geu 0027 meteorology lecture 10 wind global systems n.
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GEU 0027: Meteorology Lecture 10 Wind: Global Systems. Global Circulation. In the absence of rotation , air would tend to flow from the equator toward the poles. Hot, less dense air rising at the equator, becomes denser as it cools and descends at the poles, traveling

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global circulation
Global Circulation
  • In the absence of rotation, air would tend to flow from the equator toward the poles.

Hot, less dense air

rising at the equator,

becomes denser as

it cools and descends

at the poles, traveling

back to tropical areas

to heat up again.

slide3

Global Circulation

  • Because of earth’s rotation we have several circulation cells not just one per hemisphere
slide4

Three-cell Model

  • With the 3 cell structure of wind circulation and the combination of PGF and Coriolis, semi-permanent circulation patterns are established.
slide5

Semi-permanent Pressure and Winds

Semi-permanent structures in the atmosphere provide

consistent wind patterns and breeding grounds for

air masses.

slide14

Intertropical Convergence Zone

  • ITCZ
  • Hot equatorial air rises in convection.
  • Air moves away from the equator toward the poles.
  • Low Pressure results around the equator.
  • A band of convective thunderstorms circles the tropical areas of the globe.
slide15

ITCZ

  • Equatorial Cumulus and Thunderstorms
jet locations
Jet Locations

Jet stream locations

greatly affect

local and global

climate.

jet formation
Jet Formation

Sharply varying pressure and

temperature differences create the

exaggerated situation shown.

Tightly packed isobars create stronger

winds aloft in the frontal region.

polar jet
Polar Jet

Winds are Westerly

and parallel to the

frontal boundary.

This creates the

polar jet stream.

It is strongest in the

winter and weakest

in the summer.

seasonal polar jet changes
Seasonal Polar Jet Changes
  • Location and Velocity variations
slide27

What cause the jets?

  • L = m v r
    • r = distance from rotational axis
    • m = mass
    • v = velocity
slide29

Jupiter’s Bands

  • Higher Angular Momentum, Yields more zones?
wind jets
Wind Jets
  • Other jet formation mechanisms are less well known.
the dishpan experiment
The Dishpan Experiment
  • Uneven heating of the equator and poles of the earth.
  • Rotation.
  • Viscosity and turbulence.
rossby waves
Rossby Waves

Kinking in the jet

stream occurs on

a cyclic basis.

Weather patterns

are also somewhat

cyclic.

rossby cycle
Rossby Cycle

A complete

Rossby cycle

observed over

~ 6 weeks.

normal south pacific condition
Normal South Pacific Condition
  • Easterly “trade-winds” usually prevail and upwelling occurs
  • When exceptionally strong this cooling is called a La Nina.
el nino
El Nino
  • During an El Nino, pressure conditions (and winds) reverse.
  • Extremely warm water and wind reversal affects weather.
sea surface temperatures
Sea Surface Temperatures

A warm water wave

migrates eastward

during and El Nino

as upwelling and

cooling is severely

diminished along

the western coast

of S. America.

el nino and la nina events and enso cycle
El Nino and La Nina events, and ENSO Cycle
  • La Nina versus El Nino conditions over the past 60 years.
  • The Y-axis is a parameter calculated from a combination of:
    • air temperature
    • water temperature
    • air pressure (sea-level)
    • wind speed and direction
    • cloud cover