# 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.

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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 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 surface temperature drops with altitude strongly mixed Heated by sun on ozone temperature rises with altitude not mixed Heated from stratosphere very thin Heated from sun, solar wind very 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 > output Output rises as temperature rises Temperature steady when input = output Surface energy changes with absorption and radiation

Surface Temp Feedbacks Solar input Earth surface temperature Earth IR output

With an Atmosphere Solar energy input absorption by atmosphere Atmosphere absorbs some outgoing IR Atmosphere warms and radiates Some radiation absorbed by surface Surface energy changes with absorption and radiation IR output to space radiation by atmosphere

Atmosphere Temp Feedbacks Solar input Earth surface temperature Earth IR output Atmosphere IR absorption Atmosphere temperature Atmopsphere IR output

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