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Weather and Climate
8th grade science STAAR
What is Weather vs. Climate
• Weather is the current atmospheric
conditions, which includes temperature,
wind, humidity, etc.
• The average weather in a given area is
the climate for that area.
– Example: The weather in Lake Dallas, Tx on
June 5th is 95° F and warm, but the climate for
the area during summer is hot and dry.
Latitude and Longitude
• What is latitude? Longitude?
• Latitude = lines that measure North to
South - go from the poles at 0° to the
equator at 90°
• Longitude =is measured from the Prime
Meridian with positive values going east
and negative values going west.
– For example: at the equator what is the
climate like? What about at the north and
south poles?
What affects an area’s climate.
• Cycling of water in and out of the
atmosphere plays an important role in
determining weather and climatic patterns.
• What is the cycling of water in the
atmosphere called? WATER CYCLE
• Terms to know: Precipitation,
Condensation, Evaporation, Transpiration,
Run-off, Groundwater, Surface water
Water Cycle
What affects an area’s climate.
• CONVECTION CURRENTS –
– Uneven heating of the Earth's surface that
produces weather systems.
• Where hot air rises (less dense) and
cooler air sinks (more dense).
Sun’s role in convection currents
• You know that it is warmer at the Equator than at
the poles because Earth is tilted!
• Direct rays of sun at the equator and indirect
rays at the poles.
• The warmer, lighter air at the Equator moves
toward the cooler air at the poles. The cold
heavy air at the poles moves toward the
Equator.
• This causes a constant movement of air
movement called convection currents.
Convection Currents
• Convection currents drive (cause) wind patterns
that affect climate.
Air Masses
• Air masses are moved by convection currents
• There are two types of air masses; cold and
warm.
– Cold = dry, dense
– Warm = moist, less dense
• Cold air masses come from higher latitudes to
lower latitudes. Warm air masses do the
opposite. When they meet in the middle some
interesting weather happens!
Cold Meets The Warm
• Why is the warm air rising and going on top of
the cold air mass?
• Warm air is LESS dense.
Air Masses
• Air masses are classified by TWO letters.
• The first letter shows what the air mass
forms over:
– Continental (c)- dry air masses that form
over land
– Maritime (m) – moist air masses that form
over water.
Air Masses
• Second Letter represents the LATITUDE
and the temp.
• Arctic (A) – cold, dry air mass
• Polar (P) – cold dry air mass (not as cold
as artic
• Equatorial (E) – warmest air mass
• Tropical (T) – warm air mass (not as
warm as equatorial.
Air Masses on Globe
Air Pressure
• This is how scientists
measure air pressure.
• Air pressure is the
amount of pressure
exerted on a surface
by the atmosphere
above it.
– Barometers are used
to measure this with
units in millibars (mb).
What is this graph telling us?
• As the altitude increases what happened to the
air pressure?
– It decreases!
High Pressure System
• The air molecules
packed in to the center
of a high pressure
system doesn’t make
the right conditions for
cloud and precipitation
development
• So weather is generally
calm around a high
pressure center.
Low Pressure System
• This is an area where air
is rising and this fuels
weather change. With
rising air means rising
water vapors which leads
to clouds and the rest of
the water cycle.
• Hurricanes, cyclones and
other storms are
associated with low
pressure.
Fronts
• Fronts- boundaries between two air masses.
• they are created when high pressure systems
moves in around low pressure systems.
• They bring WEATHER CHANGES!
What Are Main Types of
Fronts?
• A cold front forms
when a fast cold air
mass runs into a slow
warm air mass.
• A cold front brings
heavy rain or snow.
• After the front passes,
cold dry air moves in,
skies clear, winds
shift, and
temperatures drop.
What Are Main Types of
Fronts?
• A warm front forms
when a fast-moving
warm air mass
overtakes a slowermoving cold air mass.
• After the front passes,
weather tends to be
warmer and more
humid.
•
What Are Main Types of
An occluded front forms
• A stationary front forms
Fronts?
when a warm air mass is
when air masses meet, but
caught between two cooler
air masses.
• Occluded fronts cause
weather to turn cloudy
and rain or snow may
fall.
neither can move the other.
• Stationary fronts often
bring many days of
clouds and precipitation.
Front Symbols
• All symbols are put on an isobar
• Isobars are lines that show areas with equal
air pressure
• Cold front –
• Warm front –
• Stationary Front –
• Occluded Front -
Weather Maps
• A weather map can be used to predict
temperature and precipitation for several
days in a given area
• See if you can find the pressure systems
and fronts on the following maps
Can you read the map?
Station Symbols
• You will see symbols
like these from
weather stations
scattered about.
• They tell information
about cloud cover,
barometric pressure,
dew point,
temperature, current
precipitation, etc.
Station Model
Winds
• Winds move excess heat around the
Earth.
• They are caused by air flowing from high
pressures to low pressures!
– When air moves downward you have HIGH
PRESSURE develop.
– When air rises you have LOW PRESSUE
develop.
Winds…
• Winds do not all blow the same direction
though they are effected by two main
things:
– Coriolis Effect – Winds are forced to the right
in the northern hemisphere and to the left in
the southern hemisphere
– Convection cells – Heat from the sun
powers these.
Wind Directions
Ocean Currents
• Ocean currents affect local and global
weather conditions.
• They have a much slower, long lasting
effect on climate than winds.
• They move slowly and retain more heat
than the atmosphere.
• They are driven by the Sun and the
rotation of the earth (Coriolis Effect).
Types of Ocean Currents
• Surface Currents – driven by winds, only
10% of water in the ocean- only the top
layer.
– Gulf Stream – a surface current that travels
along eastern part of the US – causes warmer
climates in Europe.
• Deep Water Currents – these are colder
(denser) layers that make up 90% of the
ocean currents. They are caused by the
the change in density causes these
currents
El Niño
• El Niño is a mass of warm water that moves
eastward as trade winds relax. Originates in
the PACIFIC OCEAN.
• El Niño causes warm water brings torrential
rains to parts of the world that are not prepared
for such weather.
• For reasons that scientists still do not
completely comprehend, every few years the
trade winds blow less or stop blowing at all.
They can also change direction.
• It causes a build-up of warm water off the coast
of South America and Africa and causes weather
changes all over the globe.
Tracking El Nino
Hurricanes and Cyclones
• A cyclone is a huge revolving storm that
is caused by winds blowing around a low
pressure area.
• Tornadoes are also a type of cyclone with
a tighter, faster spinning vortex of wind.
• Cyclones develop over the oceans near
the equator. A cyclone will not develop
unless the surface water temperature is at
least 26° C (80° F). Warm air rises and
creates area of low pressure.
Hurricanes and Cyclones
• A hurricane is a huge storm that forms
over warm ocean water! Hurricanes can
cause extreme amounts of damage
depending on their size and wind speeds.
• The main purpose of a hurricane is to
move heat away from the tropics. So the
sun is the main energy source for
hurricanes.
• Types of damage caused by hurricanes
reaching land are strong winds,
flooding, storm surge, and tornadoes.
Which would you rather experience?
• Hurricane!
• Cyclone!