 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 (vapor from plants)

 Evapotranspiration = Evaporation + Transpiration

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

 EUREKA!!-Evaporation EUREKA!!-Evaporation  Transpiration- a flashback to biology Transpiration- a flashback to biology

 Dry Bulb Temperature (DB): Air temperature

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

 Sling psychrometer: instrument used to measure the dry bulb and wet bulb temperatures

 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?

 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

 Dewpoint (DP): the temperature to which air must be cooled for it to reach saturation

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

 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

 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) degrees Celsius degrees Celsius degrees Celsius degrees Celsius

 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 degrees C degrees C

 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?

 If the dry-bulb temperature is 19 degrees Celsius and the wet-bulb temperature is 17 degrees Celsius, find the dew point 1. Not possible to determine degrees C degrees C degrees C

 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  degrees C

 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?

 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  degrees C  3. 5 degrees C  4. 1 degrees C

 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?

 DB=  WB=  DB-WB=  Dewpoint=

 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: %

 If the RH is 50%, the air could hold 50% more moisture  As air temperature approaches DP (point of saturation), the RH approaches 100%

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

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?

 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

 Find the RH when the dry-bulb temperature is 20 degrees Celsius and the wet-bulb temperature is 20 degrees Celsius % 2. 91% 3. 20% 4. 0%

 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%

 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?

 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%

 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?

 If the air temperature is 14 degrees C and the relative humidity is 60%, what is the dewpoint temperature?

 DB=  WB=  DB-WB=  Relative Humidity=