Activity 6: Clouds & Precipitation

CLOUD FORMATION AND PRECIPITATION

Summary:

There are four main types of clouds and many forms of precipitation. In this activity we will explore cloud formation and precipitation by observing and recording weather data, as well as setting up our own "cloud chamber" to observe evaporated water vapor as it condenses and precipitates.

Instructional Method: Demonstration

Goal: To show students how clouds and rain are formed.

Objectives: Students will be able to:

• Match photos of clouds with the proper names.
• List at least 5 different forms of precipitation.
• Label condensation and precipitation on the Hydrology worksheet.
• Illustrate 5 steps in cloud formation, including: evaporation, rising/saturation, cooling, condensation, and precipitation.

Time:

Lecture- 5 steps of cloud formation (25 min)
Setup (15 min)
Activity (30 min)
Lecture - clouds with illustrations (30 min)

Materials Needed:

• Hot plate or other heat source
• Water
• Large glass or jar
• Ice
• Metal pan
• Stand to support inverted bowl over heated water
• Supporting overheads, cloud cards and visuals
• PDF Hydrology Worksheet

Vocabulary:

cirrus
condensation
cooling
cumulus
evaporation
nimbus
precipitation
saturation
stratus
water vapor

Background:

Warm, moist air rises from Earth's surface. As it rises it begins to cool, raising the Relative Humidity of the air. When the relative humidity reaches 100%, the air is saturated with water. When this happens, water begins to condense in the atmosphere, and clouds begin to form.

The type of cloud formed is dependent on several weather factors including air temperature, relative humidity, wind speed, and air pollution. Most meteorologists agree that water could stay in the atmosphere as humidity indefinitely. Impurities in the air such as dust, smoke or air pollution attract and hold water molecules together forming large droplets. Clouds form as the air reaches saturation and droplets begin to form around these impurities.

The four main types of clouds are:

• Cirrus: Wispy clouds high in the atmosphere, made almost entirely out of ice crystals. Cirrus clouds rarely ever produce rain.
• Nimbus: Rain producers. Always occur in conjunction with another type of cloud; i.e. there is no "nimbus" cloud, however there is a cumulonimbus and a nimbostratus cloud type.
• Stratus: Flat layer, uniform base. In mountains, these clouds are responsible for fog. Not a very dense cloud- usually the sun can be seen through them.
• Cumulus: Fair weather clouds. These puffy bright white clouds are often detached from each other. They have flat bases and round or domed tops resembling cauliflower. The bases of these clouds can sometimes merge creating the appearance of one large cloud. When this happens, cumulus clouds can produce thunderstorms.

As all clouds types form, water droplets bump into each other forming larger water droplets. Eventually, the water droplets become too heavy to remain suspended in the clouds, and gravity pulls them to the surface. This process is called precipitation.

Precipitation occurs in many forms, most commonly rain, but also as snow, sleet, hail and virga (desert rain that evaporates before it hits the ground). Even fog and dew are considered to be precipitation.

In this activity we will explore cloud formation and precipitation by observing and recording weather data, as well as setting up our own "cloud chamber" to observe evaporated water vapor as it condenses and precipitates.

Instructional Procedures:

1. Place water into metal pan, and turn on the hot plate. Do not allow the water to boil. It needs to warm. (This will simulate and speed up the idea of evaporation.)
2. Place an inverted container into the water.
3. Place ice or a cold pack on top of the inverted glass bowl or aquarium as soon as you have turned on the hotplate. Waiting too long may cause the glass container to break.
4. Let the water warm and observe container sides for any condensation.
5. As the water evaporates it rises. As it is captured at the top of the bowl, the air begins to saturate, and at the same time the vapor starts to cool.
6. You should start to see vapor condensing on the inside top of the bowl. As the water continues to accumulate, droplets grow too heavy to remain suspended in the bowl and fall into the pan of water below. This is precipitation.

Discussion:

What is happening to the water? From where did the falling water come? How did it get there? What is evaporation? What does it mean to be saturated (see sponge activity in the landform unit for an additional saturation activity)? Does air get hotter or colder as it rises in the earth's atmosphere? How does what we just did in the classroom apply in nature? What happens to precipitation in nature? Where does the water go? What is virga, and how does that happen?

Extension:

Using the overheads and cloud cards, define each basic type of cloud and explain the characteristics of each. Keep a cloud calendar in the classroom, check the weather outside each day, and identify the types of clouds observed and any significant weather for the day. Write it on the calendar. You can also repeat the activity but add a little salt into the water, and then catch some of the precipitation and taste it. Why isn't it salty?

Discussion:

Which types of clouds do we see most often? Will this change as the season changes? Which types of clouds produce rain? Which clouds are primarily ice crystals and seldom rain? Do we ever see more than one kind of cloud in the sky at the same time? What happens then? What time of day did we see the most clouds? In the afternoon? Why is that? (Lead them back to the idea that heat = evaporation = cloud formation and the afternoon is when it is the hottest.)

Included National Parks and other sites:

Bryce Canyon National Park
Everglades National Park
Mount Rainier National Park

Photos:

Cumulus Clouds Over Table Cliffs
Storm Building at Bryce Canyon

Utah Science Core:

Kindergarten Standard 3 Objective 1
1st Grade Standard 3 Objective 1,2
1st Grade Standard 5 Objective 1
2nd Grade Standard 2 Objective 2
4th Grade Standard 1 Objective 1,2
4th Grade Standard 2 Objective 1,2,3
5th Grade Standard 1 Objective 2

 

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