Download air mass

Weather Forecasting
How Air Moves
• Recall the solar variation on the Earth…….
• What location on the Earth receives the most
direct sunlight?
• What causes wind (air) to blow?
• Air moves (H) High pressure  (L) Low pressure
Formation of Air Masses
air mass a large body of air with similar
temperature and moisture content throughout
• When air pressure differences are small, air
remains relatively stationary.
• Air masses that form over frozen polar regions
are very cold and dry.
• Air masses that form over tropical oceans are
warm and moist.
Continental and Maritime Air Masses
• Continental polar (cP) air masses are cold and dry.
• Continental tropical (cT) air masses are warm and dry.
• Maritime polar (mP) air masses are moist and cold.
• Maritime tropical (mT) air masses are moist and warm.
?What do you think happens when moist
maritime air masses travel to new locations?
•6 different air masses affect N.America
In summer, polar air masses usually bring cool, dry weather.
In winter, very cold and wet weather to the northern United States.
Moist:
summer rain, winter snow
dry, hot weather to deserts in the summer
Warm, moist air
H: HIGH PRESSURE SYSTEM
• A high pressure system is an area that has diverging
winds (spreading out) on the surface.
• Anticyclone: clockwise in Northern Hemisphere
• fair or dry weather, because sinking air does not
promote cloud formation.
L: Low Pressure System
• A low pressure system is an area that has converging
winds on the surface.
• Cyclones: counterclockwise in Northern Hemisphere
• Stormy weather is often associated with low pressure
systems
Hurricane Katrina, August 28, 2005
Weather Maps
• Atmospheric Pressure: the amount of atmospheric mass
above a specific location
• Isobars: line drawn on a weather map connecting points of
equal pressure
• Wind barbs: shows the wind direction and speed
Fronts animation
• Play fronts
FRONTS
• A cool air mass is more dense than warm air
mass.
• Front: the boundary that forms between air
masses of different densities.
• Changes in weather take place along the various
types of fronts.
• Many fronts occur in the mid-latitudes due to
variation in temperature.
• Why don’t we see fronts in the tropics?
COLD FRONT
cold front: cold air mass displaces warm air mass, forces warm air up
(wedge)
• If the warm air is moist, clouds,
showers, and thunderstorms.
Direction of flow
Cold front animation
• Play cold front
Warm Fronts
warm front: warm air displaces cold air
• A warm front produces very cloudy with precipitation over a
large area and may cause violent weather.
Warm front animation
• Play warm front
Stationary and Occluded Fronts
stationary front: a front between warm and cold
air masses that is moving very slowly or not at
all.
Somewhat cloudy, light precipitation
occluded front: a front that forms when a cold air
mass overtakes a warm air mass and lifts the warm
air mass off the ground and over another air mass
Stormy weather (cyclone) produced
Play: Reading a Weather Map
Weather vs Climate
• Weather is a short term, atmospheric
phenomena interaction. Measured in
minutes, hours, days, weeks or months.
• Climate is how the atmosphere behaves and
changes over a long period of time. (30 years
or more)
Why is it warmest during the middle of the day
and cooler in the morning and evening?
• The Sun’s rays hit the surface more directly in
the middle of the day as it is overhead. The
same amount of energy is released during the
morning and evening hours, but the Sun’s rays
are hitting the surface at an angle and the
energy is spread out over a larger area.
Relative Humidity
• When people say "It's not the heat--it's the
humidity!" they're really referring to the
relative humidity, or the amount of water in
the air at a certain temperature compared to
how much water the air can hold at that
temperature.
Relative Humidity
• Air, like all gases, expands at higher
temperatures. So air can hold more water
vapor at higher temperatures than it can at
lower temperatures. The amount of humidity
in the air affects how quickly water can
evaporate from surfaces such as roads, lakes,
even your skin!
Relative Humidity
• For example, at an air temperature of 80
degrees, 60 percent humidity might be very
comfortable. But at 90 percent humidity,
sweat evaporates from your skin very slowly,
and you feel hot and sticky.
Local Weather Report
1. What is the current weather like in Athens,
Georgia?
2. Why are those conditions present?
3. What is the projected weather for
tomorrow?
4. What is the current temperature in Athens?
5. What are the wind conditions in Athens?
Coriolis Effect Lab
• Before we go upstairs to do the Coriolis Effect
lab here are a few facts.
Why Air Moves?
• Wind is created by differences in air pressure.
The greater the pressure is, the faster the
wind moves. The difference in air pressure is
generally caused by the unequal heat of the
Earth.
• Air moves from high to low
• Winds moves from poles to equator
Why Air Moves?
• Temperature and pressure difference on
Earth’s surface create three wind belts in the
Northern Hemisphere and three wind belts in
the Southern Hemisphere. The Coriolis effect
which occurs when winds are deflected by
Earth’s rotation also influences wind patterns.
What is the Coriolis Effect?
• Winds don’t blow directly North or South.
The movement of wind is affected by the
rotation of the Earth, causing the wind to
travel in a curved path rather than a straight
line. The curving or moving objects, such as
wind, by Earth’s rotation is called the Coriolis
Effect. Because of this, the winds in the
Northern Hemisphere curve to the right, and
those in the Southern Hemisphere curve to
the left.
What is the Coriolis Effect?
• The circulation of the atmosphere and of the
oceans is affected by the rotation of Earth on
its axis. Earth’s rotation causes its diameter to
be greatest through the equator and smallest
through the poles.
• Because each point on Earth makes one
complete rotation every day, points near the
equator travel farther and faster in a day than
points closer to the poles do.
What is the Coriolis Effect?
• When air moves toward the poles, it travels
east faster then the land beneath it does. As a
result, the air follows a curved path. The
tendency of a moving object to follow a
curved path rather than a straight path
because of the rotation of Earth is called the
Coriolis effect.
What is the Coriolis Effect?
• Air moving south from the pole is deflected to
the right because the air moves east slower
than the ground beneath it does.
• Air moving north from the equator is
deflected to the right because the air is
moving east faster than the ground beneath it
is.
Coriolis Effect Lab
• The rotation of Earth in an easterly direction
causes the Coriolis effect. The Coriolis effect,
in turn, influences the direction of all freemoving objects, such as air and water. The
Coriolis effect greatly influences the
movement of global wind patterns and ocean
currents.
• How does the Coriolis effect deflect the
movement of air and water in each
hemisphere?