Discovering a Dipole Phenomenon In the South Indian Ocean Subtropics
- Opening a New Era in Elucidation of Atmospheric Ocean Interaction -


January 12, 2001
JAMSTEC
NASDA






 Dr. Toshio Yamagata, Director of Climate Variations Research Program (Prof. of the Univ. of Tokyo), Dr. Swadhin K. Behera and other research scientists of the Program, which is a part of FRSGC, established as a joint project, by NASDA (President: Mr. Shuichiro Yamaguchi) and JAMSTEC (President: Mr. Takuya Hirano), has discovered an previously undetected large scale climate change in the subtropical area of the Southern Indian Ocean. This climate change is equivalent to El Nino in the Pacific Ocean, and the Dipole Mode phenomenon in the Indian Ocean. The researchers have named this phenomenon as the "Subtropical Dipole Mode (SDM)". Their findings will be printed in Geophysical Research Letters, published on January 2001.

Background
 In September 1999, Dr. Yamagata, Dr. Saji Hameed and other research staff discovered the Dipole Mode phenomenon in the tropical area of the Indian Ocean, and their findings were printed in Nature (published on September 2). Their results led to rational explanations for the causes of drought in the eastern part of the Indian Ocean and floods in coastal countries of East Africa, which were until that time, attributed to El Nino with several unexplainable facets. However the causes of flooding in Central and South Africa remained a mystery.

Findings
 The researchers investigated atmosphere & ocean data, such as sea surface temperature (SST), wind, precipitation of the past 40 years, and discovered that a dipole phenomenon occurs in the subtropical area of the central part of the southern Indian Ocean every few years. In addition, it has become clear that this phenomenon is an independent of any atmosphere/ocean interaction, with no causal relation to the dipole phenomenon discovered in September 1999 (Figure 1 and Figure 2c), and that it has a major influence over the floods and drought occurring in the Central and South Africa, which has not been explained by El Nino in the Pacific Ocean and the Dipole Mode (DM) in the Indian Ocean (Figures2a and 2b). (In positive SDM years, precipitation increases in the central and southern portion of the African continent, causing floods, while in negative SDM years, it decreases, causing drought.)

 The researchers plan to make a computer simulation experiment, using the coupled atmosphere/ocean model. Based on the result of this experiment, they intend to be able to increase the accuracy of predicting climatic change. This will then enable them to contribute to elucidation of complicated interaction between the atmosphere and ocean, and to prevention of weather disasters occurring in the surrounding countries of the Indian Ocean.


Reference
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