Lesson 1
Chapters 1 & 2
Lesson 2
Chapter 3 & Instrument Supplement
Lesson 3
Weather Maps
Lesson 4
Chapter 4
Lesson 5
Chapter 5
Lesson 6
Chapter 6
Lesson 7
Chapter 7
Lesson 8
Chapter 8
Lesson 9
Chapter 9
Lesson 10
Chapter 10
Lesson 11
Wind Shear and Turbulence
Lesson 12
Icing
Lesson 13
Visibility
Lesson 14
Case Study/Self-Briefing
Lesson 15
Case Study/Self-Briefing
Lesson 16
Case Study/Self-Briefing

LESSON 4

Magnitude and Direction of Forces

This applet (Thanks to Jeff Wilson from the Australian Met Bureau) allows you to test your understanding of the relationship between wind speed and direction and the pressure gradient, Coriolis, and Friction forces.

To help you understand these concepts, use the applet below to answer questions on Geostrophic Wind

To help you understand these concepts, use the applet below to answer questions on Friction

This applet has 6 parameters "startLatitude" between -90 & 90 "startGradient" values between -15 & 15 -ve gradient has high pressure to North of low "background" is the background gif image of 360 lines by 420 elements covering 90S to 90N "plotvalues" is a toggle to show the actual values (true) or not (false) "plotgeo_arrows" is a toggle to allow plotting the geostrophic & ageostrophic winds (true) or hide (false) "wind_units" is "m/s" or "kts" "press_units" is "hPa" or "MB"
Geostrophic winds
Use the upper left-hand slider to set the friction force to "0"
Use the upper right-hand slider to set the pressure gradient force to -5 hPa / 5 degree latitude
Use the slider on the left to set latitude to 40N

For a constant pressure gradient force what is the relationship between latitude and windspeed? Test this relationship by varying the latitude. As you change the latitude what happens to the magnitude of the coriolis force? Why is this?
Increase the magnitude of the pressure gradient force. What happens to the windspeed? What happens to the coriolis force? Is this what you expected?

Adjust the latitude value to within a few degrees of the equator. What happens to the windspeed? Why does the windspeed change like this? Is this windspeed realistic? Would the geostrophic assumption be valid in the tropics.

More information on the Geostrophic Wind.

Friction
Use the upper left-hand slider to set the friction force to "0"
Use the upper right-hand slider to set the pressure gradient force to -4 hPa / 5 degree latitude
Use the slider on the left to set latitude to 40N How should friction change the magnitude and direction of the wind?
Now increase the friction force. What impact does this have on the magnitude and direction of the actual windspeed? In what direction does the Coriolis force act, how does this change as the friction force increases?

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This web based lab section is being developed with assistance from the College of Letters and Science and the Cooperative Institute of Meteorological Satellite Studies.   Material presented is Copyrighted (C) 2000 by Steve Ackerman .  Feel free to use this material for non-profit educational purposes!