Do You Know Why Storms Rotate Clockwise Or Counter Clockwise?

Tropical cyclones, also known as hurricanes or typhoons, are one of the most devastating weather events that can occur on Earth. These powerful storms are capable of causing widespread damage, such as flooding, gusty winds, and storm surges. The Coriolis force is a critical factor in the formation and intensification of tropical cyclones. Let us explore the Coriolis force and its impact on tropical cyclones. But first, let us begin with understanding the Coriolis force.

Coriolis Force

The Coriolis force, also known as the Coriolis effect, is a phenomenon that occurs due to the Earth's rotation. As the Earth rotates, any object that moves across its surface appears to deflect to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This deflection is caused by the Coriolis force, which is proportional to the speed of the object and the latitude at which it is located. Actually, the Coriolis force is an apparent force that arises when an object is moving in a rotating reference frame, such as the Earth's surface. The force causes the object to move in a curved path, rather than a straight line, even though no actual force is acting on the object. Now, let's find out what is a tropical cyclone.

Tropical Cyclone And Its Formation

A tropical cyclone is a type of storm system characterised by a low-pressure centre and strong winds, typically speeds of 74 miles per hour (119 kilometres per hour) or higher. Tropical cyclones are fueled by warm, moist air over the ocean and typically form in the tropics, between 5 and 30 degrees latitude.

The formation and intensification of tropical cyclones rely on several factors, including a large sea surface with temperatures above 27°C, the presence of the Coriolis force, small variations in vertical wind speed, a pre-existing weak low-pressure area or low-level-cyclonic circulation, and upper divergence above the sea level system. The energy that intensifies the storm comes from the condensation process in the towering cumulonimbus clouds around the storm centre. The continuous supply of moisture from the sea further strengthens the storm. However, once the storm reaches land, the moisture supply is cut off, and the storm begins to dissipate.

A tropical cyclone's structure includes a strong spiraling wind around the center, known as the eye, which is a region of calm with subsiding air. Surrounding the eye is the eye wall, where there is a strong spiraling ascent of air to greater heights reaching the tropopause, with the wind reaching maximum velocity in this region, sometimes reaching up to 250 km per hour. Torrential rain occurs in the eye wall. Rain bands may radiate from the eye wall, and trains of cumulus and cumulonimbus clouds may drift into the outer region.

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The diameter of a mature tropical cyclonic storm can vary between 150 and 250 km, with a diameter of 600 to 1200 km in the Bay of Bengal, Arabian Sea, and Indian Ocean. The storm moves slowly, about 300 to 500 km per day. When a tropical cyclone crosses the coast, it is called the landfall of the cyclone. Cyclones that cross the 20°N latitude generally recurve and are more destructive. Tropical cyclones can also create storm surges that inundate the coastal lowlands. Ultimately, the storm weakens and dissipates once it moves over land. A schematic representation of the vertical structure of a mature tropical cyclonic storm is shown in the following figure.

Effect Of Coriolis Force On Tropical Cyclones

Coriolis force heavily impacts tropical storms including the provide spark for the rotation, and determining the path, size, and intensity of tropical cyclones.

For Rotation Of Tropical Cyclones

The Coriolis force is required for the formation of a rotating storm. As warm, moist air rises over the ocean, it begins to spin due to the Coriolis force. This spinning air creates a low-pressure area at the surface, which draws in warm, moist air from the surrounding area. As this air rises and cools, it releases its moisture, which fuels the storm and causes it to intensify. Without the Coriolis force, there would be no rotation and no tropical cyclones.

Determine The Path of Tropical Cyclones

The Coriolis force also affects the path that a tropical cyclone takes. As a storm intensifies, it tends to move towards higher latitudes, where the Coriolis force is stronger. This is why most tropical cyclones tend to move from east to west in the tropics and then curve towards the north or south as they move towards higher latitudes.

Determine The Size And Intensity

The impact of the Coriolis force on tropical cyclones can be seen in the size and intensity of the storms. In the Northern Hemisphere, tropical cyclones tend to be smaller and more intense due to the stronger Coriolis force. In the Southern Hemisphere, tropical cyclones tend to be larger and less intense due to the weaker Coriolis force.

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