Pressure Gradients

Understanding Pressure Gradients

pressure-gradient-pictureSince wind is produced bydifferences in air pressure, it is important to understand pressure gradients, which are the circular lines around a high or low pressure system. Air pressure is created by the motion, size, and number of gas molecules present in the air. This varies based on the temperature and density of the air mass.


The Pressure Gradient and Other Effects on Wind

Within the atmosphere, there are several forces that impact the speed and direction of winds. The most important though is the Earth’s gravitational force. As gravity compresses the Earth’s atmosphere, it creates air pressure- the driving force of wind. Without gravity, there would be no atmosphere or air pressure and thus, no wind.

The force actually responsible for causing the movement of air though is the pressure gradient force. Differences in air pressure and the pressure gradient force are caused by the unequal heating of the Earth’s surface when incoming solar radiation concentrates at the equator. Because of the energy surplus at low latitudes for example, the air there is warmer than that at the poles. Warm air is less dense and has a lower barometric pressure than the cold air at high latitudes. These differences in barometric pressure are what create the pressure gradient force and wind as air constantly moves between areas of high and low pressure.

To show wind speeds on a weather map, the pressure gradient is plotted using isobars mapped between areas of high and low pressure. Bars spaced far apart represent a gradual pressure gradient and light winds.

Lines that are closer together show a steep pressure gradient and strong winds.

Finally, the Coriolis Force and friction both significantly affect wind across the globe. The Coriolis Force makes wind deflect from its straight path between high and low pressure areas and the friction force slows wind down as it travels over the Earth’s surface.


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