Heat Transfer in the Atmosphere Hot or Not? Why?

Energy in the Atmosphere Nearly all energy in the Earth’s atmosphere comes from the sun. Energy travels to the Earth in the form of electromagnetic waves. Waves are classified by wavelength, or the distance between waves. Most of the energy from the sun reaches the Earth in the form of visible light and infrared radiation, and a small amount of ultraviolet radiation. Infrared radiation is a form of energy with wavelengths longer than red. Infrared is not seen, but can be felt as heat.

What Happens to UV Radiation? UV rays have wavelengths shorter than violet, so they have more energy. UV rays can cause skin and eye damage. Energy from the sun is absorbed by within the atmosphere by water vapor, CO2, clouds, dust, and the ozone layer. Clouds reflect radiation back into space Dust and other gases scatter radiation in all directions The Earth’s surface absorbs radiation, and reradiates it as longer wave infrared (heat)

Greenhouse Effect Molecules of greenhouse gases (water vapor and carbon dioxide) Absorb infrared radiation radiated from the earth’s surface Causes molecules to vibrate- transforming absorbed energy into heat in the troposphere This process keeps the troposphere at a reasonable temperature for life.

Heat vs. Temperature Matter is made up of atoms or molecules that are vibrating and has energy of motion (kinetic energy) When a substance is heated, the molecules move faster and the temperature rises. Heat is a form of energy Heat is the total kinetic energy in an object. Temperature is related to intensity, such as the degree of “hotness”. Temperature is a measure of the average kinetic energy. (so, thermometers measure the average energy in an object.) Heat moves from the higher temperature substance to the lower temperature substance.

Three Methods of Heat Transfer Conduction- transfer of heat through matter by molecular activity Convection – is the transfer of heat by movement of heated material (usually in liquids and gases) Radiation – transfer through wave energy

Conduction Conduction is heat transfer from molecule to molecule If someone touches an ice cube or hot plate they know because the heat is transferred from the warmer object to the cooler object from molecule to molecule. Remember heat always travels from high concentration to low concentration. If something feels cold, it is because the heat is going from you to it.

Conduction - continued

Conduction Questions- Suppose a human could live for two hours (120 minutes) unclothed in air at 10 C.   How long could he live in water at 10 C? How do the thermal conductivities of water and air compare?

Convection Convection is heat transfer by a circulation of rising warm material (less dense) and sinking cooler material (denser). Convection is the most effective method of heat transfer for liquids and gases. Heated molecules expand, become less dense and rise. Meanwhile, the cooler, more dense material above drops to replace the rising molecules This is known as a convection current.

No Convection- No Clouds

Natural Convection

Convection in the Earth

Convection- continued- How does convection work in your home Convection- continued- How does convection work in your home? In a freezer?

Conceptual questions - Explain the following: Wind chill factor.     Drapes hung close to a cold window.   Clothing- To keep warm on a cold day, should you wear a fur coat with the hair inside, or out?   Should you lower the blinds and draw the curtains on a hot day?

Radiation Radiation is heat transferred by infrared waves. We have all felt the warmth of the sun or heat from a camp fire without touching them. We also know that light colored clothing reflects the heat and dark absorbs the heat. This is all due to infrared radiation or radiant heat. We also know that on a summer day, the infrared gets in our car and heats it up, but is absorbed inside the car and when you open the door.

Radiation - continued Summer clothing:  white reflects radiant energy better than black. Until equilibrium is reached, white stripes on roads are at a lower temperature than unpainted asphalt. Wrap an ice-cube in black cloth and another in aluminum foil and place both in the sunshine.  What will happen?

Radiation – solar panels

Challenge Questions  The sun goes down, snow falls on cement playground and on an asphalt road.       Why does the snow on the road melt sooner than on the cement?  Two different materials at the same temperature have different emissivities. Which one glows the brightest?  Why are fireplace pokers made of iron and not copper?  Some animals have hair which is composed of solid tubular strands, while others have hollow, air-filled tubes.  Where would one more likely find the latter animal:  In cold climates, or warm?

Conceptual Questions When one steps from a shower on a cold morning, why does the tile floor seem so much colder than the air? Place a wooden spoon and a metal spoon in the freezer.   Which will cool faster?  After several hours, what would they feel like? Why do people become "flushed" when overheated?