Yang Yiing-Jang

No Thumbnail Available
Last Name
Yang
First Name
Yiing-Jang
ORCID

Search Results

Now showing 1 - 15 of 15
  • Article
    Experimental and numerical studies of sound propagation over a submarine canyon northeast of Taiwan
    (IEEE, 2015-01-09) Lin, Ying-Tsong ; Duda, Timothy F. ; Emerson, Chris ; Gawarkiewicz, Glen G. ; Newhall, Arthur E. ; Calder, Brian ; Lynch, James F. ; Abbot, Philip A. ; Yang, Yiing-Jang ; Jan, Sen
    A study of sound propagation over a submarine canyon northeast of Taiwan was made using mobile acoustic sources during a joint ocean acoustic and physical oceanographic experiment in 2009. The acoustic signal levels (equivalently, transmission losses) are reported here, and numerical models of 3-D sound propagation are employed to explain the underlying physics. The data show a significant decrease in sound intensity as the source crossed over the canyon, and the numerical model provides a physical insight into this effect. In addition, the model also suggests that reflection from the canyon seabed causes 3-D sound focusing when the direction of propagation is along the canyon axis, which remains to be validated in a future experiment. Environmental uncertainties of water sound speed, bottom geoacoustic properties, and bathymetry are addressed, and the implications for sound propagation prediction in a complex submarine canyon environment are also discussed.
  • Preprint
    The formation and fate of internal waves in the South China Sea
    ( 2015-03) Alford, Matthew H. ; Peacock, Thomas ; MacKinnon, Jennifer A. ; Nash, Jonathan D. ; Buijsman, Maarten C. ; Centurioni, Luca R. ; Chao, Shenn-Yu ; Chang, Ming-Huei ; Farmer, David M. ; Fringer, Oliver B. ; Fu, Ke-Hsien ; Gallacher, Patrick C. ; Graber, Hans C. ; Helfrich, Karl R. ; Jachec, Steven M. ; Jackson, Christopher R. ; Klymak, Jody M. ; Ko, Dong S. ; Jan, Sen ; Johnston, T. M. Shaun ; Legg, Sonya ; Lee, I-Huan ; Lien, Ren-Chieh ; Mercier, Matthieu J. ; Moum, James N. ; Musgrave, Ruth C. ; Park, Jae-Hun ; Pickering, Andrew I. ; Pinkel, Robert ; Rainville, Luc ; Ramp, Steven R. ; Rudnick, Daniel L. ; Sarkar, Sutanu ; Scotti, Alberto ; Simmons, Harper L. ; St Laurent, Louis C. ; Venayagamoorthy, Subhas K. ; Wang, Yu-Huai ; Wang, Joe ; Yang, Yiing-Jang ; Paluszkiewicz, Theresa ; Tang, Tswen Yung
    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.
  • Article
    Internal solitons in the northeastern south China Sea. Part I: sources and deep water propagation
    (IEEE, 2004-10) Ramp, Steven R. ; Tang, Tswen Yung ; Duda, Timothy F. ; Lynch, James F. ; Liu, Antony K. ; Chiu, Ching-Sang ; Bahr, Frederick L. ; Kim, Hyoung-Rok ; Yang, Yiing-Jang
    A moored array of current, temperature, conductivity, and pressure sensors was deployed across the Chinese continental shelf and slope in support of the Asian Seas International Acoustics Experiment. The goal of the observations was to quantify the water column variability in order to understand the along- and across-shore low-frequency acoustic propagation in shallow water. The moorings were deployed from April 21–May 19, 2001 and sampled at 1–5 min intervals to capture the full range of temporal variability without aliasing the internal wave field. The dominant oceanographic signal by far was in fact the highly nonlinear internal waves (or solitons) which were generated near the Batan Islands in the Luzon Strait and propagated 485 km across deep water to the observation region. Dubbed trans-basin waves, to distinguish them from other, smaller nonlinear waves generated locally near the shelf break, these waves had amplitudes ranging from 29 to greater than 140 m and were among the largest such waves ever observed in the world’s oceans. The waves arrived at the most offshore mooring in two clusters lasting 7–8 days each separated by five days when no waves were observed.Within each cluster, two types of waves arrived which have been named type-a and type-b. The type-a waves had greater amplitude than the type-b waves and arrived with remarkable regularity at the same time each day, 24 h apart. The type-b waves were weaker than the type-a waves, arrived an hour later each day, and generally consisted of a single soliton growing out of the center of the wave packet. Comparison with modeled barotropic tides from the generation region revealed that: 1) The two clusters were generated around the time of the spring tides in the Luzon strait; and 2) The type-a waves were generated on the strong side of the diurnal inequality while the type-b waves were generated on the weaker beat. The position of the Kuroshio intrusion into the Luzon Strait may modulate the strength of the waves being produced. As the waves shoaled, the huge lead solitons first split into two solitons then merged together into a broad region of thermocline depression at depths less than 120 m. Elevation waves sprang up behind them as they continued to propagate onshore. The elevation waves also grew out of regions where the locally-generated internal tide forced the main thermocline down near the bottom. The “critical point” where the upper and lower layers were equal was a good indicator of when the depression or elevation waves would form, however this was not a static point, but rather varied in both space and time according to the presence or absence of the internal tides and the incoming trans-basin waves themselves.
