Winds 2009

Wind is the horizontal movement of air from an area of high pressure to an area of low pressure. All winds are caused by differences in air pressure All winds are caused by differences in air pressure Most differences in air pressure are due to unequal heating in the atmosphere Most differences in air pressure are due to unequal heating in the atmosphere Water has a higher specific heat than sand, so it heats much slower. Water has a higher specific heat than sand, so it heats much slower. Cool, dense air sinks and has higher air pressure Cool, dense air sinks and has higher air pressure Warm, less dense air rises and has lower pressure Warm, less dense air rises and has lower pressure

Why Air Moves Air Rises at the Equator and Sinks at the Poles As the cold air sinks, it creates areas of high pressure around the poles. This cold polar air then flows toward the equator. Pressure Belts Are Found Every 30º Convection cells are separated by pressure belts, bands of high and low pressure.

Global Winds Caused by global convection currents. Caused by global convection currents. They blow steadily from specific directions over great distances. They blow steadily from specific directions over great distances. The high pressure cool air at the poles tries to fill in the low pressure areas at the equator. The high pressure cool air at the poles tries to fill in the low pressure areas at the equator. This causes the global winds. This causes the global winds. This is why the weather systems tend to always come from west to east in Georgia. This is why the weather systems tend to always come from west to east in Georgia.

Pressure Cells The earth is encircled by several broad prevailing wind belts. The earth is encircled by several broad prevailing wind belts. The three primary circulation cells are known as the: Hadley cell; Ferrel cell; and Polar cell. The three primary circulation cells are known as the: Hadley cell; Ferrel cell; and Polar cell.

Why Air Moves, continued The Coriolis Effect The apparent curving of the path of currents due to the Earth’s rotation is called the Coriolis effect. This causes winds to curve to the right in the northern hemisphere, and the opposite in the southern hemisphere.

Measuring Winds Winds are described by their direction and speed Winds are described by their direction and speed A wind vane determines wind direction A wind vane determines wind direction The name of a wind is the direction it is coming from so a north wind is from the north. It is headed to the south. The name of a wind is the direction it is coming from so a north wind is from the north. It is headed to the south. Wind speed is measured with an anemometer. Wind speed is measured with an anemometer.

Wind Chill Wind blowing over your skin removes body heat. The increased cooling that a wind can cause is called the wind chill factor. Wind blowing over your skin removes body heat. The increased cooling that a wind can cause is called the wind chill factor.

Local winds are... Winds that blow over short distances Winds that blow over short distances Caused by unequal heating of the earth’s surface within a small area Caused by unequal heating of the earth’s surface within a small area This creates local convection currents. This creates local convection currents. Form only when no winds are blowing from far away Form only when no winds are blowing from far away

Sea Breeze In the morning the sand heats up much faster than the water, so the air above the sand is hotter. In the morning the sand heats up much faster than the water, so the air above the sand is hotter. Hotter air is less dense, so it rises. Hotter air is less dense, so it rises. The cooler air over the ocean will push in to cause the hot air to rise. The cooler air over the ocean will push in to cause the hot air to rise. So in the morning the wind is in your face as you face the ocean. So in the morning the wind is in your face as you face the ocean.

Sea Breeze 2 1. Warm air over land rises 1. Warm air over land rises 2. Sea Breeze moves inland 2. Sea Breeze moves inland 3. Cumuli develop aloft and move seaward 3. Cumuli develop aloft and move seaward 4. Upper level return land breeze 4. Upper level return land breeze 5. Cool air aloft sinks over water 5. Cool air aloft sinks over water 6. Sea Breeze 6. Sea Breeze

Land Breeze At night, the sand cools very quickly, while the ocean temperature changes very little. At night, the sand cools very quickly, while the ocean temperature changes very little. So the warm air over the ocean rises, pushed up by the cooler air over the beach. So the warm air over the ocean rises, pushed up by the cooler air over the beach. So the wind will hit your back as you look out over the ocean at night. So the wind will hit your back as you look out over the ocean at night.

Land Breeze 2 1. Cool air over land sinks 1. Cool air over land sinks 2. Land Breeze moves out over water 2. Land Breeze moves out over water 3. Relatively warmer water heats air which then rises 3. Relatively warmer water heats air which then rises 4. Upper level return sea breeze 4. Upper level return sea breeze 5. Cool air over land sinks 5. Cool air over land sinks

Sea/Land Breezes