Weather and ClimateWeather and Climate

Chapter 2Chapter 2

February, 2011 February, 2011

Bell WorkBell Work

What is condensation?What is condensation?

What is dew point?What is dew point?

Can you find dew in the air?Can you find dew in the air?

What is weather?What is weather?

WeatherWeather– A condition in the atmosphere at a A condition in the atmosphere at a particularparticular

time and placetime and place

Water in the AirWater in the Air

1. Water in the air effects 1. Water in the air effects weatherweather

2. Forms of water in the air2. Forms of water in the air– A.A. Gas Gas

As water vaporAs water vapor

– B. SolidB. Solid IceIce (snowflakes) (snowflakes)

– C.C. Liquid Liquid rainrain

Water CycleWater Cycle

1. 1. ConstantConstant movement of water from land to movement of water from land to air and back to land againair and back to land again

2. Precipitation-2. Precipitation-– ““Let it Snow” labLet it Snow” lab

““Let it Snow Lab”Let it Snow Lab”

Follow DirectionsFollow Directions Equipment needed is at the lab stationsEquipment needed is at the lab stations Lab Safety?Lab Safety?

““Let it Snow”Let it Snow”

Graduated CylinderGraduated Cylinder

““Let it Snow”Let it Snow”

BeakerBeaker

““Let it Snow” Let it Snow” RulesRules

1. No throwing snow1. No throwing snow 2. No walking in the snow2. No walking in the snow 3. No eating snow……….yuck!!!!!!!!3. No eating snow……….yuck!!!!!!!! 4. Act like MATURE 74. Act like MATURE 7thth graders. graders.

Water Cycle ReviewWater Cycle Review

1. 1. CondensationCondensation– Water vapor cools and changes back into liquid droplets Water vapor cools and changes back into liquid droplets

(how clouds form)(how clouds form) 2. Evaporation2. Evaporation

– Liquid waterLiquid water changes into changes into water vaporwater vapor 3. 3. TranspirationTranspiration

– Plants release water vapor into the airPlants release water vapor into the air 4. Precipitation4. Precipitation

– RainRain, , snowsnow, , sleetsleet, or , or hailhail falls from the clouds to Earth’s falls from the clouds to Earth’s surfacesurface

HumidityHumidity

1. Humidity (pg. 37) in book1. Humidity (pg. 37) in book– Amount of Amount of water vaporwater vapor or or moisturemoisture in the air in the air

2. As water 2. As water evaporatesevaporates – Humidity of the air increasesHumidity of the air increases

33. Warmer. Warmer air holds air holds moremore water vapor water vapor 4. 4. ColderColder air holds air holds lessless water vapor water vapor

Relative HumidityRelative Humidity

1. Relative Humidity1. Relative Humidity– AmountAmount of moisture the air holds compared to the of moisture the air holds compared to the

maximummaximum amount it can hold at that temperature amount it can hold at that temperature

Amount of water in the air Amount of water in the air ÷÷ Amount of water the air can hold x 100Amount of water the air can hold x 100

2. Saturated 2. Saturated – When air holds all the water that it can When air holds all the water that it can holdhold at that at that

temperaturetemperature– Saturated air has a relative humidity of Saturated air has a relative humidity of 100%100%

Water Vapor Versus TemperatureWater Vapor Versus Temperature 1. If the temperature stays the same-1. If the temperature stays the same-

– Relative humidity Relative humidity changeschanges as water vapor as water vapor entersenters and and leavesleaves the air the air

2. The more 2. The more water vaporwater vapor that is in the air that is in the air– The The higherhigher the relative humidity is the relative humidity is

3. Relative humidity is affected by 3. Relative humidity is affected by changeschanges in the temperaturein the temperature– If water vapor in the air If water vapor in the air stays the samestays the same,,

Relative humidity Relative humidity ↓↓ as temperature as temperature ↑↑ Relative humidity Relative humidity ↑↑ as temperature as temperature ↓ ↓

Bell WorkBell Work

What is relative humidity?What is relative humidity?

Does warm air hold (more or less) water Does warm air hold (more or less) water vapor than cold air?vapor than cold air?

Measuring Relative HumidityMeasuring Relative Humidity

1. Psychrometer1. Psychrometer 2. Instrument used to 2. Instrument used to

measuremeasure relative relative humidity humidity

Measuring Relative HumidityMeasuring Relative Humidity

1. 1. Sling Sling PsychrometerPsychrometer 2. Has 2 thermometers2. Has 2 thermometers

– A. DryA. Dry bulb measures bulb measures temperaturetemperature

Measuring Relative HumidityMeasuring Relative Humidity Sling PsychrometerSling Psychrometer

– B. Wet bulb is covered with B. Wet bulb is covered with a damp clotha damp cloth

– C. As air passes C. As air passes overover the the wet-bulb, the water in the wet-bulb, the water in the cloth begins to cloth begins to evaporate,evaporate, and the thermometer begins and the thermometer begins to to coolcool

– D. If there is D. If there is lessless humidity in humidity in the air, the water in the cloth the air, the water in the cloth will evaporate will evaporate moremore quickly quickly and the temperature will and the temperature will dropdrop

