Fist of an Angry Cloud

August 06, 2011

Fist_of_an_angry_cloud (3)
: Phil Plait; Phil's Web site
Summary Author: Phil Plait; Jim Foster

Looking out my office window a few weeks back, I spotted this cloud looking like it was angrily defiant and ready to punch the sky. At first, I thought it might be a convective cloud that would build into something more substantial, but it turned out to be just a puffy, fair weather cloud (Cumulus mediocris) seen at the right moment. Newly formed cumulus clouds tend to have sharp boundaries and contain only liquid water, though, they may extend higher than the freezing level (0 degree C isotherm). They'll often take on a "cauliflower appearance."

Growth is strongly related to the cloud's environment. If drier air surrounding the developing cloud mixes into the cloud (entrainment), the rate of evaporation is increased and thereby its positive buoyancy is decreased via evaporational cooling. Subsidence around the cloud can encourage a new cloud to develop in the same vertical column as the original cloud, but in this case, alas it was not to be. Photo taken on July 2, 2011.