Weather Unit Interactive Notes
Weather Unit Interactive Notes Table of Contents....30
Illustrations: Air, the Atmosphere, and Air Pressure….31
Notes: Air, the Atmosphere, and Air Pressure….32
Illustrations: Weather Instruments….33
Notes: Weather Instruments….34
Illustrations: The Water Cycle….35
Notes: The Water Cycle....36
Illustrations: Cloud Types….37
Notes: Cloud Types….38
Illustrations: Types of Precipitation….39
Notes: Types of Precipitation….40
Illustrations: Storms….41
Notes: Storms….42
Illustrations: Fronts & High and Low Air Pressure….43
Notes: Fronts & High and Low Air Pressure….44
Air, the Atmosphere, and Air Pressure
We have weather because we have air, an atmosphere, and air
pressure. The atmosphere is a blanket of air that surrounds the Earth.
The Earth’s gravity holds it in place. The atmosphere is made up of 4
different layers and the lowest layer is the troposphere, where all of our
weather occurs.
Air pressure is the push of air against its surroundings. It is the
result of the weight of the air. Air that weighs more has greater air
pressure and air that weighs less has less air pressure. The closer you get
to Earth, the greater the air pressure gets because there are more air
particles. The higher you go in the atmosphere, the less air pressure
there is because there are fewer air particles.
Air pressure is figured out by temperature. Cool air weighs more
than warm air because the particles are closer together. This usually
gives us a higher air pressure. In warm air, the air particles are spread
farther apart, so they have less weight. This gives us lower air pressure.
Weather Instruments
A meteorologist is a person who studies the weather. When a
meteorologist wants to predict the weather, he or she has to use several
different types of weather instruments to gather data for their predictions.
A thermometer measures the temperature of the air. The
temperature is the amount of heat energy in the atmosphere.
Meteorologists use them to predict the temperature for the day.
A barometer measures air pressure. High air pressure indicates
fair weather, and low air pressure indicates stormy weather. When the
meteorologist tells us that the barometer is falling, it usually means that
stormy weather is coming.
An anemometer measures wind speed. It looks like a bunch of
cups spinning around a stick. The faster the anemometer spins, the faster
the wind is blowing.
A rain gauge measures the amount of precipitation. It usually
looks like a tube with a ruler on it. After it rains, the meteorologist checks
the rain gauge to measure how much rain has fallen.
The Water Cycle
The water cycle is the cycle of Earth’s water through evaporation,
condensation, and precipitation. Clouds are formed when heat from the
sun warms water in oceans, lakes, ponds, and streams. As the water gets
warm, it evaporates, or turns into a gas, and rises into the air. The
higher the evaporated water rises, the cooler it gets. As the water vapor
cools, it condenses into water droplets, which form clouds. Sometimes
the water vapor condenses into water droplets that are so heavy, they fall
back down to the Earth as precipitation, and flow back into oceans,
lakes, and streams. Then the cycle starts all over again.
Cloud Types
There are many, many different types of clouds, and each type is
associated with a different type of weather. Knowing your cloud types
can help you predict the weather. The 4 basic types of clouds are cirrus,
stratus, cumulus, and cumulonimbus.
Cirrus clouds are feathery clouds that are high up in the sky. They
are wispy and transparent. They are associated with fair (good) weather.
However, they may indicate that rain or snow will fall within several hours.
Stratus clouds are smooth, gray clouds that cover the whole sky
and block out direct sunlight. They look like a blanket in the sky. Light
rain and drizzle are usually associated with stratus clouds.
Cumulus clouds are fluffy and white with flat bottoms. They look
like giant cotton balls. They are usually associated with fair weather.
However, when they get larger and darker on the bottom, they become
cumulo-nimbus clouds.
Cumulo-nimbus clouds are giant, black, fluffy clouds that may
bring thunderstorms or tornadoes.
Types of Precipitation
All forms of precipitation start as water vapor that condenses
around microscopic particles.
Rain forms when the cloud droplets coalesce, or come together,
and the air temperature and ground temperature are above freezing.
Snow forms when the cloud droplets coalesce, and the air
temperature is below freezing. If the ground temperature is also below
freezing, the snow will accumulate, but if it is not, the snow will melt.
Sleet forms when the air temperature is below freezing which
makes the rain drops freeze, but the ground temperature is above
freezing, so it makes surfaces slick and wet.
Hail forms in cumulo-nimbus clouds, which can be up to a mile
high and are very windy inside. Cold air in the cloud turns droplets into
ice crystals. As the crystals fall and pick up water vapor, they get caught
in an updraft and refreeze. This happens over and over again until they
are heavy enough to fall from the clouds as hail.
Storms
Thunderstorms are formed when warm, moist air rises rapidly,
forming cumulonimbus clouds. They often form along cold fronts.
Thunderstorms produce heavy rain, wind, lightning, thunder, and
sometimes hail. The rain from the storms can cause flash floods, and the
lightning can cause fires, damage property, and hurt people.
Hurricanes form in the tropics over oceans between June and
November, when huge amounts of warm, moist air get pushed higher by
colder, heavier air, creating a violent, whirling storm. Hurricanes are low
pressure areas. They have winds of 74-150 miles per hour and can travel
up to 80 m.p.h. They can cover an area as wide as 360 miles. In the
center of the hurricane is a calm area called the eye, where the sun shines
and the sky is clear. They cause damage with strong winds, heavy rains
that cause floods, and giant waves that smash into shore. They usually
die out once they reach land or move over cold ocean water.
Tornadoes form over land, occurring most commonly in the US, in
the spring and early summer, when cold, heavy air is pushed over warm,
moist air. The warm, moist air pushes itself through the layer of cold air
with a spiraling motion. Strong winds form around a center of low
pressure, forming a tornado. Tornadoes have winds of up to 500 m.p.h.
and can move from 25-40 m.p.h. They are accompanied by lightning,
heavy rain, wind, and last about 8 minutes. The strong winds of the
tornado destroy almost everything in its path. The low pressure inside of
the tornado can cause buildings to explode, and can suck up trees, cars,
houses, people and animals.
Fronts & High and Low Air Pressure
A front is the boundary between air masses of different
temperatures and humidity. There is usually some sort of precipitation
along the front, because there is usually warm, moist air rising, which
causes precipitation.
In a cold front, a cold air mass moves under a warm air mass. A
cold front brings brief, heavy precipitation, and then colder weather.
In a warm front, a warm air mass moves up a slope of a cold air
mass. A warm front brings steady, light precipitation, and then warmer
weather.
Large masses of air with different pressures move over the Earth.
Cold masses of air have higher pressures than warm masses of air. These
different air masses bring different types of weather.
A low pressure system usually brings stormy weather. This bad
weather covers a large area. A low pressure system is shown with an L
on a weather map.
A high pressure system brings sunny weather. It is usually
shown with an H on a weather map.