This applet allows you to test your understanding of the basic geostrophic wind equation. 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
Set the friction force to "0"
Set the pressure gradient force to 5 hPa / 5 degree latitude
Set latitude to 40S

Write down the equation for the geostrophic wind. In plain english what does this equation describe about the relationship between latitude, windspeed and the pressure gradient force?
Now test your relationship

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.

Balanced Flow
Set the pressure gradient force to -4hPa/ 5 degree of latitude
Set the latitude to 40S
Set the friction force to "0"

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? What is the relationship between the geostrophic and ageostrophic wind.