Global Hydroclimatological Teleconnections Resulting from Tropical Deforestation
Abnormal Weather October 22, 2007. Teleconnections Teleconnections: relationship between weather or...
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Transcript of Abnormal Weather October 22, 2007. Teleconnections Teleconnections: relationship between weather or...
Teleconnections
• Teleconnections: relationship between weather or climate patterns at two widely separated locations– ENSO– PDO– AMO
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
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
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
• 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
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
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
• 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 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)
• 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
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
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)
• 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
• 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
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
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