weather the condition of the outside air or atmosphere at
TRANSCRIPT
weather – the condition of the outside air or
atmosphere at a particular time and place.
climate - the average weather conditions over
a very long period of time
o The climate of a region will also determine
the type of plants that grow there and the
types of animals that live there.
cloud – a mass of tiny water droplets or ice
crystals in the air
o water vapor must lose heat energy before
clouds can form
Types of Clouds
1. cirrus clouds - thin wispy clouds that form high in the sky
o form when wind is strong
o if they get bigger and thicker, it's an indication of a
change in weather
2. stratus clouds - flat, horizontal clouds that form in layers.
o form when a large mass of air is gently lifted into the
atmosphere.
o usually form at low altitudes and cover large areas of
the sky.
o tend to block out sunlight.
o Fog is a stratus cloud that forms near Earth's surface.
o might bring light mist or drizzle
3. cumulus clouds - fluffy, white clouds that look like pieces
of cotton balls with flat bottoms
o form as warm air rises and are usually a sign of fair
weather.
4. cumulonimbus clouds
o can cause lightning, thunder, hail, strong rains, strong
winds, and tornadoes
o have a dark base; towers in the sky
o can be found from near the ground to up to 75,000
feet
****Clouds that bring precipitation usually start with nimbo or
end with nimbus
High Clouds - form above 18,000 feet
cirrus
cirrocumulus
cirrostratus
Middle Clouds - form between 6,500 feet to 18,000 feet
altocumulus
altostratus
Low Clouds - form below 6,500 feet
stratus
stratocumulus
nimbostratus
cumulus
Weather Instruments
rain gauge – measures the amount of rain
wind vane – shows wind direction – where the
wind is coming from
anemometer – measures wind speed
barometer – measures air pressure
hygrometer – measures the amount of water
vapor in the air – the humidity
AIR PRESSURE – the weight of the atmosphere pressing at a
certain place
Air pressure can also tell us about what kind of weather
we might have. Changes in air pressure mean that the
weather is about to change
o HIGH PRESSURE = fair weather
o LOW PRESSURE = rainy or stormy weather
Air pressure has the greatest effect on wind
speed.
Air pressure changes depending on the
altitude.
o HIGHER ALTITUDE = Decreased air pressure
o LOWER ALTITUDE = Increased air pressure
(This is why your ears "pop" when you are
riding in an airplane or driving high into the
mountains)
air mass - a large body of air that has the same
temperature and level of humidity throughout
front - the area in which two air masses meet
cold front - forms when a cold air mass moves
under a warm air mass and causes the warm air
mass to rise.
o brings heavy rains, thunderstorms, and
sometimes snow
o temperature drops when cold front passes over
an area
warm front - forms when a warm air mass meets a
cold air mass and slowly rises over it
o brings rainy, drizzly weather conditions
o after a warm front passes over an area, the
temperature rises
occluded front - forms when a warm air mass is
caught between two cold air masses.
o brings cool temperatures and lots of rain and
snow
stationary front - occurs when a warm air mass and
a cold air mass meet, but neither front has enough
energy to push against the other
o brings many days of overcast, rainy weather
Earth’s Three Climate Zones
tropical zone – found near the equator; areas in this
zone get the most energy from the sun so they tend
to be warm to hot all year
temperate zone – found between the polar and
tropical zones; these areas tend to have seasons
with very different temperatures
polar zone – found at the Earth’s North and South
Poles; areas in this zone get the least energy from
the sun, so they tend to be cool to cold all year.
Types of Air Masses
Moisture content is noted by the first letter.
m = maritime = wet
c = continental = dry
Temperature is noted by the second letter
P = polar = cool
T = tropical = warm
Maritime Tropical - mT
o Warm and humid
o Originates closer to the Tropics over water
Maritime Polar - mP
o Cold and damp
o Originates in the Poles over water
Continental Tropical - cT
o Warm and dry
o Originates closer to the Tropics over land
Continental Polar - cP
o Cold and dry
o Originates closer to the Poles over land
Global Winds
current – a flow of air or water in a certain direction
the uneven heating of the earth’s surfaces causes
wind.
as the warm air at the equator rises, large areas of
low air pressure form there
at the poles, the air is cold so it sinks. Areas of high
pressure form there
wind blows from areas of higher pressure toward
areas of lower pressure
jet stream – an air current in the upper atmosphere
that flows from west to east
o fast flowing river of air
o winds can range from 120-250 mph
o can be thousands of miles long, a couple of
hundred miles across and a few miles deep.
o responsible for transporting highs and lows
o affects precipitation and temperatures
o marks boundaries between massive air masses
o air to the south of the jet stream is warm.
o air to the north of the jet stream is cold.
Coriolis Effect
Makes moving objects appear to curve toward the right
in the northern hemisphere and toward the left in the
southern hemisphere.
prevailing westerlies
winds that blow from the west to the east and move
toward the poles and are between 30 and 60 degrees
latitude
responsible for many of the weather movements across
the United States and Canada.
called prevailing westerlies because they’re named from
the direction where they form
polar easterlies
Form when the atmosphere over the poles cools. This
cool air then sinks and spreads over the surface. As the air
flows away from the poles, it is turned to the west by the
Coriolis effect. Because these winds begin in the east,
they are called easterlies
trade winds
air movements toward the equator.
warm, steady breezes that blow almost continuously.
Coriolis Effect makes the trade winds appear to be
curving to the west, whether they are traveling to the
equator from the south or north.
doldrums
a region of the ocean near the equator where there is
little or no wind
Breezes
sea breeze – the movement of air caused by
cool air over the ocean moving toward the
land
o occurs during the day
o land temperature near the beach is rising
more rapidly than the ocean temperature
land breeze – the movement of air created by
cool air over land moving toward the ocean
o occurs at night
o land quickly loses heat at night; water
retains heat so the air over water is warmer,
less dense and begins to rise
Ocean Currents
Warm currents from tropical areas carry warm water
near the coastlines of cooler areas. The warm water
helps keep land near the coastlines warm
Cold water currents from the poles travel toward the
equator. The cold water brings cooler temperatures
to some coastlines in those areas
Gulf Stream – a warm ocean current in the Atlantic Ocean
flows northeast along the eastern coast of the US
moves warm waters out across the Atlantic Ocean,
then towards the north
keeps weather along the eastern coast mild by
warming the air and land there during the cooler
months
Radiation from the sun warms the waters of the Gulf
Stream. Then the water warms the air above it –
warms coastal land over which it moves
El Nino – an unusual warming of the surface water in the
eastern Pacific Ocean near the equator
usually brings more rain and higher temperatures
causes rising surface temperatures of the Pacific
Ocean, drought in the western US and flooding on
the Pacific coast of South America.
La Nina – an unusual cooling of the surface water in the
eastern Pacific Ocean near the equator