A Further Extension of the Tahiti-Darwin SOI, Early ENSO Events and Darwin Pressure

Robert J. Allan CSIRO Division of Atmospheric Research, Melbourne, Australia

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Neville Nicholls Bureau of Meteorology Research Centre, Melbourne, Australia

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Phil D. Jones Climatic Research Unit, University of East Anglia, Norwich, England

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Ian J. Butterworth Bureau of Meteorology, Darwin, Australia

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Abstract

An extension of the Tahiti minus Darwin Southern Oscillation Index (SOI) from 1882 back to 1876 is reported following the recovery of early Darwin mean sea-level pressure data spanning the period 1865–81. As a result, we are able to compare, for the first time, the major 1877–78 and 1982–83 ENSO events on the basis of this commonly used index. Early Darwin and Jakarta data are also examined in terms of a measure of the Australian response to documented El Niño and/or ENSO events in 1866, 1868, 1871, 1873, 1874 and 1875.

The SOI during the 1877–78 ENSO event has a similar temporal response to that in 1982–83, but the index is slightly weaker than in the recent event. Examination of documentary evidence confirms the severity of the drought conditions that affected the Australian continent during the 1877–78 ENSO, and shows that this response is in line with the wider Indo-Pacific impacts reported in the literature. Earlier El Niño phases in 1868 and 1873 are not resolved distinctly in either the Darwin or Jakarta pressure data. This appears to illustrate that El Niño event histories do not always indicate wider ENSO influences in the Indo-Pacific basin, particularly during weak to moderate phases.

Abstract

An extension of the Tahiti minus Darwin Southern Oscillation Index (SOI) from 1882 back to 1876 is reported following the recovery of early Darwin mean sea-level pressure data spanning the period 1865–81. As a result, we are able to compare, for the first time, the major 1877–78 and 1982–83 ENSO events on the basis of this commonly used index. Early Darwin and Jakarta data are also examined in terms of a measure of the Australian response to documented El Niño and/or ENSO events in 1866, 1868, 1871, 1873, 1874 and 1875.

The SOI during the 1877–78 ENSO event has a similar temporal response to that in 1982–83, but the index is slightly weaker than in the recent event. Examination of documentary evidence confirms the severity of the drought conditions that affected the Australian continent during the 1877–78 ENSO, and shows that this response is in line with the wider Indo-Pacific impacts reported in the literature. Earlier El Niño phases in 1868 and 1873 are not resolved distinctly in either the Darwin or Jakarta pressure data. This appears to illustrate that El Niño event histories do not always indicate wider ENSO influences in the Indo-Pacific basin, particularly during weak to moderate phases.

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