What is the Pressure Gradient Force and how does it influence wind?

• A. The force from vertical pressure differences; winds move from low to high pressure.
• B. The force from horizontal pressure differences; winds move from high to low pressure, and the magnitude is proportional to the gradient.
• C. The frictional force at the surface that slows winds.
• D. The Coriolis effect that deflects winds.

Answer: (B)

The Pressure Gradient Force is the horizontal push air experiences due to differences in pressure over a distance. Air moves from areas of high pressure to areas of low pressure because the pressure difference creates a driving force. The bigger the change in pressure per unit distance (the steeper the gradient), the stronger this push and the stronger the wind.

On a weather map, closely spaced isobars mean a steep gradient and stronger winds, while widely spaced isobars mean a gentle gradient and lighter winds. The force points normal to the isobars, from high toward low pressure.

Near the surface, friction slows the wind and can tilt the balance with the Coriolis effect, but the initial cause of the wind is the horizontal pressure gradient. The other concepts—frictional forces and the Coriolis deflection—describe how the wind is redirected after the PGF starts it.