– E. If there is E. If there is moremore humidity humidity in the air, the water in the in the air, the water in the cloth will evaporate cloth will evaporate lessless and and there will be little there will be little temperature changetemperature change

Measuring Relative HumidityMeasuring Relative Humidity

Amount of water in the air Amount of water in the air ÷÷

Amount of water the air can hold x 100Amount of water the air can hold x 100

Measuring Relative HumidityMeasuring Relative Humidity

1. Psychrometer1. Psychrometer

-a. Find the -a. Find the dry bulbdry bulb

readingreading

-b. Find the -b. Find the wet bulbwet bulb

readingreading

-c. Find the -c. Find the differencedifference

-d. Find RH-d. Find RH

Bell WorkBell Work

1. Which 1. Which

Bell WorkBell Work

Fill in the blanksFill in the blanks If the humidity is low, a ______amount of If the humidity is low, a ______amount of

water will evaporate from a wet-bulb water will evaporate from a wet-bulb thermometer and the _____ between the thermometer and the _____ between the wet-bulb reading and the dry-bulb reading of wet-bulb reading and the dry-bulb reading of the psychrometer will be high.the psychrometer will be high.

If the dry bulb reads 10 C, and the If the dry bulb reads 10 C, and the difference between the thermometers is 8 C, difference between the thermometers is 8 C, the relative humidity is_______.the relative humidity is_______.

CondensationCondensation

1. Process when a 1. Process when a gasgas, , like water vapor, becomes like water vapor, becomes a a liquidliquid

2. Before condensation 2. Before condensation can occur, the air must be can occur, the air must be saturatedsaturated: it must have a : it must have a relative humidity of relative humidity of ___100%________100%_____

3. Condensation occurs 3. Condensation occurs when when saturatedsaturated air air coolscools

Dew PointDew Point

1. Air can become 1. Air can become saturatedsaturated when water when water vapor is added to the air……vapor is added to the air……

or when it or when it coolscools to its dew point to its dew point

2. Dew Point-2. Dew Point-

temperature to which temperature to which air air must must coolcool to to become saturatedbecome saturated

Example……Example……

Dew PointDew Point

3. Before it can 3. Before it can condensecondense,,

water vapor must have water vapor must have a a surfacesurface to condense to condense onon

Bell WorkBell Work

What is condensation?What is condensation?

What is dew point?What is dew point?

Can you find dew in the air? Can you find dew in the air?

Making DewMaking Dew

1.1. The ice brought the temperature of the can The ice brought the temperature of the can down to dew point and the moisture in the down to dew point and the moisture in the air condensed.air condensed.

2.2. It formed from the water vapor in the air.It formed from the water vapor in the air.

3.3. The other items in the room were not at The other items in the room were not at dew pointdew point

4.4. It is the temperature at which dew forms.It is the temperature at which dew forms.

5.5. LowerLower

Making DewMaking Dew

6. All the items would be wet.6. All the items would be wet.7. When you take a hot shower or bath, you 7. When you take a hot shower or bath, you

add moisture to the air and it condense on add moisture to the air and it condense on the cold mirror.the cold mirror.

8.At night, these things cool down to the dew 8.At night, these things cool down to the dew point temperature and the water vapor in the point temperature and the water vapor in the condenses on them.condenses on them.

9. No, not all things can cool down to dew 9. No, not all things can cool down to dew point.point.

Making DewMaking Dew

10. Dew does not fall, it forms10. Dew does not fall, it forms

11. It evaporates11. It evaporates

Making FrostMaking Frost

1. It formed from water vapor in the air1. It formed from water vapor in the air 2. Yes2. Yes 3. The temperature of the can was below 3. The temperature of the can was below

freezing pointfreezing point 4. Both are formed from water vapor in the 4. Both are formed from water vapor in the

air. They both form on cool surfaces.air. They both form on cool surfaces. 5.Dew is a liquid. Frost is a solid.5.Dew is a liquid. Frost is a solid.

Making FrostMaking Frost

6. No. Frozen dew would look like frozen drops of 6. No. Frozen dew would look like frozen drops of water. Frost is made of tiny crystals. When dew water. Frost is made of tiny crystals. When dew forms and then freezes, frozen dew is created. forms and then freezes, frozen dew is created. Frost is formed when water vapor turns directly Frost is formed when water vapor turns directly into a solid, skipping the liquid phase. into a solid, skipping the liquid phase. (sublimation)(sublimation)

7. Dew is formed when water vapor in the air 7. Dew is formed when water vapor in the air condenses of surfaces that have cooled down to condenses of surfaces that have cooled down to dew point. Frost is formed at freezing pointdew point. Frost is formed at freezing point

Making FrostMaking Frost

8. Frost forms on objects at Earth’s surface. 8. Frost forms on objects at Earth’s surface. Snow forms in the atmosphere and falls to Snow forms in the atmosphere and falls to the ground.the ground.

9. Snow9. Snow

CloudsClouds

Clouds-Clouds-– Are a collection of millions of tiny water droplets Are a collection of millions of tiny water droplets

or ice crystalsor ice crystals