  • Article
    Barotropic tide in the northeast South China Sea
    (IEEE, 2004-10) Beardsley, Robert C. ; Duda, Timothy F. ; Lynch, James F. ; Irish, James D. ; Ramp, Steven R. ; Chiu, Ching-Sang ; Tang, Tswen Yung ; Yang, Yiing-Jang ; Fang, Guohong
    A moored array deployed across the shelf break in the northeast South China Sea during April-May 2001 collected sufficient current and pressure data to allow estimation of the barotropic tidal currents and energy fluxes at five sites ranging in depth from 350 to 71 m. The tidal currents in this area were mixed, with the diurnal O1 and K1 currents dominant over the upper slope and the semidiurnal M2 current dominant over the shelf. The semidiurnal S2 current also increased onshelf (northward), but was always weaker than O1 and K1. The tidal currents were elliptical at all sites, with clockwise turning with time. The O1 and K1 transports decreased monotonically northward by a factor of 2 onto the shelf, with energy fluxes directed roughly westward over the slope and eastward over the shelf. The M2 and S2 current ellipses turned clockwise and increased in amplitude northward onto the shelf. The M2 and S2 transport ellipses also exhibited clockwise veering but little change in amplitude, suggesting roughly nondivergent flow in the direction of major axis orientation. The M2 energy flux was generally aligned with the transport major axis with little phase lag between high water and maximum transport. These barotropic energy fluxes are compared with the locally generated diurnal internal tide and high-frequency internal solitary-type waves generated by the M2 flow through the Luzon Strait.
  • Article
    Mean structure and variability of the cold dome northeast of Taiwan
    (The Oceanography Society, 2011-12) Jan, Sen ; Chen, Chung-Chi ; Tsai, Ya-Ling ; Yang, Yiing-Jang ; Wang, Joe ; Chern, Ching-Sheng ; Gawarkiewicz, Glen G. ; Lien, Ren-Chieh ; Centurioni, Luca R. ; Kuo, Jia-Yu
    The "cold dome" off northeastern Taiwan is one of the distinctive oceanic features in the seas surrounding Taiwan. The cold dome is important because persistent upwelling makes the region highly biologically productive. This article uses historical data, recent observations, and satellite-observed sea surface temperatures (SST) to describe the mean structure and variability of the cold dome. The long-term mean position of the cold dome, using the temperature at 50 m depth as a reference, is centered at 25.625°N, 122.125°E. The cold dome has a diameter of approximately 100 km, and is maintained by cold (< 21°C) and salty (> 34.5) waters upwelled along the continental slope. The ocean currents around the cold dome, although weak, flow counterclockwise. The monsoon-driven winter intrusion of the Kuroshio current onto the East China Sea shelf intensifies the upwelling and carries more subsurface water up to the cold dome than during the summer monsoon season. On a shorter timescale, the cold dome's properties can be significantly modified by the passage of typhoons, which creates favorable physical conditions for short-term Kuroshio intrusions in summer. The surface expression of the cold dome viewed from satellite SST images is often not domelike but instead is an irregular shape with numerous filaments, and thus may contribute substantially to shelf/slope exchange. As a result of persistent upwelling, typhoon passage, and monsoon forcing, higher chlorophyll a concentrations, and thus higher primary productivity, are frequently observed in the vicinity of the cold dome.
