How Do Clouds Form?
Clouds form when water evaporates from rivers, ponds, oceans, and lakes. The air containing this evaporated water vapor rises and expands at higher altitudes where the air pressure is lower. The expanding air cools, and as this cooling occurs, the water vapor condenses (changes) from a vapor to a liquid. Many tiny water droplets form and a cloud is born. Conditions have to be just right for clouds to form. Nature needs tiny droplets of water, something for the droplets to cling to (particles like dust, salt, or smoke) and the right temperature. A variety of cloud types form depending upon their height, air movement, and the amount of water vapor and condensation particles. The basic cloud types include the following: • Stratus (spread out or layered). These clouds are low to the ground and layered. • Fog is very close to the ground. • Stratus clouds may predict rain. • Cirrus (curly, wispy). These clouds are the highest and are made of ice crystals. They may predict a change in weather
Regardless of the type of cloud the basic principles that govern the forming of clouds are the same. Air containing water vapor rises, the water vapor condenses out of the air, and a visible body of water vapor, or cloud, forms. There are several types of clouds, but the basic classifications are stratus, cirrus, and cumulus. The first step of a cloud’s formation is evaporation, transpiration, and the heating of air. Evaporation and transpiration, collectively called evapotranspiration, are vital parts of the hydrologic cycle. Evaporation occurs when a body of water, like a lake or ocean, is heated by the sun so that the water of the surface sublimates, or turns into a vapor. During transpiration, plants “sweat” water through their leaves and stems as part of a cooling process. This water then turns to vapor and mixes with air. Similarly, water from the soil may also turn into vapor when exposed to heat and air. As a consequence of the ground and water surfaces becoming warm, the air n
National Science Standards: Content Standard A: Science As Inquiry Content Standard D: Earth and Space Science • Objects in the Sky • Changes in the Earth and Sky These activities encourage students to observe clouds and look for patterns. *NOTE: Activities increase in diffulculty. Educators/Parents may want to work through all activities or choose those most appropriate for their students/children. (BACKGROUND INFORMATION) What do we already know about clouds? • Clouds form when water vapor condenses (changes from a vapor to a liquid) around condensation particles (such as dirt, dust, and smoke). • Clouds can be categorized based upon their height and shape. • Three basic cloud types are stratus (low level, spread out), cumulus (puffy), and cirrus (high level, wispy). Activity One – Cloudy Weather This activity is modified and used with the permission of the AIMS Education Foundation, http://AIMSedu.org. It can be found in the AIMS Publication, Primarily Earth. notebook paper or a bla
Clouds are possibly the most interesting (and beautiful) of all weather phenomena. While there are a wide variety of cloud shapes and sizes, they are all made of the same thing: condensed water or ice. Clouds form when rising air, through expansion, cools to the point where some of the water vapor molecules “clump together” faster than they are torn apart by their thermal energy. Some of that (invisible) water vapor condenses to form (visible) cloud droplets or ice crystals. The cloud example pictured above is considered “convective”, because it is produced from warm air pockets rising directly (“convecting”) from the underlying surface. Convective clouds are typically smaller, a hundred yards to several miles across. “Stratiform” clouds, in contrast, typically cover much larger areas and are caused by much broader layers of more slowly rising air (see below), often associated with extratropical cyclone activity. Stratiform clouds have a more uniform, featureless appearance, and often
Objective In this experiment you will investigate how pressure in the atmosphere is linked to the formation of clouds by making a cloud chamber. Project Note: January 2009 It has come to our attention that there are problems with the Procedures in this project, and we can no longer recommend it as a good science fair project. If you need help choosing another project please try our Topic Selection Wizard. We apologize for any inconvenience. Introduction Why is it that on a cold day we can see our breath? The answer is that the air we breathe out contains moisture in the form of water vapor. When that warm, moist air meets the cold, dry air outside, a cloud forms. There must be three main ingredients present in order for clouds to form (UCAR, 2000): • Moisture – There must be sufficient water vapor in the air to build a cloud. • Cooling air – The air temperature must decrease enough for water vapor to condense. • Condensation nuclei – Tiny particles, invisible to the human eye, such as
