The tornadoes they are not formed by chance or even by the will of the gods, there must be particular atmospheric conditions that at least favor their birth. Usually these are situations of strong instability, with winds that have very different directions and intensity and also directions, depending on the altitude.
How tornadoes are formed
Because yes trumpets of tornadoes it is also necessary that there is a mass of hot air with a high rate of humidity that is underneath a mass of cold, and even dry air. The heat tends to rise, the cold to descend, physics reminds us, so these masses would like to swap places and in an attempt to do so, while very variable and strong winds are going crazy, a strong storm is created. Tornadoes can form in association with storm phenomena of all kinds but usually occur in conjunction with particularly violent storms such as supercells.
We arrived at the unleashing of a strong storm with violent and confused winds, in this context real vortices can also form which are atorigin of the tornadoes. When the eddies are created due to the collision between the hot updraft and the cold descending one, they give rise to short and not particularly violent tornadoes.
Worse are the consequences if the winds are born with the storm itself producing an intense rotation inside it. We talk mesocyclones then, a phenomenon that is not very frequent and that we find when varying winds of progressive intensity and direction blow.
Even jet streams can give rise to a tornado. These are cold currents at high altitudes that contribute to the formation and rotation of the cumulonimbus. This creates thunderstorms that can also include tornadoes, starting from the ascending sector and showing a counterclockwise rotation in the northern hemisphere and clockwise in the southern hemisphere. In the eye of the storm, therefore in the center of the rising air column, a depression forms, an area with a very different pressure from the external one, and the air is literally sucked up to the ground.
Characteristics of the tornadoes
Now that we understand how tornadoes are formed, let's take a closer look at its characteristics. Also called tornadoes, they are vortexes of air that are created at the base of a cumulonimbus and are discharged to the ground. They are almost always accompanied by the occurrence of very strong thunderstorms, with winds that blow even at 500 km / h. The storms that most frequently create tornadoes are le supercells.
Among all the atmospheric phenomena that we know, certainly these are among the most violent and with a rather high destructive potential. In the Mediterranean area they are not very frequent but when they do, they do a lot of damage.
Maybe we have some pictures of the tornadoes occurring in the United States: they have a funnel shape. When they occur on dry land, soil, debris and boulders enter the vortex and also spin whirlwind making everything more dangerous.
There is no standard measure for these phenomena, the basis can have a diameter ranging from 100 to 500 meters, only in truly extraordinary cases is it possible to have larger dimensions, up to 1 km. As the position of the cumulonimbus changes, the height of the tornado also changes, usually it is never less than 100 meters but not even more than 1 km.
As for the duration, it is really short, but in those few minutes all hell breaks loose. On average, tornadoes can last 5 to 15 minutes and they move at a variable speed during their journey ranging from 30 to 100 km / h
Categories of tornadoes
From a purely anthropocentric perspective, we classify tornadoes for theirs destructiveness which is calculated considering its duration, the speed and intensity of the winds. The most terrible are those generated by supercells in certain geographical areas such as the United States where there are fully favorable atmospheric and geographical conditions. Variable winds, strong jet streams at high altitude. high thermal contrast between the air masses involved.
By empirically evaluating the damage caused, a classification of tornadoes was created, represented by Fujita scale advanced which is the equivalent of the Mercalli Scale for earthquakes. Here are the various levels, with an indication of the wind speed.
- WEAK 105–137 km / h
- MODERATE 138–178 km / h
- SIGNIFICANT 179–218 km / h
- STRONG 219-266 km / h
- DESTROYING 267–322 km / h
- CATASTROPHIC> 322 km / h
As for the damage, which is what interests most, at the weak level we talk about falling tree branches, shingles out of place. In the case of catastrophic whirlwind, almost everything is razed to the ground, the trees uprooted.
Fortunately, the most frequent tornadoes are weak and moderate ones, the devastating ones are very rare and the strong ones are only 5% of the total. There is another way to classify tornadoes that is mainly used in England. This is the TORRO staircase and ranges from T0 for extremely weak tornadoes to T11 for the most violent tornadoes ever recorded.