Temperature Structure of the Atmosphere Chapter 5

 Greenhouse effect is powered by lapse rate. –Has to be cold higher in atm.  Have to add in processes not found in layer model –Need moist convection  Greenhouse effect is powered by lapse rate. –Has to be cold higher in atm.  Have to add in processes not found in layer model –Need moist convection

 T structure of atm is coupled to T of ground by convection. –Warm air rises and carries heat –As it expands, it cools.  Leads to dec. in T with inc. altitude.  If atm were incompressible, like water, there would be little change in T with altitude. –no gh effect because amount of outgoing IR would be the same whether it came from the ground or high in the atm.  T structure of atm is coupled to T of ground by convection. –Warm air rises and carries heat –As it expands, it cools.  Leads to dec. in T with inc. altitude.  If atm were incompressible, like water, there would be little change in T with altitude. –no gh effect because amount of outgoing IR would be the same whether it came from the ground or high in the atm.

Typical T and P of atm as a function of altitude  Troposhpere - 90% of gas molecules, weather, climate models  Stratosphere  More layers above….  P nonlinear with altitude (exponential)  Troposhpere - 90% of gas molecules, weather, climate models  Stratosphere  More layers above….  P nonlinear with altitude (exponential)

Fig P and depth are linear  Water is not compressible  So it increases linearly with depth  Water is not compressible  So it increases linearly with depth

Adiabatic expansion  Lapse rate - T dec. w/altitude  Adiabatic - air heats/cools by expansion/compression, not due to T of air around it. –Dry vs. moist  Lapse rate - T dec. w/altitude  Adiabatic - air heats/cools by expansion/compression, not due to T of air around it. –Dry vs. moist

Sinking = compressing = heating

 Effect of water on the T profile of atm.  Air cools as it rises, water vapor condenses to droplets, releases LH.  So, moist adiabat is less than dry.  Effect of water on the T profile of atm.  Air cools as it rises, water vapor condenses to droplets, releases LH.  So, moist adiabat is less than dry.

Water vapor & latent heat  3 phases of water  Vapor = liquid + heat  Latent heat = energy tied up in water vapor –Sensible heat – what we measure with a thermometer –Condensation - LH SH  3 phases of water  Vapor = liquid + heat  Latent heat = energy tied up in water vapor –Sensible heat – what we measure with a thermometer –Condensation - LH SH

ConvectionConvection  Carries heat (along with radiation and conduction)  Transfers heat from equator to poles  Occurs in fluids (liquid & gas)  Driven by heating from below  Molecules move energetically, fluid expands, density decreases.  Carries heat (along with radiation and conduction)  Transfers heat from equator to poles  Occurs in fluids (liquid & gas)  Driven by heating from below  Molecules move energetically, fluid expands, density decreases. Stable Heating from below

Convection in the layer model  Layer model from chapter 3 didn’t have convection.  T of atm. layer decreases with altitude  But, in earlier model, heat is only carried upward by radiation.  Need to add convection to the model.  Layer model from chapter 3 didn’t have convection.  T of atm. layer decreases with altitude  But, in earlier model, heat is only carried upward by radiation.  Need to add convection to the model.

A B C D 0 m 3000 m 0 m DALR = 10 deg C/Km SALR = 6 deg C/Km Point A: T = 30 deg C 1000 m Point B: T = 20 deg C Point C: T = 8 deg C Point D: T = 38 deg C

Convection in the layer model If we add convection to the layer model then we have to add another set of heat arrows.

Lapse rate & gh effect  The steeper the lapse rate, the stronger the gh effect.  If the atm were incompressible, like water, and convection maintained a uniform T w/altitude then there would be no gh effect.  Raise CO 2 in atm raises the altitude in the atm where IR escapes to space.  The steeper the lapse rate, the stronger the gh effect.  If the atm were incompressible, like water, and convection maintained a uniform T w/altitude then there would be no gh effect.  Raise CO 2 in atm raises the altitude in the atm where IR escapes to space. A A B A to B - Inc. amount of gh gas. IR to space at a higher altitude (new skin altitude). But, the skin T stays the Same (red line). Inc. in skin T altitude -- inc. ground T

Take Home Points  Air in the upper troposphere is colder due to moist convection.  Sunlight heats surface, air rises and cools –P decreases with altitude –T decreases as a gas expands  LH is released as SH as water vapor condenses.  Lapse rate is controlled by the moist adiabat.  Strength of gh effect depends on the lapse rate. –Need another set of arrows in our model!!  Air in the upper troposphere is colder due to moist convection.  Sunlight heats surface, air rises and cools –P decreases with altitude –T decreases as a gas expands  LH is released as SH as water vapor condenses.  Lapse rate is controlled by the moist adiabat.  Strength of gh effect depends on the lapse rate. –Need another set of arrows in our model!!