• Wind and Structures
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• v.19 no.5
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• pp.505-522
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• 2014

While effects of the atmospheric boundary layer flow on engineering infrastructure are more or less known, some local transient winds create difficulties for structures, traffic and human activities. Hence, further research is required to fully elucidate flow characteristics of some of those very unique local winds. In this study, important characteristics of observed vertical velocity profiles along the main wind direction for the gusty Bora wind blowing along the eastern Adriatic coast are presented. Commonly used empirical power-law and the logarithmic-law profiles are compared against unique 3-level high-frequency Bora measurements. The experimental data agree well with the power-law and logarithmic-law approximations. An interesting feature observed is a decrease in the power-law exponent and aerodynamic surface roughness length, and an increase in friction velocity with increasing Bora wind velocity. This indicates an urban-like velocity profile for smaller wind velocities and rural-like velocity profile for larger wind velocities, which is due to a stronger increase in absolute velocity at each of the heights observed as compared to the respective velocity gradient (difference in average velocity among two different heights). The trends observed are similar during both the day and night. The thermal stratification is near neutral due to a strong mechanical mixing. The differences in aerodynamic surface roughness length are negligible for different time averaging periods when using the median. For the friction velocity, the arithmetic mean proved to be independent of the time record length, while for the power-law exponent both the arithmetic mean and the median are not influenced by the time averaging period. Another issue is a large difference in aerodynamic surface roughness length when calculating using the arithmetic mean and the median. This indicates that the more robust median is a more suitable parameter to determine the aerodynamic surface roughness length than the arithmetic mean value. Variations in velocity profiles at the same site during different wind periods are interesting because, in the engineering community, it has been commonly accepted that the aerodynamic characteristics at a particular site remain the same during various wind regimes.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.1
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• pp.25-33
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• 2008

Water waves are generated mainly by winds in open seas and large lakes. They carry a significant amount of energy from winds into near-shore region. Thereby they significantly contribute to the regional hydrodynamics and transport process, producing strong physical, geological and environmental impact on coastal environment and on human activities in the coastal area. Furthermore an accurate prediction of the hydrodynamic effects due to wave interaction with offshore structures is a necessary requirement in the design, protection and operation of such structures. In the present paper surface and internal waves scattering by thin surface-piercing and bottom-standing vertical barriers in a two-layer fluid is analyzed in two-dimensions within the context of linearized theory of water waves. The reflection coefficients for surface and internal waves are computed and analyzed in various cases. It is found that wave reflection is strongly dependent on the interface location and the fluid density ratio apart from the barrier geometry.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.51 no.5
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• pp.579-589
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• 2018

Data from the two bottom moorings of ADCP (acoustic doppler current profiler), coastal weather station and CTC (conductivity temperature depth) observations for 2001 were analyzed to describe the physical processes associated with upwelling off the southeast coast of Korea. Winds were favorable for upwelling during summer, but were not correlated with currents. Shoaling of isotherms toward the coast due to the baroclinic tilting of the strong East Korean Warm Current (EKWC) provided a favorable background for immediate upwelling-response of surface temperature to southerly winds. This baroclinic effect was supported by a significant inverse coherence between the upper-layer current and bottom temperature near the coast. This upwelling is similar to the Guinea Current upwelling, which is driven by remote forcing (Houghton, 1989). Persistent southward flow was observed below approximately $10^{\circ}C$ isotherm throughout the observation period.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.25 no.1
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• pp.15-28
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• 1992

