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

Weather Factors

Earth Science

Chapter 16

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


Wind

• Horizontal movement of air from high pressure to low pressure

• Caused by air pressure differences• Differences caused by uneven

atmosphere heating – convection currents


Measuring Wind

• Direction by weather vane• 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


Wind-Chill Factor

• Wind blowing over you removes body heat• Makes you feel colder• Faster wind – greater wind-chill factor


Local Winds

• Blow over short distances• Unequal heating over a small area• Only form when large-scale winds are

small


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


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


Global Winds

• Blow steadily from specific directions over long distances

• Temperatures near poles are lower than over equator• Sunlight is less direct


Global convection currents

• At surface, winds blow from poles toward the equator

• High in atmosphere, winds blow from equator towards poles


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


Calm areas• Doldrums

• 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


Global wind belts

• Trade winds• 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


Polar front

• Where polar easterlies meet prevailing westerlies

• Mixing of warm and cold air has a major effect on weather


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


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.


Water Cycle

• As the sun heats the land and oceans, the amount of water in the atmosphere changes.


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


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


Discuss

• Analyzing Data, p. 562• Questions 1, 2, and 4


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


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


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


Stratus clouds

• Form in flat layers • “spread out”• Usually cover all or most of the sky• Produce precipitation when they thicken

• Nimbostratus


Alto- clouds

• Form between 2 and 6 km high• Altocumulus and altostratus• “High”• Higher than regular cumulus and

stratus, but lower than cirrus


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


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?


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


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)


Sleet

• Happens when rain falls through air that is below the freezing point

• Sleet has ice particles less than 5 mm in diameter


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


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


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


Droughts

• Long periods of unusually low precipitation


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


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


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?

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