In this lab, students learn about three-dimensional aspect of the atmosphere. Air operating both horizontally and vertically results in a mosaic of weather phenomena. Through a hands-on experiment, students will learn how the weather variables dew point and humidity (moisture) result in cloud formation. Continuing the multi-dimensional profile of the atmosphere, students examine adiabatic lapse rate and environmental lapse rate. Water plays a key role in our climate system, thus students explore water vapor in the atmosphere. The water study leads to an overview of how thunderstorms form. An on-line thunderstorm simulator allows students to view how large convective clouds form.
Students will learn the following: • How the vertical and horizontal profiles move in the atmosphere • How dew point and humidity (as well as conduction and convection as forms of heat transfer influence cloud formation) • How adiabatic and environmental lapse rate operate in the atmosphere • How moist air influences the atmosphere • How thunderstorms are formed
CONTEXT FOR USE
The format suggested for this lesson is a lab. This lab requires some lab equipment, and thus would work best in a lab room; or in a seminar room with precautions taken (towels, nearby access to a heat source and a place to temporarily store ice, other necessary materials). Access to a SmartBoard or LCD projector is necessary for the thunderstorm simulator. See “Description and Teaching Materials” below for link to the source lab.
ACTIVITY DESCRIPTION AND TEACHING MATERIALS
Below is a brief description of the terms and concepts covered in the lab (see link below for lecture notes):
· A key concept is the vertical motion of air parcels, a process known as convection. Convection is a form of heat transfer where the vertical distribution of heat by convection affects the vertical profile of temperature in a gas or liquid (which will be explored in a hands-on activity). This movement creates clouds, removes pollutants away from the Earth’s surface, and helps mix the atmosphere.
· The transfer of heat in matter through molecular motion requires actual contact between two objects. This process is called conduction. As water parcels near the bottom warm, they become less dense than the surrounding fluid and rise. The same process occurs in the atmosphere. Here the ground acts like the metal base of the kettle, and air parcels replace the water. During the day, the ground warms up because it absorbs the Sun’s radiation. Air parcels in contact with the ground warm up by conduction, become lighter than their surroundings, and rise. At night, the ground loses its heat by radiation, the air parcels come in contact with it and become denser than they were before.
I. Hands-on Lab - Cloud Formation
Purpose: Understand the key ingredients for the formation of clouds in the Earth’s atmosphere.
Pre-lab discussion questions:
· As air is compressed (squeezed), will it become warmer, or will it become cooler?
· As air rises, will it be compressed, or will it expand? How will this affect its temperature?
· What are “condensation nuclei” (small particles or aerosol upon which water vapor attaches to initiate condensation)? Give two examples (dust particulates, sea salt, sulfur and nitrogen oxide aerosols).
1. Fill the cup near the top with cold water and then pour it into the plastic bottle. Use a funnel if one is available. Firmly screw on the lid. Shake the bottle vigorously for 30 seconds. Squeeze the bottle for several seconds to increase the pressure, and then release it to allow the air inside to expand. Squeeze and release several times as you watch the air in the bottle. Record observations.
2. Unscrew the cap from the bottle. Light a match, blow it out, and then hold the smoking match inside the tilted bottle for about 2 seconds. Quickly replace the cap. Squeeze and release as you did in procedure #1. Record observations.
3. Empty the cold water from the bottle, and pour (use funnel) a cup of very hot tap water into it. Replace the cap, and shake the bottle for 30 seconds. Squeeze, release, and observe. Record observations.
4. Unscrew the cap, and hold a match into the bottle as you did in procedure #2. Quickly replace the cap, and then squeeze, release, and observe. Record observations.
· Which of your four trials resulted in the best cloud formation?
· Was cloud formation more impressive when smoke particles were present in the bottle?
· Did the cloud appear when you caused high pressure on the air in the bottle (by squeezing), or when you caused low pressure (by releasing)?
· Which provided more vapor in the bottle . . . the hot water, or the cold water?
· In your experiment, what served as the “condensation nuclei”?
· Why did the cloud disappear when you squeezed the bottle? You must use the term “dew point” (the temperature at which the air can no longer hold all of its water vapor, and some of the water vapor must condense into liquid water) in your answer.
