Excerpt: Sea Breeze activity from Lessons from the Sand

cover image of Lessons from the SandEver wonder where sand comes from? Or why shells are colored differently? Or how to estimate the size of a wave? Featuring more than forty fun hands-on activities for families with children, Lessons from the Sand: Family-Friendly Science Activities You Can Do on a Carolina Beach, reveals the science behind the amazing natural wonders found on the beaches of North Carolina and South Carolina. Easy-to-do experiments will help parents and kids discover the ways water, wind, sand, plants, animals, and people interact to shape the constantly changing beaches we love to visit.

See our previous post in which a twelve-year-old budding naturalist reports on his experiments using the book on the Outer Banks. In the following excerpt (pp. 38-42), authors Charles O. Pilkey and Orrin H. Pilkey explain how the sea breeze shapes the beach. Families can observe this phenomenon for themselves through this fun sea breeze activity.

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Activity 7

Sea Breeze

You don’t need a weatherman to know which way the wind blows.
                                   —Bob Dylan (American singer and songwriter)

Mother and daughter stood together on an empty beach, watching the waves come thundering in.
“How are beaches formed?” asked the daughter.
“Waves make beaches,” answered the mother, “by pushing sand around.”
“So what makes the waves?”
“The wind, of course.”
“Why does the wind blow?”
“Heat from the sun,” said the mother, “causes the air to move around.”
“How come the sun is hot?”
“Hydrogen atoms fuse together, giving off light and heat. It’s kind of like a nuclear bomb,” explained the mother.
“Why do the atoms fuse together?”
“Gravity.”
“Oh, so the sun’s gravity makes beaches. What makes gravity?”
“You ask a lot of questions,” said the mother. “Let’s go for a swim.”

Everything in nature is connected by an intricate chain of cause and effect, though we don’t always see all the links in the chain. It’s easy to stand on a beach, for example, and watch waves moving sand around, but we tend to forget it’s the wind that makes the waves. In that sense, wind is the fundamental cause of major changes on a beach.

illustration of girl feeling the sea breeze

Illustration © Charles O. Pilkey.

Sea Breeze

When the breeze blows from sea to land, it’s called an onshore wind or, simply, a sea breeze. When the wind blows from land to sea, it’s known as an offshore wind or land breeze. During conditions of fair weather, sea and land breezes are nearly always present at the beach. What’s interesting is how these breezes predictably change every day.

What You Need

Access to a beach during the day and at night.

What to Do

Visit the beach during the day (midafternoon is best) at a time of fair weather when no storms are passing through. Note the direction and strength of the wind. Is it an onshore or offshore breeze?

Return to the same beach late in the evening or very early in the morning before sunrise. Where is the wind coming from? Is the direction of the wind at night the same during the day? What about wind strength?

Repeat this activity over the course of several days. How does the wind change in direction and strength everyday? Why? What effect does the land/sea breeze have on waves, currents or the plants beyond the dunes?

diagram of movement of sea breeze during the day

During the day, warm air rising over land is replaced by cooler air coming from the sea. This creates a cool breeze known as a sea breeze or an onshore wind. (Illustration © Charles O. Pilkey.)

 

diagram of movement of sea breeze at night

At night, warm air over the sea rises and is replaced by cooler air coming from land. This creates a land breeze or an offshore wind. (Illustration © Charles O. Pilkey.)

More about the Sea Breeze

During the day the wind comes in from the ocean, while at night it flows from land to sea. This daily reversal in wind direction happens because land gets heated by the sun faster than water does. As the land gets warmer, it heats the air above it. The air expands, becomes less dense and rises. Cooler, denser air above the nearby sea sinks and moves landward.

At night it’s the opposite. The sea is warmer because it retains heat from the sun longer than does land. The air above the sea, being warmer and less dense, rises. Cooler, denser air from land moves in to replace the rising sea air. Because the temperature difference between land and sea is greatest during the day, the wind is generally stronger during the day.

The sea breeze affects beaches in several ways:

  • It increases wave height, which in turn strengthens longshore currents (Activity 4).
  • It affects the tidal range (Activity 6) by piling up seawater along the shore. Land breezes push water away from shore.
  • The sea breeze shapes plants by blowing salt spray into the dunes and maritime forests (see Activity 29).

Wind direction has seasonal as well as daily changes. Summer winds on the east coast generally come from the southwest. In the winter, winds often come from the northeast. Wind direction determines the direction of the longshore current.

Did You Know?
Sea breezes in the summer bring cool, moist air from the water into the coastal plain. As the air rises over warm land, it cools and condenses, forming clouds. That’s why you see a lot of clouds over land in the afternoon and why afternoon thunderstorms are so common.

The Beaufort Wind Scale (at the Beach)

In 1805 British admiral Francis Beaufort devised a wind scale to help sailors estimate wind speed. The scale, based on the observed effects of wind on the sea and on land, is still used by mariners today, though in a modified form. Use the Beaufort Wind Scale to estimate wind speed at your beach. Compare your estimates with the wind conditions reported by local news channels. What do you see happening on the beach as the wind speed increases?

table of the Beaufort Wind Scale

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From Lessons from the Sand: Family-Friendly Science Activities You Can Do on a Carolina Beach by Charles O. Pilkey and Orrin H. Pilkey. Copyright © 2016 by Charles O. Pilkey and Orrin H. Pilkey. Illustrations © 2016 by Charles O. Pilkey.

Charles O. Pilkey is an artist and writer living in Mint Hill, North Carolina. Orrin H. Pilkey is James B. Duke Professor Emeritus of Earth Sciences at Duke University and co-author of How to Read a North Carolina Beach: Bubble Holes, Barking Sands, and Rippled Runnels.