottom into the thermocline was deployed for the first time in
the Gulf Stream at 68°W. The temperatures, pressures, and velocities at
the uppermost instrument indicate the Gulf Stream moved back and forth
across the mooring site, so that the entire Stream was sampled in time;
hence the data may be used to examine horizontal as well as vertical
structure of the Stream. The two key points to the success of the
analysis are: 1)the well-defined relationship between temperature and
cross-stream distance in the thermocline, enabling the use of the former
as a horizontal coordinate; and 2)a daily-changing definition of Gulf
Stream flow direction based on the shear between the thermocline and
2000 m depth. Time-series of daily-rotated velocities may be used to
calculate empirical orthogonal functions for the long- and cross-stream
vertical structures, which are decoupled and are respectively baroclinic
and barotropic. Using the inferred horizontal coordinate one can
estimate mass, momentum and kinetic energy fluxes for four individual
events when the entire Stream swept by the mooring. The results agree
well with historical data. Bryden's (1980) method has been used to
calculate vertical velocities from the temperature equation; the
resulting time-series of w are visually coherent throughout the water
column and their vertical amplitude structure is reminiscent of that for
a two-layer system. The rms vertical velocities are large (0(.05 cm/s)),
and these as well as other estimates have been used to explore the
validity of the quasi-geostrophic approximation at the mooring site. The
Rossby number for the thermocline flow is about 0.3, and for the deep
flow is ≤ 0.1.
The entire data set may also be used to construct a horizontal and
vertical profile of velocity in the Gulf Stream, from which a
cross-section of the mean potential vorticity can be produced. The
latter shares many common feature with cross-sections from past work for
a nearby site, as well as analogous data from a three-layer numerical
model, thus suggesting that they are robust features of Gulf Stream-like
currents. These features are, in particular, a strong jump from low to
high values crossing the Stream from south to north; and a change in the
sign of the potential vorticity gradient on isothermal surfaces for
T > 12°C.
To complement the analysis of the observational data, a set of
diagnostic calculations has been performed on an eddy-resolving qeneral
circulation model, to provide a complete picture of the kinetic energy
budgets of the free jet and its environs. It is found that the
downstream convergence of kinetic energy in the decelerating jet is
balanced primarily by an ageostrophic flow against the pressure gradient,
which in turn implies some conversion of kinetic to available potential
energy in the region. Energetic analysis of the observations as well as
the numerical data suggests barotropic and baroclinic instabilities may
be equally important to the kinetic energy budgets in the Stream.
Because there is but one mooring, the dynamics governing the
fluctuations remain elusive. Nonetheless, a kinematic framework is
proposed, which is consistent with the data and accounts for a variety of
unusual features that arise in the original analysis (for example,
distinct asymmetries in the four Gulf Stream crossings, and the rather
large vertical velocities). It is sugqested that the data we are now
capable of collecting is proffering fundamentally new attributes of the
Gulf Stream, which must be included and accounted for in future
theoretical work
Assessing the energetics and dynamics of the Gulf Stream at 68W from moored current measurements
The energetics and dynamics of the Gulf Stream at 68W have been investigated using year-long time series of velocity and temperature throughout the water column. The major results that have emerged are as follows: (1) There is a net conversion of mean to eddy kinetic and potential energies, the barotropic mechanism being almost twice as strong as the baroclinic. These energy exchanges are dominated by what is happening in the upper 1000 m of the water column. (2) Comparison with other studies suggests that the mooring site may be characterized as a region of downstream spatial growth in eddy energy, with a growth rate of 3–4 × 10−3km−1. (3) Curvature changes due to the changing Stream path are sufficient to balance stretching of the water column below the thermocline, the dominant measurable effect in the vorticity equation. (4) A kinematic scheme including and relating barotropic cross-stream velocities, local temperature changes, stretching, and curvature changes is shown to be generally consistent with the observed data. (5) The vertical mass divergence ∂w/∂z affects continuity at lowest order, and may be associated with along stream changes in transport, a vertical redistribution of the alongstream momentum flux, or changing Stream width
Deep circulation in the tropical North Atlantic