· Identify the letters of the five situations listed below that would contribute to cloud formation (support your responses):
a. Moist air is forced upward as it encounters the Cascade Mountain Range.
b. Tomorrow’s forecast calls for an area of high pressure to be centered over your region.
c. The westerlies cause air to flow down the east side of the Rockies into Cut Bank, Montana.
d. During the afternoon, air over a large air force base begins to rise because it is so much hotter than air over the surrounding forest.
e. In autumn, the Santa Ana winds blow down from the mountain slopes of interior California out to the sea.
f. Intensely heated air over the equator rises in an area called the intertropical convergence zone.
g. As part of the global circulation pattern, air 30 degrees north of the equator is sinking in an area called the horse latitudes.
h. An intense low pressure system moves across the Midwest.
i. A cold air mass from Canada pushes into a mass of warm humid air over Nebraska.
· How do particles such as smoke or dust help clouds form? (What is their role?)
II. Description of terms and concepts, continued:
The first law of thermodynamics is a physical law that extends the principle of conservation of energy to include heat and work. In thermodynamics the simplest form of energy conservation is the balance of between internal energy and the amount of heat added to the body minus work done by the body on its surroundings. Adiabatic expansion results in cooling due to the lowering of pressure, density, and temperature in a parcel. The opposite, warming, occurs when the parcel is compressed.
The balance between the force of pressure and gravity is the hydrostatic balance.
The rate of change of temperature with height in a dry air parcel, the adiabatic lapse rate, is fixed. The measured local vertical profile of temperature in the air is called the environmental lapse rate.
Atmospheric water plays an extremely important role in the climate system due to three outstanding properties: vapor absorbs infrared radiation; vapor acts as a reservoir of heat; and in its condensed phase in the atmosphere, as water droplets, form clouds and absorbs infrared radiation, and reflects this radiation back into space.
Moist air contains water in its vapor form. When air containing water vapor is lifted up it begins to cool in the dry adiabatic lapse rate; but when it reaches its due point temperature, saturation occurs, and water droplets begin to condense inside the rising parcel, forming a cloud.
Moist air is less stable than dry air because of latent heat involved in moist convection. Clouds and rain are the visible aspect of the convection process. For thunderstorms to form, differential warming - heating one parcel more than the neighboring ones, and the instability it triggers - causes vertical motion.
III. Thunderstorm Simulation
Students view the thunderstorm simulator. The simulator demonstrates how the properties of conduction and convection, when working in concert, result in large scale storms
· In the simulator, how are the different forms of heat transfer at work?
· Taking into consideration the cloud formation lab, what must is the relationship between dew point, humidity, temperature and thunderstorm formation?
· What principles of lapse rate and moisture take effect in the formation of thunderstorms?
· Describe the process of vertical motion visible through the simulator.
· Diagram and explain what atmospheric conditions are necessary for thunderstorms to form.
Below are the links for source material and resources:
· EESC course page for Lapse Rate, Moisture, and Clouds Lecture, 2007 (updates forthcoming this summer):
· EESC course page (2011 course, only accessible to Columbia University students):
· Hands-on cloud formation lab:
· Thunderstorm Simulator:
Handouts and Directions:
· Lecture overview
· Lab instructions
· Un-tinted 2 liter plastic bottle with lid
· Book of matches
· 12 oz. Styrofoam cup (or similar container)
· Funnel (optional)
· Hot water
· Ice water
Cloud Formation, Moisture, Lapse Rate and Thunderstorms (LAB)
The Word version of the module
Instructors/TAs may find it useful to refer to lecture notes from the following lecture: • Lapse Rate, Moisture, and Clouds (http://eesc.columbia.edu/courses/ees/climate/syllabus.html)
Students summarize their findings in a lab report.
REFERENCES AND RESOURCES
Below are the links for source material and resources: • EESC course page for Lapse Rate, Moisture, and Clouds Lecture (publicly accessible site; updates forthcoming this summer): http://eesc.columbia.edu/courses/ees/climate/lectures/atm_phys.html#part6 • EESC course page for more information on a lecture associated with the lab (only accessible to Columbia University faculty and students): https://courseworks.columbia.edu/cms/ • Hands-on cloud formation lab from the State of Montana: www.ivymerriot.com/montanascience/lessons/Cloud%20Lab.pdf • Thunderstorm Simulator for hands-on portion of the lab: http://www.psc.edu/research/graphics/gallery/mxue.php
Air and water shift and change our climate. In this lab, students learn about the major movement of air and water movement that create weather. Through discussions and hands-on activities, students will walk away with a greater understanding of how and why the Earth’s climate system operates.