Why is wind speed slower over land then over the ocean?

A Weather Lesson Plan

Girl with the umbrella in strong wind
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The winds, whether generated by a coastal storm or an afternoon summer sea breeze, blow faster over the ocean than over the land because there is not as much friction over the water. The land has mountains, coastal barriers, trees, human made structures, and sediments that cause a resistance to the wind flow. The oceans do not have these impediments, which impart friction therefore; the wind can blow at a greater velocity.

Wind is the movement of air. The instrument used to measure wind speed is called an anemometer. Most anemometers consist of cups attached to a support that allow them to spin in the wind. The anemometer rotates at the same speed as the wind. It gives a direct measure of the speed of the wind. Wind speed is measured by using the Beaufort Scale.

The following online game will help students learn how wind directions are designated, with links to static diagrams that can be printed and displayed on an overhead projector. http://earthguide.ucsd.edu/earthguide/diagrams/wind_direction/wind_direction.html

Materials include anemometers, a Large coastal relief map, an electric fan, clay, carpet sections, boxes, and large rocks (Optional).

Place a large coastal map on the floor or distribute individual maps to students working in groups. Ideally try and use a relief map with high elevations. Most students will enjoy making their own relief maps by modeling clay into the shapes of mountains, and other coastal geological features, pieces of shag carpet can be used for grassland, small model houses or just boxes representing buildings or other coastal structures can also be placed on the map’s land area.

Whether constructed by the students or purchased from a supplier, make sure that the ocean area is flat and the land area is of sufficient evaluation to obscure the ammeter that will be placed on the landmass from direct contact with the generated wind that will blow in from the ocean. An electric fan is placed on the area of the map designated as the “Ocean.” Next place one anemometer on the place designated as the ocean and another anemometer on the land area behind the various obstructions.

When the fan is turned on the anemometer cups will spend based on the air speed generated by the fan. It will become immediately obvious to the class that there is a visible difference in wind speed based on location of the measuring instrument.

If a commercial anemometer was used with wind speed-readings display capabilities, have the students recorded the wind speed for both instruments. Ask individual students to explain why there is a difference. They should state that evaluation above sea level and the topography of the land’s surface offers resistance to the wind’s speed and rate of movement. Emphasize that winds blow faster over the ocean because, there are no natural barriers to cause friction where as, the winds over land blow slower because the natural land objects cause friction.

Coastal barriers islands are unique landforms that provide protection for diverse aquatic habitats and serve as coastal mainland's first line of defense against the impacts of severe storms and erosion. Have the students examine a photo-image of coastal barriers and make clay models of the landform. Repeat the same procedure using the fan and the anemometers. This visual activity will reinforce how these unique natural barriers help slow down the wind speeds of coastal storms and thereby help moderate some of the damage caused that these storms can inflict.

Conclusion and Assessment

Once all the students have completed the activity discuss with the class their results and the rational for their answers.

Enrichment and Reinforcement Activity

As an extension assignment and for reinforcement purposes students can construct homemade anemometers. The following links connects to websites with directions for making simple anemometers:


The following web resource shows the onshore wind flow pattern from the Pacific Ocean in real time, over the Central California Coast. http://www.weather.nps.navy.mil/profiler/map/loopcc.html

Students will conduct a simulation exercise that will help them understand that winds blow faster over the ocean then over coastal land because natural land objects (mountains, coastal barriers, trees, etc) cause friction.