The shape of the shock wave (influenced by different speed in different altitudes), and the temperature and humidity of different atmospheric layers determine the appearance of the Wilson clouds. During nuclear tests, condensation rings around or above the fireball are commonly observed. Rings around the fireball may become stable and form rings around the rising stem of the mushroom cloud. The lifetime of the Wilson cloud during nuclear air bursts can be shortened by the thermal radiation from the fireball, which heats the cloud above to the dew point and evaporates the droplets.