The months-long rainy season, or monsoon, that drenches northwestern Mexico each summer, reaching into Arizona and New Mexico and often as far north as Colorado and Northern California, is unlike any monsoon in the world, according to a new analysis by an earth scientist from the University of California, Berkeley.
The months-long rainy season, or monsoon, that drenches northwestern Mexico each summer, reaching into Arizona and New Mexico and often as far north as Colorado and Northern California, is unlike any monsoon in the world, according to a new analysis by an earth scientist from the University of California, Berkeley.
The so-called North American monsoon is important for delivering water to semi-arid areas of the American Southwest — 50% of Arizona’s and New Mexico’s precipitation comes from monsoon rains between July and September — but in recent years has also fueled wildfires around the West. The northern tail of the monsoon sometimes brings thunderstorms and thousands of lightning strikes to California, igniting wildfires.
The word monsoon conjures images of the monsoons of South Asia, where for several months each summer repeated downpours flood India and Bangladesh. These and other monsoons, such as those in Brazil and across Africa, are generated when intense summer sunlight causes the atmosphere to be heated over the continent more than over the nearby ocean, which draws humid air from the sea and dumps the moisture on land during intense storms.
But detailed supercomputer simulations of North American weather patterns show that the North American monsoon occurs when Mexico’s Sierra Madre Occidental mountains divert the eastward-trending jet stream toward the equator and then upward over the mountain slopes, cooling the moist tropical air from the eastern Pacific until it condenses and falls as rain.
Read more at University of California - Berkeley
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