Recently, the world followed the arrival and consequences of two major storms in the Caribbean, United States, China and the Philippines: Hurricane Florence Super Typhoon Mangkhut. The two phenomena caused the death of at least 110 people in the countries they passed through, in addition to leaving an immense trail of destruction.
The truth is that, annually, the news is filled with information about typhoons, tornadoes, hurricanes and cyclones across the planet. Why do these storms happen? And why are they classified in different ways? And the names, where do they come from?
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Typhoon, cyclone, hurricane, tornado... the passage of tropical storms through different parts of the world brings up different concepts and a single question: what is the difference between these events?
Essentially, typhoons, hurricanes and cyclones are the same meteorological phenomenon. These are intense revolving storms caused by falling
atmospheric pressure in a smaller area and its temperature higher than the surrounding areas.Differences in pressure and temperature form over warm tropical waters, generating circular winds that can reach speeds of 300 km/h. The cyclone is commonly described with the above characteristics and encompasses the other phenomena we know.
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Nomenclature variations are due to geographic location and intensity. Like this? If it happens in the west of the Pacific and in the southeast of the Indian Ocean, will be a typhoon. But, if it occurs in the waters of the Atlantic, Caribbean and Northeast Pacific, it will be a hurricane.
Let's see, below, more in-depth characteristics of each type of storm, how they form, their classification and the risks of happening in Brazil.
The National Institute for Space Research (INPE) classifies the tropical cyclone as a low atmospheric pressure system whose center has closed circulation. The winds then blow into and around this center.
Speaking like this, cyclones even seem harmless, but in reality, the well-known funnels can turn into a destruction machine! Winds can reach over 250 km/h forming a spiral with a diameter of up to 1,500 km!
As we have already seen, cyclones can receive different nomenclatures, such as hurricane and typhoon, depending on where they occur. A curiosity about both, including, is that their winds rotate clockwise in the Southern Hemisphere and counterclockwise in the Northern Hemisphere. If they sweep over other parts of the Indian and Pacific oceans, they are called cyclones.
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The duration of a tropical cyclone can vary from days to weeks and, over that time, they cause great damage. The destructive power of a typhoon or hurricane is due to its displacement capacity, between 10 and 50 km/h, and the storms that accompany them.
In addition to the tropical cyclone classification, this phenomenon has another variation, the extratropical. These occur in areas of mid-latitudes and are formed by low pressure systems and do not bring heat in their core. This type even happens in the south of Brazil and it is the movements that bring with them the cold fronts that arrive along the coast.
O hurricane is a tropical cyclone with sustained winds that reach more than 118 km/h and have a hot core. This storm forms in the Caribbean Sea, North Atlantic Ocean, Northeast Pacific, and Gulf of Mexico. Oh, a curiosity! In English, hurricane is translated by the name hurricane in reference to the Caribbean god of evil, Hurrican.
O typhoon, in turn, it's a type of cyclone whose characteristics are similar to those presented by the hurricane. The difference is that this phenomenon only happens in the west and northwest of the Pacific and in the southeast of the Indian Ocean. If the winds of a typhoon reach 241 km/h, it is called a super typhoon.
You tornadoes are a rotating column of air usually formed during a very strong storm. The nomenclature of this phenomenon also varies according to the place where it forms – if the whirlpool rises on land, it is called a tornado. If formed in water, it is called a waterspout.
The whirlpool winds rotate with intense speed in a spiral with an average diameter of 2 km. Its size is smaller than a hurricane, as well as its relatively short duration – between 10 minutes and an hour. But make no mistake, these storms are enough to cause irreparable damage!
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The speed reached by the winds of a tornado can reach 50 km/h, which makes it the most destructive of atmospheric disturbances. The devastation capacity of this type of storm increases due to its displacement speed – from 30 to 60 km/h.
The diameter of its spiral even helps the observer to differentiate it from a cyclone. As the latter can reach an area that exceeds 1,500 km, it can only be viewed in full from satellite images. On the other hand, the tornado can be seen with the naked eye, since the area of \u200b\u200bits diameter rarely exceeds 2 km.
The best known image of a cyclone is that huge spiral that drags itself through the affected territory. That shape is developed when the winds reach the necessary speed for the formation of a cyclone. The middle of the spiral is called the “eye”, a region of relative calm and free of clouds.
Around it is the “eye wall”, a storm band whose diameter reaches 1,500 km. In this part, the most intense winds and thunderstorms circulate. Two factors are essential for the regions we have mentioned to be the most prone to receiving hurricanes: temperature above 26°C in the first 50 meters of the ocean and light winds over the ocean heated.
Under these conditions, the evaporation of ocean water accumulates in the form of clouds in the lower atmospheric layer, creating a band of low pressure. As a result, the hot air rises quickly and the cold air present in the upper parts descends towards the center of the storm.
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From there, winds running in the opposite direction cause the storm to begin to rotate, also influenced by the rotation of the Earth. The clumps come together as they move through the sea and feed the cyclone as more water is evaporated.
