Chapter 6 - Stability and Cloud Development Flashcards
Explain the difference between environmental lapse rate and dry adiabatic rate.
Environmental lapse rate = the rate at which the temperature of the air surrounding us will change with altitude.
Dry adiabatic rate = the rate at which the temperature of an air parcel of unsaturated air will decrease with altitude.
What is a stable atmosphere and how can it form?
In a stable atmosphere, a lifted parcel of air will be colder (heavier) than the air surrounding it. The atmosphere becomes more stable as the surface air cools, the air aloft warms, or a layer of air sinks over a vast area.
List and explain several processes by which a stable atmosphere can be made unstable.
The atmosphere becomes unstable as the surface air warms, the air aloft cools, or a layer of air is either mixed or lifted.
Why are there usually large spaces of blue sky between cumulus clouds?
Around the cloud the air is sinking. This is because of evaporation at the outer edge of the cloud, which cools the air. Another reason is the completion of the convection current started by the thermal, cool air wants to replace the rising warm air.
How is it possible for a layer of air to become convectively unstable and absolutely stable at the same time?
Convective instability is the potential instability created when lifting a layer of absolutely stable air with a dry top and a moist bottom. So when the layer of air is close to the surface it is stable but when brought vertically up it becomes unstable. It is stable but due to difference in humidity it can become unstable if forced to rise since the top and bottom change by dry and moist adiabatic respectively. It is stable but convectively unstable since it is dry at the top and moist at bottom.
The layer becomes thicker as it moves up and hence temp change is bigger at the top than at the bottom. Ex. Pollution and inversions.
Are the bases of convective clouds generally higher during the day or the night? Explain.
The convective cloud base is higher when the difference between temperature and the dew point is large. Bigger difference can hence be obtained by a high surface temperature and a low dew point, dry air. since the temperature is warmer during the day than night and the air is dryer during the day, the cloud bases would be higher during the day. Surface temperature is much closer to dew point during the night so when rises it creates clouds.
