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 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)

1.28 degrees Celsius2.26 degrees Celsius3.25 degrees Celsius4.24 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 3. -9 degrees C4. -14 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 determine2.18 degrees C3.17 degrees C4.16 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 4. -7 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 2. -5 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

1.100%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=