Mr Twister Weather Ed
How does a tornado form?
Do all Tornadoes and Mesocyclones spin the same direction?
There are a number of processes that are responsible for rotation of a tornado and a supercell. The environment has to be just right.
1.First, there is the mesocyclone, that is larger than the tornado itself, yet close to the ground the mesocyclone can be narrowed by the strong updraft: this process, called vortex stretching, intensifies the circulation, due to angular momentum conservation. If the stretching continues, a narrow funnel may result. This funnel is made visible by the low core pressure. Cooling causes condensation, and the cloud droplets make the funnel appear.
2.Most tornadoes result from the tilting of rotation around a horizontal axis. This horizontal vorticity is due to vertical shear of the wind in the storm's environment. Most supercell storms form in a sheared environment, with poleward winds near the ground and intense westerly winds aloft. The horizontal vortex tubes then are tilted as the air turns to rise in the storm's updraft, creating a component of twist about a vertical axis. Vertical vorticity due to vortex tilting is usually intensified further by vortex stretching. The wind shear responsible for the horizontal vorticity may be storm-induced, rather then environmental.
3.A cold pool often forms under mature severe storms, due to the evaporation of rain below the cloud base, and because of mid-level entrainment of air with a much lower equivalent potential temperature than the surface air. The boundary between the cold pool and the warm, moist inflow is called the gust front. Horizontal vorticity is generated by the temperature differences across the gust front. This baroclinically generated vorticity is advected into the main updraft by the low-level inflow over the gust front, and the vorticity advection spins up the updraft.
At surface level, winds spiral inward toward a tornado then spiral rapidly upward in corkscrew fashion within the tornado. The sense of rotation is cyclonic (counterclockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere) in the majority of tornadoes, but not in all of them. Anticyclonic tornadoes (clockwise rotation in the Northern Hemisphere), though rare, do occur, accounting for less than 2 percent of all tornadoes. Anticyclonic tornadoes usually are less intense, but on April 4, 1981, an F4 tornado that took three lives and injured 53 in West Bend, Wis. displayed rare clockwise rotation.
