Southwest Climate Bimodal and Unimodal rainfall Winter precipitation
• • • 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 30 -day (ending 15 Jan 2011) temperature departures (degree C) Last 90 Days 90 -day (ending 16 Jan 2011) % of average precipitation 90 -day (ending 15 Jan 2011) temperature departures (degree C)
Watch these videos http: //www. youtube. com/watch? v=f. N_Nm. Cpry 3 8&feature=related http: //www. youtube. com/watch? v=1 o. KIJIfp. R 6 U&feature=related http: //www. youtube. com/watch? v=Os. Yne. Lon. QF 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 7. Rain 4. Hot air rises 2. Surface absoprtion 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
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