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Weather
Tornados and Hurricanes
Both are rotating storms. Rotation of a liquid or gas around a central
axis is known as a vortex. Hurricanes form over warm ocean waters.
Tornados form when cold dry air meets warm
moist air.
Layers of the Atmosphere
Troposphere is the densest
layer, 90% of the atmosphere’s
total mass. Stratosphere is very cold and
contains the ozone layer which
absorbs UV radiation. Mesosphere is the coldest
layer. Contains strong winds. Thermosphere is is the
thinnest layer and contains
the ionosphere. This is a
layer of charged particles
that absorb harmful
radiation.
Air Pressure
As altitude increase air pressure decreases.
Humid air has lower air pressure than dry
air.
Cooler air will have higher air pressure than
warmer air.
The Source of
Earth’s Heat
•
Earth’s heat comes in the
form of radiation from the sun
and is called solar energy. •Remember soil heats and cools
faster than water!!!
• About half of the energy that
reaches earth is absorbed by
the land and ocean. The rest is
absorbed by the atmosphere or
reflected into space. !
Absorption and
Reflection
• Dark
surfaces such as forests
will absorb 95% of the energy
they receive. • Snow on the other hand only
absorbs 5% and reflects 95%
back. • Differences in how the earth’s
surfaces absorb heat are part
of the reasons that winds form
and weather patterns change. !
•
When certain gases, like
carbon dioxide, build up in the
atmosphere, more heat is
absorbed. • This raises the temperature of
the atmosphere, as well as the
earth’s surface.
Heating of Earth
• Radiation: Energy from the sun travels as
electromagnetic radiation. • Conduction: Transfer of thermal energy by
direct contact. The air near the earth’s
surface is heated this way. • Convection the transfer of energy in a
liquid or gas by circulation.
Why Air Moves
Air moves because of differences in air
pressure. Differences in air pressure are caused by the
uneven heating of earth’s surfaces. Hot rising air will have low air pressure, and
cool sinking air will have high air pressure.
The circular movement of air due to heating
and cooling is called a convection current.
Local Winds
• Local wind is also caused by the uneven
heating of earth’s surface, but effect only a
small area. • Water will heat and cool more slowly than
land creating sea and land breezes.
• Dark surfaces will heat more quickly than
light colored ones. •
High elevations cool more quickly than
low elevations.
Land and Sea Breezes
Valley and Mountain
Breezes
Convection in a room
Global Winds
Due to the pressure belts, winds in particular
belt blow in the same direction. These winds are part of the global
circulation pattern. They blow across the
entire globe. Trade winds, Easterlies, and Westerlies are
global winds.
Global Wind Patterns
Pressure Belts
Air near the equator is heated the most, and
rises. Eventually it cools and sinks back
down. Sinking air causes high pressure belts.
Rising air causes low pressure belts.
Pressure Belts
The Water Cycle
Water enters the atmosphere as a gas
through evaporation and transpiration
(plants). Water condenses, or changes from a gas to a
liquid, as it cools. Liquid water returns to earth by precipitation
(rain, snow, hail, sleet, etc...)
Humidity
Humidity is the amount of water vapor in the
air. Relative humidity is the amount of water
vapor the air contains relative to the
maximum amount it can hold at a particular
temperature. Hotter air can hold more water vapor. Dew point is the temperature the air must
cool to have 100% relative humidity.
Relative Humidty
Basic Cloud Forms
Clouds
Clouds are collections of millions of tiny
water droplets or ice crystals. Clouds are formed when water vapor cools to
the air’s saturation point.
Cumulus Clouds
•
•
Puffy with a flat bottom.
•
Generally mean fair
weather, but can for
cumulonimbus clouds
which can create
thunderstorms and
tornadoes.
Formed when warm air
rises. Stratus Clouds
•
A flat layer of clouds
which blocks the sun. •
Caused by gentle lifting
of a large body of air
into the atmosphere. •
Fog is a stratus cloud at
ground level.
•
Nimbostratus clouds are
dark and usually produce
Cirrus Clouds
•
Feathery white clouds at
high altitudes. •
•
Made of ice crystals. May indicate bad
weather approaching if
they thicken and move
to a lower altitude.
Air Masses
Air Masses
Large areas of air with the same
temperature and humidity. Air masses get these characteristics for the
area they form over. Jet stream moves these air masses around. When 2 or more air masses meet a boundary
called a front is formed.
Jet Stream
Weather Fronts
Cold Front
•
A cold air mass meets a
warm air mass and
pushes underneath. •
Cold fronts are fast
moving. •
The cold front usually
creates storms as it
displaces the warm air. •
Cooler temperatures
follow.
Warm Front
•
A warm air mass
meets and
overrides a cold
air mass. •
Warm fronts bring
drizzly
precipitation. •
After the front
passes,
temperatures are
warmer and skies
clear.
Occluded Front
•
A faster moving cold
air mass overtakes a
slow warm air mass
and forces the warm
air upward. •
The cold air mass
continues advancing
until it meets another
cold mass. •
Occluded fronts bring
cool temps. and heavy
precipitation.
Stationary Front
•
A cold and warm air
mass meet but little
horizontal movement
occurs. •
This produces weather
similar to a warm front.
Data Collection
Meteorologist collect data on temperature,
air pressure, wind speed, and many other
things. Doppler radar and Satellite images.
Barometer measures pressure.
Thermometer measures temperature.
Anemometer measures wind speed.
Weather Maps
Meteorologists use the data they collect to
create weather maps, which allow them to
forecast weather. Isobars show areas of equal pressure on the
map. Fronts show the boundaries of air masses.
Weather Forecasting
Weather Map Symbols
Two Main Types of
Currents
• Thermohaline
• Surface or Wind Driven
Types of Ocean
Currents
• Thermohaline: Driven by temperature and
the uneven heating of the earth’s surface. • Water at the equator is heated and rises
and moves toward the poles. Water at
the poles sinks and moves along the
ocean floor to the equator.
Wind Driven
• Run along the surface of the ocean. • Water is pushed by the global winds: Trade
wind, Westerlies, Easterlies.
• Water is warmed near the equator and
cooled near the poles.
Wind Driven Current
Near Shore Wind
Driven Currents
• Upwelling : When wind pushes water near
shore creating a low pressure area which
then allows deeper water to rise
Near Shore Current
Ocean Currents and
Climate
• Watch the video clip about ocean currents
and climate. • Answer the following questions. • 1. Why is London warmer than Calgary
even though they are at the same
latitude?
• 2. Why is Perm colder than Juneau
despite being due east?
Video
• http://www.youtube.com/watch?
v=HgoANl_97kM
Effect on Climate
• Ocean currents bring warm and cool water
to different parts of the world. • Air masses form over these currents and
take on the same characteristics. • The warm Gulf Stream brings warm water
from the equator toward England
moderating its climate. • Ocean also cools slowly in winter and
warms slowly in summer.