1. Air Pressure

2.  Is the weight of air above you  It is exerted in all directions-up, down, sideways  Measured using an instrument called a barometer

3. How do we measure air pressure?  Units called millibars (mb)  Standard sea level pressure is 1013 mb.  Any number higher than 1013 mb is considered high pressure  Any number lower than 1013 mb is considered low pressure

4. What causes wind?  Answer  horizontal differences in air pressure!  Air flows from high to low pressure  The unequal heating of Earth’s surface generates pressure differences.  Solar radiation is the ultimate energy source for wind

5.  What determines wind speed? –The greater the pressure difference, the greater the wind speed! –These pressure differences are called a pressure gradient.

6. Isobars…  Lines of equal air pressure on a weather map  Closer the lines are together, the windier it is in that location  Farther a part the lines are, the calmer the winds in that location

7. Weather map with isobars

8. High pressure- anticyclone Low pressure-cyclone

9.  Air around high pressure flows clockwise and outward  Air around low pressure flows counterclockwise and inward How does air move?

10. Draw the pictures below:

11. Let’s review!!- Copy Qs and answer in partner groups.  Which instrument measures air pressure?  If the isobars are close together, what does that indicate?  What kind of weather is associated with high pressure?  What kind of weather is associated with low pressure?  Answer Qs on your NOTES sheet.