Winds • Winds are defined as the horizontal movement of air. • Winds are named by where they blow from.
Local Winds • Different materials heat at different rates. • Along the shore the land surfaces will heat faster during the day. • The water surfaces will be cooler due to the slower heating.
Local Winds • This results in the air over land being warmed. • As it warms it expands and floats up creating an area of low pressure.
Local Winds • The area over water cools causing the air to contract. • This creates an area of high pressure.
Local Winds • The high pressure forces the air from the ocean to the low pressure on the land.
Local Winds • This is called an on shore or Sea Breeze
Winds • You will see that winds always blow from an area of High pressure to an area of Low pressure. • WINDS BLOW FROM HIGH TO LOW
Local Winds • At night the process is reversed. • The land cools quickly creating a high pressure over land. • The water retains its heat creating a low pressure over the water.
Local Winds • This results in the high pressure over land pushing the air to the low pressure over the ocean. • This is called a land or off shore breeze.
Local Winds • Sea breezes and Offshore breezes are very consistent. • In early morning, before the land heats, you can be sure the winds will blow out to the water. • It is a great place to fly kites.
Global Winds • Heating of the planet is not uniform • The Earth receives more heat at the equator and less heat at the poles • This results in low pressure at the equator and high pressure at the poles
Global Winds • If winds blow from high pressure to low pressure you would expect North winds in the northern hemisphere and South winds in the southern hemisphere.
As we do not have winds always blowing from the North there must be other factors influencing the wind patterns. • The rotation of the Earth. • The rotation causes the winds to shift and the convection cells to break up into 3 cells in each hemisphere.
Global Winds • All of these factors combine to form our Global wind patterns.
Global Winds • These winds were used by sailors to move around the planet so our names come from them. • The bands of winds north and south of the equator are called the Trade Winds.
Global Winds • The band north of the equator blow from the Northeast and are called the Northeast Trade Winds. • The band south of the equator blow from the Southeast and are called the Southeast Trade Winds.
Global Winds • The bands between 30o and 60o in both hemispheres blow from the Southwest in the northern hemisphere and the Northwest in the southern hemisphere. • We generally refer to them as Westerlies.
Global Winds • At the north pole the wind blows from the Northeast. • At the south pole the wind blows from the Southeast. • These are generally called the Polar Easterlies.
Global Winds • Keep in mind that wind is the horizontal movement of air. • Areas of high and low pressure will have no wind. • Ships sailing into these areas became becalmed.
The low pressure at the equator is the equatorial low. • The common name is the Doldrums. • Think about it ………
Global Winds • At 30o North and 30o South there is the Sub tropical High. • These areas were called the Horse latitudes. • The name comes from the dead horses that were thrown overboard when the ship was becalmed.
Global Winds • At 60o North and 60o South is the Sub Polar Low. • At the Poles there is the Polar High. • Early sailors didn’t spend much time in these regions so they have no common name.
Global Winds • Early sailors used the trade winds or the polar easterlies to sail to the “New World”. • They would then use the westerlies to sail back to the “Old World”
Weather Systems • We live in a region where the westerlies and the jet streams are all moving air from the west to the east. • When you are watching the radar on the weather where does the precipitation usually come from? • What could be driving these systems?