1. Weather Factors
Earth Science
Chapter 16

2. Electromagnetic waves
A form of energy that can travel through empty space
The form of energy we get from the sun
Earth Science Chapter 16

3. Wind Horizontal movement of air from high pressure to low pressure
Caused by air pressure differences
Differences caused by uneven atmosphere heating – convection currents
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4. Measuring Wind Direction by weather vane Speed by anemometer
Arrow points to direction wind comes from
Name of wind tells you direction it comes from
A south wind comes from the south, blows towards the north
Speed by anemometer
Wind turns cups around axle
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5. Wind-Chill Factor Wind blowing over you removes body heat
Makes you feel colder
Faster wind – greater wind-chill factor
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6. Local Winds Blow over short distances
Unequal heating over a small area
Only form when large-scale winds are small
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7. Sea breeze
Local breeze that blows from an ocean or lake to land during the day
Land warms up faster than water
Cool air from water blows inland underneath the warm air over the land
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8. Land breeze
Local breeze that blows from land over an ocean or lake during the night
Land cools faster than water
Cool air from land blows out underneath the warm air over the water
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9. Global Winds
Blow steadily from specific directions over long distances
Temperatures near poles are lower than over equator
Sunlight is less direct
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10. Global convection currents
At surface, winds blow from poles toward the equator
High in atmosphere, winds blow from equator towards poles
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11. Coriolis effect Earth spins, so winds follow curved paths
In northern hemisphere, they curve toward the right
In southern hemisphere, they curve toward the left
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12. Calm areas Doldrums Horse latitudes Near equator
Warm air rising quickly with little wind
Horse latitudes
At about 30° north and south of equator
Air cools and sinks
Sailors stuck here ran out of food and water for their horses and threw them overboard
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13. Global wind belts Trade winds Prevailing Westerlies Polar easterlies
From horse latitudes towards equator
Sailors relied on them to move cargo ships
Prevailing Westerlies
From horse latitudes towards poles
Blow from west to east
Important in US weather
Polar easterlies
Blow cold air away from poles
East to west
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14. Polar front Where polar easterlies meet prevailing westerlies
Mixing of warm and cold air has a major effect on weather
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15. Jet streams About 10 km above Earth’s surface
Bands of high speed winds
West to east at 200 to 400 km/hr
Wander north and south across wavy path
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16. Discuss How is wind related to air temperature and air pressure?
Compare the conditions that cause a sea breeze with those that cause a land breeze.
Briefly describe the three major global wind belts and where they are located.
Earth Science Chapter 16

17. Water Cycle
As the sun heats the land and oceans, the amount of water in the atmosphere changes.
Earth Science Chapter 16

18. Humidity The amount of water vapor in the air
Expressed as a percent of how much the air can hold
Called relative humidity
Amount air can hold depends on temperature
Warmer air can hold more
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19. Psychrometer Measures relative humidity
Two thermometers: wet-bulb and dry-bulb
When “slung”, the wet-bulb is cooled by evaporation
Higher humidity  slower evaporation  less cooling
Earth Science Chapter 16

20. Discuss Analyzing Data, p. 562 Questions 1, 2, and 4
Earth Science Chapter 16

21. Cloud formation Water vapor in the air condenses to liquid or ice
Needs
Cooling
Cold air holds less water vapor
Begins to condense when it reaches the dew point temperature
Particles
Water vapor needs a surface to condense on
Mostly salt crystals, dust, and smoke for clouds
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22. Cirrus clouds Wispy and feathery “Curl of hair”
Only form above 6 km in altitude
Made of ice crystals
Cirrocumulus clouds
Look like rows of cotton balls or fish scales
Usually mean there is a storm coming
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23. Cumulus clouds Look like fluffy piles of cotton “Heap” or “mass”
Form less than 2 km high, but can grow in size and height
Small ones mean good weather
Towering ones – cumulonimbus – make thunderstorms
-nimbus means rain
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24. Stratus clouds Form in flat layers “spread out”
Usually cover all or most of the sky
Produce precipitation when they thicken
Nimbostratus
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25. Alto- clouds Form between 2 and 6 km high Altocumulus and altostratus
Higher than regular cumulus and stratus, but lower than cirrus
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26. Fog Clouds that form at or near the ground
Often when ground cools after a warm, humid day
More common near water
Can form near mountains as warm, moist air moves up and cools
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27. Discuss What process is involved in cloud formation?
Describe the three main types of clouds
When are clouds formed by ice crystals instead of water drops?
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28. Precipitation Water that falls from clouds and reaches Earth’s surface
Cloud droplets or ice crystals must get large and heavy enough to fall through the air
Colliding and combining
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29. Rain Most common precipitation Drops at least 0.5 mm in diameter
Drizzle is smaller (0.05 – 0.5 mm)
Mist is smallest (0.005 – 0.05 mm)
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30. Sleet
Happens when rain falls through air that is below the freezing point
Sleet has ice particles less than 5 mm in diameter
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31. Freezing Rain
Raindrops fall through cold air, but don’t freeze until they hit a surface
Smooth, thick layer of ice builds up on everything
Weight can break tree branches
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32. Snow Water vapor in clouds converted directly into ice crystals
Endless different shapes, all with six sides or branches
May join in larger clumps that make crystals hard to see
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33. Hail Ice pellets larger than 5 mm in diameter
Forms only inside cumulonimbus clouds during thunderstorms
Small ice pellets get carried upwards by drafts
Pass through cold region many times, adding more ice each time
Eventually get too heavy and fall
Can cause heavy damage
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34. Droughts Long periods of unusually low precipitation
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35. Cloud seeding Trying to make precipitation during droughts
So far, not very successful
Tiny crystals of silver iodide and dry ice are sprinkled into clouds
Water vapor can condense on silver iodide particles
Dry ice helps cool the water vapor to condense faster
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36. Measuring precipitation
Snow
Measuring stick
Melting and measuring water
Not as accurate – fluffy snow has less water, but is deeper
Rain
Rain gauge
May have a funnel at the top to make it more accurate
Collects deeper water which is easier to measure
Helps minimize evaporation
Earth Science Chapter 16

37. Discuss Compare and contrast freezing rain and sleet.
How do hailstones become so large?
A thunderstorm produces precipitation in the form of ice particles that are about 6 mm in diameter. What type of precipitation would this be?
Earth Science Chapter 16