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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

Abnormal Weather

October 22, 2007

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

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
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
  • Precipitation increases over the American southwest during ENSO events
  • Increase in fuels
  • Succeeding La Nina or normal weather patterns dries fuels
  • Preconditioning
  • Fire suppression
enso and crop yields
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
enso and crops
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
la nina
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
pacific decadal oscillation pdo
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
  • 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
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
atlantic multidecadal oscillation amo
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
  • 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
  • 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
  • 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