An optimization strategy in wind-driven circulation with uncertain forcing problem off the southeastern coastal waters of Korea

김종규,김헌태,Kim Jong-Kyu,Kim Heon-Tae 한국해양환경·에너지학회 2001 한국해양환경·에너지학회지 Vol.4 No.2

한국 남동해역 취송순환에서의 부정확한 외력의 바람응력 문제에 대한 최적화 방법의 유용성에 관하여 검토하였다. 바람응력은 모델 및 수치적 정식화 과정에서 상층 경계조건 및 외력항으로 고려되었다. 그리고 바람응력 평가에 대한 최적화 방법의 적용성 및 모델변수의 초기값 추정치의 중요성을 검토하였다. 최적화 연구로부터 동해 남부해역의 취송순환에 관한 동한난류의 수송량 변화 및 통해 난수층의 형성과 분포특성을 바람응력, 바람응력 회전성 및 상층두께의 변동으로부터 파악할 수 있음을 확인하였다. We demonstrated the importance of initial estimates of model parameters and the utility of an optimization approach of the uncertain forcing of wind-driven circulation off the southeastern coastal waters of Korea. The wind stress represents the upper boundary condition in this model and enters in the model equation as a forcing term in the numerical formalism. The wind field contributes to maintain the almost time-independent distribution of the upper layer thickness feature in a north-south direction and negative wind stress curl to maintain the formation of warm eddy off the southeastern coastal waters of Korea. Elucidated is the variational characteristics of the East Korean Warm Current due to the variations of the zonally averaged wind stress (southward transport) from the seasonal variations of the meridional transport by the Ekman transport.

Role of wind stress in causing maximum transport through the Korea Strait in autumn

Cho, Y.K.,Seo, G.H.,Kim, C.S.,Choi, B.J.,Shaha, D.C. Elsevier 2013 Journal of marine systems Vol.115 No.-

Observations show that the maximum transport for the Tsushima Current (TC) through the Korea Strait occurs in autumn. For the TC, variation in transport changes the physical properties of the water as well as the distribution of nutrients, plankton, and other materials in the Japan/East Sea. Despite the importance of the TC, research is yet to unravel the cause of the maximum transport for the TC in autumn. In this study, observational data and numerical modeling data were analyzed in an effort to explore this phenomenon. The maximum transport through the Korea Strait was determined to be the result of the maximum onshore transport crossing the shelf break in the East China Sea (ECS); this transport is driven by strong northeasterly wind stress. Ekman transport driven by wind in the ECS is the primary cause of the maximum transport for the TC through the Korea Strait in autumn.

Is Ekman pumping responsible for the seasonal variation of warm circumpolar deep water in the Amundsen Sea?

Kim, T.W.,Ha, H.K.,Wahlin, A.K.,Lee, S.H.,Kim, C.S.,Lee, J.H.,Cho, Y.K. Pergamon Press ; Elsevier Science Ltd 2017 Continental shelf research Vol.132 No.-

<P>Ekman pumping induced by horizontally varying wind and sea ice drift is examined as an explanation for observed seasonal variation of the warm layer thickness of circumpolar deep water on the Amundsen Sea continental shelf. Spatial and temporal variation of the warm layer thickness in one of the deep troughs on the shelf (Dotson Trough) was measured during two oceanographic surveys and a two-year mooring deployment. A hydrographic transect from the deep ocean, across the shelf break, and into the trough shows a local elevation of the warm layer at the shelf break. On the shelf, the water flows south-east along the trough, gradually becoming colder and fresher due to mixing with cold water masses. A mooring placed in the trough shows a thicker and warmer layer in February and March (late summer/early autumn) and thinner and colder layer in September, October and November (late winter/early spring). The amplitude of this seasonal variation is up to 60 m. In order to investigate the effects of Ekman pumping, remotely sensed wind (Antarctic Mesoscale Prediction System wind data) and sea ice velocity and concentration (EASE Polar Pathfinder) were used. From the estimated surface stress field, the Ekman transport and Ekman pumping were calculated. At the shelf break, where the warm layer is elevated, the Ekman pumping shows a seasonal variation correlating with the mooring data. Previous studies have not been able to show a correlation between observed wind and bottom temperature, but it is shown here that when sea ice drift is taken into account the Ekman pumping at the outer shelf correlates with bottom temperature in Dotson Trough. The reason why the Ekman pumping varies seasonally at the shelf break appears to be the migration of the ice edge in the expanding polynya in combination with the wind field which on average is westward south of the shelf break.</P>

Current Structure and Volume Transport in the Jeju Strait Observed for a Year with Multiple ADCP Moorings

신창웅,민홍식,이석,강현우,구본화,김동국,박준성,권순열,최병주 한국해양과학기술원 2022 Ocean science journal Vol.57 No.3

