Effects of the North Pacific Oscillation and Enso on Seasonally Averaged Temperatures in Califlornia

The North Pacific Oscillation (NPO) and the El Niño-Southern Oscillation (ENSO) have effects on California that are of interest to energy producers and consumers. In particular, changes in the NPO are associated with statewide shifts in simultaneous wintertime temperatures, and, to a lesser extent, temperatures in the following summer. Observations over the period 1960 to 2001 indicate that the seasonally averaged temperature anomaly associated with the NPO is about 0.7 C in winter and 0.2 C in summer. The response is not linear; the warmth associated with positive NPO events is stronger than the cooling associated with negative NPO events. The seasonal temperature changes are accomplished by a simple shift in the distribution of daily average temperatures over much of California. However, over the Sierra Nevada, the shape of the daily temperature distribution changes as well, with the positive phase of the NPO associated with a smaller standard deviation in daily average temperature. This effect is probably too small to be of practical importance for energy producers, however. The seasonally averaged difference in temperature due to the NPO makes about a 150-heating-degree-day difference over the winter. The change in seasonally averaged temperatures due to ENSO is a considerably weaker effect than that due to the NPO; effects on energy producers due to ENSO are therefore more likely to arise from changes in precipitation in the Pacific Northwest.