Seasonal and Daily temperatures

1. Chapter 3 Seasonal and Daily temperatures

2. Why the Earth has seasons • Earth revolves in elliptical path around sun every 365 days. • Earth rotates counterclockwise or eastward every 24 hours. • Earth closest to Sun (147 million km) in January, farthest from Sun (152 million lm) in July. • Distance not the only factor impacting seasons.

6. Why the Earth has seasons • The amount of energy that reaches the Earths surface is influence by the distance from the Sun, the solar angle, and the length of daylight. • When the Earth tilts toward the sun in summer, higher solar angles and longer days equate to high temperatures.

8. Why the Earth has seasons • Seasons in the Northern Hemisphere • Summer solstice: June 21, Sun directly above Tropic of Cancer, Northern Hemisphere days greater than 12 hours • Winter solstice: December 21, Sun directly above Tropic of Capricorn, Northern Hemisphere days less than 12 hours • Autumnal and Spring Equinox: September 22, Marc 20, Sun directly above Equator, all locations have a 12 hour day

12. Stepped Art Fig. 3-8, p. 63

14. Why the Earth has seasons • Special Topic: First day of winter • December 21 is the astronomical first day of winter, sun passes over the Tropic of Capricorn; not based on temperature.

15. Why the Earth has seasons • Seasons in the Southern Hemisphere • Opposite timing of Northern Hemisphere • Closer to sun in summer but not significant difference from north due to: • Greater amount of water absorbing heat • Shorter season

16. Simplified Surface Energy Balance • NET R = • + SW (insolation) • – SW (reflection) • + LW (infrared) • – LW (infrared) Figure 3.13

17. Local temperature variations • Southern exposure: warmer, drier locations facing south. Implications for • Vegetation • Viniculture • Ski slopes • Landscaping • Architecture

19. Local temperature variations • Environmental Issues: Solar Heating • In order to collect enough energy from solar power to heat a house, the roof should be perpendicular to the winter sun. • For the mid-latitudes the roof slant should be 45°- 50°

20. Daily temperature variations • Each day like a tiny season with a cycle of heating and cooling • Daytime heating • Air poor conductor so initial heating only effects air next to ground • As energy builds convection begins and heats higher portions of the atmosphere • After atmosphere heats from convection high temperature 3-5PM; lag in temperature

23. Daily temperature variations • Properties of soil affect the rate of conduction from Earth to atmosphere • Wind mixes energy into air column and can force convection.

24. Daily temperature variations • Nighttime cooling • As sun lowers, the lower solar angle causes insolation to be spread across a larger area • Radiational cooling as infrared energy is emitted by the Earth’s surface • Radiation inversion: air near ground much cooler than air above • Thermal belt

26. Stepped Art Fig. 3-14, p. 69

28. Daily temperature variations • Protecting crops from cold • Cover • Smudge pots • Fans • Sprinklers

31. The controls of temperature • Latitude: solar angle and day length • Land & water: specific heat • Ocean currents: warm and cold currents • Elevation: cooling and increase range

32. Land–Water Heating Differences  • Evaporation • Transparency • Specific heat • Movement • Ocean currents and sea surface temperatures • Marine vs. continental effects

33. Land–Water Heating Differences   Figure 3.20

36. Global Temperature Ranges Figure 3.28

37. Air temperature data • Daily, monthly, yearly temperature • Range: maximum minus minimum • Mean: average of temperature observations • Maximum: highest temperature of time period • Minimum: lowest temperature of time period

39. Air temperature data • Special topic: What’s normal? • Climate normal is the 30 year average for a given temperature variable.

40. Air temperature data • The use of temperature data • Heating degree-day: people heat when temperature below 65°F • Cooling degree-day: people cool when temperature above 65°F • Growing degree-day: temperature above of below base temperature for specific crop

44. Air temperature and human comfort • Body heats through metabolism • wind-chill index • Hypothermia • Body cools through emitting infrared energy and evaporation of perspiration

45. Wind Chill Table Figure 1

46. Heat Index Table Figure 2

47. Air temperature and human comfort • Observation: 1000 degrees • Thin air at the top of the atmosphere does not have enough molecules to create a high temperature as measured by a thermometer.

48. The Urban Environment Figure 3.29

49. Measuring air temperature • Thermometers: liquid-in-glass, maximum, minimum, electrical resistance, bimetallic • ASOS • Thermistors • Infrared sensors

50. Urban Heat Island Figure 3.30