Wind, the role of pressure gradient force

MANKATO, Minn. (KEYC) - Wind is an invisible force. Its presence can be felt, indirectly seen, and measured by weather instruments. The Sun is the driving force for most winds. Uneven heating, from the Sun, across different parts of the Earth, causes pressure differences. Those pressure differences are areas of high pressure and areas of low pressure. Naturally, wind will travel from areas of high pressure towards areas of low pressure. A change in pressure across a given distance is called a pressure gradient. A pressure gradient force is then the net force between these two different areas of pressure.

To give you an example think of two points. Point A has a pressure of 1013 millibars and point B has a pressure of 995 millibars. Since point A has a higher pressure, air will travel from point A to point B. If you know the distance between the two points you can calculate the pressure gradient force. In general though, the greater the pressure difference the faster the flow of air will be, or in other words the higher the winds will be.

On a weather map, a pressure gradient can be seen by looking at a plotted surface map. Solid, circular and or oval shaped, lines are isobars, which are constant lines of pressure. The closer the lines are together the higher the pressure gradient is, which in return means faster winds.

If you would like to see pressure gradient force in action, try this. Take an air pump needle and stick it into the valve of an inflated ball, like a basketball. You will notice that the air flows effortlessly out of the ball until it’s flat. The reason the air flows out of the ball is due to the pressure gradient force. Air within the ball has a higher pressure so it is flowing to the outside where the air pressure is lower. At first there is a higher pressure gradient force between the air inside the ball and the air outside. This will result in air flowing out of the ball at a faster rate. Eventually, the pressure within the ball and the pressure outside the ball will be close to equal, resulting in air flowing out at a much slower pace.