Do You Remember? 1. Which heats faster: land or water? 2. What causes the transfer of energy (heat) from one object to another? 3. Which has greater temperature variation: land or water?

Moisture, Clouds and Precipitation 2.5.4c Explain the importance of water vapor and its influence on weather (clouds, relative humidity, dew point, precipitation).

Objectives Today I will be able to: ◦ Evaluate the most important gas in the atmosphere. ◦ Compare and contrast saturation and relative humidity.

Key Points - Moisture Water vapor is the most important gas for understanding atmospheric processes. Water vapor makes up 0-4 % of atmospheric gases. Air that has reached its water vapor capacity is said to be saturated. Warm, saturated air contains more water vapor than cold air. Relative humidity is the ratio of air’s water-vapor content to its capacity to hold water vapor at that same temperature.

Water in the Atmosphere Water exists in three different forms. What are they? 1.SOLID Examples: Snow, ice 2.LIQUID Examples: Rain, water 3.GAS Examples: Clouds, water vapor How do each of these forms of water influence weather?

Water in the Atmosphere  When it comes to understanding atmospheric processes, water vapor is the most important gas in the atmosphere.  Why do you think water vapor is so important?

Water in the Atmosphere Even though water vapor is important, it only makes up from 0 – 4% of the atmospheric gases. When have you felt water vapor at close to 4%? What about 0%? How do you know? ◦ Water vapor is the HUMIDITY that you feel in the air!

Water in the Atmosphere What do you think the word “SATURATED” means? What do you think it would mean if air is Saturated? Air that has reached its water vapor capacity is said to be saturated.

Water in the Atmosphere Warm, saturated air contains more water vapor than cold air. Dew point is the temperature to which air is cooled to reach saturation. ◦ The point at which condensation can occur When have you noticed the humidity more, in the summer or in the winter? That’s because warm air can hold more water vapor!

Water in the Atmosphere Relative humidity is the ratio of air’s water- vapor content to its capacity to hold water vapor at that same temperature. Relative humidity indicates how near the air is to saturation, not the actual quantity of water vapor in the air. Relative Humidity varies with temperature. Cooling air increases its relative humidity. Warming air decreases its relative humidity.

Water in the Atmosphere Relative Humidity – Why does lowering the air temperature cause Relative humidity to increase? ◦ Because colder air cannot hold as much water vapor! Why does increasing air temperature cause relative humidity to decrease? ◦ Because warm air can hold more water vapor and it will take more water vapor for it to become saturated. ◦ Why is it important to know humidity? Why is it important to know humidity?

Vocabulary and Questions Define the following terms: Water vapor Saturation Relative humidity Answer the following questions: 1. What gas is most important for understanding atmospheric processes? 2. Water vapor makes up what fraction of atmospheric gases? 3. Which holds more water vapor: warm air or cool air? 4. How is the humidity different from the summertime to the wintertime?

Matching- answer a, b or c for each of the situations. Situation 1. Water vapor is added 2. Air temperature decreases 3. Water vapor is removed 4. Air temperature increases Change in Relative Humidity: A. Increases B. No change C. decreases

Follow up 1. Air that has reached its water-vapor capacity is said to be: a. Dry b. unstable c. stable d. saturated 2. The ratio of air’s water content to its capacity to hold water at the same temperature is: a. Vapor pressure b. relative humidity c. specific humidity d. wet adiabatic rate 3. Water vapor makes up what fraction (%) of atmospheric gases?

Objectives I will be able to: ◦ Describe how air is lifted to form clouds. ◦ Differentiate between the different types of clouds by making a poster. ◦ Describe the weather associated with the different types of clouds.

Key Points - Clouds When air is compressed the air temperature rises and the air molecules move faster. Processes that lift air include orographic lifting, frontal wedging and convergence. Examples of condensation nuclei include dust, smoke and salt particles. Nimbus means “rainy cloud”. Cumulonimbus clouds are often associated with thunder and lightning.

Cloud Formation Cloud Formation When air is allowed to expand, it cools, and when it is compressed, it warms.  When air is compressed the air temperature rises and the air molecules move faster.  Air compression causes temperature changes even though heat isn’t added or subtracted.

Cloud Formation Clouds form because as you go up in elevation, it gets colder. Cold air cannot hold as much water vapor so it transforms into clouds. Cool, expanded air Warm, compressed air

Cloud Formation  Four mechanisms that can cause air to rise are orographic lifting, frontal wedging, convergence, and localized convective lifting.  Fill out each box with the underlined words and a picture as we discuss them. Orographic lifting occurs when mountains act as barriers to the flow of air, forcing the air to ascend. 1. Orographic Lifting

Cloud Formation A front is the boundary between two adjoining of air masses having contrasting characteristics. 2. Frontal Wedging Processes that lift the air How does the relatively flat central region of the US receive precipitation?

Orographic Lifting and Frontal Wedging 1. Orographic Lifting 2. Frontal Wedging

Cloud Formation Cloud Formation Convergence is when air flows together and rises. 3. Convergence Localized convective lifting occurs where unequal surface heating causes pockets of air to rise because of their buoyancy. 4. Localized Convective Lifting Processes That Lift Air

Convergence and Localized Convective Lifting 3. Convergence 4. Localized Convective Lifting

Cloud Formation Cloud Formation  For any form of condensation to occur, the air must be saturated. Generally, there must be a surface for water vapor to condense on.  Types of Surfaces Condensation nuclei are tiny bits of particulate matter that serve as surfaces on which water vapor condenses when condensation occurs in the air. Examples of condensation nuclei include dust, smoke and salt particles. Condensation – How clouds form

Cloud Types and Precipitation  Clouds are classified on the basis of their form and height. Types of Clouds

Cloud Types and Precipitation  There are three basic forms of clouds. All other clouds one of these three or are combinations or modifications of them. 1.Cirrus (cirrus = “curl of hair”) are clouds that are high, white, and thin. 2.Cumulus (cumulus = “a pile”) are clouds that consist of rounded individual cloud masses. 3.Stratus (stratus = “a layer”) are clouds best described as sheets or layers that cover much or all of the sky. Types of Clouds by Form

Cloud Types and Precipitation What type of cloud is this? Cirrus

Cloud Types and Precipitation What type of cloud is this? Cumulus

Cloud Types and Precipitation Cloud Types and Precipitation What type of cloud is this? Stratus

Cloud Types and Precipitation 1. High Clouds Cirrus clouds are high, white, and thin. Cirrostratus clouds are flat layers of clouds. Cirrocumulus clouds consist of fluffy masses. 2. Middle Clouds – “Alto” Altostratus clouds create a uniform white to gray sheet covering the sky with the sun or moon visible as a bright spot. Altocumulus clouds are composed of rounded masses that differ from cirrocumulus clouds in that altocumulus clouds are larger and denser. Types of Clouds by Height

Cloud Types and Precipitation 3. Low Clouds Stratus clouds are best described as sheets or layers that cover most of the sky. Nimbostratus clouds are the main precipitation makers. Stratocumulus clouds have a scalloped bottom that appears as long parallel rolls or broken rounded patches. Types of Clouds by Height

Cloud Classification

Answer the following 1. What happens when air is compressed? a. Air temperature rises. b. Air temperature cools. c. Air molecules move faster. d. both a and c 2. What term means “rainy cloud”? a. stratus b. nimbus c. cumulus d. cirrus 3. Name one example of condensation nuclei: