256 research outputs found
Marginal sea overflows and the upper ocean interaction
No full textAuthor 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): 387-403, doi:10.1175/2008JPO3934.1.Marginal sea overflows and the overlying upper ocean are coupled in the vertical by two distinct mechanisms—by an interfacial mass flux from the upper ocean to the overflow layer that accompanies entrainment and by a divergent eddy flux associated with baroclinic instability. Because both mechanisms tend to be localized in space, the resulting upper ocean circulation can be characterized as a β plume for which the relevant background potential vorticity is set by the slope of the topography, that is, a topographic β plume.
The entrainment-driven topographic β plume consists of a single gyre that is aligned along isobaths. The circulation is cyclonic within the upper ocean (water columns are stretched). The transport within one branch of the topographic β plume may exceed the entrainment flux by a factor of 2 or more.
Overflows are likely to be baroclinically unstable, especially near the strait. This creates eddy variability in both the upper ocean and overflow layers and a flux of momentum and energy in the vertical. In the time mean, the eddies accompanying baroclinic instability set up a double-gyre circulation in the upper ocean, an eddy-driven topographic β plume. In regions where baroclinic instability is growing, the momentum flux from the overflow into the upper ocean acts as a drag on the overflow and causes the overflow to descend the slope at a steeper angle than what would arise from bottom friction alone.
Numerical model experiments suggest that the Faroe Bank Channel overflow should be the most prominent example of an eddy-driven topographic β plume and that the resulting upper-layer transport should be comparable to that of the overflow. The overflow-layer eddies that accompany baroclinic instability are analogous to those observed in moored array data. In contrast, the upper layer of the Mediterranean overflow is likely to be dominated more by an entrainment-driven topographic β plume. The difference arises because entrainment occurs at a much shallower location for the Mediterranean case and the background potential vorticity gradient of the upper ocean is much larger.SK’s support during the time of his Ph.D.
research in the MIT/WHOI Joint Program was provided
by the National Science Foundation through
Grant OCE04-24741. JP and JY have also received
support from the Climate Process Team on Gravity
Current Entrainment, NSF Grant OCE-0611530. JY has
also been supported by NSF Grant OCE-0351055
Overflows and upper ocean interactions : a mechanism for the Azores current
No full textThesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2006.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 155-162).The oceanic response to overflows is explored using a two-layer isopycnal model. Overflows are a major source of the dense water of the global deep ocean, originating from only a few marginal seas. They enter the open ocean as dense gravity currents down a continental slope and play a crucial role in the deep ocean circulation. To understand the dynamics of these overflows, previous studies simplified their dynamics by treating the overlying ocean as inactive. This simplification may be a first approximation for the overflow but not for the overlying ocean. The Mediterranean overflow, for example, entrains about 2 Sv of overlying Atlantic water when it enters the Atlantic through Gibraltar Strait. The upper ocean must balance the mass loss and vortex stretching associated with entrainment. Thus for the upper ocean, overflows represent a localized region of intense mass and PV forcing. The simulations in this study show that in the upper layer, entrainment forces a cyclonic circulation along bathymetric contours. This is a topographic [beta]-plume and its transport depends on the entrainment region size and the topographic slope.(cont.) Baroclinic instability also develops and creates eddy thickness flux to the in-shore direction, forcing a double gyre topographic [beta]-plume near the strait due to eddy PV flux convergence on the in-shore side of the continental slope and divergence on the offshore side. When the upper oceanic response to overflows is examined specifically for the Mediterranean overflow, the upper ocean is found to establish two trans-Atlantic zonal jets, analogous to the Azores current and the Azores Counter current. These two zonal jets are an extension of the topographic [beta]-plume driven by the overflow. Because the eddies in the steep slope region near Cape St. Vincent drive a mean flow across the slope, the topographic [beta]-plume connects to the Atlantic Ocean to become a basin scale flow. This thesis shows that overflows can induce a significant circulation in the upper ocean, and for the Mediterranean overflow, this circulation is a basin scale flow.by Shinichiro Kida.Ph.D
The annual cycle of the Japan Sea throughflow
No full textAuthor 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): 23–39, doi:10.1175/JPO-D-15-0075.1.The mechanism responsible for the annual cycle of the flow through the straits of the Japan Sea is investigated using a two-layer model. Observations show maximum throughflow from summer to fall and minimum in winter, occurring synchronously at the three major straits: Tsushima, Tsugaru, and Soya Straits. This study finds the subpolar winds located to the north of Japan as the leading forcing agent, which first affects the Soya Strait rather than the Tsushima or Tsugaru Straits. The subpolar winds generate baroclinic Kelvin waves along the coastlines of the subpolar gyre, affect the sea surface height at the Soya Strait, and modify the flow through the strait. This causes barotropic adjustment to occur inside the Japan Sea and thus affect the flow at the Tsugaru and Tsushima Straits almost synchronously. The barotropic adjustment mechanism explains well why the observations show a similar annual cycle at the three straits. The annual cycle at the Tsugaru Strait is further shown to be weaker than that in the other two straits based on frictional balance around islands, that is, frictional stresses exerted around an island integrate to zero. In the Tsugaru Strait, the flows induced by the frictional integrals around the northern (Hokkaido) and southern (Honshu) islands are in opposite directions and tend to cancel out. Frictional balance also suggests that the annual cycle at the Tsugaru Strait is likely in phase with that at the Soya Strait because the length scale of the northern island is much shorter than that of the southern island.S. Kida is supported by KAKENHI (22106002). B. Qiu is supported by NASA (NNX13AE15G). J. Yang is supported by the U.S. National Science Foundation. X. Lin is supported by the Natural Science Foundation of China (41222037 and U1406401), China’s National Basic Research Priorities Programme (2013CB956202), and the Global Air-Sea Interaction Project (GASI-03-01-01-02).2016-07-0
Overflows and upper ocean interaction : a mechanism for the Azores Current
No full textSubmitted 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 2006The oceanic response to overflows is explored using a two-layer isopycnal model.