  • Article
    Circulation and intrusions northeast of Taiwan : chasing and predicting uncertainty in the cold dome
    (The Oceanography Society, 2011-12) Gawarkiewicz, Glen G. ; Jan, Sen ; Lermusiaux, Pierre F. J. ; McClean, Julie L. ; Centurioni, Luca R. ; Taylor, Kevin ; Cornuelle, Bruce D. ; Duda, Timothy F. ; Wang, Joe ; Yang, Yiing-Jang ; Sanford, Thomas B. ; Lien, Ren-Chieh ; Lee, Craig M. ; Lee, Ming-An ; Leslie, Wayne ; Haley, Patrick J. ; Niiler, Pearn P. ; Gopalakrishnan, Ganesh ; Velez-Belchi, Pedro ; Lee, Dong-Kyu ; Kim, Yoo Yin
    An important element of present oceanographic research is the assessment and quantification of uncertainty. These studies are challenging in the coastal ocean due to the wide variety of physical processes occurring on a broad range of spatial and temporal scales. In order to assess new methods for quantifying and predicting uncertainty, a joint Taiwan-US field program was undertaken in August/September 2009 to compare model forecasts of uncertainties in ocean circulation and acoustic propagation, with high-resolution in situ observations. The geographical setting was the continental shelf and slope northeast of Taiwan, where a feature called the "cold dome" frequently forms. Even though it is hypothesized that Kuroshio subsurface intrusions are the water sources for the cold dome, the dome's dynamics are highly uncertain, involving multiple scales and many interacting ocean features. During the experiment, a combination of near-surface and profiling drifters, broad-scale and high-resolution hydrography, mooring arrays, remote sensing, and regional ocean model forecasts of fields and uncertainties were used to assess mean fields and uncertainties in the region. River runoff from Typhoon Morakot, which hit Taiwan August 7–8, 2009, strongly affected shelf stratification. In addition to the river runoff, a cold cyclonic eddy advected into the region north of the Kuroshio, resulting in a cold dome formation event. Uncertainty forecasts were successfully employed to guide the hydrographic sampling plans. Measurements and forecasts also shed light on the evolution of cold dome waters, including the frequency of eddy shedding to the north-northeast, and interactions with the Kuroshio and tides. For the first time in such a complex region, comparisons between uncertainty forecasts and the model skill at measurement locations validated uncertainty forecasts. To complement the real-time model simulations, historical simulations with another model show that large Kuroshio intrusions were associated with low sea surface height anomalies east of Taiwan, suggesting that there may be some degree of predictability for Kuroshio intrusions.
  • Article
    Eddy-Kuroshio interactions : local and remote effects
    (John Wiley & Sons, 2017-12-11) Jan, Sen ; Mensah, Vigan ; Andres, Magdalena ; Chang, Ming-Huei ; Yang, Yiing-Jang
    Quasi-geostrophic mesoscale eddies regularly impinge on the Kuroshio in the western North Pacific, but the processes underlying the evolution of these eddy-Kuroshio interactions have not yet been thoroughly investigated in the literature. Here this interaction is examined with results from a semi-idealized three-dimensional numerical model and observations from four pressure-sensor equipped inverted echo sounders (PIESs) in a zonal section east of Taiwan and satellite altimeters. Both the observations and numerical simulations suggest that, during the interaction of a cyclonic eddy with the Kuroshio, the circular eddy is deformed into an elliptic shape with the major axis in the northwest-southeast direction, before being dissipated; the poleward velocity and associated Kuroshio transport decrease and the sea level and pycnocline slopes across the Kuroshio weaken. In contrast, for an anticyclonic eddy during the eddy-Kuroshio interaction, variations in the velocity, sea level, and isopycnal depth are reversed; the circular eddy is also deformed to an ellipse but with the major axis parallel to the Kuroshio. The model results also demonstrate that the velocity field is modified first and consequently the SSH and isopycnal depth evolve during the interaction. Furthermore, due to the combined effect of impingement latitude and realistic topography, some eddy-Kuroshio interactions east of Taiwan are found to have remote effects, both in the Luzon Strait and on the East China Sea shelf northeast of Taiwan.
  • Technical Report
    Acoustics and oceanographic observations collected during the QPE Experiment by Research Vessels OR1, OR2 and OR3 in the East China Sea in the Summer of 2009
    (Woods Hole Oceanographic Institution, 2010-08) Newhall, Arthur E. ; Lynch, James F. ; Gawarkiewicz, Glen G. ; Duda, Timothy F. ; McPhee, Neil M. ; Bahr, Frank B. ; Marquette, Craig D. ; Lin, Ying-Tsong ; Jan, Sen ; Wang, Joe ; Chen, Chi-Fang ; Chiu, Linus Y. S. ; Yang, Yiing-Jang ; Wei, Ruey-Chang ; Emerson, Chris ; Morton, David ; Abbot, Ted ; Abbot, Philip A. ; Calder, Brian ; Mayer, Larry A. ; Lermusiaux, Pierre F. J.
