Air Masses, Global Winds, and FrontsPresentation Transcript
Meteorology – the study of
atmospheric phenomena (weather and
•“Meteor” is derived from ancient Greek
meaning “high in the air.”
•Clouds, raindrops, fog, and rainbows are
Types: hydrometeors, lithometeors, electrometeors.
Weather – the current state of the atmosphere.
What is the weather in our area?
Climate – the long-term average state of
atmosphere in a particular area.
What is the climate in Hawaii? Alaska?
What are the “reasons for the seasons?
•A large body of air that takes on the characteristics of
the area over which it forms. Air masses can cover
hundreds of thousands of square miles.
1) (cP) continental polar - cold, dry, stable
2) (cT) continental tropical - hot, dry, stable air aloft--unstable surface
3) (mP) maritime polar - cool, moist, and unstable
4) (mT) maritime tropical - warm, moist, usually unstable
1. Polar latitudes P - typically located poleward of
60 degrees north and south Latitude. Cold.
2. Tropical latitudes T - typically located within
about 25 degrees of the equator. Warm.
3. continental c - located over large land massesdry.
4. marine m - located over the oceans----moist
1. Continental Polar (cP): cold temperatures and dry.
•Those who live in northern portions of the United States expect
cold weather during the winter months. These conditions usually
result from the invasion of cold arctic air masses that originate
from the snow covered regions of northern Canada.
2. Maritime Polar (mP): Cool temperatures and rich in moisture.
3. Continental Tropical (cT) – hot and dry.
The air usually only influences the US in summertime as warm, dry
air is pumped up off of the Mexican Plateau.
It is usually fairly stable and dry, and if it becomes stagnant over the
midwest, results in a drought.
Deaths associated with the 1995 heat wave in the midwest were the
result of cT and mT air which stagnated over the central and eastern
part of the US this last summer.
4. Maritime Tropical (mT): forms over the ocean near the equator.
Warm, moist air. Brings hot & humid weather.
•Maritime tropical air masses originate over the warm waters of the
tropics and Gulf of Mexico, where heat and moisture are transferred
to the overlying air from the waters below. The northward movement
of tropical air masses transports warm moist air into the United
States, increasing the potential for precipitation.
Air Mass Characteristics
•An air mass can acquire some the characteristics of
the surface beneath it. This is known as air mass
modification, where the exchange of heat or
moisture with the surface occurs.
Describe how the rotation of Earth
affects the movement of air.
Compare and contrast wind systems.
Identify the various types of fronts.
– jet stream
The Coriolis effect, which is a result of Earth’s rotation,
causes moving particles such as air & water to be deflected
to the right in the northern hemisphere and to the left in the
The Coriolis effect combines
with the heat imbalance
found on Earth to create
distinct global wind
systems that transport
colder air to warmer
areas and warmer air
to colder areas.
Coriolis Effect and Weather Systems 2 min
Demo: Coriolis Effect
Global Wind Systems
Global Wind Systems
There are three basic zones, or wind systems, in
1. The trade winds, the first major wind
zone, flows at 30° north and south latitude,
where air sinks, warms, and returns to the
equator in a westerly direction.
Around 30° latitude, known as the horse
latitudes, the sinking air associated with
the trade winds creates a belt of high
pressure that in turn causes generally
weak surface winds.
Global Wind Systems
When air converges it is forced upward and
creates an area of low pressure in a process
Near the equator, convergence occurs over
a large area called the intertropical
convergence zone (ITCZ), also called the
The ITCZ migrates south and north of the
equator as the seasons change.
The ITCZ is characterized by a band of
cloudiness and occasional showers.
Global Wind Systems
Other Wind Zones
2. The prevailing westerlies, the second major
wind zone, flows between 30° and 60° north
and south latitude in a circulation pattern
opposite that of the trade winds.
– The prevailing westerlies are responsible for
much of the movement of weather across the
3. The polar easterlies, the third major wind
zone, lies between 60° latitude and the poles.
– In both hemispheres, the polar easterlies are
characterized by cold air.
Jet streams are narrow bands of high-altitude,
westerly winds that flow at speeds up to 185 km/h
at elevations of 10.7 km to 12.2 km.
– The polar jet stream
separates the polar
easterlies from the
– The jet stream affects the
intensity of weather
systems by moving air of
different temperatures from
one region to another.
In the middle latitudes, air masses with different
characteristics sometimes collide, forming a front.
A front is the narrow region separating two
air masses of different densities that are
caused by differences in temperature, pressure,
The interaction between the colliding air masses
can bring dramatic changes in weather.
There are four main types of fronts: cold fronts,
warm fronts, stationary fronts, and occluded fronts.
1. Cold Fronts
– In a cold front, cold, dense air displaces warm air and
forces the warm air up along a steep front.
– Clouds, showers, and
sometimes thunderstorms are
– In a warm front, advancing warm air displaces
2. Warm Fronts
– The warm air develops a gradual frontal slope rather
than a steep boundary.
– A warm front is characterized by extensive cloudiness
3. Stationary Fronts
– A stationary front is the result of two air masses
meeting and neither advancing into the other’s
territory, stalling the boundary between them.
- May rain for days.
4. Occluded Fronts
– An occluded front is the result of a cold air mass
overtaking a warm front, wedging the warm air
– Precipitation is common on both sides of an occluded