When discussing stability in atmospheric sciences, we typically think about air parcels, or imaginary blobs of air that can expand and contract freely, but do not mix with the air around them or break apart. Atmospheric Stability & Lapse Rates Adiabatic Processes Examples of stability and instability in relation to air and parcel temperatures (created by Britt Seifert). In this chapter we will connect these concepts to the buoyancy of air parcels, and learn to use thermodynamic diagrams to visualize movement.
The topic of stability in atmospheric science is important because the formation of clouds is closely related to stability or instability in the atmosphere. This is an example of neutral stability.Įach of these concepts can be applied to motions of air parcels in the atmosphere. However, if the same boulder were to be placed on flat ground (green circle below) and you were to push it, it would change position, but remain in its new position. If you were able to push the boulder just a little bit in any direction, it would begin to roll downward and accelerate away from its initial position. To visualize the concept of instability, imagine the same boulder at the top of a hill (red circle below). Despite exerting a force on the boulder and causing an initial displacement, it would return to its initial position, and the net displacement would be zero. If you were strong enough to push the boulder from its initial position partway up one of the hills, it would roll back to the bottom once you let go. In order to visualize the concept of stability, you might imagine a boulder sitting at the bottom of a canyon surrounded by steep hills, as depicted in the figure below by the blue circle. Instability in the atmosphere is a concept that is intimately connected with thunderstorms, cumulus development, and vertical motion. A perfect cumulus cloud just west of Magic Island (photo by Sarah Williamson). Such clouds are in a constant state of change, and thus represent the atmosphere in an unstable state. When you see a fluffy cumulus cloud, you might notice them changing shape from one minute to the next. An unstable object is likely to fall or change position with time. The opposite is true with something that is “unstable”.
When you think of the word “stable,” you typically think of an object that is unlikely to change or something that is balanced.
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