    This document describes data, sensors, and other useful information pertaining to the ONR sponsored QPE field program to quantify, predict and exploit uncertainty in observations and prediction of sound propagation. This experiment was a joint operation between Taiwanese and U.S. researchers to measure and assess uncertainty of predictions of acoustic transmission loss and ambient noise, and to observe the physical oceanography and geology that are necessary to improve their predictability. This work was performed over the continental shelf and slope northeast of Taiwan at two sites: one that was a relatively flat, homogeneous shelf region and a more complex geological site just shoreward of the shelfbreak that was influenced by the proximity of the Kuroshio Current. Environmental moorings and ADCP moorings were deployed and a shipboard SeaSoar vehicle was used to measure environmental spatial structure. In addition, multiple bottom moored receivers and a horizontal hydrophone array were deployed to sample transmission loss from a mobile source and ambient noise. The acoustic sensors, environmental sensors, shipboard resources, and experiment design, and their data, are presented and described in this technical report.
  • Article
    Observations of a freshwater pulse induced by Typhoon Morakot off the northern coast of Taiwan in August 2009
    (Sears Foundation for Marine Research, 2013-01-01) Jan, Sen ; Wang, Joe ; Yang, Yiing-Jang ; Hung, Chin-Chang ; Chern, Ching-Sheng ; Gawarkiewicz, Glen G. ; Lien, Ren-Chieh ; Centurioni, Luca R. ; Kuo, Jia-Yu ; Wang, Bee
    In this paper we describe large-scale impacts from a typhoon on the circulation over the continental shelf and slope north of Taiwan. Typhoon Morakot was a category 2 tropical storm that landed in central Taiwan, but caused destruction primarily in southern Taiwan from Aug. 8–10, 2009. The typhoon brought record-breaking rainfall; approximately 3 m accumulated over four days in southern Taiwan. River discharge on the west coast of Taiwan increased rapidly from Aug. 6–7 and peaked on Aug. 8, yielding a total volume 27.2 km3 of freshwater discharged off the west coast of Taiwan over five days (Aug. 6–10). The freshwater mixed with ambient seawater, and was carried primarily by the northeastward-flowing Taiwan Strait current to the sea off the northern coast of Taiwan. Two joint surveys each measured the hydrography and current velocity in the Taiwan Strait and off the northeastern coast of Taiwan roughly one week and two and a half weeks after Morakot. The first survey observed an Ω-shaped freshwater pulse off the northern tip of Taiwan, in which the salinity was ∼1 lower than the climatological mean salinity. The freshwater pulse met the Kuroshio and formed a density front off the northeastern coast of Taiwan. The hydrographic data obtained in the second survey suggested that the major freshwater pulse left the sea off the northern and northeastern coasts of Taiwan, which may have been carried by the Kuroshio to the northeast. Biogeochemical sampling conducted after Morakot suggested that the concentrations of nutrients in the upper ocean off the northern coast of Taiwan increased remarkably compared with their normal values. A typhoon-induced biological bloom is attributed to the inputs both from the nutrient-rich river runoff and upwelling of the subsurface Kuroshio water.
  • Article
    Research highlights from the Asian Seas International Acoustics Experiment in the South China Sea
    (IEEE, 2004-10) Lynch, James F. ; Ramp, Steven R. ; Chiu, Ching-Sang ; Tang, Tswen Yung ; Yang, Yiing-Jang ; Simmen, Jeffrey A.
    The Asian Seas International Acoustics Experiment (ASIAEX) included two major field programs, one in the South China Sea (SCS) and the other in the East China Sea (ECS). This paper summarizes results from the work conducted during April and May 2000 and 2001 over the continental shelf and slope in the northeastern South China Sea, just east of Dongsha Island (Pratis Reef). The primary emphasis of the field program was on water-column variability and its impact on acoustic propagation loss. The reader is steered to the appropriate paper within this Special Issue when more information on a specific topic is desired.
