Air Pressure and Wind

1
Air Pressure and Wind
2
Air Pressure - Targets

• Explain how wind forms.
• List the units used to measure air pressure.
• Read an air-pressure map.
• Describe the relationship between air pressure
  and wind direction.

3
Air Pressure

• Key ideas for this chapter.
• Air moves from areas of high pressure to low
  pressure.
• Hot areas on the surface cause areas of low
  pressure.

4
Air Pressure

• Air Pressure the weight of the atmosphere
  pushing on an object.
• Wind Air moving horizontally from high pressure
  to low pressure.
• Air pressure is measured with a barometer.
• Air pressure at sea level
• 29.92 inches of mercury
• 1013.2 millibars
• High pressure relative to surrounding area

5
Barometric Pressure range
Hurricane Katrina 902 millibars (Aug 2005)
6
(No Transcript)
7
Air Pressure

• Air pressure maps use isobars lines of equal
  pressure
• Like topographic maps
• Closely spaced lines steep gradient (big change
  in pressure)

8
(No Transcript)
9
Wind Targets

• List the factors that affect wind speed and
  direction.
• Explain the relationship between surface
  temperature and air pressure.
• Create a diagram showing all the major wind belts
  and explain how the wind belts form.
• Explain how different types of breezes form.

10
Wind

• Things that affect wind direction
• Coriolis effect from Earths spin
• objects are deflected to the right in the
  northern hemisphere (to the left in the south)
• Friction slows wind affects direction near
  Earths surface

11
Wind

• Cyclones low pressure centers
• Air flows inward (convergence)
• Anticyclones high pressure centers
• Air flows outward (divergence)

L
H
12
                                                
                     Circulation within a high
pressure system in the Northern Hemisphere
13

• Hurricane Katrina

Which way is the air flowing near the center of
the hurricane? What is the direction of the
surface winds (cw or ccw)? Are the winds
converging or diverging?
What about The Day After Tomorrow?
14
(No Transcript)
15
Convection cells cause wind belts. Jet streams
form between wind belts.
16
Wind

• Three major wind cells in each hemisphere
• Air rises near equator (equatorial low)
• Air descends at 30o (subtropical highs)
• Air rises at 60o (subpolar lows)
• Air descends at 90o (polar high)
• Winds are named for the direction they blow FROM.
  
• A north wind blows from the north.

17
Wind

• Land and Water heat at different rates creating
  monsoons and sea breezes
• Breezes from density changes
• Valley Mountain breezes
• Chinooks

18
Above forming a valley breeze Right forming
a mountain breeze
19

• ? Forming a sea breeze
• In the diagram below, which season creates a sea
  breeze?
• What weather does this create?