This study uses a series of CGCM (coupled atmosphere-ocean general circulation model) experiments to examine the role of Indian and Pacific oceans in affecting the transition between the Indian and Australian Monsoons. A total of three CGCM simulations are performed: the Pacific Run, Indo-Pacific Run, and Indian-Ocean Run. In each CGCM run, air-sea interactions are restricted to a certain portion of the Indian-Pacific Ocean by including only that portion of the cean in the ocean model component of the CGCM. The Pacific Run includes only the tropical Pacific Ocean in the CGCM; the Indian-Ocean Run includes only the Indian Ocean in the CGCM; and the Indo-Pacific Run includes both the Indian and Pacific Oceans in the CGCM.

It is found that the transition from a strong (weak) Indian summer monsoon to a strong (weak) Australian summer monsoon can only be produced in the CGCM simulations that include an interactive Pacific Ocean in the model. Also, the transition from a strong (weak) Australian summer monsoon to a weak (strong) Indian summer monsoon can only be produced in the simulations that include an interactive Indian Ocean in the model. When both the interactive Indian and Pacific Oceans are included in the model, the Indo-Pacific Run produces a biennial variations in the Indian and Australian monsoon. A strong (weak) Indian/Australian monsoon year is followed by a weak (strong) Indian/Australia monsoon in the next year. How the Indian and Pacific Oceans affect the transitions between Indian and Australian monsoons will be discussed.