Global Winds

Jeanne OmvigMaple Lake High School

Why Air Moves

• The Movement of air caused by differences in Air Pressure this is called wind.

• The greater the pressure difference, the faster the wind moves.

Causes of Pressure Difference

• Generally caused by the unequal heating of the earth.– The equator receives more direct solar energy

than other latitudes, so at the equator it is warmer.

– Therefore the air is less dense-Rises– This creates low pressure

Cold Air

• Cold air is more dense and sinks- This creates high pressure

• The highest pressure is found along the Poles.– What do you think is happening around the

equator is the air sinking or rising?

Circular Patterns

• Convection Cells- When air travels in circular patterns

• Convection Cells are separated by Pressure Belts.

• Pressure Belts are found every 30 degrees of latitude.– Ex. At about 3 north and 3 south air cools and 0̊0̊ 0̊� 0̊�

starts to sink

Coriolis Effect

• Coriolis Effect- The apparent curving of the path of a moving object from an otherwise straight path due to the Earth rotation.

• Northern Hemisphere winds traveling north curve to the east and winds traveling south curve to the west.

Global Winds

• Polar Easterlies-the wind belts that extend from the poles to 6 and 9 latitude in both 0̊0̊ 0̊� 0̊�hemispheres

• Westerlies-prevailing winds that blow from west to east between 3 and 6 latitude in 0̊0̊ 0̊� 0̊�both hemispheres.

• Trade Winds-Prevailing winds that blow northeast from 30 south and 3 north ̊� 0̊�latitude to the equator.

The Doldrums

• Doldrums- The trade winds of the Northern and Southern Hemispheres meet in an area around the equator– Very little wind because the warm rising air

creates low pressure– Means sluggish or dull

Horse Latitudes

• At about 30 North and 30 South Latitude, ̊ ̊ ̊� ̊�sinking air creates an area of high pressure. These areas are called horse latitudes.– Given when ships were struck in this windless

area, horses where sometimes thrown overboard to save drinking water for the sailors.

– Sinking air is very dry– Deserts are located in the horse latitudes

Jet Streams

• Jet Streams are a narrow belt of strong winds that blowing the upper troposphere

• They can reach a speed of 400 km/hr.• They affect the movement of storms• Do not follow regular path

Local Winds

• Local winds generally move short distances and can blow from any direction

• Local geographic features, such as a shoreline or a mountain can produce a temperature differences that can cause local winds.– Ex. During the day warm land air rises and the

cold ocean air replaces it.– Ex. During the night the land cools faster than

water, so the wind blows toward the ocean

Mountain and Valley Breezes

• These are an example of local winds. Campers in mountainous areas may feel a warm afternoon quickly change into a cold night soon after sunsets.