  • Article
    Internal tide and nonlinear internal wave behavior at the continental slope in the northern south China Sea
    (IEEE, 2004-10) Duda, Timothy F. ; Lynch, James F. ; Irish, James D. ; Beardsley, Robert C. ; Ramp, Steven R. ; Chiu, Ching-Sang ; Tang, Tswen Yung ; Yang, Yiing-Jang
    A field program to measure acoustic propagation characteristics and physical oceanography was undertaken in April and May 2001 in the northern South China Sea. Fluctuating ocean properties were measured with 21 moorings in water of 350- to 71-m depth near the continental slope. The sea floor at the site is gradually sloped at depths less than 90 m, but the deeper area is steppy, having gradual slopes over large areas that are near critical for diurnal internal waves and steep steps between those areas that account for much of the depth change. Large-amplitude nonlinear internal gravity waves incident on the site from the east were observed to change amplitude, horizontal length scale, and energy when shoaling. Beginning as relatively narrow solitary waves of depression, these waves continued onto the shelf much broadened in horizontal scale, where they were trailed by numerous waves of elevation (alternatively described as oscillations) that first appeared in the continental slope region. Internal gravity waves of both diurnal and semidiurnal tidal frequencies (internal tides) were also observed to propagate into shallow water from deeper water, with the diurnal waves dominating. The internal tides were at times sufficiently nonlinear to break down into bores and groups of high-frequency nonlinear internal waves.
  • Article
    The Kuroshio and Luzon Undercurrent east of Luzon Island
    (The Oceanography Society, 2015-12) Lien, Ren-Chieh ; Ma, Barry ; Lee, Craig M. ; Sanford, Thomas B. ; Mensah, Vigan ; Centurioni, Luca R. ; Cornuelle, Bruce D. ; Gopalakrishnan, Ganesh ; Gordon, Arnold L. ; Chang, Ming-Huei ; Jayne, Steven R. ; Yang, Yiing-Jang
    Current structure, transport, and water mass properties of the northward-flowing Kuroshio and the southward-flowing Luzon Undercurrent (LU) were observed for nearly one year, June 8, 2012–June 4, 2013, across the Kuroshio path at 18.75°N. Observations were made from four platforms: an array of six subsurface ADCP moorings, two Seagliders, fivepressure inverted echo sounders (PIES), and five horizontal electric field (HEF) sensors, providing the most detailed time series of the Kuroshio and Luzon Undercurrent water properties to date. Ocean state estimates of the western boundary current system were performed using the MIT general circulation model—four-dimensional variational assimilation (MITgcm-4D-Var) system. Prominent Kuroshio features from observations are simulated well by the numerical model. Annual mean Kuroshio transport, averaged over all platforms, is ~16 Sv with a standard deviation ~4 Sv. Kuroshio and LU transports and water mass pathways east of Luzon are revealed by Seaglider measurements. In a layer above the salinity maximum associated with North Pacific Tropical Water (NPTW), Kuroshio transport is ~7 Sv and contains North Equatorial Current (NEC) and Western Philippine Sea (WPS) waters, with an insignificant amount of South China Sea water on the shallow western flank. In an intermediate layer containing the core of the NPTW, Kuroshio transport is ~10 Sv, consisting mostly of NEC water. In the lower layer of the Kuroshio, transport is ~1.5 Sv of mostly North Pacific Intermediate Water (NPIW) as a part of WPS waters. Annual mean Luzon Undercurrent southward transport integrated to 1,000 m depth is ~2.7 Sv with a standard deviation ~2 Sv, carrying solely WPS waters below the salinity minimum of the NPIW. The transport of the western boundary current integrated over the full ocean depth east of Luzon Island is ~14 ± 4.5 Sv. Sources of the water masses in the Kuroshio and Luzon Undercurrent are confirmed qualitatively by the numerical model.
