Feature article

The Southwest Pacific Climate in 2002

By Stuart Burgess, Ashmita Gosai, and Dr Jim Salinger, NIWA

The year 2002 was one of more contrasts across the Southwest Pacific. Important drivers of the annual pattern were the development of the El Niño conditions during the second half of the year (See Fig.1), the decreased strength of the trade winds, and the distribution of warm sea surface temperature (SST) anomalies.

Anomalous equatorial westerlies occurred about and west of the Dateline and in the central Pacific from July through November. The El Niño began to affect rainfall distribution, from August onwards as shown in the monthly outgoing long-wave radiation (OLR) and rainfall anomaly patterns. The equatorial region of enhanced convection had then moved east to lie over Kiribati (Refer to Fig.2 The 2002 annual OLR anomaly map). The South Pacific Convergence Zone (SPCZ) was generally further south than usual during the first half of the year. For the rest of the year, the SPCZ was situated near its average location about and west of the Dateline, but was fairly inactive further east.

Annual rainfall was less than 75% of average from the Northern Cook Islands across to the Society Islands of central French Polynesia.The 2002 rainfall total at Tahiti- Faaa (1061 mm) was only 65% of average, and one of the lowest on record there. Rainfall was also well below average in the Coral Sea and along the Queensland coast of Australia, associated with above average surface pressure over much of Australia.

A large area of very enhanced rainfall and well below average OLR occurred over Western and Eastern Kiribati, with totals exceeding 150% of average on many islands. The 2002 rainfall total at Tarawa (3492 mm) was 174% of average, and one of the highest on record there. Rainfall was also above average in parts of Fiji and southern Tonga, associated with below average surface pressures in that region.

Surface air temperatures along the equator were largely influenced by the warm ENSO event, being about 0.5°C above average there, Over Kiribati they were at least 1.0°C above average.

Fig 1: The Southern Oscillation Index (SOI). The solid line represents the 3-month running mean, while the coloured bars show monthly standard deviations (blue for positive, red for negative).

Fig 2: 2002 climate patterns. Outgoing Long-wave Radiation (OLR) anomalies, in Wm^-2 are represented by hatched areas, and rainfall percentage of average, shown by numbers. High radiation levels (yellow) are typically associated with clearer skies and lower rainfall, while cloudy conditions lower the OLR (blue) and typically mean higher rainfalls.