The phenomenon often observed in a swirling tornado is called a vortex. A vortex occurs when rotating air creates a whirling motion, leading to the formation of the tornado's characteristic funnel shape. This phenomenon specifically occurs due to differences in air temperature and pressure, generating strong winds and upward drafts. Vortices are not only related to tornadoes but can also be seen in various natural occurrences, such as whirlpools and dust devils, illustrating the principles of fluid dynamics.