Transcript MORE Air Pressure Info - Catawba County Schools

MORE Air
Pressure Info
Made especially for you…
BAROMETER
• High pressure- High mercury level
• Low pressure- low mercury level
When a barometer
a falling that means
low pressure.
A rising barometer
indicates high
pressure.
What is “air pressure”…
-Think of air pressure as little
molecules of air…
– Picture an inflated balloon, the
molecules of air inside are in a high
pressure zone inside of that balloon
because they are tightly compacted
together; when you release that balloon
the air comes out into a low pressure
zone, where there is more space for the
air molecules.
High Pressure Zones
• Cold, dense (heavy/tightly
compacted), air sinks
• Cold air cannot hold much water, so
this leads to clear skies and calm
weather conditions
• A barometer will read higher than 30
inches when there is a high pressure
zone
Low Pressure Zones
– Warm air, less dense (lighter/more
spread out) rises
– Warm air rises into the atmosphere,
cools as it gets higher and attaches onto
dust particles- forming clouds
– Once the water vapor becomes too
heavy- precipitation occurs
– A barometer will read lower than 30
inches if it is a low pressure zone
Density
How tightly packed molecules are.
High Pressure- Tightly
compacted/close together air
particles
Low Pressure- More spread
out, room to move, room for
moisture
Cold air is more dense than
warm air.
Warm air is less dense than
cold air.
When Air Pressures Meet
High and low air pressures do not
they push against each other.
MIX-
A cold front occurs when a faster-moving cold air mass forms a
wedge that drives under a warm air mass. It can cause weather
changes like thunderstorms and even tornadoes.
A warm front happens when a warm air mass moves up at a
gradual slope over a cold air mass, usually resulting in less
drastic weather change.
Air Pressure & Wind
• The wind blows because air has weight. Cold air
weighs more than warm air, so the pressure of
cold air is greater. When the sun warms the air,
the air expands, gets lighter, and rises. Cooler,
heavier air blows to where the warmer and
lighter air was, or in other words, wind usually
blows from areas of high air pressure to areas of
low pressure. If the high pressure area is very
close to the low pressure area, or if the pressure
difference (or temperature difference) is very
great, the wind can blow very fast.
How Air Pressure Effects
Weather
• U.S. winters- High pressure from NW
Canada moves to SE U.S., bring cool
and dry weather
• U.S. summers- Low pressure from
Gulf of Mexico comes to NE U.S.
brining warm, wet conditions
Fronts
• When two air masses
meet, the air within them
does not easily mix. That
is to say that the air in
one air mass will not
easily mix with the air
from another air mass.
Instead the air stays
within its own air mass.
Because of this, a border
forms between two
clashing air masses, as
they rub together. This
border is called a front.
Mountain and Valley
Breezes
During the day the surface of a mountain heats the air up faster
than a valley floor can, creating an area of low pressure at the
mountain top. The cool air in the valley is attracted to this low
pressure zone, creating a breeze that blows from the valley to
the mountain.
*Birds often fly with these breezes in order to preserve their
energy.*