decadal and quasi-periodic processes Flashcards
1
Q
North Atlantic Oscillation (NAO)
A
- difference in pressure between Azores high and Iceland low
- Positive NAO = large difference in pressure, milder wetter conditions in Western Europe
- Negative NAO = smaller pressure difference, weaker westerly winds, increased chance of cold easterly winds dominating
2
Q
Atlantic Multidecadal Oscillation (AMO)
A
- large geographical scale
- every 70 years or so, ma be speeding up due to human influence
- historical tree ring evidence
- positive AMO = North Atlantic has anomalous warm sea surface temperature, Southern Atlantic is cooler than average
- Negative AMO = North Atlantic cooler, South Atlantic warmer
3
Q
positive AMO
A
- North Atlantic has anomalous warm sea surface temperatures
- South Atlantic cooler than usual
- lasts up to several decades
- appears to be driven by changes in the Atlantic Meridional Overturning Current
- increased rainfall in Europe, African Sahel and Florida/ north west USA
- increased risk of hurricanes
- lower rainfall in midwest USA
4
Q
negative AMO
A
- North Atlantic sea surface temperatures cooler
- South Atlantic sea surface temperatures warmer
- reduced rainfall in Europe, African Sahel and Florida/ north west USA
- lower risk of hurricanes in North Atlantic
- higher rainfall in central USA
5
Q
Pacific decadal oscillation (PAO)
A
- causes unknown, possible linked to changes in atmospheric pressure or lasting effects of El Nino events
- can last for 20-30 years
- Positive PDO = warm phase
- Negative PDO = cool phase
6
Q
positive PDO
A
- warm phase
- horseshoe of relatively warm sea surface temperature along west coast of US, large tongue of warm water extends westward into the South Pacific
- similar pattern to El Nino but spread over a larger region of the US
- south and east USA and Indian monsoon warmer and wetter
- West and northwest USA and China/Japan cooler and drier
- associated with periods of more rapid global warming
7
Q
negative PDO
A
- cool phase
- horseshoe of relatively cool sea surface temperatures running along west coast of USA
- large tongue of relatively cold water extending westward into South Pacific
- similar pattern to El Nina but spread across more of the northern pacific
- southwest USA colder and drier
- increased rainfall in Eastern Australia
- Japan warmer and wetter
- associated with slower rates of global warming and more mixing of colder deep ocean waters and warmer surface waters
8
Q
El Nino Southern Oscillation (ENSO)
A
Normal conditions
- trade winds in a Westerly direction push warm surface water towards the western Pacific
- cold water replaces surface water on the West coast of South America through upwelling
- clouds and rainfall in east Asia and Australasia
- cool dry conditions in South America
- El Nino is the weakening/reversing of these trade winds
- La Nina is the strengthening of the trade winds
9
Q
El Nino
A
- westerly trade winds over Pacific weaken or reverse
- no upwelling on the west coast of South America means warmer surface waters
- releases large amounts of heat energy into the atmosphere, global temperatures increase
- increase risk of floods in Peru
- increase risk of droughts in Indonesia/India and Brazil
- can limit development of tropical storms in North Atlantic
10
Q
La Nina
A
- strengthening of westerly trade winds over the Pacific
- increased upwelling in Peru
- slows global warming
- cooler drier conditions in equatorial East Pacific
- heavier rains in South East Asia
- increased risk of tropical cyclones in China
- can enhance development of hurricanes in north Atlantic (low wind shears)
