- Slides: 28
Winds What causes winds?
Air Pressure Air pressure is the measure of the force with which air molecules push on a surface The air pressure is strongest in the Troposphere because of Earth’s gravity
Wind Wind is the movement of air. Winds are caused by differences in air pressure. (Cause of Wind) air moves from areas of high (cold air-low temperature) pressure to areas of low (warm air-high temperature) pressure (High Pressure Low Pressure) Differences in air pressure is caused by differences in the temperature of the aircaused by unequal/uneven heating of the Earth
Why is the Earth Unequally Heated The Earth is unequally heat because it is titled on its axis. More of the sun’s direct rays hit the equator making the temperature at the equator warmer and the air less dense creating areas of low pressure (L) The tilt of the Earth on its axis causes seasons on the Earth
The planet is heated unevenly by the sun, mainly because. . . the earth is covered with primarily two completely different substances, land water which heat and cool at different rates. the earth is a sphere, with the equator heated more intensely than the poles. the earth is tilted on its axis, which creates seasonal differences at certain latitudes. the earth rotates on its axis, which means at any one time, half the earth is in day and the other in night.
Differences in air pressure are caused by unequal heating of the Earth. Cool air has higher air pressure so it flows underneath (sinks) the warm, less dense air. A. B. C.
Rising Air at the Equator Because the Earth is tilted on its axis, the equator receives more direct solar energy from the sun. Air at the equator is warmer than any where else on Earth. This less dense warm air rises creating areas of Low Pressure (L)
Sinking Air at the Poles At the poles, the air is colder and denser than surrounding air, so it sinks. Creating areas of high pressure (H)
Why does warm air cause areas of low pressure? Warm air causes areas of low pressure (L) because the air is less dense than the surrounding air and it rises
Why does sinking cold air cause areas of high pressure? Sinking cold air causes high pressure (H) because sinking air presses down on the air beneath it.
Coriolis Effect The apparent curving of path of winds and ocean currents due to the Earth’s Rotation Winds in the Northern Hemisphere curve east. Winds in the Southern Hemisphere curve west
Global Winds Created by unequal heating of Earth’s surface.
Global Winds… cont… The movement of air between the poles and the equator produces global winds. Coriolis effect produces patterns of air circulation called global winds.
Global Wind Belts Major global wind systems: Polar easterlies, westerlies, and trade winds.
Doldrums • Where the trade winds meet around the equator • Very little wind because the warm air rising = low pressure
Horse Latitudes • High pressure areas… 300 N and 300 S • Very week winds
Global Winds The combinations of convection cells and the Coriolis Effect produce patterns of air circulation called global winds
Jet Streams Bands of high speed winds Upper troposphere and lower stratosphere Blow from west to east at speeds of 200 -400 km/hr. Help airplanes save fuel and time when traveling east.
Local Winds that blow over short distances and are caused by unequal heating of Earth’s surface within a small area.
Sea Breeze (Day) Land heats up faster than water. Hot air over land rises (Low Pressure), cool air over water falls (High Pressure). Winds move from the water (High Pressure) to the land (Low Pressure).
Sea Breeze- (Day) Sea Breeze – a wind that blows from an ocean or lake onto land. Air moves from areas of High Pressure (H) to areas of low Pressure (L)
Land Breeze-Night Land Breeze – the flow of air from land to a body of water. Air moves from areas of high pressure (H) to areas of Low pressure (L)
Land Breeze (Evening) Land cools off faster than water. Cool air over land falls (High Pressure), warm air over water rises (Low Pressure). Winds move from the land (High Pressure) to the water (Low Pressure).
Wind Vane Measuring Winds are described by their direction and speed. Wind direction is determined with a wind vane – points in the direction the wind is moving! Wind speed is measured with an anemometer. The increased cooling that a wind can cause is called the wind chill factor. Anemometer – The cups catch the wind, turning faster when the wind blows faster.
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.
Wind-chill factor The wind-chill factor is the increased cooling that a wind can bring.