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 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– –1998 was most intense on record No two ENSO events are alike. They all differ in size, location, and duration

ENSO

Normal

ENSO

Normal Year

ENSO

ENSO Year

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

La Nina

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: and AMO cool phases: and 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 and increase This means a decrease in precipitation for the eastern US Important implications for water managers Florida exempt