In-Class Activity 2
28 September 2006
The Atmosphere - Driving Force for the Ocean

Goal: The large-scale atmospheric circulation drives much of the surface circulation of the ocean. At first glance, atmospheric circulation seems almost impossibly complicated. The goal of this activity is to demonstrate how a few simple rules can be used to make sense of the large-scale atmospheric circulation.

Rule #1 – Warm air rises; cold air sinks.

Rule # 2 – There are three vertical circulation cells in each hemisphere.

Rule # 3 – The Coriolis effect deflects motion to the right in the northern hemisphere and to the left in the southern hemisphere.

Rule #4 – Where cells meet, air moves either down (toward the Earth’s surface) or up (away from Earth’s surface) and surface winds are weak.

Rule #5 – As air rises, it becomes more moist; as air sinks, it dries out.

For this activity, the instructor guided the class through a demonstration of how the large-scale atmospheric circulation (shown in Fig. 8.12 of the 4th Ed., or Fig. 8.13 of the 5th Ed) could be constructed from the series of simple rules listed above.  All students who participated received full credit (an A).  For the activity, we considered only the northern hemisphere. Students are encouraged to repeat this exercise on their own and to do the exercise for the southern hemisphere.