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Abnormal Weather

Abnormal Weather October 22, 2007 Teleconnections Teleconnections: relationship between weather or climate patterns at two widely separated locations ENSO PDO AMO Ocean Currents ENSO events ENSO events are a disruption of the ocean-atmosphere system in the tropical Pacific

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Abnormal Weather

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  1. Abnormal Weather October 22, 2007

  2. Teleconnections • Teleconnections: relationship between weather or climate patterns at two widely separated locations • ENSO • PDO • AMO

  3. Ocean Currents

  4. ENSO events • ENSO events are a disruption of the ocean-atmosphere system in the tropical Pacific • El Niño = warm phase, La Niña = cool phase • El Nino Southern Oscillation • El Nino – ocean • Southern Oscillation – atmosphere

  5. ENSO • Changes in pressure patterns alter path of jet stream • Mainly concentrated in the Pacific Ocean • Measured using Southern Oscillation Index • Differences in pressure observed in Tahiti and Darwin, Australia • Also monitored using remote sensing data

  6. ENSO Occurs once every 3 to 5 years (but varies) • Major ENSO events in last 25 years: 1982–1983, 1986–1987, 1991–1993, 1997–1998, 2002–2003 • 1997–1998 was most intense on record • No two ENSO events are alike. They all differ in size, location, and duration

  7. ENSO

  8. ENSO

  9. ENSO

  10. Normal

  11. ENSO

  12. Normal Year

  13. Normal Year

  14. ENSO

  15. ENSO Year

  16. ENSO Year

  17. ENSO Year

  18. Australia-Drought and bush fires • Indonesia, Philippines-Crops fail, starvation follows • India, Sri Lanka-Drought,fresh water shortages • Tahiti-6 tropical cyclones • South America-Fish industry devastated • Across the Pacific-Coral reefs die • Colorado River basin-Flooding, mud slides • Gulf states-Downpours cause death, property damage • Peru, Ecuador-Floods, landslides • Southern Africa-Drought, disease, malnutrition

  19. Wildfires • Precipitation increases over the American southwest during ENSO events • Increase in fuels • Succeeding La Nina or normal weather patterns dries fuels • Preconditioning • Fire suppression

  20. ENSO and Crop Yields • El Nino events are associated with LOW grain yields in Asia and Australia and HIGH grain yields in North America • In the SE Coastal Plain, El Nino years tend to be cool (and wet) and La Nina years warm (and dry) between October and April

  21. ENSO and Crops • In the SE, crops yields are higher after an El Nino winter and lower after a La Nina year • The neutral ENSO phase has above average vegetation response

  22. La Nina • La Niña brings extreme normal conditions • Not all El Niño events are followed by La Niña events • La Niña events increase wildfires in the SE and Atlantic hurricanes

  23. La Nina

  24. La Nina

  25. Pacific Decadal Oscillation (PDO) • 20 to 30-year cycles • Discovered 1996 • Involves two regions of sea-surface temperatures and related air pressure: • 1) the northern and tropical western Pacific • 2) the eastern tropical Pacific, along the west coast of North America

  26. PDO • 1947 – 1977: Cool (negative) Phase - region 1 had higher than normal temperatures and region 2 had lower than normal temperatures • 1997 – 1999: Warm (positive) Phase – region 1 had lower than normal temperatures and region 2 had higher than normal temperatures • Despite several years of cool phase values, we are still considered to be in warm phase

  27. PDO and ENSO • PDO impacts the strength of ENSO events • When PDO is in the warm phase, El Nino’s are stronger • Southern US has wetter than normal winters; Northern US is drier • When PDO is in the cool phase, El Nino’s are weaker

  28. Atlantic Multidecadal Oscillation (AMO) • 20 – 40 year cycles • Has warm (positive) and cool (negative) phases • AMO impacts ENSO strength and increases hurricane activity • During warm phases, the US experiences decreased rainfall • Been reconstructed back to 1650 AD • Measure of SST in North Atlantic between Equator and 70°N

  29. AMO • AMO warm phases: 1860-1880 and 1930-1960 • AMO cool phases: 1905-1925 and 1970-1990 • AMO involves strengthening (warm phase) and weakening (cool phase) of the North Atlantic Thermohaline Circulation

  30. AMO • During an AMO warm phase, El Nino events are muted, providing less winter precipitation • During an AMO cool phase, El Nino events are not affected • When AMO is positive and PDO is negative, the majority of the US experiences drought conditions • Example: 1930s Dust Bowl

  31. AMO • AMO entered warm phase in 1995 • Global temperatures expected to mimic those between 1930-1960 and increase • This means a decrease in precipitation for the eastern US • Important implications for water managers • Florida exempt

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