Transcript atmosphys - barransclass

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
Heating Curve for Water
Water temperature with heating
temperature (C)
200
steam
Water boils
150
100
50 Ice melts
Liquid water
0
ice
-50
-100
0.0E+00
1.0E+06
2.0E+06
heat input (J/kg)
3.0E+06
4.0E+06
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 sun, solar wind
very thin
mesosphere
Heated from stratosphere
very thin
stratosphere
Heated by sun on ozone
temperature rises with altitude
not mixed
troposphere
Heated from surface
temperature drops with altitude
strongly mixed
surface
Greenhouse Effect
Warmth from the atmosphere
Planet with No Atmosphere
Temperature rises if input > output
Output rises as temperature rises
Temperature steady when input = output
IR output to
space
Solar energy input
Surface energy
changes with
absorption and
radiation
Surface Temp Feedbacks
Solar input
Earth surface
temperature
Earth IR
output
With an Atmosphere
Atmosphere absorbs some outgoing IR
Atmosphere warms and radiates
Some radiation absorbed by surface
IR output to
space
Solar energy input
radiation by
atmosphere
absorption by
atmosphere
Surface energy
changes with
absorption and
radiation
Atmosphere Temp Feedbacks
Solar input
Atmopsphere
IR output
Earth surface
temperature
Earth IR
output
Atmosphere
temperature
Atmosphere
IR absorption