The geostrophic wind is a balance between which two forces?

• A. Pressure gradient force and gravitational force
• B. Temperature gradient and wind shear
• C. Pressure gradient force and Coriolis force
• D. Friction and Coriolis force

Answer: (C)

The geostrophic wind is defined by a balance between the pressure gradient force and the Coriolis force. When air moves in response to the difference in air pressure, the pressure gradient force acts to push the air from areas of high pressure to areas of low pressure. However, as this air begins to move, the Coriolis force, which is caused by the rotation of the Earth, acts perpendicular to the direction of the wind, causing the wind to deflect to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This deflection results in a wind flow that is parallel to the isobars, rather than blowing directly from high to low pressure, which is characteristic of geostrophic balance.

In contrast, the other choices incorporate forces that do not establish the geostrophic wind's foundational definition. The gravitational force and friction both play roles in different atmospheric processes but are not part of the geostrophic wind balance. The temperature gradient and wind shear pertain to different phenomena, such as the development of weather fronts and turbulence. Understanding the interplay between the pressure gradient force and the Coriolis force is crucial for interpreting wind patterns at larger scales in the atmosphere.