Global and Local Winds i

What causes wind? Caused by a difference in air pressure due to unequal heating of the atmosphere.

Winds are created by…. • Heating the air, decreases pressure (warm air rises creating a low pressure) • Cool air rushes into replace the warm air (cooler dense air, produces high pressure) • As air goes from high to low pressure, winds form.

Coriolis Effect • Coriolis Effect – Rotation of the Earth causes moving air and water to change directions • Northern Hemisphere winds curve to the right • Southern Hemisphere winds curve to the left. http://www.youtube.com/watch?v=mcPs_OdQOYU

There are 2 types of winds… 1. Local Winds 2. Global 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 Westerlies – Polar Easterlies

Visual of Global Winds

These are located at the equator, surface winds are calm and weak. Doldrums These are located at the equator, surface winds are calm and weak. Why are they called doldrums? Sailors found that there were no winds near the equator for a period of time. The ships were essentially stuck in one place, not being able to move forward. These calm periods were called doldrums. Today, to be “stuck in the doldrums” means that you’d like to be doing something, but you’re stuck waiting for something to happen so you can begin moving forward.

Trade Winds Named from their ability to quickly propel trading ships across the ocean - found between about 30° latitude and the equator - steady and blow about 11 to 13 mph - In the Northern Hemisphere, the trade winds blow from the northeast and are known as the Northeast Trade Winds - In the Southern Hemisphere, the winds blow from the southeast and are called the Southeast Trade Winds.

Prevailing Westerlies • Strong winds • Located in the belt from 30-60 degrees latitude in both hemispheres. • Has an impact on the US weather

Polar Easterlies • Cold, but weak winds • Near the north and south poles • US weather is influenced by these • Cooling takes place between the 50-60 degree latitude as it approaches the poles

Jet Stream • 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

What brings certain weather phenomenon? El Nino La Nina occurs when the surface temperature rises above the normal water temperature in the Equatorial Pacific Ocean creating more humidity in the atmosphere Known to increase number of hurricanes Occur more frequently (every 3-7 years) occurs when the surface temperature falls below the normal water temperature in the Equatorial Pacific Ocean creating a more dry atmosphere Known to create drought conditions

Local Winds • Cover short distances • Blow from any direction • 2 Types of Local Winds – Sea Breezes- from sea to land – Land Breezes – from land to sea

What’s the difference?

How do sea and land breezes work?