Mar 30, 2001
Headed by Program Director Dr. Motoyoshi Ikeda, a group of researchers at the International Arctic Research Center (IARC) - a division of the FRSGC, which was established as a joint project by NASDA (President: Mr. Shuichiro Yamanouchi) and JAMSTEC (President:Mr. Takuya Hirano) - have been conducting research into two areas: the Arctic Ocean sea ice cover, which naturally subject to variation, has exhibited a steadily decreasing trend over the past 30 years; and the counterclockwise polar vortex above the Arctic, which although naturally fluctuating (Arctic Oscillation), has been gradually strengthening. Through this research they have discovered feedback between these two phenomena.
Their findings will be published in the scientific journal, Geophysical Research Letters, 1 April 2001 (Vol.28, No.7, p 1275).
Until now, the prevailing theory attributed the decrease in Arctic sea ice area to global warming induced by increasing carbon dioxide, which causes higher temperatures in the Arctic region and leads to a reduction in sea ice. Once the sea ice decreases, solar radiation is absorbed into the ocean during summer, causing a further rise in ocean temperatures, thereby resulting in a greater reduction in sea ice (Fig. 1).
Findings and Consideration
By using a box model (Fig. 2) and conducting simulation calculations, Dr. Ikeda (Program Director) and his colleagues discovered feedback between a strong polar vortex and reduced sea ice (or conversely, a weak polar vortex and increased sea ice). While there are natural variations in sea ice and Arctic Oscillation associated with the polar vortex, their findings show that the decreasing trend in the sea ice correlates with the strengthening of the polar vortex (Fig.3 and Fig.4).
The Arctic Oscillation is already known to exert a considerable influence on temperature variations in northern Japan. If these cycles and future conditions could be predicted, the anticipated benefit to people's lives in Japan would be substantial. Therefore, continued research into prediction of global change using atmosphere-ocean-sea ice models in the Arctic region, together with an understanding of global change, is of utmost importance.
Future Research Topics
This study has suggested the possibility that, as the sea ice becomes thinner, positive feedback occurs between the polar vortex, sea ice, and surface layer in the Atlantic Ocean. Caused by this feedback, the Arctic sea ice area decreases dramatically, accompanied by the strengthening polar vortex. The importance with positive feedback lies in the rate of intensification of the polar vortex in relation to the decrease of sea ice area, pointing to the need for research on atmospheric models that will provide more accurate estimate of this process. Simultaneous monitoring of the rate of oceanic flow from the Arctic Ocean into the Atlantic Ocean is also required. Although satellites can be used to monitor the sea ice area and motion, a system providing in situ monitoring of ocean currents needs to be implemented.
Joint Promotion Office, Frontier Research System for Global Change
Mr. Hishida(TEL: +81-45-778-5615)
Mr. Kawasaki(TEL: +81+45-778-5700)
JAMSTEC (Japan Marine Science and Technology Center)
Public Relations, Training and Education Division of Administration Department
URL: http://www.jamstec.go.jp/ (JAMSTEC)
NASDA (National Space Development Agency of Japan)
Public Relations Office
URL: http://yyy.tksc.nasda.go.jp/ (NASDAQ)
1. IARC Research on Climate Change in the Arctic Region
In March 1997, the then Japanese Prime Minister, Ryutaro Hashimoto, and U.S. Vice-President, Al Gore, held talks on the "Common Agenda for Cooperation on Global Perspective" (Common Agenda) and agreed on the importance of bilateral cooperation in promoting research in the fields of global change and its prediction.
The IARC (Director: Dr. Shunichi Akasofu) is a research institute that was established in Alaska, based on this Japan-US Common Agenda. Since the beginning of 1998, under the Program Director, Dr. Motoyoshi Ikeda, the IARC/FRSGC has continued research of the diminishing sea ice - an index of global warming - and the related atmospheric and oceanic changes.
2. Mechanism of Sea Ice Decrease
It is widely known that while Arctic sea ice is subject to recurring natural variations, it has been decreasing over the past 30 years. The mechanisms that have been suggested as being responsible for this decrease in sea ice are not only the increase in anthropogenic CO2, but also natural phenomena such as the variation in the polar vortex, as well as low stratus clouds that prevent heat radiating into space. Nevertheless, many aspects have remained unclear. Last year, however, findings from data analyses and modeling studies showed that the sea ice decrease was also attributable to the intensifying polar vortex. The Program Director, Dr. Ikeda, considered the possibility of feedback between the sea ice area and polar vortex, and explained the interaction between the fluctuations in sea ice area and the variation in the polar vortex, using a simplified box model (Fig.2).
Explanation of Terms
A westerly wind that is found at approximately 10 km altitude above the Arctic and, when seen from above, forms a counter-clockwise vortex circulating around the North Pole.
The variations in the intensity of the polar vortex. The oscillation has various cycles ranging from several weeks to decades.