In the previous chapter we considered the humidity of air near the surface, and in the next we shall deal with cloud formation, often at levels far above the ground. The connection between the two is usually the uplift of low-level air. In the present chapter we will examine how the uplift results from features of the temperature profile (Section 1.6) and the humidity profile (Section 6.6).
There are several ways of creating uplift:
(a) wind may be forced to rise by hills (orographic uplift),
(c) converging low-level winds squeeze air upwards,
(d) diverging upper-level winds suck air from below, or
(e) turbulence within strong winds over rough terrain stirs some air down and some up.
In all those cases, the uplift is forced. Alternatively, there may be uplift caused by thermal convection due to the spontaneous buoyancy of warmed air; it is this process in particular which is considered in the present chapter. More than one process may operate in practice. For instance, a cold front (Chapter 13) might initiate uplift, which is then continued by convection.
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