subtropical high-pressure cells westerlies bermuda high azores high figure 6.14

Subtropical High-pressure Cells

• Westerlies

• Bermuda high

• Azores high

Figure 6.14

Rossby WavesRossby Waves

Great waving undulations within the westerlies flow of

geostrophic winds.

IInstrumental 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 20-30 year cycles– Now known to heavily influence climate and

wildfire activity

North Atlantic Oscillation (NAO)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)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

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, 2002–2003

• 1997–1998 was so intense, it disrupted global weather

Normal

Normal Year

ENSO

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