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Lecture 2

# EESA09H3 Lecture Notes - Lecture 2: Canadian Pacific Air Lines, Westerlies, Horse Latitudes

Department
Environmental Science
Course Code
EESA09H3
Professor
Tanzina Mohsin
Lecture
2

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Lecture 2
What is wind?
Movement of air in an ordered fashion
Difference in pressure forms a pressure gradient
Air flows from high pressure to low pressure called pressure gradient force
Coriolis force
Fictitious force due to rotation of the earth
In northern Hemisphere, causes a deflection to the right of the motion, to the left in the
Southern Hemisphere
Formulated mathematically by Gaspard Gustave de Coriolis in 1835; described by
Is related to the distance from the equator
Acts at right angle to the wind affecting the direction
Summary facts
PGF is always directed from higher pressure towards the lower pressure
Steep PG (closely spaced isobars) indicate strong PGF and high winds
When the wind starts to blow, the Coriolis force causes it to bend to the right of its
intended path in the Northern Hemisphere and to the left of its intended path in the
Southern hemisphere
Geostrophic Wind
Balance between PGF and Coriolis:
Blows parallel to isobars
Typical 1km or so above the Earth’s surface
Surface Winds
Below 1km, the wind is influenced by friction
Global Circulation
3 broad categories of atmospheric circulation:
o Global: 10000 of km
o Synoptic: 100 to 1000 km
o Small scales: <100 km
There is more energy released in the Polar Regions than is received from the sun. The
reverse is true for the equatorial region
One Cell Theory
One large overturning atmospheric cell, where air rises at the equator, moves pole ward
and then sinks at the pole. Also called one large Hadley cell after George Hadley
Energy is transported as sensible (heat you feel) and latent heat (due to the change in
phase) from equator to pole. Latent heat transport occurs when moist equatorial air moves
poleward, cools, condenses and releases latent heat
The theory works fine if the earth did not rotate. However, there is til and land/water
contrast, which also play a role for the weather system on Earth
o Rotation introduces the Coriolis effect
o Tilt causes seasonality
o Continentality causes land/ sea variation due to varying thermal inertia
Three Cell Theory