The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY (한국해양학회지:바다)

The Korean Society of Oceanography (한국해양학회)
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Change of Coastal Upwelling Index along the Southeastern Coast of Korea

동해 남부 연안용승지수의 변화

  • SHIN, CHANG-WOONG (Ocean Circulation and Climate Research Center, Korea Institute of Ocean Science and Technology)
  • 신창웅 (한국해양과학기술원 해양순환.기후연구센터)
  • Received : 2019.01.11
  • Accepted : 2019.02.13
  • Published : 2019.02.28
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Abstract

Long-term trends and recent variations of upwelling index (UI), which affects significantly ecosystem in southwestern part of the East Sea, were investigated. The UI was calculated with the NCEP/NCAR reanalysis data from January 1948 to September 2018. The mean UI has positive value that causes upwelling in April to August with a peak in July. The long-term reducing trend of UI was in statistically significant in June and July, and the sum of UI in May, June and July also showed same result. Through the atmospheric pressure analysis around the Korean peninsula, it was found that the trend of the UI was the influence of the pressure change trend in the northwestern region ($35-50^{\circ}N$, $114-129^{\circ}E$) of the southwestern part of the East Sea. Investigating UI in recent 7 years from 2012 to 2018, it was revealed that the UI was bigger than 3 times of standard deviation in July 2013. This was result from the sea level pressure difference became larger in the southwestern part of the East Sea than normal year due to the lowered air pressure in the northeastern region of China and the strengthened high air pressure of western peripheral of the North Pacific High. On the other hand, the UI in July 2018 was negative when the impact of the North Pacific High and the low air pressure in the northeastern China was weak. Due to the decreasing trend of UI and its large year-to-year variation in southwestern part of the East Sea, continuous monitoring is necessary to know the influence of coastal upwelling on the ecosystem.

동해 남서부 해역의 해양생태계에 큰 영향을 미치는 연안용승의 변화를 파악하기 위해 1948년 1월부터 2018년 9월까지의 NCEP/NCAR 재분석자료를 이용하여 용승지수를 계산하였다. 평균 용승지수는 4월부터 8월까지 용승이 발생하는 양의 값이 보이며 7월에 최대 값이 나타났다. 용승지수의 장기 변화는 6월과 7월에 통계적으로 유의미한 감소추세가 나타났으며, 5, 6, 7월 용승지수의 합도 통계적으로 유의미한 감소 경향을 보였다. 한반도 주변의 대기압 분석을 통하여 용승지수의 변화 추세는 동해남부해역을 기준으로 북서쪽 영역($35-50^{\circ}N$, $114-129^{\circ}E$)의 기압 변화 추세의 영향이라는 것을 밝혔다. 최근 7년간(2012년-2018년)의 용승지수 분석결과 2017년 7월에 용승지수가 표준편차의 3배 이상 높은 것을 발견하였다. 이것은 중국 북동쪽 지방에 평년과 다르게 저기압이 발달하였고 북태평양고기압이 일본과 대만 사이까지 영향을 주어 동해 남부에 큰 기압 차이가 발생했기 때문이었다. 반면에 평년에 비하여 북쪽의 저기압과 남쪽의 고기압의 영향이 적었던 2018년 7월은 용승지수가 음의 값이었다. 동해남부 연안용승지수는 기후변화에 따라 감소하는 경향을 보이고 경년변동이 커서 생태환경에 대한 영향을 파악하기 위해서는 지속적인 모니터링이 필요하다.

Keywords

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Fig. 1. Climatological mean wind fields of NCEP/NCAR reanalysis data from 1948 to 2018 in January (a) and July (b).

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Fig. 2. Study area with wind data stations of the NCEP/NCAR W (35°N, 130°E) and the Ulsan buoy U (35.35°N, 129.84°E) (a). Pressure data points to calculate mean sea level pressure in the northwest (blue dots) and the southeast (red dots) of the wind data point W (b).

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Fig. 3. Zonal wind scatter plots and linear regression line between Busan and station W (a), and the same as (a) except the meridional wind (b). Zonal wind scatter plots and the linear regression line between station U and station W (c), and the same as (c) except the meridional wind (d).

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Fig. 4. Contours of alongshore wind speed at station W (35°N, 130°E) of NCEP/NCAR reanalysis data.

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Fig. 5. Time plots of the upwelling indices and linear regression lines (red line) for each month. Horizontal and vertical axes represent time (year) and upwelling index (kg·(m·s)-1), respectively.

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Fig. 7. The time plot of the sum of upwelling indices of May, June and July (the light blue line) and its 10 years moving average (the blue line). Linear regression lines for the whole period (the red line) and a recent 30-year period (the green line) were added. The mean values of upwelling indices from 1948 to 1966 and from 1967 to 2018 were represented by the red dashed lines.

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Fig. 8. Monthly mean sea level pressures (SLP) and its standard deviations in the northwest area (a), in the southeast area (c), and their differences (e). Monthly linear trends, confidence intervals of 95%, and p-values for the SLP in the northwest area (b), in the southeast area (d), and their differences (f). See Fig. 2 (b) for the area.

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Fig. 9. Monthly correlation coefficients (r) between the sea level pressure differences (horizontal axis, unit: millibar) and the alongshore wind speeds (vertical axis, unit: m·s-1). Red lines represent linear regression lines.

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Fig. 10. Yearly variations of the upwelling indices for 7 years (from 2012 to 2018) from March to August. Red solid lines and red dotted lines represent recent 30 years (from 1989 to 2018) mean and its standard deviations, respectively.

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Fig. 11. Climatological mean of sea level pressure in July from 1989 to 2018 (a), mean sea level pressure in July 2013 (b) and July 2018 (c). Unit is millibar.

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Fig. 12. Mean of sea level pressure averaged in May, June and July from 1948 to 1967 (a) and from 1968 to 2018 (b). Unit is millibar.

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Fig. 6. (a) Monthly mean upwelling indices and its standard deviations. (b) Monthly linear regression coefficients, 95% confidence intervals and p-values of the coefficients.

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