Lecture 4: Lecture 4: Heat Transfer and Energy BalanceHeat Transfer and Energy BalanceCh. 1, p. 5; See EarthsClimate_Web_Chapter.pdf, p. 6-15]

For more advanced reading materials, please see http://www.geo.utexas.edu/courses/387h/ScheduleGPC_detail.htm

Forms of Heat Transfer in the Atmosphere and OceansForms of Heat Transfer in the Atmosphere and Oceans

RadiationRadiation

ConductionConduction

ConvectionConvection

Sensible HeatSensible Heat

Latent HeatLatent Heat

Radiation:Energy transferred though Energy transferred though magnetic waves. magnetic waves.

Can radiation transmits heat Can radiation transmits heat through vacuum?through vacuum?

ConductionConduction

Conduction of Conduction of heat energy heat energy occurs as occurs as warmerwarmer molecules molecules transmit transmit vibration, and vibration, and hence heat, hence heat, toto adjacent adjacent coolercooler molecules.molecules.

Warm ground Warm ground surfaces heat surfaces heat overlying air overlying air by conduction.by conduction.

Could conduction occurs in vacuum?

ConvectionConvection

Convection occurs Convection occurs when when hotterhotter water water risesrises and and coldcold water water sinkssinks, which helps , which helps distribute heat distribute heat energy.energy.

Is convection or conduction a more effective way of transporting heat?

Convection of Sensible Heat (you can feel it!)Convection of Sensible Heat (you can feel it!)

The Development of ConvectionThe Development of Convection

Convection is heat energy moving as a Convection is heat energy moving as a fluidfluid from from hotter to hotter to coolercooler areas.areas.

Warm air at the ground surface rises as a thermal bubble expands, Warm air at the ground surface rises as a thermal bubble expands, consumes energy, and hence cools.consumes energy, and hence cools.

Latent HeatLatent Heat

As As water moves toward vaporwater moves toward vapor it absorbs latent ( it absorbs latent (e.g. not e.g. not sensed or hiddensensed or hidden) heat to keep the molecules in rapid motion.) heat to keep the molecules in rapid motion.

Latent HeatLatent Heat

Latent Heat Energy for StormsLatent Heat Energy for Storms

Latent heat releasedLatent heat released from the billions of vapor droplets from the billions of vapor droplets during during condensationcondensation and cloud formation and cloud formation fuelsfuels storm energy needs, storm energy needs, warmswarms the air, and encourages the air, and encourages tallertaller cloud growth. cloud growth.

Radiation, Convection and Conduction

Warming Earth's AtmosphereWarming Earth's Atmosphere

Solar radiation passes first through the upper atmosphere, but only Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface does it generate sensible heat to after absorption by earth's surface does it generate sensible heat to warm the ground and generate longwave energy.warm the ground and generate longwave energy.This heat and energy at the surface then warms the atmosphere This heat and energy at the surface then warms the atmosphere from below.from below.

Incoming Solar Radiation (Insolation)Incoming Solar Radiation (Insolation)

At the top of the At the top of the atmosphereatmosphere

Processes That Affect Insolation

Earth’s Radiation Budget (Global Average)Earth’s Radiation Budget (Global Average)

Earth reflects 30% directly back to space, absorbs Earth reflects 30% directly back to space, absorbs about 20% in the atmosphere, and absorbs about 50% about 20% in the atmosphere, and absorbs about 50% at the surface.at the surface.Earth’s lower atmosphere is warmed by radiation, Earth’s lower atmosphere is warmed by radiation, conduction, convection of sensible heat and latent conduction, convection of sensible heat and latent heat.heat.

The Global Energy Budget: Driver of Atmospheric Motion

However, the tilt of theEarth means this balanceis not maintained for eachlatitude

A balance exists between the incoming solar andoutgoing longwave energy averaged over the globe and the year

DEFICITSURPLUS

• To compensate for this energy imbalance, winds in the atmosphere and currents in the oceans transport cold air and water toward the equator

• About 1/3 of this transport occurs from the evaporation of tropical waters and subsequent transport into high latitudes, where it condenses and releases latent heat

• About 1/3 occurs from the poleward transport of warm waters by ocean currents

• The remaining 1/3 occurs from middle latitude cyclones and anticyclones

At the end of this lecture, can you answer these questions?

• 1. How many forms through which heat and energy can be transferred in the earth climate system?

• 2. What roles do these form of heat transfer play in energy balance of the Earth climate system? E.g., How energy is absorbed by the earth, how is this absorbed energy balanced by other forms of heat/energy transfer?

• In what part of the earth radiative heating exceeds radiative cooling? How is heat transported from the regions of net surplus to net lost?