| NATS 101 Lecture 6 Greenhouse Effect and Earth-Atmo Energy Balance |
| Review Items |
| Heat Transfer | |
| Latent Heat | |
| WienÕs Displacement Law Ramifications | |
| Stefan-Boltzman Law Ramifications |
| New Business |
| Selective Absorption and Emission | |
| Earth-Atmo Energy Balance |
| Modes of Heat Transfer |
| Latent Heat Take 2 |
| General Laws of Radiation |
| All objects above 0 K emit radiant energy | |
| Hotter objects radiate more energy per unit area than colder objects, result of Stefan-Boltzman Law | |
| The hotter the radiating body, the shorter the wavelength of maximum radiation, result of WienÕs Displacement Law | |
| Objects that are good absorbers of radiation are also good emittersÉtodayÕs lecture! |
| SunÕs Radiation Spectrum |
| Sun - Earth Radiation Spectra |
| What is Radiative Temperature of Sun if Max Emission Occurs at 0.5 mm? |
| Apply WienÕs Displacement Law | |
| How Much More Energy is Emitted by the Sun than the Earth? |
| Apply Stefan-Boltzman Law | |
| Radiative Equilibrium |
| Radiation absorbed by an object increases the energy of the object. | ||
| Increased energy causes temperature to increase (warming). | ||
| Radiation emitted by an object decreases the energy of the object. | ||
| Decreased energy causes temperature to decrease (cooling). | ||
| Radiative Equilibrium (cont.) |
| When the energy absorbed equals energy emitted, this is called Radiative Equilibrium. | |
| The corresponding temperature is the Radiative Equilibrium Temperature. |
| Why Selective, Discrete Absorption/Emission? |
| Life as we perceive it: A continuous world! | |
| Atomic perspective: A quantum world! |
| Energy States for Atoms |
| Electrons can orbit in only permitted states | |
| A state corresponds to specific energy level | |
| Only quantum jumps between states | |
| Intervals correspond to specific wavelengths |
| Energy States for Molecules |
| Molecules can also rotate, vibrate, librate | |
| But only at specific energy levels or frequencies | |
| Quantum intervals between modes correspond to specific wavelengths |
| Selective Absorption |
| The Bottom Line | |
| Each molecule has a unique distribution of quantum states! | |
| Each molecule has a unique spectrum of absorption and emission frequencies of radiation! |
| Absorption |
| Visible (0.4-0.7 mm) is absorbed very little | |
| O2 an O3 absorb UV (shorter than 0.3 mm) | |
| Infrared (5-20 mm) is selectively absorbed | |
| H2O & CO2 are strong absorbers of IR | |
| Little absorption of IR around 10 mm – atmospheric window |
| Total Atmospheric Absorption |
| Visible radiation (0.4-0.7 mm) is not absorbed | |
| Infrared radiation (5-20 mm) is selectively absorbed, but there is an emission window at 10 mm |
| Simple Example of the
Greenhouse Effect (0% Solar absorbed, 100% IR absorbed) |
| Global Solar Radiation Balance (Not all Solar Radiation SR reaches the surface) |
| Atmosphere Heated from Below |
| Global Atmo Energy Balance |
| Summary |
| Greenhouse Effect (A Misnomer) | |
| SFC Warmer than Rad. Equil. Temp | |
| Reason: selective absorption of air | |
| H2O and CO2 most absorbent of IR | |
| Energy Balance | |
| Complex system has a delicate balance | |
| All modes of Heat Transfer are important |
| Assignments for Next Lectures |
| Ahrens (next lecture) | |
| Pages 42-50 | |
| Problems 2.15, 2.16, 2.18 |