11.9.2.3 Pacific

Climate model simulations of current-climate means of temperature and precipitation were investigated by Jones et al. (2000, 2002) and Lal et al. (2002) for the South Pacific. The AOGCMs available at the time of these studies simulated well the broad-scale patterns of temperature and precipitation across the region, with the precipitation patterns more variable than for temperature in the models considered, and with some significantly underestimating or overestimating of the intensity of rainfall in the high-rainfall zones. All models simulated a broad rainfall maximum stretching across the SPCZ and ITCZ, but not all models resolved a rainfall minimum between these two regions. A problem of simulating the spatial structure of the MJO resulting in tendencies for the convective anomaly to split into double ITCZs in the Pacific is also discussed in Section 8.4.8.

Analysis of the MMD simulations shows that the average model value overestimated the annual mean temperature from 1980 to 1999 by 0.9°C over a southern Pacific region, with 50% of the deviations varying from 0.6°C to 1.2°C. Over the North Pacific, the simulated ensemble average temperature for the same period was only 0.7°C above the climatology, with half of the model deviations from the climatology ranging from 0.2°C to 1.0°C. Average precipitation was overestimated by 10%, but individual model values varied from –7 to 31% in the southern Pacific region, whereas in the northern Pacific the mean model output for precipitation almost agreed with the climatology, while the individual models deviated from –13 to 13%. Thus, the models are better at simulating rainfall in the northern Pacific than in the southern Pacific and the quality of the simulations, both north and south, were not much different from those for the Indian Ocean.