Weather Fronts

INTRODUCTION

In the atmosphere surrounding the earth air is constantly moving. A large area of air that moves together and has constant temperature and humidity is called and air mass. Air masses of different conditions do not easily mix. The boundary between air masses of different conditions is called a front. Let’s explore fronts and interacting air masses.

MATERIALS

• Aquarium
• Water
• Red and blue food coloring
• 2 plastic beakers
• Washers

WHAT TO DO

1. Fill the aquarium almost to the top with room temperature water.
2. Place a few washers in the bottom of each beaker, and fill one beaker with very cold water. Fill the other beaker with very hot water.
3. Add two drops of blue food coloring to the beaker of cold water and add two drops of red food coloring to the beaker of hot water.
4. Pick up one beaker in each hand and position them over opposite ends of the aquarium. At the same time drop each of the beakers carefully in the water.
5. Watch how the colored water from each beaker moves throughout the water in the aquarium.

QUESTIONS

1. In what direction did the hot water move? In what direction did the cold water move?
2. What does this tell you about how the weather works? How does hot air move? How does cold air move?

SUMMARY

Much of our observable weather is caused by the interactions of different air masses. Warm air is less dense than cold air, so warm air rises and warm air exerts less pressure than cold air. As air cools, it becomes denser, so it sinks and also exerts greater pressure. A mass of warm air, or a low-pressure region, usually brings rain or snow because in low pressure regions air is being warmed and is rising. As the air rises the water vapor it contains condenses. A mass of cold air, or a high-pressure region usually means dry weather.

The boundaries between air masses, or fronts, can be classified as either warm or cold fronts. If the air behind the front is warmer than the air ahead of it, it is a warm front. At a warm front the warm air rises up over the cold air at a gentle slope. The moisture in the warm air condenses as it rises, forming clouds, making rain or snow possible. If the air behind the front is cooler then it is a cold front. At a cold front, the cold air wedges under the warm air, causing the warm air to rise quickly. The moisture in the quickly rising warm air condenses to form thick clouds and storms.

SOURCE

Michael Allaby. How the Weather Works. The Readers Digest Association, Inc. Pleasantville, New York, 1995. ISBN 0-7621-0234-9

© S. Olesik, WOW Project, Ohio State University, 2002.