El Niño was long considered a reliable tool for predicting future precipitation in the southwestern United States, but its forecasting power has diminished in recent cycles, possibly due to global climate change. In a new study, scientists and engineers demonstrate a new method for projecting wet or dry weather in the winter ahead. This new method, a interhemispheric teleconnection, could promise earlier and more accurate prediction of winter precipitation in California and the southwestern U.S. The researchers called the new teleconnection the New Zealand Index because the sea surface temperature anomaly that triggers it begins in July and August in the southwestern Pacific Ocean, close to New Zealand. As the sea surface temperature in the region cools down or heats up, it causes a change in the southern Hadley cell, an atmospheric convection zone from the equator to about the 30th parallel south. This prompts a commensurate anomaly east of the Philippine Islands, which, in turn, results in a strengthening or weakening of the jet stream in the Northern Hemisphere, having a direct influence on the amount of rain that falls on California between November and March. For the study, an interdisciplinary team of scientists analyzed sea surface temperature and atmospheric pressure in 1- and 2-degree cells around the globe from 1950 to 2015. The team said this resulted in the unexpected discovery of persistent sea surface temperature and atmospheric pressure patterns in the southwestern Pacific Ocean that exhibited a strong correlation with precipitation in Southern California, Nevada, Arizona and Utah.
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