Announcements

• Survey on Sakai

• Homework 1 on class web site (also available on Sakai)

• Quiz 1 available on Sakai after class (10 points)

• Pre-test on Sakai (10 points)

Atmospheric Physics

what drives the weather

Specific Heat

How much energy it takes to raise the temperature of a substance

• The same energy input raises the temperature of land more than water

– or–

• It takes more energy to raise the temperature of water than land

Expanding and Contracting

• Compressing a gas adds energy to it– Its molecules speed up– Its temperature rises

• A gas expanding against its surroundings loses energy– Its molecules slow down– Its temperature drops

Expanding and Contracting

• The same amount of gas occupies more volume at a higher temperature.

• That same volume of cool air weighs more.

• Cool air sinks, pushing warm air up.

Convection

• Hot water stayed on top, cold stayed on the bottom

• Hot water moved to the top, cold to the bottom (with mixing)

Phase Changes

• Melting, boiling, freezing, condensing…• Water freezes at 0 °C, boils at 100 °C (well,

at 92 °C in Laramie)

• Not all heat transfer is expressed as a temperature change.

Evaporation of a Liquid

• More energetic jostling = higher temperature

• An especially fast molecule at the surface may detach!

Evaporation of a Liquid

• More energetic jostling = higher temperature

• An especially fast molecule at the surface may detach!

Evaporation

• Evaporating molecules carry away energy

• Remaining liquid cools (lower energy)

Latent heat

• Energy required to change the phase of 1 kg of substance

• Water’s latent heat of fusion (melting):

335,000 J/kg = 80 Cal/kg

• Water’s latent heat of vaporization:

2,255,000 J/kg = 539 Cal/kg

ice

Liquid water

steam

Water temperature with heating

-100

-50

0

50

100

150

200

0.0E+00 1.0E+06 2.0E+06 3.0E+06 4.0E+06

heat input (J/kg)

temperature (C)

Heating Curve for Water

Water boils

Ice melts

Condensation

• Vapor condenses to liquid only when:– its concentration is high enough and– its temperature is low enough

• Rising humid air forms clouds– air rises and cools– moisture condenses to droplets

Condensation

• Vapor condenses to liquid most easily on a surface (solid or liquid)– Wall of the bottle– Smoke particles

Layers of the Atmosphere

thermosphere

Heated from surfacetemperature drops with altitudestrongly mixed

Heated by sun on ozonetemperature rises with altitudenot mixed

Heated from stratospherevery thin

Heated from sun, solar windvery thin

troposphere

stratosphere

mesosphere

surface

Greenhouse Effect

Warmth from the atmosphere

Planet with No Atmosphere

Solar energy input

IR output to space

Temperature rises if input > outputOutput rises as temperature risesTemperature steady when input = output

Surface energy changes with absorption and radiation

Surface Temp Feedbacks

Solar inputEarth surface temperature

Earth IR output

With an Atmosphere

Solar energy input

absorption by atmosphere

Atmosphere absorbs some outgoing IRAtmosphere warms and radiatesSome radiation absorbed by surface

Surface energy changes with absorption and radiation

IR output to space

radiation by atmosphere

Atmosphere Temp Feedbacks

Solar inputEarth surface temperature

Earth IR output

Atmosphere IR absorption

Atmosphere temperature

AtmopsphereIR output