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Lecture 4: Heat Transfer and Energy Balance
Ch. 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 Oceans
Radiation
Conduction
Convection
Sensible Heat
Latent Heat
Radiation:
Energy transferred though
magnetic waves.
Can radiation transmits heat
through vacuum?
Conduction
Could conduction
occurs in vacuum?
Conduction of
heat energy
occurs as
warmer
molecules
transmit
vibration, and
hence heat, to
adjacent cooler
molecules.
Warm ground
surfaces heat
overlying air
by conduction.
Convection
Is convection or conduction a more
effective way of transporting heat?
Convection occurs
when hotter water
rises and cold water
sinks, which helps
distribute heat
energy.
Convection of Sensible Heat (you can feel it!)
The Development of Convection
Convection is heat energy moving as a fluid from hotter to cooler
areas.
Warm air at the ground surface rises as a thermal bubble expands,
consumes energy, and hence cools.
Latent Heat
As water moves toward vapor it absorbs latent (e.g. not
sensed or hidden) heat to keep the molecules in rapid motion.
Latent Heat
Latent Heat Energy for Storms
Latent heat released from the billions of vapor droplets during
condensation and cloud formation fuels storm energy needs, warms
the air, and encourages taller cloud growth.
Radiation, Convection and Conduction
Warming Earth's Atmosphere
Solar radiation passes first through the upper atmosphere, but only
after absorption by earth's surface does it generate sensible heat to
warm the ground and generate longwave energy.
This heat and energy at the surface then warms the atmosphere
from below.
Incoming Solar Radiation (Insolation)
At the top of the atmosphere
Processes That Affect Insolation
Earth’s Radiation Budget (Global Average)
Earth reflects 30% directly back to space, absorbs about 20%
in the atmosphere, and absorbs about 50% at the surface.
Earth’s lower atmosphere is warmed by radiation, conduction,
convection of sensible heat and latent heat.
The Global Energy Budget: Driver of Atmospheric Motion
A balance exists between
the incoming solar and
outgoing longwave energy
averaged over the globe
and the year
SURPLUS
DEFICIT
However, the tilt of the
Earth means this balance
is not maintained for each
latitude
• 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?