For a better understanding, see in the figure below which are the stages of tropical storm formation:
When you watch the news about the arrival of hurricanes, have you noticed that they mention the loss of strength when hitting the coast? This is because, while over the ocean, storms intensify with variations in wind and height.
Thus, they produce ever lower pressures at the center of the spiral and ever stronger winds at the surface. Arriving on the continent, a region that is colder and drier than the sea, they lose their primary source of energy, the ocean, and enter a dissipation phase.
Florence, Harvey, Irma, Jose, Katia… Have you noticed that all hurricanes are named after people? And do you know why?
The United Nations meteorological agency, WMO, explains that the practice of naming tropical cyclones dates back to the beginning of the 20th century and was created as a way to facilitate the rapid identification of these phenomena and, thus, issue alerts and pass on information to the media.
Initially, the phenomena were named randomly, but in 1953, experts began to identify them with shorter names listed in alphabetical order. WMO began to alternate titles between female and male names starting in 1979. Therefore, the most recent hurricanes were chronologically named Harvey, Irma, Jose and Katia.
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Six named lists are used each year. Therefore, names that appeared in 2015 will appear again in 2021. Some exceptions, however, are applied to this rule when storms occur whose damage is extremely severe. This was the case with hurricanes Otto and Matthew in 2016.
The damage and deaths caused caused their names to be crossed out and replaced by Owen and Martin, respectively.
Hurricanes are classified according to the speed of the winds and also the degree of destruction they cause. The scale commonly used for this measurement is the Saffir-Simpson, developed in 1970 by engineer Herbert Saffir and doctor Robert Simpson.
The following image describes well how the classification of hurricanes according to the Saffir-Simpson scale.
The figure shows the rating assigned by the scale to a tropical storm, ranging from 1 to 5. For a cyclone to be classified as a hurricane, its winds must have a minimum speed of 119 km/h and are then placed in Category 1.
If the winds stabilize between 154 and 177 km / h, the hurricane moves to Category 2, with more serious damage observed where it passes. The next category, 3, fits hurricanes with winds between 178 and 209 km/h, registering even more destructive power.
Category 4 concentrates winds between 210 and 249 km/h. The last category, 5, classifies the rarest and also most serious types of hurricanes, those whose winds reach speeds above 250 km/h. Just to give you an idea of how powerful hurricanes in this category are, Storm Florence, the most recent to hit the United States, was classified as Hurricane 1 and killed 32 people.
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There is another scale that measures the intensity of cyclones, the Beaufort Scale. The system classifies the intensity of the winds of a cyclone, which, to receive this nomenclature, must be equal to or greater than index 10. At that point, storms reach speeds in excess of 88 km/h.
At certain times of the year, it is common to watch the news or read information on the internet mentioning “hurricane season” in certain regions of the world. What does that mean? This term refers to the months when tropical storms are most common.
The calendar varies depending on the region where cyclones, typhoons and hurricanes occur. See how your occurrence is distributed:
In the past, people were surprised by the arrival of these storms due to the lack of a technological device to predict them. Today, satellites and specific computers manage to track them several days in advance, which allows evacuation of the affected areas.
The images of the trails of destruction left by the cyclones scare anyone, don't they? And in Brazil, can this happen? The occurrence of hurricanes in Brazilian lands is a little more unlikely because our territory does not combine the determining factors for this type of storm.
The waters of the South Atlantic Ocean are less warm in addition to the fact that winds close to the surface are more intense. With this, the formation of hurricanes is, fortunately, inhibited. But what about Hurricane Catarina, the one that happened in 2004? Yes, the coast of Rio Grande do Sul and Santa Catarina was hit by winds of 180 km/h in March of that year.
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The extraordinary case was recorded because it evolved into a tropical cyclone when it brought together the elements necessary for its formation: calm winds, warm waters and the maintenance of the "eye" of the hurricane, that is, its center. This type of event is rare in Brazil, but not impossible. It is enough that, again, the same conditions are met.
As we have seen, a cyclone originates from high temperatures on the ocean surface, so nothing more natural than associating its occurrence with global warming. In fact, an article published by National Geographic points to discussions between scientists about the effects of the phenomenon on the increase in the strength and frequency of hurricanes.
Theoretically, higher atmospheric temperatures would lead to increased temperatures on the sea surface. Consequently, stronger hurricanes would form. The consensus is that the occurrence of hurricanes in stronger categories, such as 4 and 5, has practically doubled since the early 1970s.
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Furthermore, it is observed that the duration and speed of tropical cyclones have increased by about 50% in the last half century. However, experts have not yet reached a consensus to affirm any connection between climate change and hurricanes.
The report of the Intergovernmental Panel on Climate Change, published in 2012, states that it is “likely that the tropical cyclone mean maximum wind speed increases, although increases may not occur in all basins oceanic”. The same study points out that "it may happen that the global frequency of tropical cyclones decreases or remains essentially unchanged."
