Why do hurricanes have an eye?

In the past decade or so, it seems like hurricane after hurricane has made landfall and caused major destruction. Hurricane Sandy, Hurricane Mathew, Hurricane Harvey, Hurricane Irma, Hurricane Michael - the list goes on and on.
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But how do hurricanes form and why do hurricanes have an eye? Up next, we’ll tackle these questions and many more, as we start to uncover why hurricanes have become so much more destructive in the past decade.

​What is a hurricane?

Hurricanes are a type of tropical storm marked by wind speeds over 74 mph (33 m/s), and a circular rotating motion with a clear, low pressure center or eye. These storms are called hurricanes when they originate in the Atlantic ocean and typhoons or tropical cyclones when they form elsewhere. ​

How do hurricanes form?

In order to form a hurricane, we need a few key ingredients, namely: warm water and wind. 
The warm water evaporates as wind blows across the surface of the ocean. This warm air on the surface of the ocean then rises causing a region of low pressure. 

Air from the surrounding area then moves to replace the vacant space left behind by the rising air to fill in this low pressure area. This new air subsequently heats up and rises, continuing the cycle. 

The warm air rising into the atmosphere and cooling to its dew point causes the formation of clouds. The winds and storm system spin because of this cycling of the air and something called the Coriolis effect. 
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At the center of the spinning storms is a calm, low pressure point called the eye. When the winds in the storm reach 39 mph (17 m/s) it is considered a tropical storm and when the winds reach 74 mph (33 m/s) it is classified as a hurricane.

What is the Coriolis Effect?

The Coriolis effect causes water and air to curve as they travel over long distances across the Earth. More specifically, this effect is seen in the displacement of water and air traveling along a north-south axis. 

In the northern hemisphere, air is displaced to the right, while, in the southern hemisphere, it is displaced to the left. The Coriolis effect can manifest itself in various ways, affecting everything from weather patterns and airplane flight paths to ocean circulation. 

But, what causes the Coriolis effect, you might ask?

The Coriolis effect is caused by the rotation of the earth. Since the earth is a sphere, a cross section of the earth taken at the equator has a larger circumference than the circumference of a cross section taken closer to a pole. 

Both of these cross sections are spinning around the same axis but the one at the equator has a farther distance to travel. Because of this, the equator spins faster than the poles. 

This difference in speed causes water or air travelling away from the equator along earth's surface to be displaced. The original momentum is preserved as air or water travels along a north-south axis, which causes a curving path as it travels over parts of earth that are spinning at a different speed. 
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As the earth rotates from the west to the east, air and water are displaced toward the east, which is to the right in the northern hemisphere and to the left in the southern hemisphere.

How does the Coriolis effect affect hurricanes? ​

The Coriolis effect encourages the trademark spinning motion of hurricanes. The air in a hurricane wants to move toward the low pressure eye, but as it flows to the center it gets deflected, partially by the Coriolis effect, which causes the storm’s characteristic circulating motion. 

Since the Coriolis force has a different effect in the northern and southern hemispheres, hurricanes in the northern hemisphere spin counterclockwise while hurricanes in the southern hemisphere spin clockwise.

What exactly is the eye of the hurricane? ​

The eye of a hurricane is the calm, clear center of the storm. The hurricane rotates around the eye which itself forms a cylindrical, tube-like shape. The eye of a hurricane can range between 20 to 40 miles wide and is surrounded on all sides by the storm. The barrier between the storm and the eye is called the eyewall, which contains some of the most ferocious parts of a hurricane. ​

Why do hurricanes have an eye?

Scientists do not fully understand how or why the eye of a hurricane forms; many different theories have been proposed, but there is no universally agreed upon explanation. 

One theory is that the Coriolis effect causes wind to be deflected from the center of the storm creating the calm eye. 

The eyewall is also theorized to play a key role in the formation of the eye. As a tropical storm strengthens into a hurricane, one section starts to rotate faster, forming the eyewall which borders the eye on all sides. 

One of the main functions of the eye is allowing air and clouds to flow into the storm through the eyewall, feeding it. Therefore, the eye also allows air from inside the hurricane to flow out into the atmosphere.

How does climate change relate to hurricanes?

Hurricanes have been increasing in strength and destructive capability in the past couple of decades. The destruction from these hurricanes has been catastrophic, but how does climate change relate to this increase in hurricane strength? 

Climate change is the shift in global and regional weather and climate patterns due to the warming of the earth caused by an increase of greenhouse gases in the atmosphere. 

Greenhouse gases trap heat energy from the sun in the atmosphere causing a greenhouse effect. Most of this excess heat -- as much as 93 percent of it -- is absorbed by the ocean. This has caused the ocean temperature in most places to rise and we know that warm water is one of the ingredients in the formation of a hurricane. 

Warm water is needed to fuel a hurricane and helps it grow in size and destructive capabilities. Other consequences of climate change, like rising sea levels and sea ice melting, may also be contributing factors in this trend.

Saiyana Toran

Saiyana Toran is a junior at Albany High School. She grew up in Berkeley and Albany, California. She plays ultimate frisbee and the flute and she works with OYA as an intern.