Meteorology: Understanding the Atmosphere            Ackerman and Knox

Jet Stream and Horizontal Temperature Gradients

Today's weather reports often discuss the position of the jet stream. A jet stream is a narrow stream of relatively strong winds (i.e. wind speeds greater than 50 knots). The term jet stream is used to describe these winds because of how they were discovered.

The existence of the polar front jet streams is tied to the presence of horizontal temperature gradients. If temperature gradients exist through a deep layer of the troposphere, a pressure gradient force increases with height throughout the layer, and therefore so does the wind. The relationship between wind speed and temperature gradients is demonstrated with the following simple model.

Use the simple model below to answer the following questions (Instructions):

1. As you change the temperature gradient what happens to the maximum wind speed?
2. What does this simple model predict about the global winds if the temperature was uniform across the globe?
3. Does this model predict stronger winds during summer or winter?
   

   Instructions

   Use the thumbwheel at the top to set the surface temperature gradient between the equator and polar regions. The gradient is shown in the upper left hand figure. The resulting maximum wind speed is plotted as a function of latitude in the lower diagram. The right hand figure shows how wind speed varies with altitude at a given latitude. Drag the orange vertical bar to adjust the latitude to use for the vertical wind speed profile.

   Equations from Stull: "Meteorology for Scientists and Engineers, 2nd Edition", Brooks/Cole 2000.