A transatlantic CTD/ADCP (Conductivity, Temperature, Depth/Acoustic Doppler Current Profiler) section along 11N, taken in March 1989, has been used to compute geostrophic velocities; geostrophic transport is required to balance in situ values of the Ekman and shallow boundary current transports. The horizontal flow structure is described for eight layers, with particular emphasis on deep and bottom waters (four layers below = 4.7°C). In the shallow layers, total North Brazil Current (NBC) transport agrees with other observations previously made in the month of March, while net northward flow of these layers across the western basin is also consistent with recent observations to the north. For each of the four deep layers, circulation patterns are illustrated by means of schematic cartoons. Each of these layers flows southward in the Deep Western Boundary Current, which has a magnitude of 26.5 Sv. Roughly half of this flow returns northward to the west of the Mid-Atlantic Ridge, confirming the existence of a hypothesized cyclonic recirculation gyre in the western basin of the tropical Atlantic. To varying degrees the deep and bottom waters also circulate cyclonically in the eastern basin, with net northward flow across this basin. Partly as a result of the unusual appearance of the North Equatorial Countercurrent in March 1989, the in situ values of the meridional overturning cell (5.2 Sv), heat flux (3.0 × 1014 W), and freshwater flux (−0.65 Sv) computed from the 11N section depart significantly from estimates of these quantities in the literature. By forcing the 11N geostrophic velocities to balance annual average Ekman and NBC transports, annual average values of these fluxes (12 Sv; 11 × 1014 W; −0.6 Sv) are obtained, and are shown to agree well with historical estimates
Absolute velocity along the AR7W section in the Labrador Sea
Author Posting. © Elsevier B.V., 2012. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 72 (2013): 72–87, doi:10.1016/j.dsr.2012.11.005.Nearly every spring since 1990, hydrographic data have been collected along a section in the Labrador Sea known as AR7W. Since 1995, lowered acoustic doppler current profiler (LADCP) data have also been collected. In this work we use data from six of these sections, spanning the time period 1995 through 2008, to determine absolute velocity across AR7W and analyze the main features of the general circulation in the area. We find that absolute velocity fields are characterized by strong, nearly barotropic flows all along the section, meaning there is no “level of no motion” for geostrophic velocity calculations. There is strong variability from year to year, especially in the strength of the boundary currents at each end; nevertheless, combining data from.all 6 sections yields a well-organized velocity field resembling that presented by Pickart and Spall (2007), except that our velocities tend to be stronger: there is a cyclonic boundary current system with offshore recirculations at both ends of the line; the interior is filled with virtually uniform, top-to-bottom bands of velocity with alternating signs. At the southwestern end of the section, the LADCP data reveal a dual core of the Labrador Current at times when horizontal resolution is adequate. At the northeastern end, the location of the recirculation offshore of the boundary current is bimodal, and hence the apparent width of the boundary current is bimodal as well. In the middle of the section, we have found a bottom current carrying overflow waters along the Northwest Atlantic Mid-Ocean Channel, suggesting one of various possible fast routes for those waters to reach the central Labrador Sea. We have used the hydrographic data to compute geostrophic velocities, referenced to the LADCP profiles, as well as to compute ocean heat transport across AR7W for four of our sections. For all but one year, these fluxes are comparable to the mean air–sea heat flux that occurs between AR7W and Davis Strait from December to May (O(50–80 TW)), and much larger than the annual average values (O(10–20 TW)).This material is based upon work supported by the National Science Foundation under Grant No. OCE-0622640. Igor Yashayaev is supported by the ocean climate monitoring program of the Department of Fisheries and Oceans Canada
Ready or Not? How Community Health Centers View Their Preparedness to Care for Newly Insured Patients
By expanding access to affordable insurance coverage for millions of Americans, the Affordable Care Act will likely increase demand for the services provided by federally qualified health centers (FQHCs), an important source of care in low-income communities. A Commonwealth Fund survey asked health center leaders in 2013 about current and anticipated workforce challenges, as well as efforts under way to prepare for the increase in patients. The majority of FQHCs reported shortages of primary care doctors (56%), especially bilingual physicians (60%). Health centers are engaged in activities to meet the needs of new patients, with 53 percent pursuing integration of behavioral health and 31 percent hiring additional clinical staff. To help them provide quality care to more patients, FQHCs will require assistance to recruit additional personnel, particularly bilingual staff and mental health professionals, and to expand access to care through telehealth and other strategies
Trans-equatorial bottom water flow in the western Atlantic : volume XLVI in a series of reports presenting data from moored current meters
Current and temperature measurements from Vector Averaging Current Meters (VACMs) deployed from
September 1992 to June 1994 as part of the Deep Basin Experiment (DBE) measuring the trans-equatorial
water flow are presented. Salinity and temperature measurements from Conductivity/Temperature/Depth
(CTD) casts taken during the mooring deployment and recovery cruises are also presented.
Six mooring sites were occupied with a total of 24 vector averaging current meters and 4 Aanderaa
current meters. Three nominal depths (3900, 4100 and 4300 m.) were occupied on each mooring. Three of
the 6 moorings had current meters at additional depths.
Basic data from the vector averaging current meters are presented both in statistical tables and
graphically as histograms, scatter plots, progressive vector diagrams and spectral diagrams. One day Gaussian
filtered plots are shown in composite displays of variables versus time.
