Showing papers by "Korean Ocean Research and Development Institute published in 1999"

A Numerical Modeling of the Upper and the Intermediate Layer Circulation in the East Sea

Abstract: Circulation in the upper and the intermediate layer of the East Sea is investigated by using a fine resolution, ocean general circulation model. Proper separation of the East Korean Warm Current from the coast is achieved by adopting the isopycnal mixing, and using the observed heat flux (Hirose et al., 1996) and the realistic wind stress (Na et al., 1992). The simulated surface circulation exhibits a remarkable seasonal variation in the flow patterns of the Nearshore Branch, the East Korean Warm Current and the Cold Currents. East of the Oki Bank, the Nearshore Branch follows the isobath of shelf topography from late winter to spring, while in summer and autumn it meanders offshore. The Nearshore Branch is accompanied by cyclonic and anticyclonic eddies in a fully developed meandering phase. The meandering and the eddy formation of the Nearshore Branch control the interior circulation in the Tsushima Current area. A recirculation gyre is developed in the region of the East Korean Warm Current in spring and grown up to an Ulleung Basin scale in summer. A subsurface water is mixed with the fresh surface water by winter convection in the northeastern coastal region of Korea. The well-mixed low salinity water is transported to the south by the Cold Currents, forming the salinity minimum layer (Intermediate Water) beneath the East Korean Warm Current water. The recirculation gyre redistributes the core water of the salinity minimum layer in the Ulleung Basin.

Application of eddy viscosity closure models for the m2 tide and tidal currents in the yellow sea and the east china sea

Abstract: A three-dimensional mode-splitting, σ -coordinate barotropic finite-difference model, with subgrid scale diffusion represented using a range of eddy viscosity closure models, is used to examine M 2 tidal elevation and currents in the Yellow Sea and the East China Sea. Four eddy viscosity formulations are considered: q 2 - q 2 l turbulence energy model (Blumberg and Mellor, 1987), Prandtl mixing length model, Davies and Furnes’ (1980) simple flow-related model with mixing length which includes the bottom boundary layer thickness, and a time and space invariant eddy viscosity with 650 cm 2 /s. The bottom friction at the sea bed is given in a quadratic form using a constant bottom friction coefficient, c f and near-bottom velocities. A series of M 2 tide model runs were carried out and optimal values of c f were determined through the comparison with tidal elevation amplitudes and phases at 203 stations. From these comparisons it is shown that the M 2 tidal charts computed with a range of eddy viscosity formulations are in good agreement with each other when optimal values of c f are chosen; comparing with M 2 tidal current amplitudes and phases at 15 stations, it is shown that tidal current distributions and its profiles are in reasonably good agreement with winter-time observations in the central part of the Yellow Sea; relatively poor results are obtained near the Chinese coast where non-tidal effects such as abrupt changes in tidal current phase in the vertical due to large freshwater discharge are pronounced. It is noted that the bottom friction coefficient has a major influence on tidal elevation and tidal currents and optimal values of bottom friction coefficient are closely related to the near-bottom eddy viscosity. The considered eddy viscosity closure models appear to work well for tidal problem when the bottom friction parameter is optimized. Results indicate that for a barotropic tide the Prandtl mixing length model which can account of the boundary layer thickness could be an useful alternative to a highly complex q 2 - q 2 l model.

Lead-210 and polonium-210 in the winter well-mixed turbid waters in the mouth of the Yellow Sea

Abstract: Concentration profiles of 210 Pb and 210 Po were measured along a traverse of the mouth of the Yellow Sea in February 1993 Winter time suspended particulate matter concentration was more than 10–100 mg l -1 in the coastal domain and less than 10 mg l -1 in the central domain Concentrations of dissolved 210 Pb over the area were low ( -1 ) due to the efficient removal of 210 Pb from the water column over the shelf Evidence for release of 210 Po is seen in a sub-surface layer, close to the sediment–water interface, where 210 Po is enriched in the dissolved form and depleted in the particles The high concentration of SPM in the mouth of the Yellow Sea appears to determine dissolved and particulate 210 Pb and 210 Po activities The atmospheric input of 210 Pb is the major source of 210 Pb in the region with minor contribution from the 210 Pb rich Kuroshio Water The K d values of 210 Po varied by a factor of 50 while the corresponding values of 210 Pb varied only by a factor of 4 It appears that in waters where particle concentrations are high (>10 mg l -1 ), the K d appears to be independent of particle concentration

