What is Wind?

Reasons for uneven heating of the Earth: The Earth is round which means the sun’s rays hit the surface at different angles, so the concentration varies over the surface Albedo- Areas with ice/ snow reflect more heat energy than areas with soil or water or vegetation. Specific Heat Capacity- Water and land have different heat capacities, making it uneven heating. The Earth is tilted. Some places are closer to the sun than others during different seasons.

What is Wind? Wind is air in motion. It is produced by the uneven heating of the earth’s surface by the sun. What are some of the reasons for uneven heating of the Earth?

Hot Air Rises Uneven heating of air creates wind. When air is heated, the molecules in air move faster and collide with greater forces. As a result, the molecules spread apart and become less dense. This causes warmer (less dense) air to rise.

How is Wind Described? Wind is described with direction and speed. The direction of the wind is expressed as the direction from where the wind came from. For example, easterly winds blow from east to west Winds have different levels of speed, such as “breeze” and “gale”, depending on how fast they blow. Wind speeds are based on a scale called the Beaufort Scale, (12 different categories of wind speeds)

The Beaufort Scale

How is Wind Measured? Wind direction is measured with a wind vane. Wind speed is measured with an anemometer.

Land and Sea Breezes

Land Breezes and Sea Breezes Sea Breeze

Sea Breeze: During the day, the land warms up faster than the water. The warm air over the land rises, while the cooler air over the water sinks down and moves in to replace the warm air.

This creates a convection current… As the warm air rises, it expands and cools. As it cools, it becomes more dense, so that it sinks back down. This creates a convection current… WIND!

Land Breeze

Land Breeze: At night, dry land cools faster than water, due to the water’s large specific heat capacity. Since the land cools faster than the water, the air above the water is now warmer and less dense than the air above the dry land.

Therefore, the path of the convection current is the opposite of the daytime current. Warmer air above the water is rising, drawing in the cooler air from the land.

Think about this… Why does Ottawa have much colder winter and much hotter summers than we do here in Halifax?