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• • • • • • Southwest Climate Bimodal and Unimodal rainfall Winter precipitation – Pacific frontal storms – El Niño Summer monsoons Arid Foresummer What SW climate (precipitation) means – Vegetation – Humans Temperature less interesting for now MAP (in.) MAT (°F) JFMAMJJASOND Northern Hemisphere Winter Northern Hemisphere Winter Winter Pacific front Maybe to SW La Niña = normal Upwelling of cold water to surface of Peruvian coast Westward flow of warm surface water Hot air rises over western Pacific Clouds miss American SW El Niño = abnormal Upwelling of cold water slackens, fails Warm surface water stalls over central Pacific Hot air rises over central Pacific Clouds hit the American SW U.S. Temperature and Precipitation Departures During the Last 30 and 90 Days Last 30 Days 30-day (ending 16 Jan 2011) % of average precipitation 90-day (ending 16 Jan 2011) % of average precipitation 30-day (ending 15 Jan 2011) temperature departures (degree C) Last 90 Days 90-day (ending 15 Jan 2011) temperature departures (degree C) Watch these videos http://www.youtube.com/watch?v=fN_NmCpr y38&feature=related http://www.youtube.com/watch?v=1oKIJIfpR 6U&feature=related http://www.youtube.com/watch?v=OsYneLonQF 4&feature=related http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/enso.shtml Niño Niña North Hemisphere Summer North Hemisphere Summer 6. Cooling air condenses 1. Incoming solar 2. Surface absoprtion 7. Rain 4. Hot air rises 5. Rising air cools 3. Surface emission Tucson, Water Year-to-Date (2007) We ended up ca. 1” below normal—few winter rains Monsoon Rainfall & SW • Some modern societal segments “immune” to rainfall variation – Stored, imported, or ground water • Critical to non-irrigated agriculture – Upland “dry” farming – Ranching • Flooding. • • • • Key Points SW has bimodal (W) and Unimodal (E) rainfall Arid Foresummer—always (?) Winter – Frontal westerlies – El Niño – Decadal variability Summer – Monsoonal southerlies – Fairly consistent