CSIRO Marine and Atmospheric Research
Past Seminars

Friday 14 May 2004, 11.30 am (Tas time)

CSIRO Auditorium, Hobart and via videoconference to Floreat and Cleveland

Gary Meyers
CSIRO Marine Research, Hobart

The years of El Nino, La Nina and interactions with
the Indian Ocean

The Indian Ocean Dipole (IOD) has been the subject of increasing interest and sometimes scientific debate since 1999 when the first papers on it were published in Nature. This paper is concerned with identifying the IOD and its relationship to the El Nino Southern Oscillation phenomenon (ENSO). The physical oceanographic characteristics of IOD are identified by reviewing selected, recently published papers. Upwelling on the Indian Ocean coasts of Java and Sumatra is identified as a key controlling process in IOD, generating the cold eastern pole observed in XBT and altimeter measurements during recent decades. Then, the relationship between IOD and ENSO is characterised by carefully classifying each year of the 20th Century as a year of El Nino, La Nina or neither; and positive IOD, negative IOD or neither. The classification is based on the latest version of the GISST data set. The method of classification is critically dependent on recognizing the important role of upwelling in both the Pacific equatorial cold tongue and off the Java/Sumatra coast. The relationship between IOD and ENSO is then described in terms of global SST patterns for cases when particular phases of the two phenomena occur together or independently.

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