CSIRO Marine and Atmospheric Research
Past Seminars

Tuesday 6 April 2004, 11.30am (Tas time)

CSIRO Auditorium, Hobart

Weidong Yu
Laboratory of Marine Science and Numerical Modelling
First Institute of Oceanography
State Oceanic Administration, Qingdao, China

Atmosphere-ocean interaction in the Pacific and Indian Oceans and their relationship

The atmospheric circulation is decomposed into the rotational and divergent components to study their interrelationship and interactions with the ocean in the Pacific and Indian Sectors. The variation of the Walker circulation cells over the two oceans, which is represented by the divergent component during the El Niño, is described from the NCAR/NCEP reanalysis data. The Walker circulation cells exhibit similar behaviour in the two oceans, that is they are significantly reversed in the sense of anomaly field, consistent with previous schematic diagrams. The variation of the rotational component shows the cyclonic/anti-cyclonic pattern standing on the north/south side of the equator in Pacific.

In the Indian Ocean, the anti-cyclonic pattern dominates over the southern part, while its counterpart in the northern hemisphere is rather weak. This atmospheric variation corresponds well with the oceanic SSTA. The rotational circulation pattern moves eastward/westward in Pacific/Indian Ocean associated with the variation of SST. Such zonal movement makes the rotational circulation show different feedback with the ocean at different stages. During the development stage, there are positive feedbacks between atmosphere and the ocean. However, the mature phase of El Niño sees the negative feedback between the rotational circulation and the ocean, which slacks the anomalous Walker circulation and further introduces an anti-cyclonic/cyclonic circulation pattern over the western Pacific and cyclonic circulation patter over the eastern Indian Ocean. Thus, the rotational circulation component contributes significantly to the phase transition of the El Niño. It could be verified that the atmosphere-ocean interactions in the Pacific and Indian Oceans are basically the same in essence and vary in a consistent way.

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