Textbook Notes (380,719)
CA (168,184)
UTSC (19,294)
EESA09H3 (9)
Chapter 2

Wind - Chapter 2 notes

5 Pages
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Department
Environmental Science
Course Code
EESA09H3
Professor
Tanzina Mohsin

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EESA09 Lecture 2
What is Wind?
Differences in air pressure (Vertical or horizontal) produce a
pressure gradient
Pressure Gradient Force In the absence of
other forces, air moves from high pressure to
low pressure
Steep PG (closely spaced
isobars) indicate strong PGF
Coriolis Force
Because the earth rotates, the rotation directly results in a fictitious force called Coriolis
Force
Gustave de Coriolis (1835)
Northern Hemisphere Deflects wind to the right
Southern Hemisphere Deflects wind to the left
Above the surface of earth (1 km or more), when there is a balance
between pressure gradient force and the Coriolis force,
geostrophic wind is formed
The only way to achieve a balance between these
forces is for the wind to flow perpendicular to the pressure
gradient
Below 1 km, wind is influenced by friction (three way balance)
Wind flows towards centre of a low and away from the high pressure centre
Global Circulation
Air has natural inclination to move from high pressure to low pressure, but is modified by:
a)Earth rotation creating the Coriolis effect causes wind to deflect (NH=R, SH=L)
b)Earth surface contributes friction which slows down and redirects (funnels) the wind
c)Land/Sea contrast leading to temperature differences between land and water
surface also influences the wind (continentality)
d)Wind vary with season (caused by tilt of earth)
www.notesolution.com
Sensible Heat Heat that you can feel
Latent Heat Stored as water vapour; heat absorbed as water evaporates, released as
water condenses
One Cell Theory One large Hadley Cell, George Hadley 1970s
Air rises at the equator, moves poleward (towards the pole) and sinks at the pole
Energy is transported as sensible heat and latent heat
Latent heat transports occurs when moist equatorial air moves poleward, cools,
condenses, and releases latent heat
Problem: Theory is wrong because the earth rotates, and is tilted
Three Cell Theory
Hadley cell Air rises at the equator, moves poleward and sinks at 30oN and 30oS
Surface flow is equatorward and produces winds from the east
Ferrel cell (William Ferrel 1856) Air between 30o to 60o in each hemisphere
Surface winds travel north and under the influence of Coriolis force turns to the east
Polar cell Air sinking at poles, rising at 60oN and 60oS
Polar easterlies produced
Trade Winds Between the equator and 30oN, wind should flow south, but the rotational
deflection causes wind to flow southwest
Westerlies (coming from west) Between 30oN to 60oN wind should flow north, but the
rotational deflection causes wind to flow northeast
Polar Easterlies (coming from the east) Between the pole and 60oN wind should flow
south, but the rotational deflection causes wind to flow southwest
Horse Latitudes - 30oN and 60oN, little wind between westerlies and trade winds
Intertropical Convergence Zone (ITCZ) or Doldrums A region of little wind between
north and south trade winds (Hadley cells), heavy precipitation
Polar Front Between ferrel and polar cell, where cold air and warm air collide (storms)
www.notesolution.com

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Description
EESA09 Lecture 2 What is Wind? Differences in air pressure (Vertical or horizontal) produce a pressure gradient Pressure Gradient Force In the absence of other forces, air moves from high pressure to low pressure Steep PG (closely spaced isobars) indicate strong PGF Coriolis Force Because the earth rotates, the rotation directly results in a fictitious force called Coriolis Force Gustave de Coriolis (1835) Northern Hemisphere Deflects wind to the right Southern Hemisphere Deflects wind to the left Above the surface of earth (1 km or more), when there is a balance between pressure gradient force and the Coriolis force, geostrophic wind is formed The only way to achieve a balance between these forces is for the wind to flow perpendicular to the pressure gradient Below 1 km, wind is influenced by friction (three way balance) Wind flows towards centre of a low and away from the high pressure centre Global Circulation Air has natural inclination to move from high pressure to low pressure, but is modified by: a) Earth rotation creating the Coriolis effect causes wind to deflect (NH=R, SH=L) b) Earth surface contributes friction which slows down and redirects (funnels) the wind c) LandSea contrast leading to temperature differences between land and water surface also influences the wind (continentality) d) Wind vary with season (caused by tilt of earth) www.notesolution.com
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