This is the largest kind of cloud, like an icecream castle or a vast cauliflower, capped by a sideways extension, the anvil. The usual great extent of the cloud's growth is caused by deep convective instability within most of the troposphere (Section 7.4). A cumulonimbus cloud is typically higher than 5 km, and often reaches the tropopause, helping define it. The depth of the cloud increases its albedo, so that it has a blinding whiteness from above and appears very dark from below.
There are vigorous updraughts within each cloud, with a speed which is typically around 5 m/s but can be over 15 m/s, implying travel from cloud base to cloud top in less than 15 minutes.
In the extreme, there have been updraughts of 60 m/s, surrounded by downdraughts of 35 m/s. The commotion leads to thunderstorms, lightning and rain (Chapters 9 and 10).
Was this article helpful?