Aim: How can we Aim: How can we measure relative measure relative

humidity?humidity?Topic: Unit 6 MeteorologyTopic: Unit 6 Meteorology

Main Idea: Measuring Relative Main Idea: Measuring Relative HumidityHumidity

1) What is a sling 1) What is a sling psychrometer?psychrometer?

• It is an instrument with two It is an instrument with two thermometers used to measure thermometers used to measure relative humidity and dewpoint.relative humidity and dewpoint.

Dry BulbDry Bulb

• Measures air temperatureMeasures air temperature• Is always the Is always the higher temperaturehigher temperature• Measured in degrees CelsiusMeasured in degrees Celsius

Wet BulbWet Bulb

• The thermometer The thermometer with the clothwith the cloth

• Evaporation Evaporation occurs, this is a occurs, this is a cooling processcooling process

• Never higher Never higher than dry bulbthan dry bulb

• Measured in Measured in degrees Celsiusdegrees Celsius

3) What do the two 3) What do the two temperatures tell you about temperatures tell you about

the air?the air?• Close temperatures= high humidityClose temperatures= high humidity• Far apart temperatures= low humidityFar apart temperatures= low humidity

How do we use the charts on page How do we use the charts on page 12 of the earth science reference 12 of the earth science reference

tables?tables?• Step 1: Find the dry Step 1: Find the dry

bulb temp. on the left bulb temp. on the left sideside

• Step 2: Subtract the wet Step 2: Subtract the wet bulb from the dry bulbbulb from the dry bulb

• Step 3: Find the Step 3: Find the difference across the difference across the top of the charttop of the chart

• Step 4: See where the Step 4: See where the column and row meetcolumn and row meet

• What is the relative humidity if the What is the relative humidity if the dry bulb is 12dry bulb is 12ooC and the wet bulb is C and the wet bulb is 88ooC?C?

SummarySummaryDry Bulb: 20Dry Bulb: 20ooC Difference Between: C Difference Between:

88

Wet Bulb: ______ Relative Humidity: Wet Bulb: ______ Relative Humidity: ________________

Dry Bulb: 13Dry Bulb: 13ooC Wet Bulb: 10C Wet Bulb: 10ooCCRelative Humidity_____ Dewpoint Relative Humidity_____ Dewpoint

Temp. ______Temp. ______

Dry Bulb: 17Dry Bulb: 17ooC Relative C Relative Humidity: 63Humidity: 63ooCC

Wet Bulb: _______ Dewpoint Temp. Wet Bulb: _______ Dewpoint Temp. ______________

Exit Card Exit Card 1)1) What is the dewpoint What is the dewpoint temperature if the dry bulb temperature if the dry bulb

2121ooC and the wet bulb is C and the wet bulb is 1818ooC?C?

2)2) What is the relative What is the relative humidity if the dry bulb is humidity if the dry bulb is

99ooC and the wet bulb is C and the wet bulb is 77ooC?C?