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 sun Earth Science Chapter 16

Wind Horizontal movement of air from high pressure to low pressure Caused by air pressure differences Differences caused by uneven atmosphere heating – convection currents Earth Science Chapter 16

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 Earth Science Chapter 16

Wind-Chill Factor Wind blowing over you removes body heat Makes you feel colder Faster wind – greater wind-chill factor Earth Science Chapter 16

Local Winds Blow over short distances Unequal heating over a small area Only form when large-scale winds are small Earth Science Chapter 16

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 Earth Science Chapter 16

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 Earth Science Chapter 16

Global Winds Blow steadily from specific directions over long distances Temperatures near poles are lower than over equator Sunlight is less direct Earth Science Chapter 16

Global convection currents At surface, winds blow from poles toward the equator High in atmosphere, winds blow from equator towards poles Earth Science Chapter 16

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 Earth Science Chapter 16

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 Earth Science Chapter 16

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 Earth Science Chapter 16

Polar front Where polar easterlies meet prevailing westerlies Mixing of warm and cold air has a major effect on weather Earth Science Chapter 16

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 Earth Science Chapter 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

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

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 Earth Science Chapter 16

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

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

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 Earth Science Chapter 16

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 Earth Science Chapter 16

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 Earth Science Chapter 16

Stratus clouds Form in flat layers “spread out” Usually cover all or most of the sky Produce precipitation when they thicken Nimbostratus Earth Science Chapter 16

Alto- clouds Form between 2 and 6 km high Altocumulus and altostratus Higher than regular cumulus and stratus, but lower than cirrus Earth Science Chapter 16

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 Earth Science Chapter 16

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? Earth Science Chapter 16

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 Earth Science Chapter 16

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) Earth Science Chapter 16

Sleet Happens when rain falls through air that is below the freezing point Sleet has ice particles less than 5 mm in diameter Earth Science Chapter 16

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 Earth Science Chapter 16

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 Earth Science Chapter 16

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 Earth Science Chapter 16

Droughts Long periods of unusually low precipitation Earth Science Chapter 16

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 Earth Science Chapter 16

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

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