What best defines atmospheric stability?

Atmospheric stability refers specifically to the degree to which vertical motion is enhanced or suppressed within the atmosphere. When the atmosphere is stable, it tends to resist vertical motions, meaning that air parcels do not easily rise or form significant vertical currents. Conversely, an unstable atmosphere promotes rising air and the development of convection.

Understanding atmospheric stability is crucial in wildland fire behavior as it significantly influences fire spread and intensity. Stable conditions may limit the development of large, active fire behavior because the vertical movement of warm air is curtailed, while unstable conditions can enhance fire growth by allowing convective currents to transport heat and gases upward, further fueling the fire.

In contrast, the other options do not accurately encompass the definition of atmospheric stability. The prominence of horizontal motion, overall pressure, and humidity levels may influence weather patterns and fire behavior, but they do not directly define stability in terms of vertical air movement.