Transcript No Slide Title

General Atmospheric Circulation
V1003 - Science and Society
Take away concepts and ideas
The Earth is heated unevenly.
Why there are seasons.
Global-scale wind patterns.
Geostrophic flow: Balance of forces that act on
atmospheric flow (Pressure gradients & gravity
balanced by Coriolis force)
Wind belts and climate zones.
Monsoonal climate.
1.
As a sphere, the Earth is unevenly heated,
equator to poles
2. As a tilted sphere, the Earth has seasons
Seasonal changes in solar energy
winter
summer
summer
winter
winter
summer
The equation of state (air)
Atmospheric Pressure is a function of
temperature and density
Ideal Gas Law: P =  R T
if pressure is constant, then what
happens to  as T increases?
Concept of horizontal motion:
Sea Breeze
Pressure imbalance = flow
1. Pressure imbalance is a FORCE
(F = m x a)
2. Law of mass continuity (empty spaces
not tolerated in fluids)
Earth’s uneven radiation
1.
2.
Earth is a sphere (uneven
radiation)
Tilted (there are seasons)
Sphere means equator gets more
radiation than poles.
Tilt mean the amount of radiation at
one location changes with time
(seasons).
Incoming (and outgoing) radiation
Heating imbalance (∆T) =
Pressure imbalance (∆P) = Winds
Q1: Knowing uneven heating and P = R T
a) Poles have low density,
equator has high
density?
b) Equator has low
density, poles have high
density?
BUT - The Earth rotates
Apparent (inertial) forces control the flow of air
in response to these pressure gradients.
Centripedal force is the force
acting on body by string
Centrifugal force is the opposite
force acted on by the ball (by its
own inertia)
Imagine a satellite in orbit
Centripetal force = Gravity
Centrifugal force = mass
and acceleration of
satellite
Exact balance sets the
angular velocity of the
satellite
The Coriolis Force
Artifact of Earth’s rotation
An apparent force which
acts on motion on the
earth’s surface
Conservation of angular
momentum
Fcoriolis = 0 on equator,
increases poleward
Coriolis Force
Cons. of Angular Momentum
Geostrophic Balance
… the pressure gradient force (∆P) is balanced
by Coriolis force.
Applies to atmosphere and ocean circulation
where friction can be ignored.
Geostrophic balance
Balance between pressure and coriolis forces
Geostrophic Balance
NORTHERN HEMISPHERE
Geostrophic flow in the
Northern Hemisphere
Counter-clockwise around
low pressure cells
Clockwise around
high pressure cells
Opposite Coriolis deflection for
opposite hemispheres
An example of Geostrophic flow
Low
High
Q2: What direction is the wind coming
FROM in Chicago, IL today?
a)
b)
c)
d)
e)
North
Northwest
West
Southwest
Northeast
Chicago
Application to Earth
Geostrophic flow gives rise to banded circulation zones
Trade Winds and the
Intertropical Convergence Zone (ITCZ)
ITCZ
Hadley Cell
Tropical convection cells
westerlies
Trade
winds
Hadley
Cell
Trade
winds
Global vegetation patterns
Rising limb of Hadley Cell
(ITCZ) = Rainforest
Descending limb of
Hadley Cell = Deserts
Global Vegetation
Incoming (and outgoing) radiation
A note on the mid-term
12
73 ± 12
10
Rough guide:
Count
8
6
A/A+ >85
4
B/B+ 73
2
C/C+ 61
0
0
20
40
Grade
60
80
100