1. Weather, Climate and Society Newton’s Laws of Motion Upper-Air Winds

2. Supplemental References for Today’s Lecture Gedzelman, S. D., 1980: The Science and Wonders of the Atmosphere. 535 pp. John-Wiley & Sons. (ISBN 0-471-02972-6)

3. Do Rocks Always Roll Downhill? Gedzelman, p 247 Upper-Level Winds PGF Today’s Question….

4. Newton’s Laws of Motion Newton’s 1st Law An object at rest will remain at rest and an object in motion will remain at a constant velocity (same speed and same direction) if the net force exerted on it is zero An external force is required to speed up, slow down, or change the direction of air

5. Newton’s Laws of Motion Newton’s 2nd Law The net force exerted on an object equals its mass times its acceleration Sum of All Forces = Mass x Acceleration Acceleration = Velocity Change / Time Acceleration = Change in Either Speed or Direction

6. Velocity, Acceleration and Force are Vectors Speed/Size Change Direction Change Original Velocity New Velocity Original Velocity New Velocity Acceleration and Force Original Velocity New Velocity Original Velocity New Velocity Acceleration and Force

7. Uniform, Circular Motion Requires Acceleration Original Velocity New Velocity Acceleration directed toward center of circle Centripetal Original Velocity New Velocity Circular Path

8. Accelerated Frame of Reference You are glued to car’s floor and drop an egg. What happens if the car begins to accelerate? Inside the car, it looks a mystery force is attracting the egg to the back of the car. Your frame of reference is accelerating. Someone outside the car sees that the egg is just accelerating to the floor, you are accelerating with the box car. A force is accelerating the car. Their frame of reference is not accelerating. Splat! (rest) time

9. Life on a Rotating Platform From perspective of person not on merry- go-round, path of ball is straight. From perspective of person on merry-go- round, path of ball deflects to left. There is an apparent force. (left click picture for animation) World Weather Project 2010 Courtesy of M. Ramamurthy U of Illinois, Urbana-Champaign Merry Go Round Link

10. Earth’s Rotation If viewed from space, earth is like a carousel! Northern Hemisphere rotates counterclockwise Southern Hemisphere rotates clockwise Gedzelman, p 240

11. Refinements Simple, right? But there are a couple of nuances We will consider both… Coriolis “force” varies with wind speed. The earth is a sphere, not flat like a carousel.

12. Ball Appears to Deflect to the Right of the Observer Gedzelman, p 242 Deflection increases if: Rotation rate increases Speed of ball increases

13. Ball Appears to Deflect to the Right of the Observer Gedzelman, p 242 Deflection increases if: Speed of ball increases slow fast

14. Ball Appears to Go Straight Gedzelman, p 242 If the ball is thrown parallel to the axis of rotation, there is no apparent deflection

15. Deflection Depends on Orientation of Axis of Rotation and Velocity Gedzelman, p 242 velocity Apparent Deflection No Deflection

16. Coriolis Force Varies with Latitude Gedzelman, p 243 Airplane Link

17. Geostrophic Adjustment A.Parcel at rest initially accelerates toward lower pressure. B.Coriolis Force rotates parcel to right in NH. C.As parcel speeds up, Coriolis Force increases. D.Eventually (about a day), PGF equals CF and flow is parallel to isobars. (left click picture to animate) World Weather Project 2010 Courtesy of M. Ramamurthy U of Illinois, Urbana-Champaign Animate Picture

18. Geostrophic Balance Pressure Gradient Force Coriolis Force Geostrophic Wind 5640 m 5700 m Geostrophic Wind Arises from a Balance Between the PGF and the Coriolis Force. PGF + Coriolis Force = 0 (Technically, it can only exist for East-West flow and for straight contours, but we will ignore that technicality.)

19. Geostrophic Balance Pressure Gradient Force Coriolis Force Geostrophic Wind 5640 m 5700 m The Balance Leads to the Wind Blowing Parallel to the Height Contours, with Lower Heights to the Left of the Wind Direction in the NH. Closer the Spacing Between the Height Contours- The Faster the Geostrophic Wind Speed.

20. PGFCor Geo

21. Today’s 500 mb Map 500 mb 1200 UTC CONUS

22. Take Home Points Rotation of Earth Accelerated Frame of Reference Introduce Coriolis “Force” Apparent Force to Account for Deflection Depends on Rotation, Latitude, Wind Speed Geostrophic Balance and Wind Balance Between PGF and Coriolis Force Geostrophic Wind Blows Parallel to Contours About One Day Required to Reach Balance

23. Do Rocks Always Roll Downhill? Gedzelman, p 247 Upper-Level Winds PGF Not if the Hill is Big Enough!