A Vortex (plural: vortices) is a spinning, often turbulent, mass of flowing fluid. Any spiral movement with a closed streamline is considered vortex flow. The speed and rate of rotation of a vortex is always greatest at the center, with progressively decreasing speed away from the center. The fluid pressure is lowest in the center of the vortex, and rises further from the center (Bernoulli’s Principle). The core of a vortex is sometimes visible due to a plume of water vapor caused by condensation in the low pressure of the core. A tornado is an example of the visible core of a vortex.
Two or more vortices that are in close proximity to one another that are traveling in the same direction will often merge into one vortex. The circulation of the merged vortex will equal that of the circulation of the principal vortices. Vortices that are circulating in opposite directions will not merge. A lot of energy is contained within the circular motion of a vortex. Hypothetically, the energy can never dissipate and the vortex would persist forever. However, the fluids contained in a vortex exhibit viscosity which does in fact dissipate energy slowly from the core throughout the vortex.
A vortex is any circular flow that possesses vorticity. Vorticity is a mathematical concept used in fluid dynamics. It is related to the amount of circulation or rotation in the fluid of a vortex. The movement of the fluid is said to be vortical if it moves in a circular pattern, or moves around an axis. In atmospheric sciences, vorticity is characterized by a large-scale rotation of air masses.
Observations of a vortex can show a spiraling motion of air or liquid around a center of rotation. Vortices can appear in a circular water current, such as from conflicting ocean tides. Turbulent flow can also produce vortices in the atmosphere. A whirling air mass in the atmosphere usually takes the form of a spiral, column, or helix. A mesovortex is an atmospheric phenomenon that is generally smaller than a hurricane, but typically larger than a tornado. A vortex can be formed on smaller scales, such as when water rushes down a drain of a sink or toilet. This occurs as the revolving mass forms a whirlpool. It is caused by water flowing out of a small opening at the bottom of the tank.
Some instances of a vortex include a ring of smoke, drag from the wing of an aircraft, a whirlpool in water caused by a hole underneath where water can drain out, a tornado, dust devil or waterspout, hurricanes, sunspots on the Sun, black holes, and spiral galaxies, such as our own Milky Way.