temperature structure of the atmosphere chapter 5

Temperature Structure of the Temperature Structure of the

AtmosphereAtmosphere

Chapter 5Chapter 5

Temperature Structure of the Temperature Structure of the

AtmosphereAtmosphere

Chapter 5Chapter 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 T structure of atm is coupled to T of ground by convection.convection.– Warm air rises and carries heatWarm air rises and carries heat

– As it expands, it cools.As it expands, it cools.

Leads to dec. in T with inc. altitude.Leads to dec. in T with inc. altitude.

If atm were incompressible, like water, there would If atm were incompressible, like water, there would

be little change in T with altitude.be little change in T with altitude.

– no gh effect because amount of outgoing IR would be the no gh effect because amount of outgoing IR would be the

same whether it came from the ground or high in the atm.same whether it came from the ground or high in the atm.

T structure of atm is coupled to T of ground by T structure of atm is coupled to T of ground by convection.convection.– Warm air rises and carries heatWarm air rises and carries heat

– As it expands, it cools.As it expands, it cools.

Leads to dec. in T with inc. altitude.Leads to dec. in T with inc. altitude.

If atm were incompressible, like water, there would If atm were incompressible, like water, there would

be little change in T with altitude.be little change in T with altitude.

– no gh effect because amount of outgoing IR would be the no gh effect because amount of outgoing IR would be the

same whether it came from the ground or high in the atm.same whether it came from the ground or high in the atm.

Typical T and P of atm as a function of altitudeTypical T and P of atm as a function of altitudeTypical T and P of atm as a function of altitudeTypical T and P of atm as a function of altitude

Troposhpere - 90% of gas molecules, weather, Troposhpere - 90% of gas molecules, weather, climate modelsclimate models StratosphereStratosphere More layers above….More layers above…. P nonlinear with altitude (exponential)P nonlinear with altitude (exponential)

Troposhpere - 90% of gas molecules, weather, Troposhpere - 90% of gas molecules, weather, climate modelsclimate models StratosphereStratosphere More layers above….More layers above…. P nonlinear with altitude (exponential)P nonlinear with altitude (exponential)

Fig. 5.2 - P and depth are linearFig. 5.2 - P and depth are linear

Water is not compressibleWater is not compressible So it increases So it increases linearly linearly with depthwith depth

Water is not compressibleWater is not compressible So it increases So it increases linearly linearly with depthwith depth

Adiabatic expansionAdiabatic expansionAdiabatic expansionAdiabatic expansion Lapse rate - T dec. w/altitudeLapse rate - T dec. w/altitude Adiabatic - air heats/cools by Adiabatic - air heats/cools by

expansion/compression, not due to T of air around expansion/compression, not due to T of air around it.it.– Dry vs. moistDry vs. moist

Lapse rate - T dec. w/altitudeLapse rate - T dec. w/altitude Adiabatic - air heats/cools by Adiabatic - air heats/cools by

expansion/compression, not due to T of air around expansion/compression, not due to T of air around it.it.– Dry vs. moistDry vs. moist

Sinking = compressing = heating

Effect of water on the T profile of atm.Effect of water on the T profile of atm. Air cools as it rises, water vapor condenses Air cools as it rises, water vapor condenses

to droplets, releases LH.to droplets, releases LH. So, So, moist adiabat moist adiabat is less than dry.is less than dry.

Effect of water on the T profile of atm.Effect of water on the T profile of atm. Air cools as it rises, water vapor condenses Air cools as it rises, water vapor condenses

to droplets, releases LH.to droplets, releases LH. So, So, moist adiabat moist adiabat is less than dry.is less than dry.

Water vapor & latent heatWater 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

ConvectionConvectionConvectionConvection Carries heat Carries heat (along with radiation and conduction)(along with radiation and conduction) Transfers heat from equator to polesTransfers heat from equator to poles Occurs in fluids (liquid & gas)Occurs in fluids (liquid & gas) Driven by heating from belowDriven by heating from below Molecules move energetically, fluid expands, density Molecules move energetically, fluid expands, density

decreases.decreases.

Carries heat Carries heat (along with radiation and conduction)(along with radiation and conduction) Transfers heat from equator to polesTransfers heat from equator to poles Occurs in fluids (liquid & gas)Occurs in fluids (liquid & gas) Driven by heating from belowDriven by heating from below Molecules move energetically, fluid expands, density Molecules move energetically, fluid expands, density

decreases.decreases.

StableHeating from below

Convection in the layer modelConvection in the layer modelConvection in the layer modelConvection in the layer model

Layer model from chapter 3 didn’t have Layer model from chapter 3 didn’t have

convection.convection.

T of atm. layer decreases with altitudeT of atm. layer decreases with altitude

But, in earlier model, heat is only carried But, in earlier model, heat is only carried

upward by radiation.upward by radiation.

Need to add convection to the model.Need to add convection to the model.

Layer model from chapter 3 didn’t have Layer model from chapter 3 didn’t have

convection.convection.

T of atm. layer decreases with altitudeT of atm. layer decreases with altitude

But, in earlier model, heat is only carried But, in earlier model, heat is only carried

upward by radiation.upward by radiation.

Need to add convection to the model.Need to add convection to the model.

A

B

C

D0 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 modelConvection in the layer modelConvection in the layer modelConvection 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 effectLapse rate & gh effect

The steeper the lapse rate, the stronger the gh effect.The steeper the lapse rate, the stronger the gh effect.

If the atm were incompressible , like water, and convection If the atm were incompressible , like water, and convection maintained a uniform T w/altitude then there would be no maintained a uniform T w/altitude then there would be no gh effect.gh effect.

Raise CORaise CO22 in atm raises the altitude in the atm where IR in atm raises the altitude in the atm where IR escapes to space.escapes to space.

The steeper the lapse rate, the stronger the gh effect.The steeper the lapse rate, the stronger the gh effect.

If the atm were incompressible , like water, and convection If the atm were incompressible , like water, and convection maintained a uniform T w/altitude then there would be no maintained a uniform T w/altitude then there would be no gh effect.gh effect.

Raise CORaise CO22 in atm raises the altitude in the atm where IR in atm raises the altitude in the atm where IR escapes to space.escapes to space.

A

A B

A to B - Inc. amount of gh gas.

IR to space at a higheraltitude (new skin altitude).

But, the skin T stays theSame (red line).

Inc. in skin T altitude -- inc. ground T

Take Home PointsTake 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!!