Cirrus cloud spreading from the top of a dying cumulonimbus. Cirrus forms from tropical cyclones, and is commonly seen fanning out from the eyewalls of hurricanes. A large shield of cirrus and cirrostratus typically accompanies the high altitude outflow of hurricanes or typhoons, and these can make the underlying rain bands—and sometimes even the eye—difficult to detect in satellite photographs. Thunderstorms can form dense cirrus at their tops. As the cumulonimbus cloud in a thunderstorm grows vertically, the liquid water droplets freeze when the air temperature reaches the freezing point. The anvil cloud takes its shape because the temperature inversion at the
Mushroom cloud stabilization altitude. Significantly smaller fireballs produce clouds with buoyancy-governed ascent. After reaching the tropopause, the bottom of the region of strong static stability, the cloud tends to slow its ascent and spread out. If it contains sufficient energy, the central part of it may continue rising up into the stratosphere as an analog of a standard thunderstorm. A mass of air ascending from the troposphere to the stratosphere leads to the formation of acoustic gravity waves, virtually identical to those created by intense stratosphere-penetrating thunderstorms. Smaller-scale explosions penetrating the tropopause generate waves of higher frequency, classified as infrasound. The explosion