• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2007년도 춘계학술대회 논문집
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• pp.204-209
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• 2007

수중에서의 하향 방향의 감쇠 계수 (Diffuse attenuation coefficient of down-welling irradiance, $K_d$)에 대한 연구는 상충 해양에 대한 열전달 수중에서의 광합성 및 다른 생물학적 과정에 대한 연구，해양 일차 생산력 추정, 대양 및 연안에서의 탁도 추정 등에 대한 연구의 보조 자료로서 해양원격탐사를 포함한 해양에 대한 연구에 매우 중요한 요소이다. 우리나라는 세계 최초의 정지궤도 해색 센서인 Geostationary Ocean Color Imager (GOCI)를 2008년 말에 통신해양기상위성 (COMS, Communication Ocean and Meteorological Satellite)에 탑재하여 쏘아 올릴 계획에 있다. 이 센서는 매일 한 시간 간격으로 한반도 주변 해역을 8회 이상 관측할 계획에 었다. 따라서 기존의 해색 센서들에 비해서 시간 해상도가 향상되기 때문에 해양 환경 모니터링에 있어서 많은 도움이 될 것으로 예상된다. 본 연구에서는 앞으로 운영될 GOCI 센서에 대한 수중에서의 하향 방향의 감쇠계수 (The diffuse attenuation coefficient of down-welling irradiance, $K_d$) 알고리즘을 현장 관측 값을 이용하여 미리 만들어 보고 이를 현재의 대표적인 해색 센서인 SeaWiFS 영상의$K_d$(490) product와 비교하여 보았다.

• 한국물환경학회지
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• 제31권4호
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• pp.367-376
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• 2015

The momentum and kinetic turbulent energy carried by the wind to a stratified lake lead to basin-scale motions, which provide a major driving force for vertical and horizontal mixing. A three-dimensional (3D) hydrodynamic model was applied to Lake Tahoe, located between California and Nevada, USA, to simulate the dominant basin-scale internal waves in the deep lake. The results demonstrated that the model well represents the temporal and vertical variations of water temperature that allows the internal waves to be energized correctly at the basin scale. Both the model and thermistor chain (TC) data identified the presence of Kelvin modes and Poincare mode internal waves. The lake was weakly stratified during the study period, and produced large amplitude (up to 60 m) of internal oscillations after several wind events and partial upwelling near the southwestern lake. The partial upwelling and followed coastal jets could be an important feature of basin-scale internal waves because they can cause re-suspension and horizontal transport of fine particles from nearshore to offshore. The internal wave dynamics can be also associated with the distributions of water quality variables such as dissolved oxygen and nutrients in the lake. Thus, the basin-scale internal waves and horizontal circulation processes need to be accurately modeled for the correct simulation of the dissolved and particulate contaminants, and biogeochemical processes in the lake.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2744-2749
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• 2008

Numerical calculations are carried out for the natural convection induced by temperature difference between a cold outer square cylinder and a hot inner circular cylinder for Rayleigh number of $Ra=10^7$. This study investigates the effect of the inner cylinder location on the heat transfer and fluid flow. The location of inner circular cylinder ($\delta$) is changed vertically along the center-line of square enclosure. The natural convection bifurcates from unsteady to steady state according to $\delta$. Two critical positions of ${\delta}_{C,L}$ and ${\delta}_{C,U}$ as a lower bound and an upper bound are ${\delta}_{C,L}=0.05$ and ${\delta}_{C,U}=0.18$, respectively. Within the defined bounds, the thermal and flow fields are steady state. When the inner cylinder locates at ${\delta}{\geq}{\delta}_{C,U}$, the space between the upper surface of inner cylinder and the top surface of the enclosure forms a relatively shallow layer where the natural convection characterized as the pure Rayleigh-Benard convection forms alternately the upwelling and downwelling plums, as a result that a series of cells known as Benard cells is derived.

