Transcript Wind - Hewlett

Wind
Air stops rising when it
meets air of equal
density, then diverges at
high level to produce
more wind which
eventually sinks
elsewhere to complete
the circulation cell
Pressure, Wind and Weather
Systems
WINDS are horizontal flows of air;
winds blow from areas of high
pressure to areas of low pressure
(nature tries to equalise pressure)
�
Insolation
Air heated by
contact with ground
expands; becomes
less dense and rises
Denser air
drawn in at
low level to
replace rising,
less dense air
LOW
PRESSURE
Sun heats up ground
Denser air drawn in at low
level to replace rising, less
dense air
Land and Sea Breezes
Land & Sea
Breezes
Land Breeze
Sea Breeze
(cool land/warm sea)
(warm land/cool sea)
 Cool air over land
moves out toward
the water and takes
the place of rising
air.
 Warm air over the
water rises.
 Warm air over the
land rises.
 Cool air over the
water moves toward
land and takes the
place of the warmer
air that has risen.
A. As the land heats
faster than the
water throughout
the day, air starts
to rise and air from
over the sea will
come in to replace
it. This is a sea
breeze circulation
(takes place during
the day).
B. As the land cools
faster than the
water throughout
the day, the air
begins to sink over
land and rise over
water. This is a
land breeze
circulation (takes
place during the
night)
Land/Sea breeze
 The temperature differences between land and
water occur because water has a much higher
heat capacity than land. This means more heat
is required to raise the temperature (or drop the
temperature) of water than that of land.
 These temperature differences cause pressure
gradient forces that force the breezes
 satellite
 Animation
Cyclones and Anticyclones
Northern Hemisphere:
Cyclone
Anticyclone
Cyclone: Low pressure,
Counterclockwise winds, cloudy and
rainy weather
Anticyclone: High Pressure,
Clockwise winds, sunny weather
Southern Hemisphere:
Cyclone
Anticyclone
Cyclone: Low Pressure, clockwise,
cloudy or rainy weather
Anticyclone: High Pressure,
counterclockwise, sunny weather
How High and Low Pressure
Works
 http://www.usatoday.com/weather/tg/whighl
ow/whighlow.htm
How Low Pressure Areas Work
 http://www.usatoday.com/weather/tg/wlowpr
es/wlowpres.htm
How High Pressure Areas
Work
 http://www.usatoday.com/weather/tg/whighp
/whighp.htm
Highs have sinking air above them,
lows have rising air.
Sinking air over highs causes dry weather,
Rising air above lows can condense and form clouds or
rain or both.
WIND DIRECTION & STRENGTH
Wind strength depends on
the difference in pressure
between the high and low
Farmers plant trees to protect orchards,
pressure systems, and the
houses, stock or prevent soil erosion
distance between them.
� This is called the PRESSURE
GRADIENT; it is a similar
concept to the physical slope
between two places, shown on
Locally, wind is channelled
a contour map. Pressure is
down streets (wind canyons).
shown by ISOBARS on a
weather map.
Strong winds also occur
� Pressure difference
in low latitudes due to
essentially depends on the
stronger heating and
temperature difference
steeper presure gradients.
between the two places.
Hurricanes and
A steep pressure gradient results
tornadoes are both
from a large pressure difference
Strong polar winds due to low
tropical phenomena.
or short distance between places
friction
and causes strong wind.
�
Hurricane in Florida
Tornado in USA
Beach windbreaks reduce windsped
by increasing friction
Wind Speeds down a Pressure Gradient
Weather map
Coriolis
Types of Surface winds:
1. Trade winds- occurs between 30o N and
30o S latitude.
2. Prevailing Westerly- occur between 30o
to 60o in both hemispheres. They blow
west to east.
3. Polar Easterlies- occurs between 60o
and the poles in both hemispheres.
They blow east to west.
Ocean Currents
Ocean Currents: movement of ocean water
 The main cause is the Coriolis Effect
Coriolis Effect: the rotation of the Earth causes the oceans
water to circle away from the equator
 Currents generally help to control climate and are useful in
moving nutrients throughout the oceans
 Northern Hemisphere currents move clockwise; while
currents in the Southern Hemisphere move counterclockwise.
Earth Science
Reference
Table