The Hurricane From the Mayan language, “Great Wind”) is a tropical depression and can only be formed above the water.This requires water temperatures of more than 27 degrees to higher depths and even wind conditions at all altitudes. These conditions are particularly pre-existing in the northern hemisphere in the second half of the year, just north of the equator, in the so-called trade wind zone.
Here, the weather is almost always cloudless over the sea and scattered but very high-yielding storm clouds can form.Many of these long-lived thunderstorms are also drifting out of Central Africa to the Atlantic Ocean. If the wind now turns more northwards, it gets a rotational impulse through the Coriolis force, resulting in a flat circulation, which now organizes the scattered standing storm towers into a vortex and ranks them. A depression – called tropical depression – is being created in the center.
Continued undisturbed wind conditions, provided tropical humid air and warm sea water, the low can further organize itself and incorporate more storm clouds into its circulation.The characteristic spiral bands of the emerging tropical storm are formed. These allow the low to use and concentrate the energy stored in the water of an enormous marine area. A tropical storm occurs when the closed circulation reaches a wind speed of at least 65 km/h.
Now the characteristic cloud wall around the center of the storm is beginning to develop.It consists of up to 200 densely packed huge storm clouds. Here, the warm humid air rises quickly into the stratosphere and spreads circularly at the top like a huge ice shade. In the center there is a descent motion, which strongly warms the core and causes the clouds to dissolve – the eye. A hurricane has emerged.
A hurricane often measures several hundred kilometers in diameter and, in extreme cases, reaches wind speeds of 350 km/h with gusts of up to 400 km/h and a core pressure of 872 hectopascals.A conventional barometer can no longer measure such a pressure. (Hurricane Patricia October 23, 2015, west coast of Mexico). The overall speed at which the storm moves is very small, from barely more than pedestrian speed to about 30 km/h.
Thus, one usually has enough time to warn and evacuate any of the populations threatened by such a storm.
The greatest damage and most deaths are not caused by the wind, but by the storm surge brought by the hurricane.On certain coasts, this storm surge can rise more than 5 meters above the normal flood level – and then there are the occasional 15 meter high waves. Inland, the storm then dissipates quickly, releasing extraordinarily large amounts of rain.
The Tornado (Spanish for “turned”) is always made over land in contrast to the hurricane and is rare in tropical areas.The conditions for its formation are mainly found in the Great Plains of the USA and immediately to the south and north adjacent areas. In North America, the large mountain ranges are transverse to the main wind direction, which at the same time allows Arctic air masses from the north and tropical moisture from the south to be transported far south and north without hindrance.
Tornadoes are always expected when a low pressure area moves from the Pacific over the Rockies in the jet stream.The mountains even deflect the jet stream, which in turn reinforces the low in the Rockies’ Lee. On its front there is a large southcurrent, which transports tropical sea air far inland.
Behind the low is the cold front, which is supplied with cold, dry air directly from the far north.As soon as this cold front moves over the mountains, the already dry air becomes even drier due to the influx of still dry desert air from the Mexican highlands, a so-called “Dry Line” creates a “dry front”, which creates a sharp air mass limit. to the humid tropikluft in the east, at this border now a whole series of massive thunderstorm storms are shooting up, because behind the border in the dry desert air there is an almost unlimited, intense solar radiation available.
Unlike the hurricane, which is weakened by wind shear (different wind direction in height than on the ground), the tornado needs this to produce rotation.Usually the whole cloud starts to turn, this is called “supercell”. Often such thunderstorm clouds then form a tornado, usually in the back part, after the rain curtain. The tornado then descends from the base of the cloud down to the ground.
A tornado therefore has only a few minutes of warning time and can often only be detected at the last moment.Like hurricanes, they are divided into a multi-part scale, the Enhanced Fujita Scale, abbreviated EF.
EF1 and EF2 are usually only small and short-lived storms with winds of up to 200 km/h.An EF3 is already very strong, EF 4 and EF 5 catastrophic. The strongest EF 5 tornadoes reach wind speeds of up to 500 km/h and reach up to 1 km wide. Strong tornadoes can move for tens of kilometers at up to 100 km/h, the same speed as the front of the low pressure area they have produced.
The damage caused by tornadoes is mostly local in nature, but is mostly total, especially with EF 4 and EF 5 storms.They are always caused by the wind itself and the debris carried in it. The rain and hail are often surprisingly low in tornadoes. In most years, tornadoes in the US have more deaths than hurricanes.
Tornadoes like to occur in “packs” when conditions are favorable, while it is extremely rare for two hurricanes to come close.
Recently, so-called “derechos” (Spanish – straight-) These are strong wind fields that are produced by a strong thunderstorm line when rain falls into a hot, dry air mass and the wind of the associated winds Cold front reinforced.They often cause significant damage to infrastructure and vegetation. Similarly, the “Haboob” (Arabic – violent storm) is emerging in the southwestern desert areas of the USA (and in Arabia).There are then huge sand and dust storms.