ATOC 181 Lecture Notes - Lecture 8: Shortwave Radio, Background Radiation, Shortwave Radiation
7 Jun 2018
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LESSON 8
ENERGY: WARMING THE EARTH AND THE ATMOSPHERE PART 2
• Transfer of heat in the atmosphere: different ways to do so (4 main ways)
o Advection
o Conduction
o Convection
o Radiation (radiant Energy)
Heat Advection
• Usually refers to horizontal transport of an atmospheric property by the wind
• Not just heat, can be something else too
• Heat advection: horizontal transport if heat in the atmosphere
• Cloud advection: horizontal cloud displacement
• Water vapour advection: Horizontal displacement of water vapour
Conduction
• Transfer of heat from molecule to molecule
• Always from warmer regions to colder regions
• Ca’t have it fro cold to warm
• If have wood rod or metal rod, hand can burn quickly when heated due to conduction
• Heat one end of the metal rod and after a while, gave some spikes with some wax attached to it and one
after the other, the wax on the spikes is melting and the spikes are falling
• The principle of it: Particles start to vibrate next to the heat, pass Energy to the next particles next to it
through collision and vibrate. Pass on to next ones and so on.
• Solid conducts the best, then liquid and then gas
• Iron conducts the fastest, for in addition to molecules, there are some electrodes that conduct too
Heat Conductibility
• Still air: 0.023 W m-1 oC-1
o low heat conductibility
• Water: 0.6 W m-1 oC-1 at 20oC
o about 30x more than still air
o higher heat conductibility, so can heat water faster than air.
o Heat travels faster through water than through air
o Take less time to heat water than air
• Copper: good conductor
o conduct heat very quickly
o Enormous: 386 W m-1 oC-1 at 20oC
Convection
• Transfer of heat by currents (essentially vertical movement) in a liquid or a gas.
• The liquid and gas moves upwards from one location to another, carrying heat along with it, and moves
down when it becomes colder than the air around
• Not really works with solid
• Hot air is less dense than cold air. Thus, hot air rises.
• From warmer areas to colder areas
find more resources at oneclass.com
find more resources at oneclass.com
• If heat porridge, porridge from the bottom will rise and at some stages, as it cools, it comes back on the
side
• Occurs at all scale
o Also happens at the surface of the sun
o Also happens at microscopic scale
o Occurs in fluids at all scale: from microscopic to gigantic scale
• If watch fire, warm air transported upwards and eventually cools and goes down on the side
• Convection cells
Atmospheric Convection
• Surface is being heated by the cell, transfer some of the heat to the air right above through conduction,
then convection start. Hot air is less dense than cold air, so will rise and expand and thus have the
thermal.
o If rises high enough, results in clouds when cool enough
• Gliders use regions where have convection, so circle around and go as high as they want. The, they will
leave this area, start gliding and look for another area where have convection
o World record: several thousands of Km of gliding
o Find regions where convection, climb and then find another one
• Other applications:
o Soaring: extending duration of flight
o Thermal soaring: fly circle within the thermal, goes where the lift is, will rise.
o Same principle in parasailing
o Can look at clouds to find where thermal is
o Thermals and sailplanes
Radiation or Radiant Energy
• Transfer of heat through/by electromagnetic waves
• If have radio and cellphones, work with electromagnetic waves
• Sun also emits electromagnetic waves
• Electromagnetic waves can be described by their wavelength, frequency and in the visible also by their
colour.
• Energy from the sun travels through the space and the atmosphere in the form of radiation
• For conduction: need substance to transfer Energy
• For convection: transfer of heat through fluids
• For radiation, no medium between sun and earth, except for the part of atmosphere
o transfer of Energy without using substances
• Wavelength: distance between two crests
o length of one complete wavelength
o Long wavelength, have low Energy
• Frequency: number of waves crests (or troughs)
that passes at given point in one second
o Measured in hertz (Hz or cycle/sec).
o use for microwaves, speed of internet
o Energy increases as wavelength increases
• X-rays: increasing Energy
o have lot of Energy
o accumulate in body when exposed to it and after a while it can be dangerous
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Energy: warming the earth and the atmosphere part 2. Lesson 8: transfer of heat in the atmosphere: different ways to do so (4 main ways, advection, conduction, convection, radiation (radiant energy) Pass on to next ones and so on: solid conducts the best, then liquid and then gas. Iron conducts the fastest, for in addition to molecules, there are some electrodes that conduct too. Thus, hot air rises: from warmer areas to colder areas. If watch fire, warm air transported upwards and eventually cools and goes down on the side: convection cells. Atmospheric convection: surface is being heated by the cell, transfer some of the heat to the air right above through conduction, then convection start. Hot air is less dense than cold air, so will rise and expand and thus have the thermal. If rises high enough, results in clouds when cool enough: gliders use regions where have convection, so circle around and go as high as they want.
