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Moisture in the atmosphere

Moisture in the atmosphere. Moisture in the atmosphere. Saturation: When the air contains as much moisture as it can hold The higher the temperature, the more moisture air can hold. Water vapor enters the atmosphere by evaporation, sublimation to a gas, and transpiration.

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Moisture in the atmosphere

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  1. Moisture in the atmosphere

  2. Moisture in the atmosphere • Saturation: When the air contains as much moisture as it can hold • The higher the temperature, the more moisture air can hold

  3. Water vapor enters the atmosphere by evaporation, sublimation to a gas, and transpiration

  4. Evapotranspiration = Evaporation + Transpiration

  5. Large amounts of energy, mostly from the sun, are needed to change liquid water into water vapor during evaporation and transpiration

  6. EUREKA!!-Evaporation • Transpiration- a flashback to biology

  7. Measuring moisture in the atmosphere

  8. Measuring moisture in the atmosphere- Dry bulb vs. wet bulb • Dry Bulb Temperature (DB): Air temperature

  9. WET BULB TEMPERATURE (WB): Air temperature measured by a thermometer with damp cloth on the end- influenced by evaporation

  10. Measuring dry bulb and wet bulb Temperatures • Sling psychrometer: instrument used to measure the dry bulb and wet bulb temperatures

  11. Let’s try them out! • Be sure the cloth is damp • Swing the psychrometer for 30 seconds (be careful- You might get spritzed!) • Write the dry bulb temperature and wet bulb temperature in the charts on the “Measuring Moisture in Our Classroom” worksheet • Find the difference between the WB and DB temperatures • What do you notice about the dry bulb temperature when compared to the wet bulb temperature?

  12. How wet bulb thermometers work and atmospheric relationships • Evaporation causes cooling • The drier the air, the greater the cooling, the lower the wet-bulb temp, the more the air would need to cool in order to become saturated

  13. Using DB, WB, and psychrometers: Dewpoint • Dewpoint (DP): the temperature to which air must be cooled for it to reach saturation

  14. The only way to change the dewpoint of the air is by adding/removing moisture

  15. Steps for Determining Dew POint • Locate the dry-bulb (air temperature) reading on the left hand side of the chart • Subtract the wet-bulb reading (measure of how dry or saturated the air is) from the dry-bulb reading • Locate the difference between the wet-bulb and dry-bulb readings across the top of the chart • Follow the horizontal row for the dry-bulb reading to the right until it meets the vertical column running down from the difference between the wet-bulb and dry-bulb readings

  16. Sample question- index cards! • If the dry-bulb temperature is 26 degrees Celsius and the wet-bulb temperature is 25 degrees Celsius, find the dew point • (Note that the wet-bulb temp will always be the same or colder than the dry-bulb) • 28 degrees Celsius • 26 degrees Celsius • 25 degrees Celsius • 24 degrees Celsius

  17. Sample Question- Index cards! • If the dry-bulb temperature is 8 degrees Celsius and the wet-bulb temperature is 2 degrees Celsius, find the dew point 1. 6 degrees C 2. 3 degrees C 3. -9 degrees C 4. -14 degrees C

  18. Connections • How does the dewpoint in the first sample question compare to that found in the second sample question? • What connection can you make between the difference between the wet bulb and dry bulb temperatures and the dewpoint temperature?

  19. challenge question!- index cards! • If the dry-bulb temperature is 19 degrees Celsius and the wet-bulb temperature is 17 degrees Celsius, find the dew point • Not possible to determine • 18 degrees C • 17 degrees C • 16 degrees C

  20. challenge question-index cards! • If the air temperature is 4 degrees Celsius and the difference between the dry bulb and wet bulb is 3 degrees Celsius, what is the dewpoint? • 1. 1 degree C • 2. 4 degrees C • 3. – 4 degrees C • 4. -7 degrees C

  21. One step further • If we know the dry bulb is 4 degrees C and the difference between the dry bulb and wet bulb is 3, what is the wet bulb temperature?

  22. Challenge question! • If the air temperature is 8 degrees C and the dewpoint is 3 degrees C, what is the difference between the DB and WB? • 1. 2 degrees C • 2. -5 degrees C • 3. 5 degrees C • 4. 1 degrees C

  23. One step further… • If we know the DB is 8 degrees C and the difference between the DB and WB is 2 degrees C, what is the wet bulb temperature?

  24. Real-time dewpoint temperature of room 1326 (on worksheet) • DB= • WB= • DB-WB= • Dewpoint=

  25. Finding relative humidity • Relative humidity (RH): the ratio of the amount of water vapor in the air to the maximum amount the air can hold • Unit for RH: %

  26. What RH means • If the RH is 50%, the air could hold 50% more moisture • As air temperature approaches DP (point of saturation), the RH approaches 100%

  27. If there are clouds/precipitation/dew/frost: a. air temp = dewpoint temp* b. RH= 100%* *or close to it

  28. Weather check! Ms. Whittaker's TeacherWeb Page On the maps… • Where would you expect the RH to be a high percentage and why? • Where would you expect the RH to be a low percentage and why?

  29. Steps For determining RH • Locate the dry-bulb reading on the left-hand side of the Relative Humidity chart • Subtract the wet-bulb reading from the dry-bulb reading • Locate the difference between the wet-bulb and dry-bulb readings across the top of the chart • Follow the horizontal row for the dry-bulb reading to the right until it meets the vertical column running down from the top

  30. Sample Problem- Index cards • Find the RH when the dry-bulb temperature is 20 degrees Celsius and the wet-bulb temperature is 20 degrees Celsius • 100% • 91% • 20% • 0%

  31. Sample problem- index cards • Find the RH when the dry-bulb temperature is 10 degrees Celsius and the wet-bulb temperature is 8 degrees Celsius • 1. 13% • 2. 76% • 3. 88% • 4. 24%

  32. Connections • How does the relative humidity in the first sample question compare to that found in the second sample question? • What connection can you make between the difference between the wet bulb and dry bulb temperatures and the relative humidity?

  33. Challenge question- Index cards • If the air temperature is 24 degrees C and the difference between the DB and WB is 10, what is the RH? • 1. 10% • 2. 24% • 3. 30% • 4. 9%

  34. One step further… • If the temperature is 24 degrees C and the difference between the WB and DB is 10 degrees C, what is the Wet Bulb Temperature?

  35. Connecting variables • If the air temperature is 14 degrees C and the relative humidity is 60%, what is the dewpoint temperature?

  36. What is the RH of this room? • DB= • WB= • DB-WB= • Relative Humidity=

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