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Robert J. Allan
,
Neville Nicholls
,
Phil D. Jones
, and
Ian J. Butterworth

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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Carsten S. Frederiksen
,
Huqiang Zhang
,
Ramesh C. Balgovind
,
Neville Nicholls
,
Wasyl Drosdowsky
, and
Lynda Chambers

Abstract

An evaluation of trial seasonal forecasts during the 1997/98 El Niño, using an atmospheric GCM forced by persisted sea surface temperature and sea-ice anomalies, is presented. Generally, forecasts of seasonal anomalies of precipitation, surface air temperature, 200-hPa geopotential height, and mean sea level pressure (MSLP) are shown to have statistically significant skill in the Tropics and subtropics, but predominantly over the oceans. Surface air temperature and 200-hPa height anomalies are also skillfully forecast over land in the 30°S–30°N latitudinal band, and, in contrast to precipitation and MSLP, also show significant skill in the extratropics. The global pattern of significant skill seems not to be oversensitive to the use of a Kuo or a mass-flux convection scheme (Tiedtke), although the global root-mean-square errors are consistently larger, in the latter case.

Results from multidecadal simulations of the model, when forced by observed sea surface temperature and sea-ice, show that the model reproduces quite well the observed global Southern Oscillation index relationships and that these go some way to explaining the skill in the model forecasts. In addition, the global patterns of skill are consistent with those seen in the model forecasts. An estimate of the role of sea surface temperature and sea-ice in forcing interseasonal climate variations, suggests that the model displays forecasts skill in those areas where this forcing plays a large, if not dominant, role. In areas where internal, or chaotic, variability plays a dominant role, the model shows little statistically significant skill.

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Cher M. Page
,
Neville Nicholls
,
Neil Plummer
,
Blair Trewin
,
Mike Manton
,
Lisa Alexander
,
Lynda E. Chambers
,
Youngeun Choi
,
Dean A. Collins
,
Ashmita Gosai
,
Paul Della-Marta
,
Malcolm R. Haylock
,
Kasis Inape
,
Victoire Laurent
,
Luc Maitrepierre
,
Erwin E.P. Makmur
,
Hiroshi Nakamigawa
,
Nongnat Ouprasitwong
,
Simon McGree
,
Janita Pahalad
,
M.J. Salinger
,
Lourdes Tibig
,
Trong D. Tran
,
Kaliapan Vediapan
, and
Panmao Zhai
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