Cyclones: Types, Formation, Stages | Impact on Weather

A “cyclone” is a low-pressure area that moves across the surface resulting in severe winds and atmospheric instability. It is also characteristic of causing the wind to rotate clockwise in the southern hemisphere and anticlockwise in the northern hemisphere. Moreover, a cyclone can produce massive cloud systems with strong storms and precipitation if the air layer is humid enough. On synoptic maps, cyclones can be identified by isobars, which are lines connecting points of equal pressure that encircle or vocalise an area. More precisely, when a core of low relative pressure is seen when the pressure significantly drops as we approach a certain location, we refer to it as a cyclone or low-pressure centre. The depth of the hurricane, or, in other words, the pressure value at its centre, will determine the degree of instability it can generate and the intensity of the winds(the lower the pressure, the more substantial its effects will be). As these systems have a large influence on weather, it is essential to know where they are located and how they can evolve. The rotation of the wind produced by a cyclone, independent of the hemisphere, establishes two distinct regions of thermal advection: to the west of the system, where colder air enters from higher latitudes, and to the west of the system, where warmer air arrives from lower latitudes. 

 

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Types of Cyclone

There are types of cyclones according to their structure and formation

1. Tropical Cyclones:

Tropical Cyclones are extremely deep centres of low pressure that form over oceanic waters in tropical latitudes and are linked to a powerful storm system with a remarkable closed circulation. Because of the way they form, they are different from the other cyclones, they have a warm core. These cyclones can produce winds faster than 252 km/h, they are also the most hazardous ones of all. For the development of a tropical cyclone, in addition to certain combined atmospheric factors, the ocean surface temperature needs to exceed 26°C. This results in significant heating of the air and, at the same time, allows for more significant evaporation.

2. Extratropical cyclones:

Extratropical cyclones dominate in mid-latitudes (between 30º and 60º latitude), with a structure and formation process very different from tropical cyclones. Although they do not have the same destructive potential as tropical storms, extratropical cyclones can nonetheless produce extremely strong winds and severe weather. In contrast to the latter, mid-latitude cyclones are cold in the core because of their dynamic, as opposed to thermal, origin. They form an atmospheric disturbance at altitude that creates an area of rise on the surface. Hence, they are far more common than tropical cyclones, even though neither the ocean surface nor a certain temperature is necessary for their creation.

3. Subtropical cyclones:

Low-pressure centres, or subtropical cyclones, can form in extratropical and tropical regions, ranging from the equator to around 50° latitude. It sets itself apart by retaining traits from both extratropical and tropical cyclones at the same time. This kind of system typically forms in mid-latitude regions with weak to moderate vertical temperature gradients, meaning that surface warming is not as great. However, in contrast to extratropical cyclones, its Latent heat is the primary energy source, which is characteristic of tropical cyclones. Mid-latitude atmospheric disturbances give rise to extratropical cyclones, also known as cold-core cyclones, which are the precursors of subtropical cyclones.

 

 

Formation and Decay Of Cyclone

Let’s understand how cyclones are formed. Cyclones form over warm ocean waters when moist air rises, creating low pressure at the surface. As the air cools, condenses, and releases heat, it intensifies winds and generates thunderstorms. With sustained wind speeds of at least 74 mph (119 km/h), cyclones evolve into powerful tropical storms.  A depression or low-pressure system must meet certain conditions to form a cyclone-

• The water on the surface of the ocean must be higher than about 26-27 degrees C: to facilitate the contribution of heat and humidity, instability and convection.
• It is necessary to have uniform air pressure, temperature, and humidity levels over a significant area.
• Convergence of the air, or its concentration towards a specific place, is an essential component of surface phenomena.
• Air divergence, or the movement of air out from a central location and towards the periphery, is required at height.
• Latitudes higher than 5 degrees are necessary because the Coriolis parameter approaches zero with proximity to the Earth’s equator.

In addition, there are other stages involved in the creation of a cyclone, which we will address in the section that follows.

 

 

Three stages of cyclone:-

There are three steps in the creation of this meteorological phenomenon. The three stages of cyclones are described in detail below.

1. Cyclone’s beginning

First, the cyclone begins with a wave-type disturbance:

• Low-pressure systems in the form of waves accompany the movement of the easterly winds, commonly known as trade winds.
• As the disturbance intensifies, it reaches the stages of tropical storm and depression. Keep in mind that these stages depend on wind speed.
• The rain and clouds are not well organised, and the wind speed is moderate. The wind then reaches 120 km/h, which is deemed a hurricane:
• A cloud system with spiral-banded organisation forms.
• Heat and humid air are always available and convert into movement energy.

2. Tropical cyclone maturity

When a phase of maturity is reached, the following things happen:

• The cyclone quickly intensifies and becomes round.
• The eye of the cyclone formed. The vortex, or centre of the cyclone is where the storm’s eye forms.
• There are high-speed winds : due to the immense pressure difference between the interior of the cyclone and the periphery.
• Cumulonimbus storm clouds first form at the cyclone’s eye, followed by nimbostratus, altostratus, and cirrostratus storm clouds that form progressively and towards the borders.

3. Decay of cyclones

The cyclone finally moves into the decay phase. Let’s observe what occurs:

• A cyclone that forms might last for around a week.
• It travels at rates of no more than 25 km/h in two different directions: southeast in the southern hemisphere and west or northwest in the northern hemisphere.
• They vanish as soon as they get to the continents because the warm, humid air supply is cut off.
• When it approaches a cold ocean, the same thing occurs: it reaches a latitude of twenty or thirty degrees, at which point it transforms into a mid-latitude depression or storm.