Why don't hurricanes occur all year round?

Weather and cyclones How tornadoes and hurricanes are created


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They swirl over land or water and destroy what crosses their path: tornadoes and hurricanes. Both are cyclones, both can leave a trail of devastation, but they arise in very different ways. How do they come about? What is the difference between a hurricane, a cyclone, and a typhoon?

Status: April 26, 2021

August 2020: Hurricane Laura devastates Cameron, Arizona Hurricane Laura reached the size of Katrina in late August in 2005. It swirled over the US mainland with winds of up to 240 kilometers per hour, causing severe devastation. This year an unusually large number of hurricanes crossed the Atlantic, so that the list of names has been used up. On it are 21 names from A to W. Storm Wilfred - the last one - developed on September 18th off the coast of Portugal. New storms are now named after the Greek alphabet.

Both weather phenomena count as cyclones, but there is one crucial difference: During Tornadoes especially in North America overland and occur locally Hurricanes above the sea. What is the difference between a hurricane, a cyclone and a typhoon? Strictly speaking, there is none: it is the same weather phenomenon, namely a tropical eddy. They only differed in their area of ​​origin - and therefore also in their name.

The difference between tornadoes and hurricanes

Tornadoes are also called "tornadoes" or "large turbines". They are smaller than hurricanes. If tornadoes are usually less than a kilometer wide, tropical cyclones like hurricanes are often 500 kilometers and larger. On the other hand, the strongest tornadoes are often more destructive than tropical cyclones, because they can reach up to 450 kilometers per hour. Tornadoes mostly arise over land, while hurricanes, cyclones and typhoons occur over the sea.

Where do hurricanes, typhoons and cyclones occur?

Tropical cyclones are named after where over the sea they develop: while the typhoon forms in the northwestern part of the Pacific off the coasts of East and Southeast Asia cyclone in the Indian Ocean. hurricane on the other hand, a hurricane is called off the American coast, which has its origin in the North Atlantic or northeastern Pacific. The hurricane season in the Atlantic usually begins in early June and lasts until the end of November.

Hurricanes: The water vortex

The prerequisites for a tropical cyclone to form are a very high temperature of the sea surface of at least 26 ° Celsius and a sufficiently large contiguous water surface from which it can draw its energy. A third requirement is the Coriolis force, which results from the rotation of the earth and acts on the wind flow. Winds are deflected to the right in the northern hemisphere and to the left in the southern hemisphere. Air masses swirl and cyclones can form.

Destructive power of hurricanes

What all cyclones have in common is their extreme destructive power: They race across the water at wind speeds of 120 to 300 kilometers per hour, absorbing immense amounts of water and often pushing a meter high tidal wave in front of them.

In order to determine the strength of a hurricane, daring pilots must fly into the eye of the storm with special aircraft equipped with measuring devices. The wind speeds are highest around the calm center. It's an extremely dangerous and expensive endeavor: these machines cost $ 100 million each to purchase.

Storms with female names are considered harmless - a mistake!

Hurricane Sandy (2012)

Sandy, Katrina or Arthur and Cristobal - since the 1970s, hurricanes have alternately been given male and female names. But whether a hurricane bears a man's or a woman's name does not matter, according to a study published by the University of Illinois in June 2014. The researchers had examined hurricanes between 1950 and 2012 and found that storms with female names caused more deaths than similarly strong storms with male names. In a test with 1,000 participants they found that all those questioned rated hurricanes with women's names as less dangerous, so to speak, as "gentler", and would therefore tend to ignore appropriate safety measures - only because the female name of the hurricane suggested less danger. The researchers emphasized that it would therefore be better to change the naming system.

The hurricane simulator: researching cyclones in the laboratory

Weather phenomena such as hurricanes can be simulated in the laboratory: The Rosenstiel School of Marine and Atmospheric Science in Miami has developed a simulation system with which hurricanes up to the highest category five can be "simulated" in the laboratory. The laboratory consists of a water tank and a fan that ensures the appropriate wind strength and gets the water going.

The ocean and atmospheric researchers want to investigate, among other things, the interaction of the air with the water surface. It is still not fully understood why some low pressure areas develop into cyclones and then into hurricanes, while others weaken again. This in turn makes predictions difficult.

Tornadoes: tornado over the mainland

In a very different way than hurricanes form on the other hand Tornadoes, of which there are around 1,200 in the United States annually, according to the US National Ocean and Atmospheric Agency (NOAA). However, these hurricanes can also arise in other countries, including Germany.

Tornado devastates small town Moore (USA) The tornado warning came fifteen minutes before the storm hit Moore, a suburb of Oklahoma City, on May 20, 2013. At least 24 people died. In a two-kilometer-wide path of destruction, two primary schools, the hospital and numerous residential buildings were razed to the ground. According to estimates, the damage ran into billions.

The distinguishing mark of these cyclones is a "trunk" that grows from the clouds towards the ground and consists of rotating air. Important ingredients for the hurricane over land are: extremely moist air that rises, strong temperature differences that create strong pressure differences and large thunderclouds as well as changing wind directions at high altitudes.

Tornadoes cannot be predicted in the long term because they form too quickly. But meteorologists know where and when it is normally "tornado season". In the spring, for example, the American Midwest, also known as "Tornado Alley", is particularly affected.

Tornadoes along cold fronts

A tornado in Sand Springs, Oklahoma, USA

Strong tornadoes form mainly along cold fronts. In the tornadoes that occur in the American Midwest, for example, polar cold air flows south from Canada and meets hot, humid subtropical air that comes from the Gulf of Mexico. There, huge thunderclouds form, in which the different air masses collide. The warm air is sucked in and shoots up in the cloud at a speed of over 100 kilometers per hour. As a result, the thundercloud explodes within a few minutes and rises to a height of 15 to 16 kilometers.

Wind shear, mesocyclones and supercell

Tornado over Oklahoma

At the same time, there must be vertical and horizontal wind shear. This means: the wind speed increases with altitude and the wind blows from different directions. As a result, eddies form around the cloud, which are sucked into the clouds with the warm updrafts, which leads to an independent rotation in the innermost updraft area of ​​the thundercloud, the so-called mesocyclones. If this mesocyclone lasts longer than 30 minutes, it is called a super cell.

The warm air that flows in on one side of the thundercloud cools down in the uppermost area of ​​the cloud, where temperatures from -70 ° Celsius to -80 ° Celsius prevail. From there, very cold and dry air flows very quickly downwards. When it hits the ground, it is sucked back into the thundercloud. A cloud trunk, also known as a funnel cloud, forms from the mesocyclone. The funnel cloud rotates faster than the mesocyclones. If the cloud trunk reaches the ground, it is a tornado. If it whirls, it works like a vacuum cleaner. Due to the suction inside, cars and roofs are torn into the air. Wind speeds of several hundred kilometers per hour can prevail at the edge of the tornado. The tornado devastates areas several hundred meters wide along its track. According to the German Weather Service (DWD), tornadoes travel at 50 to 100 kilometers per hour and leave behind a streak of devastation of five to ten kilometers.

Rare storm: There is also a swirl in Germany

In Germany, too, there are - rarely - tornadoes: In 2015, such a cyclone hit Affing in the Aichach-Friedberg district.

There is no such typical tornado area in Germany. But just like in other European countries, hurricanes of different strengths occur. According to the German Weather Service (DWD), 20 to 60 of them swirl across the country every year. Every year in Germany, on average, one person dies as a result of a hurricane. In addition, there are millions of euros in damage every year. However, particularly severe tornadoes are much rarer here than in the USA.

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