announcements survey on sakai homework 1 on class web site (also available on sakai) quiz 1...
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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
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