Winds What causes winds?

2 MAIN TYPES OF WINDS: #1) Global Winds: Large air masses created mainly as a result of the earth’s rotation, the shape of the earth and the sun’s heating power.

2 MAIN TYPES OF WINDS: #2) Local winds: Short-distance winds that are created as a result of scenery such as mountains, vegetation, water bodies, etc. Examples: sea breezes, land breezes, and mountain and valley breezes.

But what causes pressure differences? Winds are caused by differences in air pressure. Wind always blows from areas of high pressure to low pressure (H  L). But what causes pressure differences?

Differences in air pressure are caused by unequal heating of the atmosphere. Areas that receive more direct solar radiation (equator) get hotter. Areas that receive less direct solar radiation (poles) are colder. = GLOBAL WINDS

More direct sunlight causes warmer temperatures (equator). Warm temperatures cause air to EXPAND, become less dense (lighter), and rise. This creates an area of LOW PRESSURE beneath the rising air.

Less direct sunlight does not heat the earth as much, so these areas are cooler (poles). Colder temperatures cause the air to CONTRACT, get more dense (heavier). The air then sinks and creates an area of HIGH PRESSURE.

This is what causes LOCAL WINDS. The heat capacity or latent heat of different materials causes pressure differences too. This is what causes LOCAL WINDS. Remember soil vs. water in the differential heating/cooling lab. Which heated faster when the lamp was on? Which lost its heat the fastest when the lamp was off?

DURING THE DAY: The land heats faster than the ocean. Warm air over the land rises and creates an area of low pressure. Ocean water does not heat as quickly, so the air there is cooler. Cooler air sinks and creates an area of high pressure. The wind always blows from H  L, so the during the day the cool ocean breeze blows toward land.

AT NIGHT: The land loses its heat faster than the ocean, so the air over the land is cooler. Cool land air at night sinks and creates an area of high pressure. Ocean water holds onto its heat longer, so the air above the water is warmer. Warm ocean air rises and creates an area of low pressure. The wind always blows from H  L, so the at night the breeze blows from the land to the ocean.

Sea breeze (day): wind blows from ocean/lake to land. Land breeze (night): wind blows from land to ocean/lake.

THE CORIOLIS EFFECT = the apparent deflection of a freely moving object like water or air because of Earth's rotation. The path of a freely moving object appears to curve even though the actual path of the object is straight.

This is because Earth is rotating counter- clockwise beneath the object. So even though the object's path is straight, it appears to curve.

THE CORIOLIS EFFECT In the Northern Hemisphere, the curve is to the right. In the Southern Hemisphere, the curve is to the left. CK-12 Coriolis Effect Video

Example of The Coriolis Effect If an airplane flies 500 miles due north, it will not arrive at the city that was due north of it when it began its journey. Over the time it takes the airplane to fly 500 miles, that city moved, along with the Earth it sits on. The airplane will therefore arrive at a city to the west of the original city (in the Northern Hemisphere), unless the pilot compensates for the change by also veering northeast.

EXTREME WIND! The Jet Stream = fairly narrow zone of very strong winds in the upper troposphere. When people refer to the jet stream, they usually mean the polar jet stream (strongest).

EXTREME WIND! The Jet Stream Air masses have different temperature and humidity characteristics. Where two different air masses meet a jet stream forms. The jet stream moves or blocks weather systems & can help in forecasting weather.

EXTREME WIND! Monsoons = large-scale sea breezes which occur when the temperature on land is significantly warmer or cooler than the temperature of the ocean; reveres with the season. Summer = a lot of rain Winter = drought 

Measuring Wind direction A wind vane measures wind direction. The name tells where the wind is coming from. i.e. – north wind blows from the north to the south.

Wind speed An anemometer measures wind speed.