| NATS 101 Lecture 5 Greenhouse Effect and Earth-Atmo Energy Balance and the Seasons |
| 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 | |
| rotate, vibrate | |
| 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 |
| Global Solar Radiation Balance (Only half of Solar Radiation SR reaches the surface) |
| Atmosphere Heated from Below |
| Global Atmo Energy Balance |
| Summary |
| Greenhouse Effect (A Misnomer) | |
| Surface 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 |
| NATS 101 Intro to Weather and Climate Next subject: The Seasons |
| Supplemental References for TodayÕs Lecture |
| Aguado, E. and J. E. Burt, 2001: Understanding Weather & Climate, 2nd Ed. 505 pp. Prentice Hall. (ISBN 0-13-027394-5) | |
| Danielson, E. W., J. Levin and E. Abrams, 1998: Meteorology. 462 pp. McGraw-Hill. (ISBN 0-697-21711-6) | |
| Gedzelman, S. D., 1980: The Science and Wonders of the Atmosphere. 535 pp. John-Wiley & Sons. (ISBN 0-471-02972-6) | |
| Lutgens, F. K. and E. J. Tarbuck, 2001: The Atmosphere, An Intro-duction to the Atmosphere, 8th Ed. 484 pp. Prentice Hall. (ISBN 0-13-087957-6) | |
| Wallace, J. M. and P. V. Hobbs, 1977: Atmospheric Science, An Introductory Survey. 467 pp. Academic Press. (ISBN 0-12-732950-1) |
| Reasons for Seasons |
| Tilt of EarthÕs Axis - Obliquity | |
| Angle between the Equatorial Plane and the Orbital Plane | |
| Eccentricity of EarthÕs Orbit | |
| Elongation of Orbital Axis | |
| Eccentricity of Orbit |
| Slide 27 |
| Solar Zenith Angle |
| Depends on latitude, time of day & season | |
| Has two effects on an incoming solar beam | |
| Surface area covered or Spreading of beam | |
| Path length through atmosphere or Attenuation of beam |
| Beam Spreading |
| Low Zenith - Large Area, Much Spreading | |
| High Zenith - Small Area, Little Spreading |
| Beam Spreading |
| Atmospheric Path Length |
| Length of Day |
| Day Hours at Solstices - US Sites |
| Summer-Winter | |
| Tucson (32o 13Õ N) 14:15 - 10:03 | |
| Seattle (47o 38Õ N) 16:00 - 8:25 | |
| Anchorage (61o 13Õ N) 19:22 - 5:28 | |
| Fairbanks (64o 49Õ N) 21:47 - 3:42 | |
| Hilo (19o 43Õ N) 13:19 - 10:46 |
| Path of Sun |
| Hours of daylight increase from winter to summer pole | |
| Equator always has 12 hours of daylight | |
| Summer pole has 24 hours of daylight | |
| Winter pole has 24 hours of darkness | |
| Note different Zeniths |
| Noon Zenith Angle at Solstices |
| Summer-Winter | |
| Tucson AZ (32o 13Õ N) 08o 43Õ - 55o 43Õ | |
| Seattle WA (47o 38Õ N) 24o 08Õ - 71o 08Õ | |
| Anchorage AK (61o 13Õ N) 37o 43Õ - 84o 43Õ | |
| Fairbanks AK (64o 49Õ N) 41o 19Õ - 88o 19Õ | |
| Hilo HI (19o 43Õ N) 3o 47Õ (north) - 43o 13Õ |
| Is Longest Day the Hottest Day? |
| Annual Energy Balance |
| Heat transfer done by winds and ocean currents | |
| Differential heating drives winds and currents | |
| We will examine later in course |
| Summary |
| Tilt (23.5o) is primary reason for seasons | ||
| Tilt changes two important factors | ||
| Angle at which solar rays strike the earth | ||
| Number of hours of daylight each day | ||
| Warmest and Coldest Days of Year Occur after solstices, typically around a month | ||
| Requirement for Heat Transport Done by Atmosphere-Ocean System | ||
| Assignments for Next Lectures |
| Ahrens (next lecture) | |
| Pages 55-64 | |
| Problems: | |
| 3.1, 3.2, 3.5, 3.6, 3.14 |