Question

A rotating weather system has a tangential velocity of 100 m/s, diameter of 1 km, and located at a latitude where the Coriolis parameter is \( 10^{-4} \, {s}^{-1} \). Which one of the following statements is true about this weather system?

• A. It is in geostrophic balance.
• B. It is in gradient wind balance.
• C. It is a high-pressure system.
• D. It is in cyclostrophic balance.

Hint:

Cyclostrophic balance is important for small-scale, rapidly rotating systems where the centrifugal force and pressure gradient force are dominant, and the Coriolis force can be neglected.

Answer 1

The Correct Option is D

The weather system described has a tangential velocity and a given Coriolis parameter, which suggests it is a rotating system. In such a system, the balance between forces determines the wind profile. Here’s how to determine the correct balance:
- Cyclostrophic balance (Option D) occurs when the centrifugal force is balanced by the pressure gradient force in a rotating system. This is typical for small, rotating systems like tornadoes or cyclones, where the tangential velocity is large compared to the Coriolis force, and the system's scale is small (such as 1 km in diameter in this case). Cyclostrophic balance is valid when the Coriolis force is negligible.
- Geostrophic balance (Option A) applies to large-scale systems like mid-latitude cyclones where the Coriolis force balances the pressure gradient force. This is not the case here since the system's small size and large tangential velocity make cyclostrophic balance more appropriate.
- Gradient wind balance (Option B) refers to the balance between the Coriolis force, the pressure gradient force, and centrifugal force in large rotating systems. However, this system is too small and has a large tangential velocity, making this balance less relevant.
- High-pressure system (Option C) is not necessarily true for this scenario, as the weather system described does not specify whether it is a high or low-pressure system. The focus here is on the balance of forces.
Thus, the correct answer is (D) It is in cyclostrophic balance.