Vertical Motions, Relative Humidity, and Clouds

Vertical motions in the atmosphere are caused by a variety of factors  

Convection due to the solar heating of the Earth s surface. Upward velocities of 2-20 cm/s occur. 

Upward motion associated with convergence of horizontal motions (or vice versa, sinking due to divergence). This will be evident in the discussion of horizontal motions in Section 10.5. Again, vertical velocities of only cm/s usually are observed. 

Horizontal motion over topographic features at the Earth s surface. A classic example of this is seen in the cap clouds associated with flow over mountains. 

Buoyancy caused by the release of latent heat of condensation of water. As will be seen in Section 

Thus we see that vertical motions upward cause water clouds to develop conversely air that descends becomes warm, causing the RH to decrease and clouds to disappear. 

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