Subtropical High-pressure Cells Westerlies Bermuda high Azores high Figure 6.14

Rossby Waves  Great waving undulations within the westerlies flow of geostrophic winds.  I  Instrumental to the latitudinal transportation of energy.  Play an important role in determining divergence and convergence areas of the upper atmosphere.

Upper Atmospheric Circulation Rossby waves Jet stream

Rossby Waves Figure 6.17

Rossby Waves Figure 6.17

Constant Isobaric Surface Figure 6.16

Jet Stream

Jet Streams Figure 6.18

 Strong boundaries often occur between warm and cold air. In the mid-latitudes, the polar front marks this thermal discontinuity at the surface. The Polar Front and Jet Streams

Multiyear Oscillations North Atlantic Oscillation –Believed to regulate hurricane activity Pacific Decadal Oscillation –Operates on year cycles –Now known to heavily influence climate and wildfire activity

North Atlantic Oscillation (NAO)  A large scale seesaw in atmospheric mass between the subtropical high and the polar low.  Positive NAO versus negative NAO

Arctic Oscillation (AO)  Opposing atmospheric pressure patterns in northern middle and high latitudes. Warm phase versus cold phase.

Pacific Decadal Oscillation

Local Winds Land-sea breezes Mountain-valley breezes Katabatic winds Monsoon patterns

Land-Sea Breezes Figure 6.19

Mountain- Valley breezes Figure 6.20

Katabatic winds

Chinook & Santa Ana Winds  Winds that flow down the lee side of mountain ranges

Monsoonal Winds Figure 6.21

Oceanic Currents Surface Currents –Cold = high latitude –Warm = low latitude –Gyres: circulate in which directions?

Major Ocean Currents Figure 6.22 Peru Current

Oceanic Currents Deep Currents –Thermohaline circulation –Distributes energy –Effects of global warming?

Deep Currents Figure 6.23

ENSO events ENSO events are a disruption of the ocean-atmosphere system in the tropical Pacific El Nino Southern Oscillation –El Nino – ocean –Southern Oscillation – atmosphere How are they reconstructed?

El Niño Changes in pressure patterns Changes in wind patterns Mainly concentrated in the Pacific Ocean Measured using Southern Oscillation Index –Differences in pressure observed in Tahiti and Darwin, Australia –Combined to form ENSO Affects weather globally

Buoys

El Niño

Impacts of ENSO Events Marine environments Atlantic hurricanes Global precipitation patterns Wildfires

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

El Niño

ENSO When high and low pressure systems exist in some locations, they not only impact local weather conditions, but also influence the overall size, shape, and position of the entire Rossby wave pattern Teleconnections: relationship between weather or climate patterns at two widely separated locations

ENSO

Occurs once every 3 to 5 years (but varies) Is regulated by (what else) PDO – Switch to PDO warm phase in 1999 appears to have dampened ENSO Major ENSO events in last 25 years: 1982–1983, 1986–1987, 1991–1993, 1997–1998, 2002– –1998 was so intense, it disrupted global weather

Normal

Normal Year

ENSO

ENSO Year

La Nina El Niño = warm phase, La Niña = cool phase 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