Basic Meteorology Concepts
Spheres of the Earth
Lithosphere
Atmosphere
Thermal Convection
Objectives – Global Circulation
 Sketch the global pattern of winds in the three cell
model
 Discuss vertical convection in the atmosphere
 Discuss the development of tropical cyclones
 Key terms: Hadley cell, ITCZ, cyclones, anticyclones
and adiabatic
Introduction to Meteorology:
Low Pressure
High Pressure
Cyclonic Turning
(counterclockwise):
Convergence
leads to upward
vertical motions.
Anti-Cyclonic
(clockwise) Turning:
divergence
leads to downward
vertical motions.
Cold Air
Warm Air
Source: USA TODAY research by Chad Palmer, Graphic by Kevin A. Kepple
Which one is the high pressure? The low pressur
Which one is the high pressure? The low pressur
Associated with deteriorating
weather. Clouds form; lots of
precipitation.
Associated with fair weather, clear
to partly cloudy skies. No significant
weather.
Starting assumption: Poleward heat transfer
 Mid-Latitudes
 Radiation imbalance
 Low and High Pressure centers
 Manifestation of the need to move heat poleward
to maintain balance
 Air moves poleward
 Picks up heat from the oceans and continents below
 Rises at low pressure regions (such as the equator)
 Moves poleward taking its heat load with it
 Atmosphere moves ~1.5x more heat than oceans
Global Atmospheric Circulation
Single Cell Model


3 Assumptions:
1. Earth’s surface covered with water
2. Sun is always directly over the equator
3. Earth does not rotate
 Thermally direct cell – driven by the sun
 Too simplistic
Where are Highs & Lows located?
Single Cell
Model
Single Cell Model
Meteorology Today by C. Donald Ahrens
One-Cell Model
 If no net heating at any latitude: poleward export of heat
towards cooler latitudes
 Simple wind system: surface winds blow from the polar
high to the equatorial low
 The air at the equator heats up, becomes less dense and
returns to the poles at the top of the troposphere where it
cools and sinks
 This is model of simple earth with no rotation—How is the
3-cell Model different?
Three Cell Model
 Takes the first two assumptions of the single-cell model, but
the earth rotates
 Breaks down into three cells: Hadley cell, Ferrel cell and the
Polar cell (Vertical view)
 Where are the high
and low pressures
located?
 Accounts for Coriolis
Force and variations
with latitude
Three Cell Model
Hadley Cell
Ferrel Cell
Polar Cell
A quick digression: Coriolis Force
 Effect of the Coriolis Force
 Deflect currents or winds towards the
right in NH; towards the left in SH
 Winds flow toward equatorial lows
 Equatorward winds = Trade Winds
Note: WINDS are named for the direction that
they are blowing FROM
CURRENTS are named for the direction that
they are flowing TOWARDS
Coriolis “Force” facts:
The apparent deflection of objects moving over the
Earth's surface w/o being frictionally bound to it.
An “apparent” force due to the rotation of the earth.
The magnitude of the Coriolis force increases from
zero at the Equator to a maximum at the poles.
f = 2 Ω sin Φ Ω = angular rotation rate of the earth
Φ = latitude
It acts at right angles to the direction of motion
Deflections to the right in the Northern Hemisphere
Deflections to the left in the Southern Hemisphere
Hadley Cell: Three Cell Model
 4 Major areas of High Pressure:
 ~30o lat & poles
 (Subtropical
& Polar Highs)
 3 Major areas
of Low Pressure:
 Near equator
& ~60o lat
(ITCZ &
Subpolar Lows)
Atmospheric Pressure Bands
Be able to sketch the 3-cell model!!