Lesson 3: Wind at the seashore

Activity 2. Pressure and winds at the seashore (night)

Online Resource: Simple drawing of land and ocean at night

Materials:

• Overhead projector or LCD project

Advanced Preparation:

• Read through the procedure before class
• Make an overhead slide of the simple land - ocean drawing or use an LCD projector to show the drawing
• Make a copy of the Simple drawing of land and ocean at night for each student

Time needed: Teacher preparation - 5 minutes; Class activity - 20 minutes

Procedure:

1. Let’s return to the drawing of land and ocean; but now at night. How would the map differ if it were evening? How would the land and sea surface respond to the cooling? Where is the cool air sinking? (Solids heat up but also cool down more quickly than liquids.
2. During the evening, where would the high pressure develop? (High pressure develops over the cool land surface)
3. And the low pressure forms where? (Over the water)
4. Which direction does the convection cell circulate at night? If you were looking at the ocean, would you feel the breeze on your face? (The convection cell is opposite of one drawn earlier. Air moves from the land out to the ocean at the surface; you would feel the breeze from behind you

Closing the activity: Ask the students: We have looked at how convective cells are created on a small scale. When we talk about the air warming up during the day in the global sense, what is the heat source? (The sun) So in a simple world, we would just have one giant convection current. But there are complications:

1. The surface that is receiving heat is not all made up of the same material and therefore radiates – we’ve learned that the past two activities.
2. The Earth is not flat, nor does it stay still; it rotates

In the next lesson, we will explore these issues and see how convective forces work on a global scale.