Kim Kuh

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Kuh
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  • Article
    Aspiration and outflow of the intermediate water in the East/Japan Sea through the Tsugaru Strait
    (American Geophysical Union, 2008-04-01) Park, Jong Jin ; Kim, Kuh ; Yang, Joon-Yong
    Outflow of the intermediate water in the East/Japan Sea through the Tsugaru Strait is inferred from the fact that profiling floats deployed below the sill depth in the central East/Japan Sea moved out to the Northwest Pacific Ocean through the Strait. Careful analysis of the float trajectories reveals that profiling floats parked at 350m, 700m, and 800m could be uplifted from depths below the sill of the Tsugaru Strait and moved over the 140m deep sill with a probability close to 100%. Application of an analytical model for the Bernoulli suction shows that intermediate waters can be aspirated over the sill depth of the Tsugaru Strait in late winter.
  • Preprint
    Comparison between a reanalyzed product by 3-dimensional variational assimilation technique and observations in the Ulleung Basin of the East/Japan Sea
    ( 2009-04-30) Kim, Young Ho ; Chang, Kyung-Il ; Park, Jong Jin ; Park, Seon Ki ; Lee, Sang-Hyun ; Kim, Young-Gyu ; Jung, Kyung Tae ; Kim, Kuh
    Reanalyzed products from a MOM3-based East Sea Regional Ocean Model with a 3- dimentional variational data assimilation module (DA-ESROM), have been compared with the observed hydrographic and current datasets in the Ulleung Basin (UB) of the East/Japan Sea (EJS). Satellite-borne sea surface temperature and sea surface height data, and in-situ temperature profiles have been assimilated into the DA-ESROM. The performance of the DA-ESROM appears to be efficient enough to be used in an operational ocean forecast system. Comparing with the results from Mitchell et al. (2005a), the DA-ESROM fairly well simulates the high variability of the Ulleung Warm Eddy and Dok Cold Eddy as well as the branching of the Tsushima Warm Current in the UB. The overall root-mean-square error between 100m temperature field reproduced by the DA-ESROM and the observed 100-dbar temperature field is 2.1°C, and the spatially averaged grid-to-grid correlation between the two temperature fields is high with a mean value of 0.79 for the intercomparison period. The DA-ESROM reproduces the development of strong southward North Korean Cold Current (NKCC) in summer consistent with the observational results, which is thought to be an improvement of the previous numerical models in the EJS. The reanalyzed products show that the NKCC is about 35 km wide, and flows southward along the Korean coast from spring to summer with maximum monthly mean volume transport of about 0.8 Sv in August-September.
  • Article
    Global distribution of the decay timescale of mixed layer inertial motions observed by satellite-tracked drifters
    (American Geophysical Union, 2009-11-05) Park, Jong Jin ; Kim, Kuh ; Schmitt, Raymond W.
    The decay timescale of mixed layer inertial amplitudes has been estimated from satellite tracked drifter trajectories from 1990 to 2004 as the e-folding timescale of the temporal correlation functions. The decay timescales increase with latitude in all basins except the North Atlantic. A beta dispersion model shows that dephasing leads to meridional variations of the decay timescale in the North Pacific and the Southern Ocean, but meridional variations of the buoyancy structure in the North Atlantic act to compensate the beta effect, leading to a lack of meridional variation of the decay timescale in that ocean.
  • Article
    Decadal variability of the upper ocean heat content in the East/Japan Sea and its possible relationship to northwestern Pacific variability
    (American Geophysical Union, 2012-02-09) Na, Hanna ; Kim, Kwang-Yul ; Chang, Kyung-Il ; Park, Jong Jin ; Kim, Kuh ; Minobe, Shoshiro
    The upper ocean heat content variability in the East/Japan Sea was investigated using a 40 year temperature and salinity data set from 1968 to 2007. Decadal variability was identified as the dominant mode of variability in the upper ocean (0–300 m) aside from the seasonal cycle. The decadal variability is strong to the west of northern Honshu, west of the Tsugaru Strait, and west of southern Hokkaido. Temperature anomalies at 50–125 m exhibit a large contribution to the decadal variability, particularly in the eastern part of the East/Japan Sea. The vertical structure of regressed temperature anomalies and the spatial patterns of regressed 10°C isotherms in the East/Japan Sea suggest that the decadal variability is related to upper ocean circulation in the East/Japan Sea. The decadal variability also exhibits an increasing trend, which indicates that the regions showing large decadal variations experienced warming on decadal time scales. Further analysis shows that the decadal variability in the East/Japan Sea is not locally isolated but is related to variability in the northwestern Pacific.
