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# AIR PRESSURE FORCES AND WIND

AIR PRESSURE FORCES AND WIND. PRESSURE GRADIENT FORCE. Definition: The difference in atmospheric pressure per unit distance PGF acts at right angles to isobars of equal pressure. H. L. 102.2. 99.8. 101.4. 100.6. 600 km. Pressure Gradient Force = 2.4 kPa / 600 km

## AIR PRESSURE FORCES AND WIND

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1. AIR PRESSURE FORCES AND WIND

2. PRESSURE GRADIENT FORCE Definition: The difference in atmospheric pressure per unit distance PGF acts at right angles to isobars of equal pressure H L 102.2 99.8 101.4 100.6 600 km Pressure Gradient Force = 2.4 kPa / 600 km = 0.4 kPa / 100 km

3. Where are winds strongest ? Oct 18, 2004 Solution: HUDSON BAY Check the spacing of the isobars of equal surface pressure

4. CORIOLIS FORCE Source: NASA

5. FRICTION FORCE Surface roughness decreases wind speed Reduces impact of Inertial Coriolis Force Winds cross isobars, spiralling out of ANTICYCLONES (H), and into CYCLONES (L) H L

6. Can you infer wind direction & speed? weather.unisys.com

7. WINDS ALOFT ARE DISTINCT H L Air tends to be unstable in low pressure (tendency to rise) Air tends to be stable in high pressure (tendency to fall)

8. GLOBAL ATMOSPHERIC CIRCULATION

9. MAIN PRESSURE ZONES • Equatorial Low Pressure Trough • Subtropical High Pressure Cells • Subpolar Low Pressure Cells • 4. Weak Polar High Pressure Cells

10. Intertropical Convergence Zone

11. How does this relate to the “jet stream”?

12. Geostrophic wind (above strong influence of friction)

13. WIND SMALL-SCALE & LOCAL SYSTEMS CHAPTER 10

14. WIND VANE & CUP ANEMOMETER

15. SONIC ANEMOMETER ULTRASONIC SOUND WAVES DETERMINEWIND SPEED, DIRECTION & TEMPERATURE Sonic transducers

16. SNOWDRIFT

17. SNOWDRIFT http://www.wrds.uwyo.edu/wrds/rmfres/fendrift.html

18. Effect of Surface Roughness and Instability on Windspeed

19. Depth of mixing depends on: Surface Heating WIND SPEED TOPOGRAPHY SURFACE ELEMENTS

20. Effect of Eddies on Wind Inclination UNSTABLE STABLE

21. MOUNTAIN WAVES

22. ROTOR CLOUDS

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