Meteorology: Understanding the Atmosphere            Ackerman and Knox



Balance of Forces

This applet at the bottom of this page, along with the questions below will help you to better understand the basic balance of forces that generate the winds.

Geostrophic winds

Set the friction force to "0"
Set the pressure gradient force to -5 hPa / 5 degree latitude
Set latitude to 40N
For a constant pressure gradient force what is the relationship between latitude and wind speed? 
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 wind speed? 
What happens to the Coriolis force? Is this what you expected? 
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 40N
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 wind speed? 
In what direction does the Coriolis force act. How does this change as the friction force increases?


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"