Temporal variations of the path of the East Korea Warm Current(EKWC) which flows northward along the east coast of Korea were analysed to investigate whether the EKWC directly influences the existence of the so-called Warm Core in the Ulreung basin. From the 13 years(1975-1987) data of the Fisheries Research and Development Agency(FRDA), the $10^{\circ}C$ isotherm at the 100m depth and the depth of $2^{\circ}C$ isotherm and the temperature field at the 200m depth were used for identification of the path and the central position of the Warm Core. Sea surface winds computed from the surface pressure charts gave the monthly-averaged wind stress curl over the East Sea which was used for determination of the Sverdrup transport. And the mass transport stream functions were computed by use of the Sverdrup balance. The variations of the path show that the EKWC does not always have a fixed path and fluctuates with time. And the existence of the Warm Core is independent upon the presence of the EKWC even when the EKWC doesn't flow northward along the east coast of Korea. In view of the mass transport stream functions, the influences of the sea surface winds on the branching of the Tsushima Warm Currents and the presence of the EKWC were investigated. The presence of the EKWC may be hindered by the southward flow driven by the sea surface winds when the Tsushima currents are rather weak. A very weak correlation exists between the north-south component of the Sverdrup transport and the position of the Warm Core. However, a small but significant part of the southward transport across the latitudinal line of $38^{\circ}N$ indicates that cold water from the northern part of the East Sea may be driven and be forced to flow beneath the permanent thermocline in such a way that the thermal structure of the Warm Core and its position might be changed.

• Journal of Korean Society for Atmospheric Environment
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• v.15 no.4
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• pp.441-455
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• 1999

Meteorological characteristics of three high-ozone episodes in the Greater Seoul Area, selected on the basis of morning-average wind direction and speed for the 1990~1997 period, were investigated. Three high-ozone episodes thus selected were seven days of July 3~9, 1992, nine days of July 21~29, 1994, and three days of August 22~24, 1994. Along with surface meteorological data from the Seoul Weather Station, surface and 850-hPa wind fields over the Northest Asia around the Korean Peninsula were used for the analysis. In the July 1992 episode, westerly winds were most frequent as a result of the influence of a high-pressure system in the west behind the trough. In contrast, in the July 1994 episode, easterly winds were most frequent due to the effect of a typhoon moving north from the south of Japan. Despite different prevailing wind directions in the two episodes, the peak ozone concentration of each episode always occurred when a sea-land breeze developed in association with weak synoptic forcing. The August 1994 episode, selected as being representative of calm conditions, was another typical example in which peak ozone concentration rose to 322 ppb under the well-developed sea-land breeze. All three high-ozone episodes were terminated by precipitation, and subsequent rises in ozone concentrations were also suppressed by a series of precipitation afterwards. In particular, two heavy rainfalls were the main reason why the August 1994 episode, with the highest and second-highest ozone concentrations during the 1990~1997 period, lasted for only a few days.

• Journal of Environmental Science International
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• v.11 no.1
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• pp.41-56
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• 2002

In order to estimate the quantitative roles of the tide induced residual currents, density currents and wind driven currents on the residual currents in Kwangynag Bay Korea, numerical experiments with a diagnostic multi-level model were carried out. Density currents were calculated from the temperature and salinity data observed in January, May, August and November 1998. Anti-clockwise circulations are formed at the western inner part of the bay, the location from the east of Myodo Is. to the south of POSCO Co. and the place between Yeosu peninsula and Namhae Is. from the calculation results of the tide induced residual currents. Velocities of the density currents are less than 3cm/s at the western inner part of the bay and about 5cm/s at the southern entrance of the bay. Density currents get strong in summer and weak in autumn. Wind driven currents at the surface layer flow in the directions of the given winds which are the daily mean winds when the temperature and salinity observations are carried out. In the middle and lower layers, however the wind driven currents flow in the opposite direction to the surface currents as supplementary currents. The surface wind driven currents are greater than the tide induced residual currents or the density currents. The calculated residual currents including the tide induced residual currents, density currents and wind driven currents agree with the results of the current observations approximately. In the Bay, the wind driven currents affect on the residual currents greatestly and tide induced residual currents and density currents do in the second place and the third place.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.31 no.3
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• pp.359-371
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• 1998

