| NATS 101-05 Lecture 6 Seasons and Temperature Variations |
| Supplemental References for TodayÕs Lecture on Seasons |
| 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 5 |
| 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 equator to pole Heat Transport | ||
| Done by Atmosphere-Ocean System | ||
| NATS 101-05 Now on to Temperature Variations |
| Supplemental Reference for TodayÕs Lecture on Temperature Variations |
| Wallace, J. M. and P. V. Hobbs, 1977: Atmospheric Science, An Introductory Survey. 467 pp. Academic Press. (ISBN 0-12-732950-1) |
| Temperature Questions |
| What causes diurnal temperature variations? | |
| What physical processes can influence daily temperature variations? | |
| Why is MAX temperature after solar noon? | |
| Why is MIN temperature just after sunrise? | |
| What is Wind Chill Factor? (if time allows) |
| MAX Temperature near Surface |
| MIN Temperature near Surface |
| 12 and 00 UTC TUS Sounding |
| MAX-MIN Range | |
| 12oC at 925 mb 6oC at 910 mb 2oC at 800 mb 0oC by 700 mb | |
| Range decreases with height |
| Growth and Decay of Inversion Evening Morning |
| What Affects Inversion Strength? |
| Cloud Cover | |
| Clear skies-strong inversion | |
| Cloudy skies-weak inversion | |
| Land Characteristics | |
| Snow cover-strong inversion | |
| Bare ground-weaker inversion | |
| Wind Speed | |
| Calm winds-strong inversion | |
| Strong winds-weak inversion |
| When Does MAX-MIN Occur? |
| When incoming SW exceeds outgoing IR | |
| Temperature rises | |
| When outgoing IR exceeds incoming SW | |
| Temperature falls | |
| MAX occurs | |
| Late afternoon | |
| MIN occurs | |
| Just after sunrise |
| Winter-Summer Temperature Variations at Sea Level |
| Continents undergo larger changes than oceans | |
| High latitudes undergo larger changes than low latitudes |
| Controls of Temperature |
| Latitude | |
| Average temperatures in middle latitudes decrease by 5-10oC every 10o latitude | |
| Elevation | |
| Lapse rate in troposphere is 6.5oC/km | |
| Tucson (2,500 ft) July Max - 100oF | |
| Mt. Lemmon (8,500 ft) July Max - 76oF |
| Controls of Temperature |
| Ocean Currents and Prevailing Winds | |
| Warm-Gulf Stream | |
| Cold-California Current | |
| Land versus Water | |
| Heat capacity of water is 5X that of land | |
| Absorbed solar energy is distributed a greater depth in water than in land |
| Specific Heat Capacity |
| Heat required to raise temperature of 1 gm of mass 1oC. | |
| Rock has lower heat capacity than water |
| Water-Soil Heating Depth |
| Soil Temperature |
| Ocean Temperature |
| Wind Chill |
| Still air is poor conductor; lack of wind allows insulating layer of still air to form near skin | |
| Wind blows insulating layer of air from skin Forced convection or heat transport by advection |
| Summary |
| Balance between incoming and outgoing energy controls temperature rises and falls | |
| MAX late afternoon, MIN just after sunrise | |
| Diurnal temp. changes are largest at ground | |
| Affected by wind, cloud cover, land type | |
| Winter-Summer changes | |
| Largest over land, high latitudes | |
| Temperature Controls | |
| Latitude, Altitude, Land-Sea, Ocean Currents |
| Assignment |
| Ahrens | |
| Atmospheric Moisture | |
| Pages 77-89, B: 430, D: 433-436 | |
| Problems 4.1, 4.2, 4.5, 4.6, 4.9, 4.10 |