Download 4 Types of Local Winds

Wind
• Winds are caused by differences in air pressure.
• They move from areas of high pressure to low
pressure.
Air pressure and air density
• Differences in air pressure are caused by unequal
heating of the atmosphere.
• Cool air has higher air pressure so it flows
underneath the warm, less dense air.
Air pressure and air density
As air warms, it expands
and becomes less dense.
Lower density creates a
lower air pressure.
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
Wind formation
• Since the air near the equator
is less dense, it rises forming
areas of low pressure.
• The cold air near the poles
sinks because it is more
dense, forming areas of high
pressure.
• The air moves in large circular
patterns called convection
cells.
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 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.
• Have an impact on the
US weather
Polar Easterlies
• Cold but weak winds
• Found near the North and
South Poles
• US weather is greatly
influenced by these
• Cooling takes place
between the 50-60˚
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
Local Winds
• Cover short distances
• Blow from any direction
• These are the winds we feel on the ground
• They are influenced by local conditions and local
temperature variations
• 4 Types of Local Winds
– Sea Breezes
– Mountain Breeze
– Land Breezes
–Valley Breeze
Local Winds
Sea and land breezes are formed by increasing temperature
differences between the land and water.
During the day, the land heats up faster than the water, so a breeze will blow
from the sea to the land, called a sea breeze. At night land cools off faster than
the sea and wind will blow from the land to the sea (land breeze).
Local Winds
Mountain and valley breezes are examples of local winds caused by an area’s
geography.
During the day, the
mountain slopes heats up,
so the warm less dense air
flows up the mountain,
creating a valley breeze. At
night, the mountain will
cool off faster than the
valley, so the cool
mountain air descends
creating a mountain
breeze
How do we measure?
[ORIGIN from Greek anemos ‘wind’
[ORIGIN from Greek baros ‘weight’
How are winds are named?
By the directions
from which they come:
A wind coming from the west is a
west wind;
A wind or breeze coming from
the sea is a sea breeze;
A wind blowing up a mountain
from the valley is a valley breeze.
N - North, NE - Northeast, E - East, SE - Southeast, S - South,
SW - Southwest, W - West, NW - Northwest
Wind Direction & Wind Location
Chinooks are easterly winds that are found near the Rocky
Mountains.
Santa Ana winds are winds that come from the east, sweep
through southern California’s mountains and valleys, and
head toward places like Los Angeles and San Diego.
Norther (yes, norther, not northern) winds come from the
north and happen during a big change in temperature in
the United States’ Southern Plains region.
Knik southeast winds generally occur in the winter and are
specific to the area of Palmer, Alaska — a city in south
central Alaska.
Wind Speed
Wind speed is often a way of classifying storms.
• A hurricane or typhoon is a storm with winds of 74 mph or greater.
An organized storm of tropical origin in the Atlantic Ocean basin is
called a hurricane. A similar storm in the Pacific Ocean basin is
referred to as a typhoon.
• A tropical storm has wind speeds between 39 mph and 73 mph.
• A tropical depression is an organized tropical system with winds
less than 39 mph.
Wind Rose
a wind rose was included on maps in order to let the reader know which directions the 8
major winds blew within the plan view.
N
•
•
•
•
•
•
•
•
•
Winds
North – 25
Northeast-7
East – 14
Southeast-10
South – 2
Southwest - 7
West - 22
Northwest -22
NW
NE
E
W
SW
SE
S