Phytoplankton biomass and primary production in the marginal ice zone of the northwestern Weddell Sea during austral summer

Abstract: During the austral summer of 1995, distributions of phytoplankton biomass (as chlorophyll a), primary production, and nutrient concentrations along two north-south transects in the marginal ice zone of the northwestern Weddell Sea were examined as part of the 8th Korean Antarctic Research Program An extensive phytoplankton bloom, ranging from 16 to 112 mg m−3 in surface chlorophyll a concentration, was encountered along the eastern transect and extended ca 180 km north of the ice edge The spatial extent of the bloom was closely related to the density field induced by the input of meltwater from the retreating sea ice However, the extent (ca 200 km) of the phytoplankton bloom along the western transect exceeded the meltwater-influenced zone (ca 18 km) The extensive bloom along the western transect was more closely related to local hydrography than to the proximity of the ice edge and the resulting meltwater-induced stability of the upper water column In addition, the marginal ice zone on the western transect was characterized by a deep, high phytoplankton biomass (up to 8 mg Chl a m−3) extending to 100-m depth, and the decreased nutrient concentration, which was probably caused by passive sinking from the upper euphotic zone and in situ growth Despite the low bloom intensity relative to the marginal ice zone in both of the transects, mean primary productivity (26 g C m−2 day−1) in shelf waters corresponding to the northern side of the western transect was as high as in the marginal ice zone (21 g C m−2 day−1), and was 48 times greater than that in open waters, suggesting that shelf waters are as highly productive as the marginal ice zone A comparison between the historical productivity data and our data also shows that the most productive regions in the Southern Ocean are shelf waters and the marginal ice zone, with emerging evidence of frontal regions as another major productive site

Observations of high‐latitude lower thermospheric winds from Thule Air Base and Søndre Strømfjord, Greenland

Abstract: Lower thermospheric winds have been determined from Fabry-Perot interferometer (FPI) measurements of the Doppler shift of the 5577-A O(1S) emission over Thule Air Base (76.5°N, 69.0°W) and Sondre Stromfjord (67.0°N, 50.9°W), Greenland. These winds normally correspond to the altitude of the peak of the airglow O(1S) emission layer, near 97 km. The altitude ambiguity due to auroral contamination has been reduced by eliminating data when the intensity of the emission increases significantly. Contamination by airglow emission of 5577-A O(1S) originating from higher altitudes has been investigated by an FPI simulation code. The simulation results indicate that this latter emission may contribute an anomalous diurnal oscillation to ground-based 5577-A O(1S) FPI measurements of lower thermospheric wind. The agreement of diurnal phases between that deduced from the green-line measurements and that determined from simultaneous red-line observation supports this conclusion. The same simulation applied to observations from Sondre Stromfjord shows that the upper layer contamination is much weaker and is not serious. Significant day-to-day variation is evident in the lower thermospheric wind field. Average neutral winds are calculated, and a harmonic analysis is carried out to examine the major low-frequency wind components. The seasonal variations of these wind components are compared with radar data and model predictions. The observations are generally in good agreement with model results. The comparison between FPI and radar results also shows reasonable agreement. The semidiurnal amplitudes observed with the Sondre Stromfjord radar during the Lower Thermospheric Coupling Study (LTCS-I) and LTCS-2 periods are always greater than the climatological values obtained from averaging FPI and Chatanika radar observations. This result shows the variability that can be expected when comparing “instantaneous” estimates of tidal parameters with climatological results.