Temperature and salinity profies and e/s plots for 22 CTD stations are presented.Funding was provided by the National Science Foundation through
Grant No. OCE-9105834
Zonal circulation across 52°W in the North Atlantic
Author Posting. © American Geophysical Union, 2004. 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 109 (2004): C11008, doi:10.1029/2003JC002103.In July–August 1997, a hydrographic/Acoustic Doppler Current Profiler (ADCP)/tracer section was occupied along 52°W in the North Atlantic as part of the World Ocean Circulation Experiment Hydrographic Program. Underway and lowered ADCP (LADCP) data have been used to reference geostrophic velocities calculated from the hydrographic data; additional (small) velocity adjustments provided by an inverse model, constraining mass and silicate transports in 17 neutral density layers, yield the absolute zonal velocity field for 52°W. We find a vigorous circulation throughout the entire section, with an unusually strong Gulf Stream (169 Sv) and southern Deep Western Boundary Current (DWBC; 64 Sv) at the time of the cruise. At the northern boundary, on the west side of the Grand Banks of Newfoundland, we find the westward flowing Labrador Current (8.6 Sv), whose continuity from the Labrador Sea, east of our section, has been disputed. Directly to the south we identify the slopewater current (12.5 Sv eastward) and northern DWBC (12.5 Sv westward). Strong departures from strictly zonal flow in the interior, which are found in the LADCP data, make it difficult to diagnose the circulation there. Isolated deep property extrema in the southern portion, associated with alternating bands of eastward and westward flow, are consistent with the idea that the rough topography of the Mid-Atlantic Ridge, directly east of our section, causes enhanced mixing of Antarctic Bottom Water properties into overlying waters with distinctly different properties. We calculate heat and freshwater fluxes crossing 52°W that exceed estimates based on air-sea exchanges by a factor of 1.7.This work was supported by NSF grants
OCE95-29607, OCE 95-31864, OCE98-18266, and OCE-0219644
Intranasal Peptide-Based FpvA-KLH Conjugate Vaccine Protects Mice From Pseudomonas aeruginosa Acute Murine Pneumonia
Pseudomonas aeruginosa is an opportunistic pathogen causing acute and chronic respiratory infections associated with morbidity and mortality, especially in patients with cystic fibrosis. Vaccination against P. aeruginosa before colonization may be a solution against these infections and improve the quality of life of at-risk patients. To develop a vaccine against P. aeruginosa, we formulated a novel peptide-based P. aeruginosa subunit vaccine based on the extracellular regions of one of its major siderophore receptors, FpvA. We evaluated the effectiveness and immunogenicity of the FpvA peptides conjugated to keyhole limpet hemocyanin (KLH) with the adjuvant curdlan in a murine vaccination and challenge model. Immunization with the FpvA-KLH vaccine decreased the bacterial burden and lung edema after P. aeruginosa challenge. Vaccination with FpvA-KLH lead to antigen-specific IgG and IgM antibodies in sera, and IgA antibodies in lung supernatant. FpvA-KLH immunized mice had an increase in recruitment of CD11b+ dendritic cells as well as resident memory CD4+ T cells in the lungs compared to non-vaccinated challenged mice. Splenocytes isolated from vaccinated animals showed that the FpvA-KLH vaccine with the adjuvant curdlan induces antigen-specific IL-17 production and leads to a Th17 type of immune response. These results indicate that the intranasal FpvA-KLH conjugate vaccine can elicit both mucosal and systemic immune responses. These observations suggest that the intranasal peptide-based FpvA-KLH conjugate vaccine with curdlan is a potential vaccine candidate against P. aeruginosa pneumonia
Intranasal Acellular Pertussis Vaccine Provides Mucosal Immunity and Protects Mice from Bordetella Pertussis
Current acellular pertussis vaccines fall short of optimal protection against the human respiratory pathogen Bordetella pertussis resulting in increased incidence of a previously controlled vaccine- preventable disease. Natural infection is known to induce a protective mucosal immunity. Therefore, in this study, we aimed to use acellular pertussis vaccines to recapitulate these mucosal immune responses. We utilized a murine immunization and challenge model to characterize the efficacy of intranasal immunization (IN) with DTaP vaccine or DTaP vaccine supplemented with curdlan, a known Th1/Th17 promoting adjuvant. Protection from IN delivered DTaP was compared to protection mediated by intraperitoneal injection of DTaP and whole-cell pertussis vaccines. We tracked fluorescently labeled DTaP after immunization and detected that DTaP localized preferentially in the lungs while DTaP with curdlan was predominantly in the nasal turbinates. IN immunization with DTaP, with or without curdlan adjuvant, resulted in anti-B. pertussis and anti-pertussis toxin IgG titers at the same level as intraperitoneally administered DTaP. IN immunization was able to protect against B. pertussis challenge and we observed decreased pulmonary pro-inflammatory cytokines, neutrophil infiltrates in the lung, and bacterial burden in the upper and lower respiratory tract at day 3 post challenge. Furthermore, IN immunization with DTaP triggered mucosal immune responses such as production of B. pertussis-specific IgA, and increased IL-17A. Together, the induction of a mucosal immune response and humoral antibody-mediated protection associated with an IN administered DTaP and curdlan adjuvant warrant further exploration as a pertussis vaccine candidate formulation
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