What are mini tornadoes?

Answer 1

First we need to figure out what we mean by "mini tornado", as the term has no definition.

Some European and Australian news outlets refer to the tornadoes they get as "mini tornadoes" regardless of how large or strong they are. These form in the same manner as any tornado.

Some people might use the term "mini tornado" to refer to any tornado that is comparatively small and weak. These form in the same way strong tornadoes do, but with less ideal conditions. Weak tornadoes and waterspouts can form in a couple other ways as well.

Finally, sometimes small whirlwinds such as dust devils are sometimes called "mini tornadoes." These are not actual tornadoes and have their own ways of forming.

As to formation:

The classic means of tornado formation is through a kind of thunderstorm called a supercell. Supercells typically form along a cold front or dry line, at the edge of or just inside a warm, humid air mass. The storms are fueled by the warm, moist air and rotate due to interactions with a condition called wind shear, where wind speed and direction changes with altitude. The area of rotation in these storms is called a mesocyclone. Under the right conditions a downdraft can wrap around the mesocyclone, tightening and intensifying it into a tornado. Mesocyclones can sometimes be embedded in a squall line as well.

Sometimes "spin up" tornadoes can form along the turbulent leading edge of a severe squall line. These tornadoes are generally short-lived and weak. There is yet another kind of tornado called a landspout. These form when there is a broad circulation of air at ground level that gets caught in the updraft of a developing thunderstorm, which stretches and tightens it into an intense vortex. Waterspouts form in a similar way.

Finally we have other whirlwinds that are not considered tornadoes, but look a bit like them. Dust devils are the most common example. These form on days when the sun heats a patch of ground, creating a layer of extra hot air right at ground level. This will rise up in a thermal. Sometimes this updraft will catch an eddy in the wind, causing it to tighten and intensify, lifting dust and sand into the air. People have also observed things such as "haydevils" which are essentially the same thing. Finally there are the whirls that pop up on windy days. These are simply eddies that form from the wind going around things such as buildings and trees. They sometimes can be seen when they pick up snow, leaves, or other light materials.

Answer 2

It depends. There is no real definition. Sometimes people use the term to describe small whirlwinds such as dust devils, which aren't really tornadoes, or refer to small artificial vortices that simulate tornadoes.

Some have used the term to describe small, weak tornadoes that do no cause major damage.

In Europe and Australia the term seems to be applied to virtually any tornado that strikes, even ones that cause significant damage. In 2008, a tornado in France leveled a house, considered F4 damage, before growing to a relatively. It was referred to by the media as a mini-tornado despite there being nothing mini about it.

Some tornadoes, called mutliple vortex tornadoes, have smaller vortices inside the main circulation, revolcing around the center of the tornado. These are sometimes informally called mini tornadoes, though they are more preperly called suction vortices. They are not considered tornadoes in and of themselves, but rather part of a single, larger tornado.