2023-10-28 11:12:53
Twitter/@monitorwarr – 25.10.2023
Hurricane Otis passes through Mexico
The passage of Hurricane Otis through Mexico left the city of Acapulco devastated, generating major floods and destroying the facades of several buildings. The same happened in Brazil, more specifically in Rio Grande do Sul, in September this year, when a cyclone left more than 40 people dead in the region. In Santa Catarina, also in September, a tornado hit the rural region of Santa Cecília with winds of 100 km/h.
In all the cases mentioned, the regions were hit by strong winds, combined with large storms, leaving a trail of destruction. But with so many similarities, why do we have four classifications of natural phenomena? What are the differences between them?
The Professor at the Institute of Astronomy, Geophysics and Atmospheric Sciences at the University of São Paulo, Pedro Leite da Silva Dias, explains that “All these atmospheric phenomena have in common the fact that they form in regions of low atmospheric pressure in relation to the surroundings. ”
“The wind rotates in the same direction (clockwise in the Southern Hemisphere and anticlockwise in the Northern Hemisphere). Tornadoes that do not follow the direction of rotation rule rarely appear. What differentiates them is the spatial and temporal scale”, adds the professor.
Cyclone
It is a tropical storm formed in low pressure centers. The areas where cyclones form are associated with cloud formation, humidity and thunderstorms. It is a generic name used by meteorologists to designate a rotating and organized system of clouds and storms.
Commonly formed in tropical oceans, where the waters have a higher temperature — above 26ºC —, due to the heating of the air in the region close to the sea surface.
With cyclones, strong, fast-moving winds are generated. In this way, the air is brought to the center of the cyclone, where it becomes warm and humid. At this moment, it rises to the top of the phenomenon, while it is cooled, causing it to descend again. This cycle extends throughout the duration of the cyclone.
Reproduction: Flip
For some experts, the greater incidence and intensity of extratropical cyclones may have a direct connection with climate change.
There are three types of cyclones that are most common: tropical, extratropical and subtropical.
Tropical cyclones have a warm-core low pressure system. They appear in tropical waters, and have a more organized circulation within the center itself. Its intensity can vary, causing some classifications, such as: tropical disturbance, tropical depression, tropical storm or, the best known, hurricane.
Extratropicals are those that have an origin that is not tropical. It is usually associated with cold fronts, generally appearing in medium and high latitudes.
The subtropics combine what is seen in the previous two. It arises from an extratropical cyclone that begins to develop in the ocean, and collides with a warmer sea surface.
The professor raises the point that cyclones usually have a scale of hundreds of kilometers, lasting several days, unlike other phenomena that last around hours.
Typhoon
Typhoons are also tropical storms that originate from a cyclone. Their name, however, changes depending on the region in which they appear. Typhoons hit the Pacific Ocean regions, Japan, southern Asia and the eastern part of the Indian Ocean.
For the cyclone to become a typhoon, it must reach a speed of more than 150km/h. In this case, it is considered a strong typhoon. However, its winds can exceed 195km/h, considered a violent typhoon.
Tornado
The classification given to tornadoes by the National Institute for Space Research (Inpe) is that they are whirlpools of winds, with high speed, that appear in very strong storm environments. This phenomenon is born from storm clouds, reaching the ground, and causing great devastation wherever it passes.
Its size is hundreds of meters, and it has a short ‘life’, lasting a few minutes and covering between 500 and 1,500 meters. Its winds exceed 200 km/h. “Tornadoes range in size from a few hundred meters and last from minutes to around 1 hour”, explains Dias. They usually have a diameter between 100 and 600 meters, and can reach 1600 meters in width.
For the most part, tornadoes spin cyclonically when observed from above. However, some experts have already seen phenomena moving in a countercyclical direction.
Unlike cyclones, tornadoes are visible to the naked eye. This is caused by dust and dirt raised from the ground and by steam. Furthermore, they usually have a distinct noise that can be heard many kilometers away, becoming louder when the tornado touches down.
Hurricane
Finally, we have hurricanes. They arise when “the atmospheric pressure at the center of the tropical storm drops too much” causing “the winds to intensify, and the tropical storm becomes a hurricane, if it occurs in the Atlantic Ocean or the eastern Pacific Ocean”.
Hurricanes normally have a central region without the presence of clouds and with calm winds — the eye of the hurricane. The region is marked by descending air movements, alongside a large circular area with upward air movement, which culminates in causing heavy rain.
Reproduction: Flip
Furthermore, there is the issue of wind speed. A cyclone is classified as a hurricane or typhoon at speeds of 119 km/h.
“Tropical storms are formed in regions of warm water, with a lot of humidity, winds with little variation between the surface and 5 to 10 km in height. The energy that produces the intensification of tropical storms comes from the energy released in the process of changing the phase of water from the vapor state to liquid water (which occurs when clouds form). This energy warms the atmosphere, lowers pressure near the surface and sustains intensifying winds, eventually leading to the transformation of the tropical storm into a hurricane. These intense systems die when the surface water of the sea cools or when the hurricane moves over the continent and loses the source of water produced by surface evaporation”, explains the professor about how this transformation of a storm into a hurricane occurs.
El Niño and global warming in the formation of such phenomena
El Niño is “the name for a phenomenon that typically occurs in the equatorial Pacific Ocean, characterized by warmer surface temperatures”, explains the professor.
“These surface temperature anomalies occur on spatial scales of the order of a few thousand kilometers. In other words, they are disturbances much larger than the scale of hurricanes or tropical storms. It is the anomalously warm water during the El Niño phase that sustains the formation of tropical storms.”
It usually occurs on a scale of 3 to 7 years, rarely lasting more than two years. “However, potentially severe climate anomalies, depending on the intensity of warming. Changes in sea surface temperature above 1ºC already characterize the phenomenon. In the most intense cases, the anomaly can reach 2-3ºC”, warns Dias.
At this moment, the world is experiencing El Niño, which began this year.
Another important issue to highlight is the impacts of global warming on the formation and frequency of tropical storms.
“An important property of air is that the amount of moisture in the form of vapor is dependent on the air temperature. In other words, the hotter it is, the more moisture is retained in the air. Therefore, with warming, the potential for cloud formation increases, which can produce more rain”, explains the professor.
“Global warming, in addition to the direct impacts of higher temperatures, leads to the intensification of storms and/or an increase in the number of intense cyclones in some regions. And an increase in the frequency/intensity of dry periods”, adds Dias.
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