The cold water event near Gampo-Ulgi coast in summers between 1987 and 1994 are studied using sea surface temperature records at the coastal stations, ocean winds measured by SSM/I and AVHRR SST images. The response time of the cold water events by upwelling is less than two days and surface cold water expands up to the Ulleung Island. An analysis of 61 upwelling favorable winds indicates that the surface water temperature drops more than $1^{\circ}C\;in\;80\%$ of the south-westerly wind events. The linear correlation coefficient between wind impulses and the maximum temperature drops is good (0.6). It is found that the major cause of the cold water events is the along-shore wind in summer. The bottom topography and off-shore direction of the East Korean Warm Current by the potential vorticity conservation near Gampo coast also contribute the formation of the cold water along the southeast coast of Korea.

• Atmosphere
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• v.20 no.3
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• pp.343-353
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• 2010

A regional wind network with complex surface conditions must be designed with sufficient space and time resolution to resolve the local circulations. In this study, the spatial variations of the wind field observed in the Seoul and Jeju regional networks were evaluated in terms of annual, seasons, and months to assess the spatial homogeneity of wind fields within the regional networks. The coherency of the wind field as a function of separation distance between stations indicated that significant coherency was sometimes not captured by the network, as inferred by low correlations between adjacent stations. A meso-velocity scale was defined in terms of the spatial variability of the wind within the network. This problem is predictably most significant with weak winds, dull prevailing wind, clear skies and significant topography. The relatively small correlations between stations imply that the wind at a given point cannot be estimated by interpolating winds from the nearest stations. For the Seoul and Jeju regional network, the meso-velocity scale has typically a same order of magnitude as the speed of the network averaged wind, revealing the large spatial variability of the Jeju network station imply topography and weather. Significant scatter in the relationship between spatial variability of the wind field and the wind speed is thought to be related to thermally-generated flows. The magnitude of the mesovelocity scale was significantly different along separation distance between stations, wind speed, intensity of prevailing wind, clear and cloudy conditions, topography. Resultant wind vectors indicate much different flow patterns along condition of contributing factors. As a result, the careful considerations on contributing factors such as prevailing wind in season, weather, and complex surface conditions with topography and land/sea contrast are required to assess the spatial variations of wind field on a regional network. The results in the spatial variation from the mesovelocity scale are useful to represent the characteristics of regional wind speed including lower surface conditions over the grid scale of large scale atmospheric model.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2003.05a
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• pp.147-156
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• 2003

In order to improve navigational safety of ships, on ocean wave prediction model of high precision within a short time, dealing with multi-directional random waves from the information of the sea surface winds encountered at the planned ship's course, was introduced for construction of ocean wave forecasting system on the ship. In this paper, we investigated a sea disaster occurred by a stormy weather in the past. We analyzed the sea surface winds first and then carried out ocean wave hindercasting simulations according to the routes of the sunken vessel. From the result of this study, we concluded that the sea disaster was caused by rapidly developed low pressure system in Okhotsk Sea and the predicted values by the third generation wave prediction model(WAM) was agreed well with the observed significant wave height, was period, and directional wave spectrum. It gives a good applicability for construction of a practical on-board calculation system.

• The Journal of the Acoustical Society of Korea
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• v.25 no.8
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• pp.395-402
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• 2006

When an active SONAR works in the subsurface. its detection Performance is limited by the reverberation. The winds Play a primary role in the Production of bubbles in the ocean. And the bubbles as efficient scatters contribute to the reverberant field. In this Paper the effects of wind-generated bubbles on sound propagation in the subsurface are investigated as a mid-frequency Hull-mounted SONAR works. The active signal excess is calculated at source depths 3. 5. and 10m considering bubble layer for frequencies 5. 7.5, and 10kHz. The change of the near-surface sound speed tend to increase surface reverberation levels and change the active signal excess. In the 10m/s winds. the maximum detection range reduces over 3km through the near-surface . The reason is the upper refraction due to the wind-generated bubbles.