WeatherPart 3: Winds

Winds

•Caused by differences in air pressure due to unequal heating of the atmosphere• Two types – local

and global

Naming of Winds• Winds are named

after where they blow from.• So a north wind

comes from the north and blows toward the south• A sea breeze blows

from the sea on to the land.

East wind – • To?• From?Northwest wind• To?• From?Land Breeze• To?• From?

Local Winds

Sea Breeze- • The flow of air from sea to land• Happens during the day when the land warms

faster than the water• Also called an on-shore breeze

Local Winds

Land Breeze-• The flow of air from land to water• Occurs at night when the land cools off faster

than the water• Also call a land breeze

Local Winds

Monsoon –• A seasonal land and

sea breeze• During the part of the

year that it is a sea breeze it carries moisture that produces a rainy season with warm temperatures and huge amounts of rain.

• Major monsoon systems include West African and Asia-Australian monsoons.

Picture by lokenrc

This photo was taken on August 2, 2009 in South Dum Dum, Kolkata, WB, India.

Global Winds• Caused by direct

heating at the equator and indirect heating at the poles that causes higher temperatures at the equator.

• Warm air from the equator rises and moves toward the poles.• Cooler air at the

poles sinks and moves toward the equator.

Global Winds• Coriolis effect: the

apparent shift in the path of any fluid or object moving above the surface of the Earth due to the rotation of the Earth.

• In the Northern Hemisphere the Coriolis effect causes winds to curve to the right. South winds curve east and north winds curve west.• The opposite occurs

in the Southern Hemisphere where winds curve left.

Global Winds

Global Winds - Doldrums• At the equator (0°

latitude) • Surface winds are

calm• Warm rising air

produces a low pressure area that reaches many kilometers north and south of the equator

• Cooler air that flows in toward the low pressure area is warmed so rapidly it can’t move into the low pressure area, so any winds that do occur are weak.• Problem for sailing

ships

Global Winds – Horse Latitudes• At 30° latitude, north

and south, warm air from the equator begins to cool and sink• The sky is usually

clear with few clouds and little rain or wind.

• Called the horse latitudes, because ships becalmed here had to throw horses overboard when their food ran out

Global Winds – Trade Winds• Some of the air that

sinks at the horse latitudes flows back toward the equator causing warm, steady winds called trade winds• In the north the trade

winds blow from the northeast so they are called the Northeasterly Trades.

Global Winds – Prevailing Westerlies

• The cool, sinking air that continues moving toward the poles curves toward the east due to the Coriolis effect.• These winds are called

the prevailing westerlies.• Occur between 40° and

60° latitude• Often are particularly

strong

The area above Wakebarrow Scar and on Park Hill (in Great Britian) is over 200m above sea level and completely exposed to the prevailing westerlies. What few trees there are tend to be gnarled and wind-pruned. These hawthorns are reminiscent of old olive trees. © Copyright Karl and Ali and licensed for reuse under this Creative Commons Licence.

Global Winds – Polar Easterlies• Extremely cold air

flowing from the poles toward the equator. • Deflected west by

the Coriolis effect• Cold, weak winds• Cause many changes

in the weather that occur in the US

Jet Stream• Narrow belt of strong,

high-speed, high-pressure air• Flow from west to east at

altitudes above 12 km; at speeds as high as 350 km/hr• Wander up and down• Change season to season

and day to day• Affect the atmosphere

below them; create low-pressure areas

Measuring WindWind Direction:• Use a wind vane• The vane points into

the wind

Wind Speed:• Use an anemometer• Expressed in m/s,

mph, or knots (One knot = 1.852 km/h = one nautical mile = 1.151 mph)

© Copyright Miss Steel and licensed for reuse under this Creative Commons Licence

photo by Fergal of Claddagh on Flickr