Weather

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Chapter 24
Weather
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The Atmosphere
Atmosphere - a mixture of gases that surround
the earth
- contains the oxygen we need to live
- protects us from the suns harmful rays
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Atmospheric Layers - four layers based on
temperature (p. 750)
Troposphere - the lowest layer and the densest
(90 of total mass)
- contains most of the CO2, H2O vapor, cloud,
air pollution, weather, and life forms (where we
live)
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Most oxygen is produced by plants that release
it during photosynthesis
Tropopause - the boundary at the top of the
troposphere where the temperature stops
decreasing (it remains the same)
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Stratosphere - very thin and contains little
moisture
- lower layer very cold (-55C), but temp
rises as altitude increases
Ozone - a molecule of three oxygen atoms (O3)
that absorbs harmful ultraviolet radiation
(which warms the upper part)
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Mesosphere - coldest layer (-93C) with large
wind storms
Thermosphere - high temp due to gases absorbing
solar radiation (1700 C)
Does high temp mean it is hot??
Not always temp is a measurement of the average
energy of particles in motion (high temp fast
particles)
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Cont Heat on the other hand is the transfer of
energy between objects, so if high temp, but few
particles, then little heat!!!
Ionosphere - Lower thermo aurora borealis
(northern lights)
- absorption of solar energy causes gas particles
to become electrically charged (radio waves
reflected here)
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The Greenhouse Effect - thermal energy is
trapped by atmospheric gases, none escape into
space so the earth gets hotter just like a
greenhouse (p. 756)
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Atmospheric pressure and winds
Wind - moving air (Why does wind move???)
Why Air Moves!!!
- air moves due to the differences in air
pressure (the greater the difference, the faster
the wind)
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- pressure difference due to unequal heating
- cool, dense air _______, hot, less dense air
_________
- where air rises it creates low pressure,
sinking air creates high pressure
- p. 758 (why every 30 or so)
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Coriolis Effect - the curving of moving objects
(such as wind) due to the earths rotation
- winds dont blow north to south, they curve!!!
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Water in the Air
- solid . ice in clouds as snowflakes
- liquid .. water droplets in clouds
- gas .. water vapor in air
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The Water Cycle - has a great affect on the
weather
- the continuous movement of water from lakes,
oceans, etc., into the air, onto the ground,
into the ground and back to the lakes and
oceans
- sunlight provides the energy
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Condensation - occurs when water vapor cools and
changes back to liquid droplets (clouds form)
Evaporation - occurs when liquid water changes
into water vapor (gas)
Transpiration - when plants release water vapor
thru their leaves
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Precipitation - when rain, snow, sleet, or hail
fall from clouds
Runoff - water that flows across land and
collects in streams, rivers, lakes, and oceans
Humidity - the amount of water vapor (moisture)
in the air
- as water evaporates, humidity increases
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Warm air can hold more water than cold air
Relative Humidity - the amount of moisture the
air contains compared to the maximum amount it
can hold at a particular temperature
- when air holds all the water it can at a
certain temp, it becomes saturated (r.h. 100)
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- we dont notice humidity in winter cause cold
air cannot hold much water
- condensation
Dew Point - the temp to which air must cool to
become saturated
- cool grass causes dew
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Cloud Types
Cumulus - puffy white, nice weather
Cumulonimbus - larger (4 miles tall) that
produce thunderstorms
- nimbus or nimbo precipitation in cloud
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Stratus - cover large areas (no sun) (fog)
Nimbostratus - darker, produce continuous rain
Cirrus - thin, feathery, and white
- may indicate approaching bad weather
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Local Winds - winds influenced by the geography
of an area
Sea Breeze - during the day the land heats up
faster than the water so the air above the land
gets hotter, rises, and is replaced by cooler
air from over the water
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Land Breeze - at night the land cools faster so
the warm air is over the water, it rises, and is
replaced by cooler land air
Global Winds - Trade winds, Westerlies, Polar
Easterlies, Jet Streams
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Fronts - the boundary that forms when two
different types of air masses run into each
other (they do not mix)
- weather at fronts is usually cloudy and can
be stormy
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There are Four Types
Cold Front - when a cold air mass catches up to
and pushes under a warm air mass (less dense)
- the warm air rises, cools, condenses quickly
causing storms
-temps usually drop because of cooler air behind
the front
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Warm Front - when a warm air mass catches up to
and moves over a cold air mass (more dense)
- slower rising warm air condenses to give
drizzle type precipitation
- temps go UP!
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Occluded Front - when a warm air mass is squeezed
between two cold air masses and rises
- lots of precipitation
\
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Stationary Front - a cold air mass meets a warm
air mass head on with neither moving much
- yucky precipitation (not storms) for days
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High Pressure Systems
- result in clear skies bringing bright
sunshine (Waverunner!!!)
- cooler evening temps as warm air is allowed to
escape into space
- shown as a blue uppercase H on a weather map
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Low Pressure Systems
- associated with fronts and cloudy, overcast
weather therefore often means precipitation
- dont plan a picnic!!!
- shown as a red uppercase L on a weather map
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Severe Weather - weather that can cause property
damage and death
Thunderstorms - small intense weather systems
that produce strong winds, heavy rains, lightning
and thunder
- occurs when warm moist air rises rapidly in an
unstable atmosphere
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- air reaches its dew point and water vapor
condenses forming clouds (can build quickly and
tall)
Lightning - a large electrical discharge that
occurs between two oppositely charged surfaces
- when energy that is released heats the air it
expands rapidly and sends out sounds (thunder)
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Tornadoes - a small, rotating column of air that
has high wind speeds and low pressure and that
touches the ground
Hurricanes - a large rotating tropical system
with high winds
- get their energy from the condensation of water
vapor
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- needs warm, moist air to keep going
- also known as cyclones and typhoons in other
parts of the world