| Co-Investigator(Kenkyū-buntansha) |
HATTORI Hiroshi Hokkaido Tokai University School of Engineering, Professor, 工学部, 教授 (60208543)
MINOBE Shoushirou Hokkaido University Graduate School of Science, Associate Professor, 大学院・理学研究科, 助教授 (70219707)
SHIRASAWA Kunio Hokkaido University Institute of Low Temperature Science, Professor, 低温科学研究所, 教授 (50196622)
TANAKA Noriyuki Frontier Observational Research system for Global Change International Arctic Research Center, Group Leader, 地球観測フロンティア・国際北極圏研究センター, グループリーダー (10261348)
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| Research Abstract |
As a platform to integrate the entire project, we have developed a coupled ice-ocean model of the Arctic, by which the responses of the ice-ocean system to the atmospheric variability are examined, and also bio-geochemical processes are interpreted in the physical-biogeochemical version. Once the atmospheric pressure pattern is given the Arctic Oscillation (AO) signal, the model has reproduced the observed sea ice cover variability at a decadal period. The water exchange through the Fram Strait is found to increase responding to the intensified Polar Vortex. Deep convection and dense water spreading are the important oceanic processes which are not explicitly resolved in the Arctic model, and are parameterized on the basis of high resolution models. An observational study has provided better understanding of under-ice mixing.
The further analysis of the Arctic model has revealed the feedback mechanisms, by which the Arctic Oscillation and ice-cover variability could enhance each other.
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Once the ice cover reduces, more heat is given to the atmosphere, which tends to intensify the Polar Vortex. Its wind pattern increases the water exchange through the Fram Strait and gives favor to the Atlantic Water penetrating into the Arctic Ocean. Then, more sea ice melts. This positive feedback comes together with a self-oscillating system of the Arctic-Atlantic Ocean, and excites the AO.
Cloud and radiation data collected by the Soviet Union have been analyzed to present a cloud increase in the recent 40 years. This effect on the surface heat flux is equivalent to that arising from the albedo decrease due to the ice reduction. Although the sea ice has been claimed to be an important indicator for global warming in the real climate and global warming simulation, it has been strongly suggested that more parameters than sea ice and temperature should be looked into carefuly in the comparison between observed data and model results.
Bio-geochemical processes are important environmental components and also crucial to global warming through feedback to the physical component. Observations have been conducted in the Bering Sea, Baffin Bay, the Baltic Sea and Saroma Lagoon, identifying a primary species of phytoplankton in each area. Their roels for global warming have been estimated.
Hydrochemical data collected by the Soviet Union include dissolved oxygen, alkalinity, phosphate, nitrate and silicate. This data set has been analyzed, giving an evidence of vertical stretching of the water column in the Canada Basin. The vertical motion can be interpreted as a consequence of Ekman convergence or divergence responding to the AO. This striking result is expressed as the most recent outcome of this project. Less
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