Cloud Formation

CLOUD FORMATION Students will be able to: Ø Describe clouds Ø Describe steps in cloud formation Ø Identify the different types of clouds Ø Explain the role of water cycle in cloud formation CLOUD FORMATION Key Vocabulary Ø Cirrus clouds Ø Cloud Ø Cloud Condensation Nuclei (CCN) Ø Cumulus clouds Ø Dew point Ø Nimbus clouds Ø Saturated Ø Stratus clouds CLOUD FORMATION CLOUD FORMATION It is a common misconception that clouds are made up of water vapor. Water vapor is invisible and it is in the air all the time. On the other hand, clouds are visible collection of water or ice crystals in the air. CLOUD FORMATION Clouds appear when there is too much water vapor for the air to hold. The sun’s rays heat up the ocean and other bodies of water causing them to evaporate. Through evaporation, water vapor rises to the air. CLOUD FORMATION When air rises, it cools and as it goes higher, it gets colder too. Cold air cannot hold as much water vapor than warm air. As the air cools, it becomes saturated or holding as much water or moisture as can be absorbed. CLOUD FORMATION As the air becomes saturated, the water vapor in it condenses, which means it turns from a gas to a liquid. When the water vapor turns to a liquid in the sky, it forms a lot of tiny little water droplets, which cling to little bits of dust. CLOUD FORMATION Therefore, clouds can be described as the visible accumulation of water droplets or ice crystals on Earth’s surface. The water cycle plays an important role in the cloud formation. CLOUD FORMATION Condensation is one of the important processes in water cycle. Without condensation, the water cycle would not be in motion. The molecules in water vapor are farthest apart and most randomly arranged, but as water vapor cools, the molecules become more condensed and structured, forming clouds. CLOUD FORMATION Aside from water, another important component for clouds to form are the cloud condensation nuclei (CCN). These are microscopic particles suspended in the air, such as dust, ash, or salt crystal, on which water vapor condenses. This is why they are also called as cloud seeds. CLOUD FORMATION When the air is saturated with water vapor, some water vapor clings on to dusts and other microscopic particles on which it starts to condenses. As it condenses, water droplets are formed. These water droplets accumulate and get bigger and bigger, until they form clouds. CLOUD FORMATION But having water attracting nuclei is not enough for a cloud to form as the air temperature needs to be below the saturation point. Dew point is the temperature to which air must be cooled to become saturated with water vapor. It is the point of saturation where evaporation equals condensation. CLOUD FORMATION Therefore, a cloud results when a block of air containing water vapor has cooled below the point of saturation. As a bubble of air rises it moves into lower pressure since pressure decreases with height. As a result, the bubble of air expands in size as it rises. CLOUD FORMATION Once the bubble of air reaches saturation temperature or 100% relative humidity, water vapor will condense onto the cloud condensation nuclei resulting in the formation of a cloud droplet. However, the atmosphere is in constant motion. CLOUD FORMATION As air rises, drier air is added into the rising bubble of air so both condensation and evaporation are continually occurring. As a result, cloud droplets are constantly forming and dissipating. CLOUD FORMATION Therefore, clouds form and grow when there is more condensation on nuclei than evaporation from nuclei. Conversely, the dissipate if there is more evaporation than condensation. Thus, clouds appear and disappear as well as constantly change shape. CLOUD FORMATION Comprehension Check… Answer the following questions. 1. Describe clouds. 2. How are clouds form? 3. Can clouds form in a dustless, pollution-free place? Why or why not? CLOUD FORMATION Comprehension Check… Answers Answer the following questions. 1. Describe clouds. Clouds are visible accumulation of liquid water and ice crystals that are suspended in the air. 2. How are clouds form? Clouds are formed when water vapor condenses or crystallize into ice, and they cling on to dust and other microscopic particles that allow them to accumulate and be suspended in the air. 3. Can clouds form in a dustless, pollution-free place? Why or why not? It is possible but the process might take longer than usual as dust and pollutants aid in the cloud formation. TYPES OF CLOUDS CLOUD FORMATION Because certain types of clouds are associated with certain types of weather, it is possible to forecast the weather by observing and understanding these different types of clouds. Clouds are classified into three main groups: ¡ cirrus ¡ stratus ¡ cumulus CLOUD FORMATION Cirrus clouds are wispy, curly, or stringy. They are found high in the atmosphere—typically higher than 6,000 meters (20,000 feet)— and are usually made of ice crystals. Cirrus clouds usually signal clear, fair weather. Their shape often indicates the direction the wind is blowing high in the atmosphere. CLOUD FORMATION Stratus clouds are horizontal and stratified or layered. Stratus clouds can blanket the entire sky in a single pattern. They usually occur close to the Earth. Stratus clouds often form at the boundary of a warm front, where warm, moist air is forced up over cold air. CLOUD FORMATION This movement produces clouds as the moist air is cooled across the entire front. The presence of stratus clouds usually means a chilly, overcast day. If precipitation falls from stratus clouds, it is usually in the form of drizzle or light snow. CLOUD FORMATION Cumulus clouds are large and lumpy. Their name comes from the Latin word meaning “heap” or pile”. They can stretch vertically into the atmosphere up to 12,000 meters (39,000 feet) high. Cumulus clouds are created by strong updrafts of warm, moist air. CLOUD FORMATION Most forms of heavy precipitation fall from cumulus clouds. The weather they bring depends on their height and size. The higher the base of a cloud is, the drier the atmosphere and the fairer the weather will be. Clouds located close to the ground mean heavy snow or rain. CLOUD FORMATION Clouds are also classified according to how high they are in the atmosphere and what kind of weather they produce. The prefix “cirro–” refers to clouds that lie more than 6,000 meters above the Earth. Cirrocumulus and cirrostratus clouds are two examples of these “high-level” clouds. CLOUD FORMATION The prefix “alto–” indicates clouds whose bases are between 2,000 and 6,000 meters above the Earth, such as altocumulus and altostratus clouds. They are considered “mid-level” clouds and are mostly made of liquid water droplets, but can have some ice crystals in cold enough temperatures. CLOUD FORMATION The prefix “nimbo–” or the suffix “–nimbus” are low-level clouds that have their bases below 2,000 meters above the Earth. “Nimbus” comes from the Latin word for “rain”. Clouds that produce rain and snow fall into this category. CLOUD FORMATION Nimbostratus clouds bring continuous precipitation that can last for many hours. These low-level clouds are full of moisture. Cumulonimbus clouds are also called thunderheads. These clouds produce rain, thunder, and lightning. CLOUD FORMATION Many cumulonimbus clouds occur along cold fronts, where cool air is forced under warm air. They usually shrink as evening approaches, and moisture in the air evaporates. Cumulonimbus clouds gradually become stratocumulus clouds, which rarely produce rain. CLOUD FORMATION Comprehension Check… Decide whether the statement is true or false. 1. Clouds are classified into three main groups —cirrus, stratus, and nimbus. 2. Most forms of heavy precipitation fall from cumulus clouds. 3. Stratus clouds are wispy, curly, or stringy. 4. Nimbostratus clouds bring continuous precipitation that can last for many hours. 5. Altocumulus and altostratus are considered mid-level clouds. CLOUD FORMATION Comprehension Check… Answers Decide whether the statement is true or false. 1. Clouds are classified into three main groups —cirrus, stratus, and nimbus. False 2. Most forms of heavy precipitation fall from cumulus clouds. True 3. Stratus clouds are wispy, curly, or stringy. False 4. Nimbostratus clouds bring continuous precipitation that can last for many hours. True 5. Altocumulus and altostratus are considered mid-level clouds. True