1 / 51

CHAPTER 3 TEMPERATURE AND HUMIDITY EXTREMES

CHAPTER 3 TEMPERATURE AND HUMIDITY EXTREMES. Daily temperature variation. Each day is like a tiny season! Daytime heating, nighttime cooling Why do the high and low temperatures happen when they do?. Radiation inversion on calm vs. windy nights. The “diurnal cycle” of temperature.

abraham-taylor
Download Presentation

CHAPTER 3 TEMPERATURE AND HUMIDITY EXTREMES

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CHAPTER 3 TEMPERATURE AND HUMIDITY EXTREMES

  2. Daily temperature variation • Each day is like a tiny season! • Daytime heating, nighttime cooling • Why do the high and low temperatures happen when they do?

  3. Radiation inversion on calm vs. windy nights

  4. The “diurnal cycle” of temperature

  5. The “diurnal cycle” of temperature • Daily temperature range near the ground is much greater than that above the ground!

  6. The “diurnal cycle” of temperature:Effect of Clouds

  7. The Controls of Temperature • Latitude • Land and water distribution • Ocean currents • Elevation

  8. Average temperature in JanuaryImportant: Adjusted for sea level!

  9. Average temperature in July

  10. Fig. 3.15, p. 78

  11. Tale of three cities Fig. 3.14, p. 77

  12. Fig. 3.8, p. 70

  13. Extremes

  14. Fig. 3.4, p. 66

  15. Fig. 3.5, p. 67

  16. Fig. 3.9, p. 71

  17. Fig. 3.10, p. 72

  18. Temperature terms • (Note: these are kind of confusing!) • “Average temperature”: the average of the high and low temperature for the day • “Normal temperature”: a 30-year average

  19. “Normal” temperature • Not once since 1952 has the high been exactly 62! • So, interpret the “normal” high with caution – what’s normal is for the temperature to be different each year!

  20. CLL January 31 high temperature • Standard deviation = 11.5 • Mean +/- 2 standard deviations gives a range of about 39 to 85 – the high temperature will fall between these two values 95% of the time

  21. WEATHER EXTREMES ANDHUMAN DISCOMFORT • Body’s Perception: Sensible temperature • How we exchange heat energy with environment • Wind and cold • Body, like the planet, must also have a heat/energy balance if temperature is to be maintained. • Thin layer of warm molecules next to skin • Wind interferes with this, rapidly removes heat • Sensible temperature for cold weather: Wind Chill

  22. Wind chill index – factors in both temperature and wind

  23. Cold Hazards • Frostbite: Skin actually freezes and discolors • Cold, Damp Weather • A cold rainy day often feels colder than a “dry” one because water on exposed skin conducts heat away from the body better than air does • Hypothermia – body temp drops below normal • Most hypothermia occurs between freezing and 50° F, snow vs. rain, the wet really matters! • “Died of Exposure”

  24. Fig. 3.18, p. 81

  25. Humidity: water vapor in the air • The maximum amount of water vapor that can be in the air is a function of temperature • The hotter it is, the greater amount of moisture that can be in the air • If this maximum amount of water vapor is actually in the air, the air is saturated • Usually the air near the ground is not saturated (but what might happen if it is?) • Most of the time, the amount of water vapor in the air stays about the same from day to night, even though the temperature goes up and down quite a bit

  26. Humidity: water vapor in the air • Two types of humidity measures: absolute and relative • Absolute measures describe the actual amount of moisture in the air • Examples: absolute humidity, dewpoint temperature, specific humidity, mixing ratio • Relative humidity compares the amount of moisture in the air with the amount needed for saturation

  27. Specific humidity • Mass of water vapor divided by mass of air • Must add or subtract water vapor to the parcel to change the specific humidity

  28. Dew point temperature • Another absolute measure • Indicates how much you would have to cool the air to get to saturation. • The moisture needed for saturation at 60° is much less than at 80°. If the temperature is 80° and the dew point is 60°, you would have to cool the air 20° to have it be saturated

  29. Other Absolute measures • Mixing Ratio – mass of water vapor over mass of dry air (how is this different from specific humidity?) • Vapor Pressure – The actual pressure only due to water vapor. • Both of these have actual values, and saturation values for the current temperature.

  30. Relative humidity • Relative Humidity: (actual water vapor/saturation water vapor)*100 • Can use either mixing ratio or vapor pressure • RH can be changed two ways: • Change vapor content • Change saturation point (how?)

  31. RH during a diurnal cycle

  32. Absolute vs. relative humidity

  33. Dew Point (usually a better way to compare humidity) Fig. 3.20, p. 83

  34. Current dew point map http://weather.unisys.com/surface/sfc_con_dewp.html

  35. Humidity Extremes • Extreme Dew Points • Record high Td in the US occur during heat waves of summer • Td > 80°F rare in the US • Highest Td in the US (90°F): New Orleans, LA; Melbourne, FL; Appleton, WI • Extreme Dew Points • Highest Td in the world: Middle East near large bodies of extremely warm water • Red Sea: surface temperature of 98°F • Sharjah, United Arab Emirates, Td 93°F • Dhahran, Saudi Arabia, Td 95°F

  36. Fig. 3.21, p. 83

  37. Humidity + Heat (Effective Temperature) • Body cools by emitting infrared energy and perspiration evaporation • Less evaporation causes people to feel hotter (perception, remember!) • Air with 100% relative humidity is saturated because the air is holding as much water in the vapor state that it can hold (at that temperature) • The higher the relative humidity, the less evaporation

  38. Heat index – factors in both temperature and humidity Fig. 3.24, p. 87

  39. Heat index – factors in both temperature and humidity

  40. Table 3.6, p. 88

  41. Heat Wave: A genuine severe/hazardous weather type • On average, the deadliest weather in U.S. • Prolonged period of abnormally hot (& humid, usually) weather • Almost 50,000 died in Europe in 2003

  42. Table 3.5, p. 87

  43. Table 3.7, p. 89

  44. Mythbusters • “Air was so heavy and thick because of the humidity” (Yankees getting off the plane in Houston) • Humid Air and Dry Air Do Not Weigh the Same • At the same temperature and level in the atmosphere, hot, humid air is lighter (less dense) than hot, dry air • A molecule of water vapor (H2O) weighs appreciably less than a molecule of either nitrogen (N2) or oxygen (O2) • Still, it indeed does feel thick and heavy, related to perception and effective temperature.

  45. Measuring temperature • Standards for a Cooperative Station thermometer: • Placed in a shelter 2 m above ground • Shelter must be painted white • Doors must open to the north (in the N. Hemisphere) • Vented sides • Placed on a grassy area where possible

  46. Inside the shelter (photo from surfacestations.org)

  47. How closely are the standards followed? • Generally good siting; station has been in same location for 100+ years Orland, California (photo from surfacestations.org)

  48. How closely are the standards followed? • Not so good! Marysville, California (photo from surfacestations.org)

  49. Humidity Measurement Now most stations have automated equipment which uses electronic means

More Related