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Ocean and Jet Stream Currents is Cause of Warmer Globe By Patrick L. Barry May 21, 2004, 13:11 Why so Dry? The western U.S. is facing yet another summer of severe drought. Science provides some answers -- and some baffling questions. May 21, 2004: People often greet the first warm days of summer with eager anticipation for the sunny weather to come. But for many people in the western U.S., the arrival of warm weather this year is an harbinger of hard times ahead. Drought has gripped some parts of the West for as many as seven consecutive years, causing one of the worst dry spells in decades. Soils are dry; reservoirs are low. Farmers and golf course managers are vying for irrigation water, residents face water rationing measures, and the politics of water "seniority" rights is heating up between cities and between states. Hope for a reprieve fades with the departing winter, because little precipitation typically falls in the West during summer months. These regions depend on winter storms to stock the mountains with snow, which melts in summer and replenishes water supplies. The snow pack in April 2004, though, was only 40% to 75% of normal The ongoing drought, which has affected 20% to 50% of the land area of the contiguous United States, isn't as bad as, say, the Dust Bowl drought of the 1930s. Then 70% of the U.S. was dry. In the Great Plains, precious topsoil blew away, agriculture collapsed, farmers literally lost their land. "The dispossessed were drawn west," wrote John Steinbeck in The Grapes of Wrath. "Families, tribes, dusted out, tractored out. Car-loads, caravans, homeless and hungry. They streamed over the mountains--restless as ants, scurrying to find work to do--to lift, to push, to pull, to cut-- anything, any burden to bear, for food." What causes such severe droughts? Are they predictable? Scientists aren't sure, but they're learning by studying the current dry spell. Earth-orbiting satellites, which didn't exist during the Dust Bowl years, now provide crucial data about winds, rain, soil moisture, and the state of the oceans. Somewhere among those numbers lies the answer. A key factor is the temperature of water in the Pacific Ocean, says Bob Oglesby, a climate dynamicist at NASA's Marshall Space Flight Center. Sea surface temperatures (SSTs) in the Pacific alter the course of the jet stream as it flows eastward over North America. This high-altitude "river" of fast-moving air is like a conveyor belt for storms, so the path it takes across the continent has a strong effect on where rain and snow will fall. By steering the jet stream, the Pacific Ocean acts like a baton-wielding orchestra conductor directing the symphony of weather patterns across North America.Subscribe Receive Your "Free"
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