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 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. Could conduction occurs in vacuum?
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.
The Development of Convection Convection is heat energy moving as a fluid from hotter to coolerareas. 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 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.
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
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 However, the tilt of the Earth means this balance is not maintained for each latitude SURPLUS DEFICIT
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?