Download Air Pressure

Atmosphere
What Makes Up the Atmosphere?
Earth’s Atmosphere
• Different from other planets
– A mix of nitrogen and oxygen gases
• Gradually developed over 4.5 billion years
• Developed because:
– Volcanoes erupted & gases contained water vapor
– Water vapor condensed, filling oceans and caused
chemical reactions
Layers of the Atmosphere
• Troposphere-closest to Earth’s surface, dense,
nearly all life is here.
• Stratosphere-air is thinner and drier than 1st
layer, ozone blocks UV rays from sun.
• Mesosphere-coldest layer, air is very thin,
shooting stars and meteoroids are here!
• Thermosphere-high temperatures, space
exploration begins here and space shuttles fly
here.
• Exosphere-outermost layer, artificial satellites
explore and orbit here.
Air Masses
• Large masses of air
• Temperature and humidity are affected by the
area they are formed over.
• Humidity: the amount of water vapor in the
air.
– Example: Gulf of Mexico=warm and wet
Weather Terminology
• Weather: the condition of the atmosphere at a
particular time and place.
– Maritime air masses are humid because they form
over the ocean.
– Continental=dry-form over land
– Tropical=warm-form over the tropics
– Polar=cold-form over Artic
• Air Pressure: the force of the weight of air
pressing down on a unit of area
– Warm air masses=fewer air molecules, so it is less
dense and has lower air pressure
Terminology Continued
• Relative Humidity: actual amount of humidity vs.
greatest amount of moisture possible
– Example: if it’s raining, the relative humidity is
probably 100%.
• Front: the boundary between two air masses that
collide (not mix or combine)
– Example: Thunderstorms are caused when cold air
masses move very rapidly and push up a lot of warm
air very quickly.
• Global Wind: winds that blow over long distances
in predictable patterns.
Clouds
The most common form of
high-level clouds are thin and
often wispy cirrus clouds
This cirrocumulus is very thin
and lets the sun shine through
like from a blue sky.
Clouds
Cirrostratus clouds are thin,
sheet-like high clouds that often
cover the entire sky. They are so
thin that the sun and moon can
be seen through them.
Altostratus clouds are gray or bluegray mid level clouds composed of
ice crystals and water droplets. The
clouds usually cover the entire sky.
Clouds
Altocumulus clouds are mid level
clouds that are made of water
droplets and appear as gray puffy
masses. They usually form in
groups.
Stratus clouds are uniform grayish
clouds that often cover the entire
sky. They resemble fog that doesn't
reach the ground. Light mist or
drizzle sometimes falls out of these
clouds.
Clouds
Cumulus clouds are white,
puffy clouds that look like
pieces of floating cotton.
Cumulonimbus clouds are
thunderstorm clouds. They are
associated with heavy rain,
snow, hail, lightning and even
tornadoes.
Weather Forecasts
• Meteorologist-scientists who study weather
conditions to provide forecasts.
– Instruments Used:
• Barometers: to measure air pressure
• Anemometers: to measure wind speed.
• Weather balloons & satellites: collect data high up in
the troposhpere. (weather patterns & storm info that
can’t be obtained at ground level.
• Weather map: shows recent weather conditions across
a large area.
Types of Weather
Thunderstorm: begins to form
when warm, humid air moves
quickly through colder
surrounding air.
Tornado: a violently rotating
column of air that extends
downward from thunderclouds
and touches the ground. It is
smaller and more intense than a
thunderstorm.
Weather
Hurricanes: a large rotating
tropical storm system with wind
speeds of at least 74 miles per
hour.
Blizzard is a storm with snow and
wind blowing for at least three
hours at 35 miles per hour.
Visibility is almost zero during
the storm.