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NATS 101 Lecture 16 Newton’s Laws of Motion Upper-Air Winds

NATS 101 Lecture 16 Newton’s Laws of Motion Upper-Air Winds. 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). PGF. Wind. Do Rocks Always Roll Downhill?. PGF. Upper-Level Winds.

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NATS 101 Lecture 16 Newton’s Laws of Motion Upper-Air Winds

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  1. NATS 101Lecture 16Newton’s Laws of MotionUpper-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. PGF Wind

  4. Do Rocks Always Roll Downhill? PGF Upper-Level Winds Gedzelman, p 247

  5. 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

  6. 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  Acceleration Acceleration = Velocity Change / Time Acceleration = Change in Either Speed or Direction

  7. New Velocity New Velocity Acceleration and Force Acceleration and Force Original Velocity Original Velocity New Velocity Original Velocity Original Velocity New Velocity Velocity, Acceleration and Force are Vectors • Size and Direction

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

  9. 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. (rest) 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 referenceis not accelerating. time Splat!

  10. 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 anapparent force. (left click picture for animation) World Weather Project 2010 Courtesy of M. Ramamurthy U of Illinois, Urbana-Champaign Merry Go Round Link

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

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

  13. Ball Appears to Go Straight Gedzelman, p 242

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

  15. Coriolis Force Varies with Latitude Gedzelman, p 243

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

  17. Pressure Gradient Force 5640 m Geostrophic Wind 5700 m Coriolis Force Geostrophic Balance Geostrophic Wind Arises from a Balance Between the PGF and the Coriolis Force. PGF + Coriolis Force = 0 Technically, can exist only for East-West flow and for straight contours.

  18. Pressure Gradient Force 5640 m Geostrophic Wind 5700 m Coriolis Force Geostrophic Balance 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.

  19. PGF Cor Geo

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

  21. Key Concepts for Today • 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

  22. Assignment for Next Lecture • Topic –Centripetal force due to curved flow Frictional force near the ground • Reading -Ahrens pg 155-158 • Problems -6.23, 24 (24,25)

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