Moisture in the Air

Changes in States (Phases): s  l Freezing and melting l   g Condensation and evaporation s  g Sublimation Latent heat: heat energy ‘trapped’ in a state of matter. 80 + 600 calories g Heat absorbed! l Heat Released! s

Examples of: Condensation: dew, clouds, fog, drops on surfaces Evaporation: “drying off” Sublimation: snow disappearing, dry ice, frost

Sublimation Wind Condensation Precipitation Transpiration Runoff Releases Heat Precipitation Transpiration Runoff Evaporation Absorbs Heat Respiration Groundwater Aquifer

Moisture in the Air-Humidity What is humidity? Humidity is the moisture in the air. “Think of air like a sponge.” 2. Relative Humidity is the amount of moisture in the air compared to how much moisture that air could possibly hold at a certain temperature. Specific humidity vs. capacity. Expressed in %

3. Air at a certain temperature can hold only so much water 3. Air at a certain temperature can hold only so much water. See chart on page 501. a/ Warmer air can hold more water vapor. Air at 86F can hold 30 g b/ Colder air can hold less water vapor. Air at 32F can only hold 5 g

4. When air cools and its ability to hold water decreases it becomes saturated and condensation occurs. This occurs at 100% relative humidity. 5. The temperature at which water condenses out of the air is called the dew point temperature.

6. Relative Humidity Calculations: Amount of moisture in air (Specific humidity) x 100 = % RH Amount possible at temperature (capacity) Relative Humidity Problems: Find the RH of the air. 1/ Air at 86oF contains 15g of moisture but can only hold 30g. What is the RH? 2/ Air at 68oF contains 12g of moisture but can only hold 16g. What is the RH? 3/ Air at 68 oF contains 16g of moisture and can only hold 16g. What is the RH?

6. Relative Humidity Calculations: Amount of moisture in air (Specific humidity) x 100 = % RH Amount possible at temperature (capacity) Relative Humidity Problems: Find the RH of the air. 1/ Air at 86oF contains 15g of moisture but can only hold 30g. What is the RH? 2/ Air at 68oF contains 12g of moisture but can only hold 16g. What is the RH? 3/ Air at 68 oF contains 16g of moisture and can only hold 16g. What is the RH? 15g x 100 = 30g 50% RH 12g x 100 = 16g 75% RH 16g x 100 = 16g 100% RH Dew point Temp

7. Meteorologists use a Hygrometer(hair) or a Psychrometer (dry-wet bulb thermometer) to measure Relative humidity.

8. Rising Air masses and Relative humidity: Condensation and Dew Point An air mass which contains 7g of water vapor/ft3 rises into the upper troposphere. Calculate the RH of the air mass at each step shown. The amount of moisture that air can hold at a certain temperature is called the capacity (saturation point). It is shown in the table below: Temperature Capacity(saturated) 86oF 30.4g 68 oF 17.3g 60 oF 13.5g 50 oF 9.41g 40 oF 7.2g 32 oF 4.85g Temperature Specific Humidity Capacity %RH 1. 60oF 7g ? = ______% 2. 50oF 7g ? = ______% 3. 40oF 7g ? = ______% 4. 32oF 7g ? = ______% 5. At level 4. 6. Clouds-condensation (reaches dew point temperature).

8. Rising Air masses and Relative humidity: Condensation and Dew Point An air mass which contains 7g of water vapor/ft3 rises into the upper troposphere. Calculate the RH of the air mass at each step shown. The amount of moisture that air can hold at a certain temperature is called the capacity (saturation point). It is shown in the table below: Temperature Capacity(saturated) 86oF 30.4g 68 oF 17.3g 60 oF 13.5g 50 oF 9.41g 40 oF 7.2g 32 oF 4.85g Temperature Specific Humidity Capacity %RH 1. 60oF 7g 13.5 = 52% 2. 50oF 7g 9.41 = 74% 3. 40oF 7g 7.2 = 97% 4. 32oF 7g 4.85 = 100% 5. At level 4. 6. Clouds-condensation (reaches dew point temperature).

What is humidity? 7. Meteorologists use a Hygrometer(hair) or a Psychrometer (dry-wet bulb thermometer) to measure Relative humidity. 1st Find dry bulb and wet bulb temperatures after rotating psychrometer through the air. 2nd Calculate the difference between the dry and wet bulb temperatures. (subtract). 3rd Use chart on p501 to determine the relative humidity.

Dry Bulb Temp. Wet Bulb Temp. Difference % Rel. Humidity 20 C 16 C 14 C 11 C 15 C 12 C 18 C 18 C 13 C 8 C 14 C 13 C 17 C 15 C

D. Clouds 1. Cloud Formation a. Warm moist air is lighter than cold dry air. Warm moist air rises. b. Warmer air holds more water vapor than colder air. c. As you increase altitude temperatures decrease and it gets colder. Warmer air holds more water vapor. d. As warm moist air rises and it gets colder it can hold less water vapor and relative humidity increases. e. Eventually, the rising air mass gets to a colder temperature where the relative humidity reaches 100% and the air becomes completely saturated. This temperature is called the dew point temperature. f. This is when condensation occurs and water droplets come out of the air as clouds.

D. Clouds 1. Cloud Formation Warm moist air is lighter than cold dry air. Warm moist air rises. b. Warmer air holds more water vapor than colder air. c. As you increase altitude temperatures decrease and it gets colder. Warmer air holds more water vapor.

d. As warm moist air rises and it gets colder it d. As warm moist air rises and it gets colder it can hold less water vapor and relative humidity increases. e. Eventually, the rising air mass gets to a colder temperature where the relative humidity reaches 100% and the air becomes completely saturated. This temperature is called the dew point temperature. f. This is when condensation occurs and water droplets come out of the air as clouds.

2. The ingredients of a cloud are: 1/ Air 2/ Water vapor 3/ Change in T or P 4/ Condensation nucleii - dust

1/ Cumulus (Cu) Puffy, rising air, 2/ Stratus (St) layered, low 3. Cloud Types and Names (The Classification of Clouds): Three Main Types of Clouds are: 1/ Cumulus (Cu) Puffy, rising air, 2/ Stratus (St) layered, low 3/ Cirrus (Ci) feathery, high, ice

Prefixes/suffixes used to further describe cloud types are: 1/ Alto- (A) middle level 2/ Nimbus- (N) rain 3/ cumulo- (Cu) 4/ Cirro- (Ci)

Nimbostratus Cirrocumulos Altostratus Cirrus Altocumulus Cumulonimbus Cumulos

E. The Four Types of Precipitation are: 1/ Rain 2/ Snow 3/ Sleet-frozen rain 4/ Hail- from cumulonimbus clouds! Moisture 6 snow snow snow rain snow sleet rain