Understanding Convection
Clouds and weather are generally created by vertical motion of a parcel of air. If that parcel has enough moisture in it and is lifted, it will expand, cool and when the temperature reaches the dew-point the moisture will condense and cloud is born. Raise the parcel farther and moisture has to be precipitated out as the cooler parcel cannot hold as much moisture as it could when it was warmer. This is a simple idea, but the ramifications great.
Lapse Rate
The atmosphere gets colder as you go higher. That's a general rule. The rate of change in temperature as you go up is the lapse rate of the atmosphere.
Lift
Parcels of air don't just start a journey to the higher levels of the atmosphere, they have to have something to start them off. This can be several processes and once the convective journey starts, there's no stopping it till the atmosphere comes to equilibrium. The types of lift that are common are daytime heating, frontal lift, orographic lift and convergence.
Daytime Heating creates lift by the sun heating the ground which heats the lower atmosphere. As warm air is less dense than cooler air it becomes buoyant and starts to rise.
Frontal Lift is started as one air mass either rises up over another (warm front) or when it undercuts another (cold front). The air in the warm air mass is lifted as the cold air becomes thicker under it and the lifted air, again less dense, rises.
Orographic Lift is simple; air is pushed against something big (mountain) and has to go up to get past it. The lifted air is once again made less dense and rises.
Convergence is what happens at the center of a low pressure area. Wind blowing into the low gets to the center and has no place to go but up. Again, lift.
Stability
The stability of the atmosphere dictates what form of clouds are created should there be enough moisture and a bit of lift. A stable atmosphere has a low or negative lapse rate. That is it cools less than average with altitude or actually warms up with altitude (inversion). A stable atmosphere will allow the creation of stratiform clouds. An unstable atmosphere has a high lapse rate (cools more with altitude than average). In an unstable atmosphere a lifted parcel of air has free reign to keep rising.
The Adiabatic Process
An adiabatic process is a process where there is no exchange of heat across the boundary between a parcel of air and the general atmosphere. If we lift a parcel of moist air into the atmosphere by one of the lifting processes outlined above, it also undergoes a decrease in density due to expansion since there is a decreasing weight of atmosphere bearing down on it. In this instance the parcel cools as it expands until it reaches it's dew-point. When that occurs cloud develops within the parcel. The lifted parcel does not readily exchange heat with the surrounding air and consequently the cloud may persist for a long time.
Once cloud has formed the lapse rate of the parcel changes with the release of the latent heat of condensation. Now the parcel can become more buoyant as it's lapse rate has been decreased and if the dynamics of the atmosphere are right, that cloud can keep building becoming a towering cumulus or cumulo-nimbus cloud.
Understanding Turbulence
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