vortex

A vortex is a fluid-dynamic phenomenon of a region of fluid in motion around an axis. They form when a fluid, such as liquid, gas, or plasma is stirred and also are a characteristic of turbulent flow. Some situations where they occur in astrophysics:

• planetary atmospheres, e.g., Jupiter and Neptune. (On Earth, circular weather phenomena such as cyclones and tornados are examples.)
• sunspots.
• gas clouds.
• accretion disks.

Vorticity is a measure of vortex-like motion, consisting of the (vector analysis) curl of the fluid's velocity field.