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Meteorology
12.1 The Causes of Weather
Weather
Meteorology is the study of atmospheric
phenomena
 Weather is the current state of the
atmosphere.
 This is usually measured in minutes, days
and weeks

Climate

Climate is the weather
for a long period of time
for a given location.

Usually averaged over
30 or more years.

Ex. The climate is hot
and humid in Miami, but
it is snowing there today.
Air Masses

An air mass is a large
body of air that takes
on the characteristics
of the area over which
it forms.
Types of Air Masses


Moisture
Maritime vs.
Continental:
 Maritime air masses
form over waterhave more moisture
 Continental air
masses form over
land- they are drier
Types of Air Masses



Temperature
Tropical vs. Polar
 Tropical air masses
form closer to the
equator- warm
 Polar air masses
form closer to the
poles- cold
Arctic air masses are
extremely cold
Source Regions
Combine Moisture and Temperature titles to
name air masses.
 Name them after the regions where they
form.
 Continental Tropical(cT) will form over
land near the equator. Ex. Brazil, Mexico
 Maritime Tropical(cM) will form over water
near the equator. Ex. Gulf of Mexico

Examples:
Continental Polar(cP)
 Continental Tropical(cT)
 Maritime Polar(mP)
 Maritime Tropical(mT)
 Arctic(A)

Coriolis Effect

The Earth spins on its axis. This causes air
particles to deflect to the left in the N.
Hemisphere & to the right in the S.
Hemisphere
R
Wind Systems

Three wind
zones in each
Hemisphere
 Trade
Winds
 Prevailing
Westerlies
 Polar
Easterlies
Wind Zones
•The trade winds occur from the
equator to 30ºN and 30ºS. The winds at
the equator are called the doldrums and
the ones at the 30º mark are called the
horse latitudes.
•The prevailing westerlies are
between 30ºN and S up to 60ºN and S
in a pattern opposite of the trade winds.
They are responsible for moving most
weather across the US and Canada.
•The polar easterlies are between
60ºN and S and the poles. (90ºN and S)
Jet Stream

A stream of air
that circulates the
globe. Caused by
differences in
pressure between
the wind systems.
 Trade and
Westerlies
 Westerlies and
Easterlies
Fronts

A front is the narrow
region separating two air
masses of different
densities. These
differences are due to
differences in temperature,
humidity, and pressure.
 Cold
 Warm
 Stationary
 Occluded
Page 308- 309 in RED BOOK!
Cold Front – Cold dense air displaces
warm air and forces the warm air up
along a steep front
-Thunderstorms often occur along the
front
On a weather map:
solid blue line with
blue triangles that
point in direction of
the front’s motion
Cold Fronts

Cold Fronts occur when a cold air mass
runs into a warm air mass, forcing the warm
mass to rise.(notice cloud types!)
Warm Front – Advancing warm air
displaces cold air
- Extensive cloudiness and
precipitation
On a map: solid red line
with regularly spaced,
solid red semicircles
pointing in the direction
of the front's motion.
Warm Fronts

When warm masses run into cold masses
and slowly displaces it. (notice clouds!)
Stationary Front – Two air masses
meet and neither advances; air masses
“stall”
- Light wind and precipitation
On a map:
combination of
short segments
of cold and
warm front
symbols
Stationary Fronts

Stationary Fronts occur when front run in
parallel opposite directions
Occluded Front – Cold air mass
moves so rapidly that it overtakes a
warm front
- Strong winds, heavy precipitation
On a map: alternating
purple triangles and
semicircles that point
toward the direction
of motion.
Occluded

Occluded Fronts occur when two cold
fronts “pinch” a warm front up.
Front Video
High Pressure Systems

High Pressure SystemsAir sinks, then hits the
Earth’s surface and
spreads out.
 Wind blows away from
high pressure.
 Clockwise in N.
Hemisphere
 Associated with fair
weather
Low Pressure System

Low Pressure System- Air rises, must be
replaced.
 Wind blows toward center of low
pressure
 Counter-Clockwise in N. Hemisphere
 Associated with clouds and precipitation