11.9.1.3 Pacific

The Pacific region refers to equatorial, tropical and subtropical region of the Pacific in which there is a high density of inhabited small islands. Broadly, it is the region between 20°N and 30°S and 120°E to 120°W. The major climatic processes that play a key role in the climate of this region are the easterly trade winds (both north and south of the equator), the SH high pressure belt, the ITCZ and the South Pacific Convergence Zone (SPCZ; see Vincent, 1994), which extends from the ICTZ near the equator due north of New Zealand south-eastward to at least 21°S, 130°W. The region has a warm, highly maritime climate and rainfall is abundant. The highest rainfall follows the seasonal migration of the ITCZ and SPCZ. Year-to-year climatic variability in the region is very strongly affected by ENSO events. During El Niño conditions, rainfall increases in the zone northeast of the SPCZ (Vincent, 1994). Tropical cyclones are also a feature of the climate of the region, except within 10 degrees of the equator, and are associated with extreme rainfall, strong winds and storm surge. Many islands in the region are very low lying, but there are also many with strong topographical variations. In the case of the latter, orographic effects on rainfall amount and seasonal distribution can be strong.

11.9.2 Skill of Models in Simulating Present Climate

The ability of the MMD models to simulate present climate in the Caribbean, Indian Ocean and North and South Pacific Ocean is summarised in Supplementary Material Table S11.1. In general, the biases in about half of the temperature simulations are less than 1°C in all seasons, so that the model performances are, on the whole, satisfactory. There are, however, large spreads in precipitation simulations. During the last decade, steady progress has been made in simulating and predicting ENSO using coupled GCMs. However, serious systematic errors in both the simulated mean climate and the natural variability persist (see Section 8.4.7)