  • Article
    Manifestation of the Pacific Decadal Oscillation in the Kuroshio
    (American Geophysical Union, 2009-08-28) Andres, Magdalena ; Park, Jae-Hun ; Wimbush, Mark ; Zhu, Xiao-Hua ; Nakamura, Hirohiko ; Kim, Kuh ; Chang, Kyung-Il
    Pacific Decadal Oscillation (PDO) index is strongly correlated with vertically integrated transport carried by the Kuroshio through the East China Sea (ECS). Transport was determined from satellite altimetry calibrated with in situ data and its correlation with PDO index (0.76) is highest at zero lag. Total PDO-correlated transport variation carried by the ECS-Kuroshio and Ryukyu Current is about 4 Sv. In addition, PDO index is strongly negatively correlated, at zero lag, with NCEP wind-stress-curl over the central North Pacific at ECS latitudes. Sverdrup transport, calculated from wind-stress-curl anomalies, is consistent with the observed transport variations. Finally, PDO index and ECS-Kuroshio transport are each negatively correlated with Kuroshio Position Index in the Tokara Strait; this can be explained by a model in which Kuroshio path is steered by topography when transport is low and is inertially controlled when transport is high.
  • Thesis
    Instability and energetics in a baroclinic ocean
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1975-08) Kim, Kuh
    This thesis is made of two separate, but interrelated parts. In Part I the instability of a baroclinic Rossby wave in a two-layer ocean of inviscid fluid without topography, is investigated and its results are applied in the ocean. The velocity field of the basic state (the wave) is characterized by significant horizontal and vertical shears, non-zonal currents, and unsteadiness due to its westward propagation. This configuration is more relevant to the ocean than are the steady, zonal 'meteorological' flows, which dominate the literature of baroclinic instability. Truncated Fourier series are used in perturbation analyses. The wave is found to be unstable for a wide range of the wavelength; growing perturbations draw their energy from kinetic or potential energy of the wave depending upon whether the wavelength, 2πL, is much smaller or larger than 2πLρ, respectively, where Lρ is the internal radius of deformation. When the shears are comparable dynamically, L~Lρ , the balance between the two energy transfer processes is very sensitive to the ratios L/Lρ and U/C as well, where U is a typical current speed, and C a typical phase speed of the wave. For L = Lρ they are augmenting if U < C, yet they detract from each other if U > C. The beta-effect tends to stabilize the flow, but perturbations dominated by a zonal velocity can grow irrespective of the beta-effect. It is necessary that growing perturbations are comprised of both barotropic and baroclinic modes vertically. The scale of the fastest growing perturbation is significantly larger than L for barotropically controlled flows (L < Lρ ), reduces to the wave scale L for a mixed kind (L ~ Lρ ) and is fixed slightly larger than Lρ for baroclinically controlled flows (L > Lρ ). Increasing supply of potential energy causes the normalized growth rate, αL/U, to increase monotonically as L → Lρ from below. As L increases beyond Lρ, the growth rate αLρ /U shows a slight increase, but soon approaches an asymptotic value. In a geophysical eddy field like the ocean this model shows possible pumping of energy into the radius of deformation (~ 40 km rational scale, or 250 km wavelength) from both smaller and larger scales through nonlinear interactions, which occur without interference from the beta-effect. The e-folding time scale is about 24 days if U = 5 cm/sec and L = 90 km. Also it is strongly suggested that, given the observed distribution of energy versus length scale, eddy-eddy interactions are more vigorous than eddy-mean interaction, away from intènse currents like the Gulf Stream. The flux of energy toward the deformation scale, and the interaction of barotropic and baroclinic modes, occur also in fully turbulent 'computer' oceans, and these calculations provide a theoretical basis for source of these experimental cascades. In Part II an available potential energy (APE) is defined in terms appropriate to a limited area synoptic density map (e.g., the 'MODE-I' data) and then in terms appropriate to time-series of hydrographic station at a single geographic location (e. g., the 'Panulirus' data). Instantaneously the APE shows highly variable spatial structure, horizontally as well as vertically, but the vertical profile of the average APE from 19 stations resembles the profile of vertical gradient of the reference stratification. The eddy APE takes values very similar to those of the average kinetic energy density at 500 m, 1500 m and 3000 m depth in the MODE area. In and above the thermocline the APE has roughly the same level in the MODE area (centered at 28°N, 69° 40'W) as at the Panulirus station (32° 10'N, 64° 30'W), yet in the deep water there is significantly more APE at the Panulirus station. This may in part indicate an island effect near Bermuda.