The seasonal and spatial variation of the current structure and volume transport across the Jeju Strait (JS) is described based on an analysis of the data from five bottom mounted acoustic Doppler current profilers from February 13, 2020 to February 23, 2021. The current was weak and the mixed layer was well developed in winter, so the vertical current shear was not large. Whereas in summer, the inflow of high-temperature and low-salinity surface water built up the stratification, and the surface current velocity increased, resulting in a large vertical current shear. One salient feature to be found was that a westward flowing counter current in the lower layer appeared from June to December near the bottom trough of the JS. We named this seasonal counter current in the lower layer the Jeju Strait Under Current. The eastward net volume transport passing through the JS was large in summer–autumn and small in winter-spring, but did not follow a simple sinusoidal pattern. The annual mean net volume transport was 0.48 Sv (Sv ≡ 106 m3 s−1), with a minimum (0.27 Sv) in December and a maximum (0.79 Sv) in October 2020. When there were strong northerly winds in winter, a net volume transport to the west was temporarily caused by Ekman transport, but the direction reverted to the east as soon as the northerly winds lessened. When there were strong northwesterly (southeasterly) winds due to typhoons, the volume transport decreased (increased) sharply and then recovered rapidly.

태풍 통과에 따른 한국 연근해 수온 변동

서영상,김동순,김복기,이동인,김영섭,김일곤 한국환경과학회 2002 한국환경과학회지 Vol.11 No.7

While typhoons were passing by the coastal and offshore waters around the Korean peninsula, the variations of the sea surface temperature (SST) were studied. To study on the variation, the data related to the 22 typhoons among 346 typhoons which occurred in the western Pacific during 1990∼1999, daily measured field SSTs at coastal and offshore, and imageries from advanced very high resolution radiometer on NOAA satellite during 1990∼1999 were used. The average variations of the SSTs were -0.9℃ at coastal waters and -2℃ at offshore around the Korean peninsula while the typhoons were passing by. In very near coastal waters from the land, the SST was not changed because the bottom depth of the coastal waters was shallower than the depth of thermalcline, while the typhoon was passing. The temporal and spatial variation of SSTs at coastal waters in summer were depended on the various types of the typhoons' paths which were passing through the Korean peninsula. When a typhoon passed by the western parts including the Yellow Sea of the Korean peninsula, upwelling cold water occurred along the eastern coastal waters of the peninsula. The reason was estimated with the typhoon that was as very strong wind which blew from south toward north direction along the eastern shore of the peninsula, led to the Ekman transport from near the eastern coastal area toward the offshore. While cold water was occurring in the eastern coast, a typhoon passed over the coastal area, the cold water disappeared. The reason was estimated that the cold water was mixed up with the surrounding warm water by the effect of the typhoon. While a cold water was occurring in the eastern coast, a typhoon passed by the offshore of the eastern coast, there were the increasing of the SST as well as the disappearing of the cold water. While a typhoon was passing by the offshore of the eastern coast, the cold water which resulted from the strong tidal current in the western coast of the peninsula was horizontally spread from the onshore to the offshore. We think that the typhoon played the role of the very strong wind which was blowing from north toward south. Therefore, the Ekman transport occurred from the onshore toward the offshore of the western coast in the Korean peninsula.

해양 전선에서의 해양/대기의 상호작용

박래설 ( Rae-seol Park ) 한국환경기술학회 2008 한국환경기술학회지 Vol.9 No.2

본 연구에서는 환경 인자들의 확산 및 이류에 영향을 줄 수 있는 해양과 대기의 상호작용에 대한 열역학적 접근을 시도하였다. 대표적인 예로써 Gulf Stream 지역에서 스톰과의 상호작용을 살펴보고, 그 원인을 규명하고자, 수치 실험을 수행하였다. 스톰의 후면에서 나타나는 냉각은 태풍 후면의 Cold Wake와 동일한 기작에 의해 설명된다. 이러한 냉각 현상의 원인을 살펴보기 위해, 열수지를 분석하였다. 그 결과 혼합층과 혼합층 하부의 차가운 해수 사이의 열교환이 냉각의 가장 큰 원인으로 밝혀졌으며, 해수면에서의 수평 이류 또한 중요한 요인으로 간주된다. 즉, 스톰의 바람장은 Ekman 수송을 유발하고, 중심점에서의 수평 divergence에 의한 연직 방향으로의 상승 운동은 혼합층 하부의 차가운 물을 지표까지 유입시킨다. 또한 지표 근처에서의 수평방향으로의 스톰에 의한 Drag는 해수를 바람과 동일한 방향으로 움직이는 원동력이 되며, 부분적으로는 냉각에 영향을 미치게 된다. 그러나 해수면과 대기 사이의 열교환이 해수면의 냉각에 직접적으로 영향을 미치지는 않는다. This study is a trial to understand the air-sea interaction which can affect the diffusion and the advection of the air pollution. As an example of the air-sea interaction, we investigate the interaction between the storm and the Gulf Stream and execute the numerical simulation to understand the mechanism of this feature. The cooling effect that is shown behind of the storm is similar to the Cold Wake caused by the typhoon. To explain this mechanism, we analyze the heat budget at the ocean mixed layer around the storm. As a result, the heat transport between the mixed layer and the lower cold water is the main factor controlling the cooling. The wind around the storm induces the divergence and the upwelling appears at the center of the storm. This upwelling includes the cold water, and SST decreases. Also, the zonal advection by the wind stress can affect to the cooling, but the air-sea heat fluxes don`t affect to this cooling, directly.

