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A Mechanism of AMOC Decadal Variability in the HadGEM2-AO

HadGEM2-AO 모델이 모의한 AMOC 수십 년 변동 메커니즘

  • Wie, Jieun (Division of Science Education/Institute of Fusion Science, Chonbuk National University) ;
  • Kim, Ki-Young (4D Solution Co., LTD.) ;
  • Lee, Johan (National Institute of Meteorological Research) ;
  • Boo, Kyung-on (National Institute of Meteorological Research) ;
  • Cho, Chunho (National Institute of Meteorological Research) ;
  • Kim, Chulhee (Division of Science Education/Institute of Fusion Science, Chonbuk National University) ;
  • Moon, Byung-kwon (Division of Science Education/Institute of Fusion Science, Chonbuk National University)
  • 위지은 (전북대학교 과학교육학부/융합과학연구소) ;
  • 김기영 ((주)포디솔루션) ;
  • 이조한 (국립기상과학원) ;
  • 부경온 (국립기상과학원) ;
  • 조천호 (국립기상과학원) ;
  • 김철희 (전북대학교 과학교육학부/융합과학연구소) ;
  • 문병권 (전북대학교 과학교육학부/융합과학연구소)
  • Received : 2015.06.08
  • Accepted : 2015.06.19
  • Published : 2015.06.30
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Abstract

The Atlantic meridional overturning circulation (AMOC), driven by high density water sinking around Greenland serves as a global climate regulator, because it transports heat and materials in the climate system. We analyzed the mechanism of AMOC on a decadal time scale simulated with the HadGEM2-AO model. The lead-lag regression analysis with AMOC index shows that the decadal variability of the thermohaline circulation in the Atlantic Ocean can be considered as a self-sustained variability. This means that the long-term change of AMOC is related to the instability which is originated from the phase difference between the meridional temperature gradient and the ocean circulation. When the overturning circulation becomes stronger, the heat moves northward and decreases the horizontal temperature-dominated density gradients. Subsequently, this leads to weakening of the circulation, which in turn generates the anomalous cooling at high latitudes and, thereby strengthening the AMOC. In this mechanism, the density anomalies at high latitudes are controlled by the thermal advection from low latitudes, meaning that the variation of the AMOC is thermally driven and not salinity driven.

북대서양 자오면 순환(AMOC)은 그린란드 부근에서 고밀도 해수의 침강으로 유도되는데, 이것은 열과 물질을 수송시키기 때문에 기후 시스템의 중요한 요소이다. 이 연구는 전 지구 기후모델 중 하나인 HadGEM2-AO 모델에서 모의된 AMOC의 특징과 장기변동 메커니즘을 분석하였다. AMOC 지수를 이용한 지연 상관 분석을 통해 AMOC의 수십 년 변화는 해양 자체유지 변동으로 간주할 수 있었다. 즉 AMOC의 장기 변화는 남북 수온 경도와 해양 순환의 위상차로 인해 발생하는 불안정성에 의한 것으로 분석되었다. AMOC가 강해지면서 열의 북향 수송에 의해 남북 수온 경도가 작아지고, 따라서 해수의 순환과 열 수송이 줄어드는데, 이와 함께 고위도에서는 냉각이 유도되어 결과적으로 다시 AMOC가 강해지게 된다. 이 메커니즘은 저위도로부터 이류되는 열의 양에 따라 고위도 지역의 밀도 변화가 결정되기 때문에 AMOC의 변동을 염분 유도가 아닌 열적 유도 과정으로 이해할 수 있다.

Keywords

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