• 한국환경과학회지
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• 제24권12호
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• pp.1657-1671
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• 2015

In this study, the wind direction and the wind speed of the nearest temperature observations point of the National Weather Service was analyzed in order to investigate the rapid rise and drop of water temperature in the East Coast appeared after passing of the 2015 typhoon No. 9 and 11. Then the figures were simulated and analyzed using the WRF(weather research and forecast) model to investigate in more detailed path of the typhoon as well as the changes in the wind field. The results were as follows. A sudden drop of water temperature was confirmed due to upwelling on the East coast when ninth typhoon Chanhom is transformed from tropical cyclones into extra tropical cyclone, then kept moving eastwards from Pyongyang forming a strong southerly wind after 13th and this phenomenon lasted for two days. The high SST(sea surface temperature) is confirmed due to a strong northerly wind by 11th typhoon Nangka. This strong wind directly affected the east coast for three days causing the Ekman effect which transported high offshore surface waters to the coast. The downwelling occurred causing an accumulation of high temperature surface water. As a results, the SST of 15m and 25m rose to that of 5m.

• 한국해양학회지
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• 제20권3호
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• pp.6-19
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• 1985

한국 남동해안의 풍향에 따른 거의 균일한 용승현상 중 특히 울기-감포 근해역에 현저하게 나타나는 용승의 원인을 해양관측 자료와 기상, 해수면 변위 및 표층수온의 일변화 자료를 이용하여 연구하였다. 바람에 의한 용승현상이 강도에 있어 지역적인 차이를 보이는 것은 두가지 요인의 복합적인 영향에 기인한다. 첫째로 울기-감포해안에 발달한 동한난류(EKWC)로 인한 등온선의 baroclinic tilting 요인과 둘째로 남동해안 주변의 지형적 영향을 들 수 있다. 동한난류의 baroclinic tilting효과는 대체로 울기-감포해안 근처에서 가장 강하게 나타나며, 이로 인해 계절에 관계없이 얕은 대륙붕위로 저층냉수가 편중되어 나타난다. 따라서 표면 가까이 용승에 의한 냉수괴가 존재하며 결국 울기-감포해안에서만 여름에 바람에 의한 용승으로 표층수온이 낮게 나타난다. 또한 부산에서 감포에 이르는 평탄한 연안 해저지형도 저층냉수의 용승을 증가시키는 작용을 한다.

• 해양환경안전학회:학술대회논문집
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• 해양환경안전학회 2007년도 추계학술발표회
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• pp.9-14
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• 2007

한국 남해안 거제도 앞바다에 구축된 인공용승구조물로 인하여 발생하는 유동 변화를 파악하기 위해 ADCP(Acoustic Doppler Current Profiler)를 이용한 정선관측을 2003년 하계 및 추계에 실시하였다. 관측 결과 하계에는 수심 약 $30{\sim}40$ m를 기준으로 상층과 하층의 유동분포가 상이한 경계수심이 존재하였으며, 추계에는 이러한 현상이 3층 구조로 나타났다. 또한 연직유동성분은 수심과 지역에 따라 상승류와 하강류가 번갈아 분포하였으며 이러한 현상은 관측범위를 확장하였을 때도 유사한 유동분포를 보이고 있다. 한편 ADCP의 수평유동성분을 이용하여 계산된 연직전단(vertical shear) 및 상대와도(relative vorticity)는 상승류가 발생하는 지역에서 연직전단은 큰 값을 나타내었고, 상대와도는 +값으로 상승류의 방향을 나타내었다. 이러한 결과는 유동성분의 상승류 분포역과 유사하게 나타났다.

• Journal of the korean society of oceanography
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• 제32권3호
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• pp.93-102
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• 1997

Coastal circulations during the (surface condition of an) idealized cold-air outbreak are numerically investigated with two-dimensional, non-hydrostatic model in which a constant bottom-slope exists. The atmospheric forcing during a cold-air outbreak is incorporated as the surface cooling and the wind stress. When the offshore angle of the wind-stress vector, defined as the angle measured from the alongshore axis, is smaller than 45 degrees, a strong downwelling circulation develops near the coast. A sharp density front, which separates the vertically homogeneous region from the offshore stratified region, is formed near the coast and propagates offshore with time. Onshore side of the density front, small-scale circulation cells which are aligned in the direction perpendicular to the bottom begin to develop as the near-coast homogeneous region broadens. The surface cooling enhances greatly the development of the surface mixed layer by convective motions due to hydrostatic instability. The convective motions reach far below the hydrostatically unstable layer which is attached to the surface. The small-scale circulation cells are appreciably modified by the convetion cell and the density front develops far offshore compared to the case of no surface cooling. As to the effect of the bottom slope, the offshore distance of the density front increases (decreases) as the bottom slope decreases (increases), which results from the fact that the onshore volume-transport (Ekman transport) of the low-density upper seawater remains almost constant when the wind-stress is maintained constant. It is shown that the bottom slope is an essential factor for the formation of both the density front and the alongshore current when the surface cooling is the only forcing.

