What is a cyclone and how does it form?

A cyclone is a closed area of ​​low atmospheric pressure, where the winds rotate clockwise in the Southern Hemisphere. This clockwise movement concentrates moisture and heat in the center of the cyclone, that is, in the area of ​​lowest pressure. Thus, the upward movement of the air, which is hot and humid in this area, causes the formation of heavy clouds.

In the case of anticyclones, the center of high atmospheric pressure causes downward air movements.

All this air movement causes cyclones to act as a regulator of temperatures between the South and North poles and also the Equator region, providing a thermal balance of energy and water vapor in the atmosphere.

The presence of a cyclone in the oceans is quite common. The formation of the phenomenon on the continent is rarer.

Characteristics of cyclones

Altogether, cyclones can be divided into three categories: tropical, extratropical and subtropical. Find out more about each of them:

• Tropical: They are also known as hurricanes or typhoons and tend to be more intense and devastating. Its core, or low pressure center, is hot, very deep and extends from the surface to the uppermost layers of the atmosphere. Tropical cyclones form between 20° south and 20° north of the globe and are never associated with a cold front.

Tropical cyclones act in equatorial regions over the oceans and extract energy from the heat extracted from the sea. The size of an extratropical cyclone is measured from the winds. This type of phenomenon is between hundreds and thousands of kilometers long and the measurement of its radius is based on the maximum point that the most intense wind can reach.

• Extratropical: They are the most common in the country. They form between 30° and 60° of the globe in both hemispheres and are always associated with a cold front. Its core or low pressure center is cold, that is, it has lower temperatures than the external atmosphere. They occur throughout the year, but are more frequent in winter.

The intensity of this type of cyclone is measured from the pressure. This phenomenon has a diameter of thousands of kilometers and the measurement of its radius is based on the maximum point that the lines of greatest pressure can reach.

• Subtropics: have characteristics of tropical and extratropical cyclones. This type of phenomenon is more common along the coasts of the Southeast Region and Bahia and occurs between 20° and 40° of the globe in both hemispheres.

Subtropical cyclones are also measured from pressure. They usually form in the spring and are not always associated with a cold front. Subtropical cyclones are normally less intense.

Subtropical cyclones have a hot and cold core. The closer to the surface, the higher the temperatures. In the upper part of the core, temperatures decrease.

Some cyclones are named according to Brazilian Navy rules. However, this factor does not define the intensity of the phenomenon.

Phenomena in Brazil

In March 2004, the South Region was hit by a tropical cyclone named “Catarina”. The phenomenon resulted in the deaths of 11 people and caused considerable destruction, especially in the south of Santa Catarina and part of the north coast of Rio Grande do Sul.

In July 2023, the same region of the country was hit by an extratropical cyclone. At the time, the phenomenon formed on the continent and caused rain and strong winds, mainly in the states of Santa Catarina and Rio Grande do Sul.