What atmospheric condition is usually present at 300 mb above a developing surface cyclone?

• A. Convergence
• B. Neutral pressure
• C. Divergence
• D. Stagnation

Answer: (C)

In the context of atmospheric dynamics, divergence at the 300 mb level is a crucial factor in the development and maintenance of a surface cyclone. At higher altitudes, such as the 300 mb level, the air is moving outward from a localized region. This outward movement creates a decrease in air pressure aloft, which is essential for allowing the surface low-pressure system to deepen and strengthen.

As air rises in a developing cyclone, it must be compensated for by air moving away at higher altitudes, leading to divergence. This divergence at the 300 mb level facilitates the continuous ascent of air from the surface, which helps to sustain the low-pressure center. Without this divergence, the air would not be able to rise effectively, causing the cyclone to weaken rather than develop.

In contrast, the other atmospheric conditions presented do not align with the behavior typically observed at this height above a developing surface cyclone. For instance, convergence would imply an accumulation of air, conflicting with the requirement for air to be diverging to support a low-pressure system. Neutral pressure does not accurately describe the dynamic conditions necessary for cyclone development at this level. Stagnation, which suggests a lack of movement, would also not support the active processes associated with a cyclone's growth.