Transcript Weather - Ms. Racette`s Wiki

Weather
Part 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 AsiaAustralian monsoons.
This photo was taken on August 2,
2009 in South Dum Dum, Kolkata, WB, India.
Picture by lokenrc
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, highpressure 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 Wind
Wind Direction:
• Use a wind vane
• The vane points into
the wind
© Copyright Miss Steel and licensed for reuse
under this Creative Commons Licence
Wind Speed:
• Use an anemometer
• Expressed in m/s,
mph, or knots (One
knot = 1.852 km/h =
one nautical mile =
1.151 mph)
photo by Fergal of Claddagh on Flickr