6 research outputs found
The formation and fate of internal waves in the South China Sea
Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 521 (2015): 65-69, doi:10.1038/nature14399.Internal gravity waves, the subsurface analogue of the familiar surface gravity
waves that break on beaches, are ubiquitous in the ocean. Because of their strong vertical and horizontal currents, and the turbulent mixing caused by their
breaking, they impact a panoply of ocean processes, such as the supply of nutrients
for photosynthesis1, sediment and pollutant transport2 and acoustic transmission3;
they also pose hazards for manmade structures in the ocean4. Generated primarily
by the wind and the tides, internal waves can travel thousands of kilometres from
their sources before breaking5, posing severe challenges for their observation and
their inclusion in numerical climate models, which are sensitive to their effects6-7.
Over a decade of studies8-11 have targeted the South China Sea, where the oceans’
most powerful internal waves are generated in the Luzon Strait and steepen
dramatically as they propagate west. Confusion has persisted regarding their
generation mechanism, variability and energy budget, however, due to the lack of
in-situ data from the Luzon Strait, where extreme flow conditions make
measurements challenging. Here we employ new observations and numerical
models to (i) show that the waves begin as sinusoidal disturbances rather than
from sharp hydraulic phenomena, (ii) reveal the existence of >200-m-high
breaking internal waves in the generation region that give rise to turbulence levels
>10,000 times that in the open ocean, (iii) determine that the Kuroshio western
boundary current significantly refracts the internal wave field emanating from the
Luzon Strait, and (iv) demonstrate a factor-of-two agreement between modelled
and observed energy fluxes that enables the first observationally-supported energy
budget of the region. Together, these findings give a cradle-to-grave picture of
internal waves on a basin scale, which will support further improvements of their
representation in numerical climate predictions.Our work was supported by the U.S. Office of Naval Research and
the Taiwan National Science Council.2015-10-2
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The formation and fate of internal waves in the South China Sea
Internal gravity waves, the subsurface analogue of the familiar
surface gravity waves that break on beaches, are ubiquitous in
the ocean. Because of their strong vertical and horizontal currents,
and the turbulent mixing caused by their breaking, they affect a
panoply of ocean processes, such as the supply of nutrients for
photosynthesis¹, sediment and pollutant transport² and acoustic
transmission³; they also pose hazards for man-made structures in
the ocean⁴. Generated primarily by the wind and the tides, internal
waves can travel thousands of kilometres from their sources before
breaking⁵, making it challenging to observe them and to include
them in numerical climate models, which are sensitive to their
effects[superscript 6,7]. For over a decade, studies[superscript 8–11] have targeted the South
China Sea, where the oceans’ most powerful known internal waves
are generated in the Luzon Strait and steepen dramatically as they
propagate west. Confusion has persisted regarding their mechanism
of generation, variability and energy budget, however,
owing to the lack of in situ data from the Luzon Strait, where
extreme flow conditions make measurements difficult. Here we
use new observations and numerical models to (1) show that the
waves begin as sinusoidal disturbances rather than arising from
sharp hydraulic phenomena, (2) reveal the existence of >200-metre-high breaking internal waves in the region of generation
that give rise to turbulence levels >10,000 times that in the open
ocean, (3) determine that the Kuroshio western boundary current
noticeably refracts the internal wave field emanating from the
Luzon Strait, and (4) demonstrate a factor-of-two agreement
between modelled and observed energy fluxes, which allows us to
produce an observationally supported energy budget of the region.
Together, these findings give a cradle-to-grave picture of internal
waves on a basin scale, which will support further improvements of
their representation in numerical climate predictions
FROM THE GUEST EDITORS | A Collaboration for the Exploration of the Oceanography of Taiwan
The natural environment that characterizes the South China Sea and the western Pacific Ocean has attracted global attention due to the frequent and devastating natural disasters in the region, as well as the strategic importance of western Pacific nations to the global economy and political stability. In spite of this global significance, the South China Sea was still relatively unexplored from a scientific viewpoint until recently. Over the past 13 years, oceanographers from the United States and Taiwan, supported by the US Office of Naval Research and the Taiwan National Science Council, respectively, have worked together to probe this mysterious and fascinating sea. This joint effort has resulted in rewarding scientific and personal/professional partnerships, leading to a better understanding of the natural environment as well as establishing a model of long-term collaboration across the Pacific
Modeled Oceanic Response and Sea Surface Cooling to Typhoon Kai-Tak
An ocean response to typhoon Kai-Tak is simulated using an accurate fourth-order, basin-scale ocean model. The surface winds of typhoon Kai-Tak were obtained from QuikSCAT satellite images blended with the ECMWF wind fields. An intense nonlinear mesoscale eddy is generated in the northeast South China Sea (SCS) with a Rossby number of O(1) and on a 50 - 100 km horizontal scale. Inertial oscillation is clearly observed. Advection dominates as a strong wind shear drives the mixed layer flows outward, away from the typhoon center, thus forcing upwelling from deep levels with a high upwelling velocity (> 30 m day-1). A drop in sea surface temperature (SST) of more than 9°C is found in both observation and simulation. We attribute this significant SST drop to the influence of the slow moving typhoon, initial stratification and bathymetry-induced upwelling in the northeast of the SCS where the typhoon hovered
The formation and fate of internal waves in the South China Sea
Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 521 (2015): 65-69, doi:10.1038/nature14399.Internal gravity waves, the subsurface analogue of the familiar surface gravity
waves that break on beaches, are ubiquitous in the ocean. Because of their strong vertical and horizontal currents, and the turbulent mixing caused by their
breaking, they impact a panoply of ocean processes, such as the supply of nutrients
for photosynthesis1, sediment and pollutant transport2 and acoustic transmission3;
they also pose hazards for manmade structures in the ocean4. Generated primarily
by the wind and the tides, internal waves can travel thousands of kilometres from
their sources before breaking5, posing severe challenges for their observation and
their inclusion in numerical climate models, which are sensitive to their effects6-7.
Over a decade of studies8-11 have targeted the South China Sea, where the oceans’
most powerful internal waves are generated in the Luzon Strait and steepen
dramatically as they propagate west. Confusion has persisted regarding their
generation mechanism, variability and energy budget, however, due to the lack of
in-situ data from the Luzon Strait, where extreme flow conditions make
measurements challenging. Here we employ new observations and numerical
models to (i) show that the waves begin as sinusoidal disturbances rather than
from sharp hydraulic phenomena, (ii) reveal the existence of >200-m-high
breaking internal waves in the generation region that give rise to turbulence levels
>10,000 times that in the open ocean, (iii) determine that the Kuroshio western
boundary current significantly refracts the internal wave field emanating from the
Luzon Strait, and (iv) demonstrate a factor-of-two agreement between modelled
and observed energy fluxes that enables the first observationally-supported energy
budget of the region. Together, these findings give a cradle-to-grave picture of
internal waves on a basin scale, which will support further improvements of their
representation in numerical climate predictions.Our work was supported by the U.S. Office of Naval Research and
the Taiwan National Science Council.2015-10-2