Which atmospheric phenomenon is characterized by circular wind systems?

The correct answer is the phenomenon characterized by circular wind systems. Cyclones are large-scale air mass rotations that occur in the atmosphere due to the Coriolis effect, which is the result of Earth’s rotation. This effect causes the air to spiral inward toward areas of low pressure, creating circular wind patterns. Cyclones can vary in size and intensity, with tropical cyclones, such as hurricanes, being one of the most well-known examples.

While hurricanes are indeed a type of cyclone and also exhibit circular wind systems, the term "cyclone" encompasses a broader category that includes all forms of low-pressure systems with rotating winds, including extra-tropical and polar cyclones.

Thunderstorms, on the other hand, are characterized by the rapid updraft and downdraft of air, but do not typically have circular wind patterns. Fronts refer to boundaries between different air masses, leading to various weather phenomena, but are not themselves characterized by circular wind systems.