11: Atmospheric Circulation & Air Masses

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Robert Wagner
HACC, Central Pennsylvania's Community College

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11.1: Atmospheric Circulation
This section explains how differences in atmospheric pressure, combined with Earth’s rotation and surface friction, produce winds and organize atmospheric circulation. It introduces the major forces that affect wind speed and direction and examines how these forces interact to produce characteristic wind patterns. These ideas are then applied to local winds, global circulation, and upper-level winds such as the jet streams.
11.2: Air Masses and Fronts
This section examines large bodies of air and the boundaries that form where different air masses meet. Air masses acquire characteristic temperature and moisture properties from their source regions and can transport those conditions over large distances. When contrasting air masses interact, fronts develop, producing changes in temperature, wind, clouds, and precipitation that are important for understanding everyday weather and larger weather systems.
- 11.2.1: Air Masses
- 11.2.2: Surface Fronts

Chapter 11: Atmospheric Circulation & Air Masses — Introduction

The atmosphere is constantly in motion. Differences in solar heating create differences in temperature and pressure, setting air into motion and producing winds. Earth’s rotation then modifies that motion, helping create the large-scale circulation patterns that transport heat and moisture around the planet. In this chapter, we will build from the forces that influence individual winds to the global circulation of the atmosphere.

We will begin by examining the major influences on atmospheric motion, including pressure differences, the Coriolis effect, and friction. Some of this material is presented mathematically in the text, but our primary goal will be to understand what these forces do and how they affect the speed and direction of the wind. Unless specifically discussed in lecture or assigned in an activity, you do not need to reproduce or perform calculations with the more advanced equations presented in this chapter. We will then use these ideas to understand global wind patterns, atmospheric circulation cells, and jet streams.

Finally, we will examine air masses and fronts. Large bodies of air acquire temperature and moisture characteristics from the regions where they form, and their movement brings changing weather to different locations. Where contrasting air masses meet, fronts develop and can produce clouds, precipitation, and rapid changes in weather. These concepts provide an important bridge to the next chapter, where we will examine cyclones, thunderstorms, and severe weather.

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