The controversial forecast is based on satellite images depicting sea-surface temperatures in the northern Gulf of California and changes in ocean surface height off southern Mexico. According to Mitchell, analysis of data gathered over the last 10 years shows a dome of high water develops off southern Mexico in spring. The collapse of this dome in late May-early June appears associated with a northward surge of warm water along mainland Mexico's northwestern coast. This warm current supplies moisture for the North American monsoon, the summer storms that drop up to 45 percent of the Southwest's annual rainfall. This year, although satellites indicate the warm current was stronger than average, the water temperature in the current was cooler than average, making this year's prediction more uncertain.
"Our research builds on the findings of many other studies that also implicate the Gulf of California as the dominant moisture source for the monsoon," Mitchell said. "Preliminary data show a correlation between sea-surface height, northern gulf water temperature and the onset of heavy rainfall associated with the North American monsoon. A water temperature increase of just 2 degrees Fahrenheit from 84 F to 86 F, can have a major impact."
Not all scientists agree that a link exists between the gulf water and the monsoon. Mitchell describes the differences as "a healthy diversity of opinion." One thing is sure, however, he said. Meteorologists and atmospheric science researchers agree on the need for better understanding of the forces behind the monsoons.
"Accurate predictions of monsoons are not only valuable to public safety officials," he said, "they are extremely useful to power companies. Monsoonal weather patterns affect the power grid and have an impact on spot market prices." With electrical power "brown-outs" no longer hypothetical in the Southwest, a better understanding of monsoon rains is becoming increasingly more important, Mitchell said.
A nonprofit, statewide division of the University and Community College System of Nevada, DRI pursues a full-time program of basic and applied environmental research on a local, national, and international scale. Nearly 500 full- and part-time scientists, technicians, and support staff conduct some 150 research projects at DRI annually. More than 85 percent of DRI's annual $33 million operating budget consists of research grants and contracts obtained by its scientists. The balance is received from the state of Nevada for administrative costs.