Global and Local Winds
Why Air Moves Winds blow from areas of high pressure to areas of low pressure. The greater the pressure difference, the faster the wind moves. Unequal heating of the Earth causes differences in air pressure. Warm less dense air rises at the Equator and the cold dense air sinks at the Poles.
Pressure Belts Air travels in circular convection cells rising and falling about every 30 of latitude. Bands of high and low pressure, called pressure belts, separate the convection cells. Cool, sinking air causes high pressure belts near 30 north and 30 south latitude. Warm, rising air causes low pressure belts near 60 north and 60 south latitude..
The Coriolis Effect As air travels north and south across the Earth, the rotation of the Earth beneath the moving air causes an apparent curving of the winds. This apparent curving is called the Coriolis effect. Diagram of the Coriolis effect. Diagram of the Coriolis effect
Global Winds The combination of convection cells and the Coriolis effect produce patterns of air circulation called global winds. These are polar easterlies, westerlies, and trade winds.
Global Winds Don’t travel North and South because of the Earth rotating on its axis. 4 Types of Global Winds – Doldrums – Trade Winds – Prevailing Winds – Polar Easterlies
Polar Easterlies Cold, but weak winds Near the north and south poles US weather is influenced by these Cooling takes place between the degree latitude as it approaches the poles
Prevailing Westerlies Strong winds Located in the belt from degrees latitude in both hemispheres. Has an impact on the US weather
Trade Winds 30 degrees N & S of Equator Calm winds, few clouds, little rain fall Warm air rising from Equator cools and sinks Also known as Horse Latitudes
Doldrums At the equator, surface winds are calm and weak. Why would these winds be calm and weak? When would this cause a problem?
Jet Streams Discovered in 1940’s Can be found in the upper troposphere Strong high speed and high pressure Moves west to east across the US, moving storms