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

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

5. CORIOLIS FORCE Source: NASA

6. 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

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

11. 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)

13. GLOBAL ATMOSPHERIC CIRCULATION

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

16. Intertropical Convergence Zone

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

28. Geostrophic wind (above strong influence of friction)

31. WIND SMALL-SCALE & LOCAL SYSTEMS CHAPTER 10

33. WIND VANE & CUP ANEMOMETER

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

37. SNOWDRIFT

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

40. Effect of Surface Roughness and Instability on Windspeed

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

42. Effect of Eddies on Wind Inclination UNSTABLE STABLE

44. MOUNTAIN WAVES

48. ROTOR CLOUDS