• Ocean Science Journal
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• 제42권2호
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• pp.103-116
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• 2007

Seasonal changes of tide signal(s), temperature, salinity and current were studied during the years 2004-2005 in the northernmost Gulf of Aqaba, which is under developmental activities, to obtain scientific bases for best management and sustainability. Spectrum analysis revealed permanent signals of tide measurements during all seasons, which represented semidiurnal and diurnal barotropic tides. The other signal periods of 8.13, 6.10-6.32, 4.16 and 1.02-1.05 h were not detected in all seasons, which were related to shallow water compound and overtides of principle solar and lunar constituent and to seiches generated in the Red Sea and the Gulf of Aqaba. Spatial and temporal distribution of temperature, salinity and density showed significant differences between months in the coastal and offshore region and no significant differences among the coastal sites, between the surface and bottom waters and between coastal and offshore waters. Therefore, the temporal and spatial variation of water properties in the northernmost Gulf of Aqaba behave similarly compared to other parts. The coastal current below 12 m depth was weak $(3-6\;cms^{-1})$ and fluctuated from east-northeastward to west-southwestward (parallel to the shoreline), which may be related to the effect of bottom topography and/or current density due to differential cooling between eastern and western parts in the study area, and wind-induced upwelling and downwelling in the eastern and western side, respectively. The prevailing northerly winds and stratification conditions during summer were the main causes of the southward current at 6 and 12 m depths with average speed of 28 and $12cms^{-1}$ respectively.

• 한국해안·해양공학회논문집
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• 제27권6호
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• pp.419-423
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• 2015

인공용승구조물은 흐름이 구조물에 의해 상승류와 배후면의 와류가 발생한다. 이때 저층수에 포함된 영양염이 표층으로 이동되고, 표층에선 플랑크톤 및 어류의 생태활동을 촉진시켜, 어업생산성을 향상시키는 역할을 한다. 본 연구에서는 CFD를 이용하여 성층 상태를 고려한 인공용승류의 변화에 대하여 연구하고자 하였으며, 그 결과, 용승효과는 인공용승구조물의 최상부에서 가까울수록 좋은 효과가 나타났으며, 성층상태를 고려하지 않은 경우, 저층에서 표층으로 향하는 상승류 특성만 나타났으나, 성층상태를 고려한 경우, 상승류와 하강류가 반복되는 흐름특성을 확인 할 수 있었다.

• Journal of Astronomy and Space Sciences
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• 제30권4호
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• pp.231-239
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• 2013

To identify seasonal and latitudinal variations of F2 layer during magnetic storm, we examine the change of daily averages of foF2 observed at Kokubunji and Hobart during high (2000~2002) and low (2006~2008) solar activity intervals. It is found that geomagnetic activity has a different effect on the ionospheric F2-layer electron density variation for different seasons and different latitudes. We, thus, investigate how the change of geomagnetic activity affects the ionospheric F2-layer electron density with season and latitude. For this purpose, two magnetic storms occurred in equinox (31 March 2001) and solstice (20 November 2003) seasons are selected. Then we investigate foF2, which are observed at Kokubunji, Townsville, Brisbane, Canberra and Hobart, Dst index, Ap index, and AE index for the two magnetic storm periods. These observatories have similar geomagnetic longitude, but have different latitude. Furthermore, we investigate the relation between the foF2 and the [O]/[$N_2$] ratio and TEC variations during 19-22 November 2003 magnetic storm period. As a result, we find that the latitudinal variations of [O]/[$N_2$] ratio and TEC are closely related with the latitudinal variation of foF2. Therefore, we conclude that the seasonal and latitudinal variations of foF2 during magnetic storm are caused by the seasonal and latitudinal variations of mean meridional circulation of the thermosphere, particularly upwelling and downwelling of neutral atmosphere during magnetic storm.