  • Article
    Mean structure and fluctuations of the Kuroshio east of Taiwan from in situ and remote observations
    (The Oceanography Society, 2015-12) Yang, Yiing-Jang ; Jan, Sen ; Chang, Ming-Huei ; Wang, Joe ; Mensah, Vigan ; Kuo, Tien-Hsia ; Tsai, Cheng-Ju ; Lee, Chung-Yaung ; Andres, Magdalena ; Centurioni, Luca R. ; Tseng, Yu-Heng ; Liang, Wen-Der ; Lai, Jian-Wu
    The Kuroshio is important to climate, weather prediction, and fishery management along the northeast coast of Asia because it transports tremendous heat, salt, and energy from east of the Philippines to waters southeast of Japan. In the middle of its journey northward, the Kuroshio’s velocity mean and its variability east of Taiwan crucially affect its downstream variability. To improve understanding of the Kuroshio there, multiple platforms were used to collect intensive observations off Taiwan during the three-year Observations of the Kuroshio Transports and their Variability (OKTV) program (2012–2015). Mean Kuroshio velocity transects show two velocity maxima southeast of Taiwan, with the primary velocity core on the onshore side of the Kuroshio exhibiting a mean maximum velocity of ~1.2 m s–1. The two cores then merge and move at a single velocity maximum of ~1 m s–1 east of Taiwan. Standard deviations of both the directly measured poleward (v) and zonal (u) velocities are ~0.4 m s–1 in the Kuroshio main stream. Water mass exchange in the Kuroshio east of Taiwan was found to be complicated, as it includes water of Kuroshio origin, South China Sea Water, and West Philippine Sea Water, and it vitally affects heat, salt, and nutrient inputs to the East China Sea. Impinging eddies and typhoons are two of the principal causes of variability in the Kuroshio. This study’s models are more consistent with the observed Kuroshio than with high-frequency radar measurements.
  • Article
    Significant internal waves and internal tides measured northeast of Taiwan
    (Sears Foundation for Marine Research, 2013-01-01) Duda, Timothy F. ; Newhall, Arthur E. ; Gawarkiewicz, Glen G. ; Caruso, Michael J. ; Graber, Hans C. ; Yang, Yiing-Jang ; Jan, Sen
    Internal gravity waves in an area northeast of Taiwan are characterized using data from multiple sensor types. The data set includes intermittent information collected from a ship and short time series from moorings. Modeled nonlinear waves are fitted to observed nonlinear waves to provide self-consistent estimates of multiple wave parameters. A nonlinear internal wave of over 50 m amplitude, observed in deep water, is examined in detail. This wave was moving northward from the southern Okinawa Trough toward the continental shelf, and presumably formed from internal tides propagating northward from the Ilan Ridge area. A possible scenario for the formation of this wave from the internal tide is compared to related behavior south of Taiwan. On the outer continental shelf, a few large internal waves with maximum displacement greater than one-quarter of the water depth were measured with moorings. Sensors aboard ship and satellite recorded waves in this area traveling in many directions. Two possible causes (not mutually exclusive) for the multiple wave directions are scattering of nonlinear internal waves arriving from the south, and variable local generation of nonlinear gravity waves by the strong tidal and internal tidal currents. Internal tides on the shelf are relatively strong, among the strongest measured, having about 10 times greater kinetic energy density than numerous low-energy sites, which is consistent with the strong barotropic tides of the area. The ratio of diurnal baroclinic to barotropic kinetic energy found in this area is unusually high.
  • Article
    Submesoscale eddy and frontal instabilities in the Kuroshio interacting with a cape south of Taiwan
    (American Geophysical Union, 2020-04-23) Cheng, Yu‐Hsin ; Chang, Ming-Huei ; Ko, Dong S. ; Jan, Sen ; Andres, Magdalena ; Kirincich, Anthony R. ; Yang, Yiing-Jang ; Tai, Jen‐Hua
    The processes underlying the strong Kuroshio encountering a cape at the southernmost tip of Taiwan are examined with satellite‐derived chlorophyll and temperature maps, a drifter trajectory, and realistic model simulations. The interaction spurs the formation of submesoscale cyclonic eddies that trap cold and high‐chlorophyll water and the formation of frontal waves between the free stream and the wake flow. An observed train of eddies, which have relative vorticity about one to four times the planetary vorticity (f), is shed from the recirculation that occurs in the immediate lee of the cape as a result of flow separation. These propagate downstream at a speed of 0.5–0.6 m s−1. Farther downstream, the corotation and merging of two or three adjacent eddies are common owing to the topography‐induced slowdown of eddy propagation farther downstream. It is found that the relative vorticity of a corotating system (1.2f) is 70% weaker than that of a single eddy due to the increase of eddy diameter from ~16 to ~33 km, in agreement with Kelvin's circulation theorem. The shedding period of the submesoscale eddies is strongly modulated by either diurnal or semidiurnal tidal flows, which typically reach 0.2–0.5 m s−1, whereas its intrinsic shedding period is insignificant. The frontal waves predominate in the horizontal free shear layer emitted from the cape, as well as a density front. Energetics analysis suggests that the wavy features result primarily from the growth of barotropic instability in the free shear layer, which may play a secondary process in the headland wake.