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Happy Thanksgiving!!

2. MADISON’S CURRENT WEATHER
at 900 AM CST WED NOV Updated twice an hour at :05 and :25
Sky/Weather: SUNNY (CLEAR!!) Temperature: 40 F (4 C) Dew Point: 27 F (-2 C) Relative Humidity: 59% Wind: VRB6 MPH Barometer: 29.79S

3. CURRENT IR

4. CURRENT VISIBLE

5. Surface Weather Map from Today with Isobars & Fronts

6. Current Temperatures (oF) & Isotherms

7. 24 hour Temperature Change (Fahrenheit Degrees) [Current – Sun AM] (oF) & Isotherms

8. Current Dewpoints (oF)

9. Tomorrow’s 7AM Forecast
Happy Thanksgiving!

10. ATM OCN 100 - Summer 2002 LECTURE 18
THE THEORY OF WINDS: PART II - FUNDAMENTAL FORCES
A. INTRODUCTION
How do winds originate?
What factors influence the winds?

11. B. EXPLANATIONS of ATMOSPHERIC MOTION
Practical Problems
Historical Concepts
Forces of Motion & Newton's Laws

12. NEWTON’S EQUATIONS of MOTION
1st Law (Conservation of Inertia) Object at rest will remain at rest or object moving at constant velocity will continue until acted upon by a net force.
2nd Law Force = mass x acceleration.
3rd Law For every action, an equal & opposite reaction exists.

13. B. EXPLANATIONS of ATMOSPHERIC MOTION (con’t.)
Implications of Newtonian Laws
Vectors, Forces and Units
Velocity -- a vector (speed & direction)
Speed or magnitude of velocity-- a scalar [mph or meters per second, etc.]
Acceleration or rate of change of a velocity vector -- a vector [ft/sec/sec or meter/sec2]
Force -- a vector -- What causes a mass to accelerate [pounds, or Newtons]

14. C. DESCRIBING ATMOSPHERIC MOTION
Reasons for Atmospheric Motions:
Buoyancy Effects or Dynamic Effects

15. C. DESCRIBING ATMOSPHERIC MOTION
An Equation of Motion
Complications involved with Atmospheric Motion:
Spherical planet;
Rotating planet & non-inertial frame of reference.

16. An example of an equation of motion NASA

17. DESCRIBING ATMOSPHERIC MOTION (con’t.)
Three-Dimensional Equation of Motion for the Atmosphere
A vector equation;
Entails specification of all forces per unit mass (i.e., equivalent to acceleration);
All forces do not act alone;
Vector sum of individual forces equals net force.

18. Numerical Weather Prediction

19. Numerical Weather Prediction

20. Numerical Weather Prediction

21. FORCES ASSOCIATED WITH ATMOSPHERIC MOTION
Following forces influence motion of air parcels:
Pressure Gradient Force
Gravitational Force or Gravity
Coriolis Effect or "Force"
Frictional Force or Friction
Centripetal Force or more specifically --

22. PRESSURE GRADIENT FORCE
Generated by differences in pressure within a fluid element;
Responsible for initiation of all air motion;

23. Explaining Differences in Air Pressure
Low Pressure
High Pressure

24. L
Current Winds L H H

25. PRESSURE GRADIENT FORCE (con’t.)
A 3-dimensional vector that has:
Magnitude of pressure gradient force vector depends:
directly upon difference in pressure over a given distance (i.e., slope or grade equals “pressure gradient”).
Direction of pressure gradient force vector is:
from High pressure to Low pressure,
along steepest direction of pressure gradient.

26. PRESSURE GRADIENT FORCE (con’t.)

27. PRESSURE GRADIENT FORCE (con’t.)

28. GRAVITATIONAL FORCE or GRAVITY
Produced by mutual physical attraction between massive bodies;
Gravity refers to acceleration;
Acts continuously, regardless of motion;
A vector quantity that has:
Direction – toward center of earth.
Magnitude ~ 9.8 m/s2 (32 ft/s2)

29. CORIOLIS EFFECT or FORCE
Produced by earth’s rotation;
A “fictitious force” used to explain apparent deflection of moving object on a rotating frame of reference;

30. CORIOLIS EFFECT or FORCE
Produced by earth’s rotation;
A “fictitious force” used to explain apparent deflection of moving object on a rotating frame of reference;
Run coriolis.mpg from

31. CORIOLIS EFFECT or FORCE (con’t.) Speed is dependent upon latitude:

32. An example of the Coriolis Effect Fig. 9.5 Moran & Morgan (1997)
Time 1
Time 2

33. CORIOLIS EFFECT or FORCE (con’t.)

34. Coriolis Effects upon the Wind Fig. 9.6 Moran & Morgan (1997)

35. CORIOLIS EFFECT or FORCE (con’t.)
Produced by earth’s rotation;
A “fictitious force” used to explain apparent deflection of moving object on a rotating frame of reference;
Acts only after motion is initiated;
Can only modify direction of motion;
A 3-dimensional vector, but consider only horizontal component described by:

36. CORIOLIS EFFECT or FORCE (con’t.)
Magnitude of horizontal Coriolis force vector depends upon:
Rotation rate of earth (Direct relationship);
Speed of object; (Direct relationship)
Latitude (specifically, sine of latitude).

37. CORIOLIS EFFECT or FORCE (con’t.)
Direction of horizontal component of Coriolis force vector:
Causes a deflection of moving object to right of direction of motion in Northern Hemisphere; but
Deflects moving object to left of intended motion in Southern Hemisphere.

38. FRICTIONAL FORCE or FRICTION
Produced by “viscosity” (interactions of moving fluid elements with one another or with a boundary surface) due to:
random molecular motions;
large random turbulent motions of fluid associated with either:
thermal turbulence
mechanical turbulence

39. An example of Turbulent Viscosity Fig. 9.5 Moran & Morgan (1997)

40. FRICTIONAL FORCE (con’t.)
Acts only after motion is initiated;
Acts to retard motion;
Magnitude of friction force vector depends upon:
Speed of motion of fluid;
Type of surface, e.g., “surface roughness”;
Temperature structure of fluid.
Direction of friction force vector is
opposite motion vector.

41. Relative Surface Roughness Source: Stull, 1995

42. Centripetal Force Fig. 9.3 Moran & Morgan (1997)

43. CENTRIPETAL FORCE
Produces curved motion;
Opposite the “centrifugal force”;
Acts only after motion is initiated; In reality, a net force Used to describe imbalance of other forces in curved motion;

44. CENTRIPETAL FORCE VECTOR (con’t.)
Centripetal force vector is described by:
Magnitude of centripetal force vector depends upon:
Speed of instantaneous motion (a direct relationship);
Radius of curvature (an inverse relationship).
Direction of centripetal force vector is
inward toward center of curvature.

45. SUMMARIZING A 3-D Equation of Motion for Atmosphere (in word form):
Net force = Pressure gradient force gravitation force Coriolis force + friction.
Notes:
The above is a vector equation!
Since a unit mass is used, force is equivalent to an acceleration.