Lesson 2:Wind, Pressure and Altitude
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Introduction

The activity below allows you to test your understanding of the relationship between wind speed and direction and the pressure gradient, Coriolis, and Friction forces.

Questions to consider

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.

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?

Applet

Once you add friction, you will see the geostrophic wind (gWind) and the ageostrophic wind (aWind) which are components of the true wind.

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"

  Time Requirement

15-20 minutes.