Overflows are a major source of the dense water of the global deep ocean, originating
from only a few marginal seas. They enter the open ocean as dense gravity currents
down a continental slope and play a crucial role in the deep ocean circulation. To
understand the dynamics of these overflows, previous studies simplified their dynamics
by treating the overlying ocean as inactive. This simplification may be a first
approximation for the overflow but not for the overlying ocean. The Mediterranean
overflow, for example, entrains about 2 Sv of overlying Atlantic water when it enters
the Atlantic through Gibraltar Strait. The upper ocean must balance the mass
loss and vortex stretching associated with entrainment. Thus for the upper ocean,
overflows represent a localized region of intense mass and PV forcing.
The simulations in this study show that in the upper layer, entrainment forces
a cyclonic circulation along bathymetric contours. This is a topographic β-plume
and its transport depends on the entrainment region size and the topographic slope.
Baroclinic instability also develops and creates eddy thickness flux to the in-shore
direction, forcing a double gyre topographic β-plume near the strait due to eddy PV
flux convergence on the in-shore side of the continental slope and divergence on the offshore
side. When the upper oceanic response to overflows is examined specifically for
the Mediterranean overflow, the upper ocean is found to establish two trans-Atlantic
zonal jets, analogous to the Azores current and the Azores Counter current. These
two zonal jets are an extension of the topographic β-plume driven by the overflow.
Because the eddies in the steep slope region near Cape St. Vincent drive a mean flow
across the slope, the topographic β-plume connects to the Atlantic Ocean to become
a basin scale flow.
This thesis shows that overflows can induce a significant circulation in the upper
ocean, and for the Mediterranean overflow, this circulation is a basin scale flow.This work was supported by the National Science Foundation Grant OCE-0424741
The Impact of Open Oceanic Processes on the Antarctic Bottom Water Outflows
No full textAbstract
The impact of open oceanic processes on the Antarctic Bottom Water (AABW) outflows is investigated using a numerical model with a focus on outflows that occur through deep channels. A major branch of the AABW outflow is known to occur as an overflow from the Filchner Depression to the Weddell Sea through a deep channel a few hundred kilometers wide and a sill roughly 500 m deep. When this overflow enters the Weddell Sea, it encounters the Antarctic Slope Front (ASF) at the shelf break, a density front commonly found along the Antarctic continental shelf break. The presence of an AABW outflow and the ASF create a v-shaped isopycnal structure across the shelf break, indicating an interaction between the overflow and oceanic processes. Model experiments show the overflow transport to increase significantly when an oceanic wind stress increases the depth of the ASF. This enhancement of overflow transport occurs because the channel walls allow a pressure gradient in the along-slope direction to exist and the overflow transport is geostrophically controlled with its ambient oceanic water at the shelf break. Because the ASF is associated with a lighter water mass that reaches the depth close to that of the channel, an increase in its depth increases the density gradient across the shelf break and therefore the geostrophic overflow transport. The enhancement of overflow transport is also likely to result in a lighter overflow water mass, although such an adjustment of density likely occurs on a much longer time scale than the adjustment of transport.</jats:p
KL-6, a Human MUC1 Mucin, as a prognostic marker for diffuse alveolar hemorrhage syndrome.
No full textBackground: Diffuse alveolar hemorrhage syndrome is a life threatening condition with diverse etiologies. Sensitive prognostic markers for diffuse alveolar hemorrhage have not been well investigated. Serum KL-6 is a biomarker for various interstitial lung disease associated with disease activity and prognosis. The purpose of the present study was to evaluate the clinical utility of serum KL-6 level as a prognostic marker for diffuse alveolar hemorrhage.
Methods: We retrospectively collected 41 consecutive patients clinically diagnosed as having diffuse alveolar hemorrhage who were admitted to the Intensive Care Unit of Hiroshima University Hospital between 2004 and 2011. Correlation between prognosis and age, sex, laboratory findings including serum KL-6, radiological findings, ventilatory modes or therapeutic regimens were evaluated.
Results: Baseline and peak serum KL-6 levels were significantly higher in non-survivors compared with survivors. An increase in KL-6 levels during the initial week was associated with a subsequent deterioration of the oxygenation index. Higher baseline KL-6 levels and higher peak KL-6 levels were strongly correlated with death. With a cut-off level of 700 U/mL for peak KL-6, the sensitivity, specificity and accuracy for non-survival were 75%, 85% and 78%, respectively. In the multivariate analysis, only the peak KL-6 level ?700 U/ml was an independent poor prognostic factor for diffuse alveolar hemorrhage.
Conclusions: Peak serum KL-6 level ?700 U/ml may become a clinically useful marker of poor prognosis for diffuse alveolar hemorrhage.博士(医学)Philosophy in Medical Science広島大
Eddy dynamics of ß plumes
No full textSubmitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2003The importance of eddies and nonlinearities in ß-plume dynamics in the deep ocean
was investigated using reduced gravity models of the deep ocean forced by a small
region of cross isopycnal transport in the interior. The effect of topography on ß-plumes
was also examined by placing a Gaussian bump in the forcing region. Despite
the fact that the mean flow is weak in the deep ocean interior, it was found that the
nonlinearity and instabilities are still important for realistic parameter and forcing
values. The flow was dominated by eddies and was remarkably different from what
would be expected from a linear solution.This study was supported by Woods Hole Oceanographic Institution Academic
Programs Office Fellowship and National Science Foundation Grant 89542700
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