태풍의 이동경로에 따른 동해연안 수온변화 특성

박명희 ( Myung Hee Park ),이준수 ( Joon Soo Lee ),서영상 ( Young Sang Suh ),김해동 ( Hae Dong Kim ),배헌균 ( Hun Kyun Bae ) 한국환경과학회 2015 한국환경과학회지 Vol.24 No.12

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.

Interannual Variability of Upwelling Indices in the Southeastern Arabian Sea: A Satellite Based Study

Chiranjivi Jayaram,Neethu Chacko,K. Ajith Joseph,A. N. Balchand 한국해양과학기술원 2010 Ocean science journal Vol.45 No.1

Increase in sea surface temperature with global warming has an impact on coastal upwelling. Past two decades (1988 to 2007) of satellite observed sea surface temperatures and space borne scatterometer measured winds have provided an insight into the dynamics of coastal upwelling in the southeastern Arabian Sea, in the global warming scenario. These high resolution data roducts have shown inconsistent variability with a rapid rise in sea surface temperature between 1992 and 1998 and again from 2004 to 2007. The upwelling indices derived from both sea surface temperature and wind have shown that there is an increase in the intensity of upwelling during the period 1998 to 2004 than the previous decade. These indices have been modulated by the extreme climatic events like El–Nino and Indian Ocean Dipole that happened during 1991–92 and 1997–98. A considerable drop in the intensity of upwelling was observed concurrent with these events. Apart from the impact of global warming on the upwelling, the present study also provides an insight into spatial variability of upwelling along the coast. Noticeable fact is that the intensity of offshore Ekman transport off 8oN during the winter monsoon is as high as that during the usual upwelling season in summer monsoon. A drop in the meridional wind speed during the years 2005, 2006 and 2007 has resulted in extreme decrease in upwelling though the zonal wind and the total wind magnitude are a notch higher than the previous years. This decrease in upwelling strength has resulted in reduced productivity too.

2023년 태풍 카눈 통과에 따른 한국 남해 통영해역 수온 변동 연구

황재동,안지숙,김주연,주희태,민병화,남기호,이시우 해양환경안전학회 2024 해양환경안전학회지 Vol.30 No.1

한국 남해 동부 해역인 통영해역에 설치된 연안 수온 분석 결과, 태풍이 남해안에 상륙하기 전에 수온이 급격하게 상승한 것으로 나타났다. 수온 상승은 표층(5m)은 물론 저층(15m)까지 같이 발생하였다. NOAA 위성에서 관측한 표면수온자료 분석 결과, 태풍이 상륙하기 전 한국 남해 동부 해역의 동쪽 해역에 30℃의 수온을 가지는 해수가 존재하였다. 한국 남동해역은 대마난류에 의해 서쪽에서 동쪽으로 해류가 우세한 지역이나 위성 자료 분석 결과, 30℃의 해수는 동쪽에서 서쪽으로 이동한 것으로 나타나 태풍 상륙 전에 태풍에 의한 에크만 수송의 영향을 받은 것으로 나타났다. 또한 남해 동부 해역은 한국 동해 해역과 달리 수심이 깊지 않기 때문에 바람에 의한 연직 혼합으로 인해 전 수층의 수온이 일정하게 나타날 수 있다. 수층별 수온 상승이 같은 날에 발생하였기 때문에 저층 수온 상승은 연직 혼합에 의한 결과라 볼 수 있다. 따라서 한국 남동해역은 태풍의 접근 방향과 고수온의 형성 위치에 따라 에크만 수송에 의해 수온이 급 상승할 수 있는 해역임을 알 수 있다. An analysis of the coastal water temperature in the Tongyeong waters, the eastern sea of the South Sea of Korea, revealed that the water temperature rose sharply before the typhoon made landfall. The water temperature rise occurred throughout the entire water column. An analysis of the sea surface temperature data observed by NOAA(National Oceanic and Atmospheric Administration) satellites, indicated that sea water with a temperature of 30℃ existed in the eastern waters of the eastern South Sea of Korea before the typhoon landed. The southeastern sea of Korea is an area where ocean currents prevail from west to east owing to the Tsushima Warm Current. However, an analysis of the satellite data showed that seawater at 30℃ moved from east to west, indicating that it was affected by the Ekman transport caused by the typhoon before landing. In addition, because the eastern waters of the South Sea are not as deep as those of the East Sea, the water temperature of the entire water layer may remain constant owing to vertical mixing caused by the wind. Because the rise in water temperature in each water layer occurred on the same day, the rise in the bottom water temperature can be considered as owing to vertical mixing. Indeed, the southeastern sea of Korea is a sea area where the water temperature can rise rapidly depending on the direction of approach of the typhoon and the location of high temperature formation.

An optimization strategy in wind-driven circulation with uncertain forcing problem off the southeastern coastal waters of Korea

Jong-Kyu Kim(김종규),Heon-Tae Kim(김헌태) 한국해양환경·에너지학회 2001 한국해양환경·에너지학회지 Vol.4 No.2