Download Wind

Winds
What is Wind?
• Wind- The horizontal movement of air
from an area of high pressure to an
area of lower pressure.
What causes winds?:
• Winds are caused by differences in air
pressure.
• The pressure differences are caused by
unequal heating of the Earth’s
atmosphere.
What causes winds?:
• More Dense air
sinks
• Less Dense air
rises-
– (Air Has High
Pressure)
– (Air Has Low
Pressure)
How is wind measured?
• Weather Vane- an instrument used to
determine the direction of the wind.
• Anemometer- An instrument used to
measure wind speed.
Anemometer
• Cups blow in the wind and measure the
speed of the wind.
Weather Vane
• Tells the direction the wind is blowing
from.
• If it is pointing to the south- wind is
blowing from the south to the north.
Global Winds
Belts of High and Low Pressure
• Global convection cells produce global belts of high and low
pressure.
– The Doldrums: The Doldrums is a belt low pressure (rising air)
that runs along the equator. As the air rises along the equator, it
cools. This causes water vapor in the air to condense, forming
clouds and increased precipitation. As a result, most areas near
the equator are warm and wet. Most tropical rain forests are
near the equator.
– The Horse Latitudes: The horse latitudes are belts of high
pressure (sinking air) located at 30˚ north and south latitudes.
Along these latitudes, warm, dry air sinks toward the ground.
This sinking air produces belts of high pressure. Remember,
that high-pressure systems are associated with dry weather.
Most of the world’s deserts are located along these latitudes.
Global Winds
•
Prevailing winds are large-scale winds that blow in the same direction most of
the time. Prevailing winds can significantly affect an area’s climate. There are three
main groups of prevailing winds:
•
– Trade Winds: The Trade winds are prevailing winds that blow westward (from
east to west) carrying warm, moist air from the equator toward 30º north and
south latitude.
•
– Prevailing Westerlies: The Prevailing Westerlies blow eastward (from west to
east) between 30˚ to 60˚. These winds carry warm air to the middle latitudes
creating temperate climates. In the Northern Hemisphere, most of the United
States lies within these latitudes.
•
– Polar Easterlies: The Polar Easterlies are prevailing winds that blow westward
(from east to west) from the poles to 60˚ latitude. At 60˚ latitude, the Westerlies
collide with the Polar Easterlies. The warm air is forced up over the cold air.
Water vapor in the warm air condenses, producing precipitation. The poles are
extremely dry and cold areas because the air sinks there.
Local Winds
• Are winds that blow over short
distances.
• Caused by unequal heating of Earth’s
surface with in a small area.
– Land heats faster than water.
– Water cools slower than land.
Local Winds
• Sea Breeze- The flow of air
from a body of water to land.
– Water is cooler – more dense air sinks.
– Land is warmer- less dense air rises.
Local Winds
• Land Breeze- The flow of air from
land to a body of water.
– Water is warmer – less dense air rises.
– Land is cooler- more dense air sinks.
Local Winds
Valley Breeze
•
•
•
•
Occurs during the day.
Uneven heating of the mountain slopes and the valley.
Areas of lower pressure near mountain tops.
The Valley Breeze flows from the valley up the slopes.
Low Pressure
High Pressure
Local Winds
Mountain Breeze
• Occurs at nightfall.
• Areas of higher pressure along the mountain slopes.
• The air around the mountain slopes cools creating higher
pressure.
• Wind moves from the mountain slopes down into the
valley.
High Pressure
Low Pressure
Reading Wind Maps
Cloud
Cover
• The line points into the weather station from
the direction the wind came from.
• This example shows that the wind is
coming from the east.
Reading Wind Maps
Cloud
Cover
• To determine wind speed. Read the flag on
the end of the wind direction line.
• Use the chart to determine the wind
speeds in knots and mph.
• Example above: 8-12 knots (9-14mph)