From Europe to America
The recent devastation visited upon the Southeastern United States by Hurricane Helene is yet another example of how more powerful and destructive tropical cyclones have become. But even the most ferocious of storms have a soft spot, a region in the center of all that swirling cloud that remains calm and clear and free of the most severe weather. This is the eye of the storm, a phenomenon that still baffles scientists and has yet to be fully explained. But how does an eye occur, and why are some people prepared to fly an aircraft through the most extreme of weather conditions to reach it?
For an explanation, click through this gallery for some eye-popping facts.
The science behind the eye of a stormIn appearance, a hurricane resembles a colossal whirlpool, a gigantic mass of revolving air. But how exactly do hurricanes and other tropical storms form, and why do they have an eye?
The National Oceanic and Atmospheric Administration (NOAA) defines a hurricane as a type of storm called a tropical cyclone, which forms over tropical or subtropical waters.
Hurricanes are typically marked by wind speeds over 74 mph (119 km/h), and a circular rotating motion with a clear, low pressure center: the eye.
These storms are called hurricanes when they originate over the Atlantic Ocean and typhoons or tropical cyclones when they form elsewhere. However, when a storm's maximum sustained winds reach 74 mph, it is often just referred to as a hurricane.
In order to come to life, a hurricane needs two basic ingredients, namely warm water and wind. It begins to take shape from a cluster of thunderstorms that suck up the warm, moist air and move it high into Earth's atmosphere.
This humid air mass generates a region of low pressure, which in turn creates a storm system that converts the warm air into energy, thus powering the hurricane's circular winds.
The winds and storm system spin because of this cycling of the air. But momentum is also achieved by something called the Coriolis effect.
Simply put, the Coriolis effect describes the pattern of deflection taken by objects not firmly connected to the ground as they travel long distances around Earth. It causes air and water to curve as they travel, and is responsible for many meteorological and oceanographic phenomena.
For example, due to the Coriolis effect hurricanes in the Northern Hemisphere spin in a counterclockwise direction, while hurricanes in the Southern Hemisphere (known as cyclones) spin in a clockwise direction. And the greater the speed of the hurricane's rotation, the greater the strength of the Coriolis effect.
The eye of a hurricane or tropical cyclone is a region of mostly calm, clear weather in the center of the storm. This central area is of very low barometric pressure, in fact as much as 15% lower than that of the surrounding storm.
The eye is roughly circular in shape, typically 19–40 miles (30–65 kilometers) in diameter. It is surrounded on all sides by the storm.
The hurricane rotates around the eye, which itself is an area of light wind speeds and no rain.
The barrier between the storm and the eye is called the eyewall. This is a ring of towering thunderstorms where the most ferocious weather and highest winds of the storm occur. It's the most devastating region of any hurricane.
An eye is always larger at the top of the storm, and smallest at the bottom of the storm. This is because the rising air in the eyewall follows isolines (contour lines) of equal angular momentum, which also slope outward with height. This sometimes gives the eye an appearance resembling a sports stadium from the air.
Generally speaking, the more powerful the hurricane the smaller the eye tends to be.
Eyewalls can replace themselves. In meteorology, eyewall replacement cycles naturally occur in intense tropical cyclones with maximum sustained winds greater than 74 mph. In this satellite image of Cyclone Emnati, the inner wall of the storm is being replaced by a new outer wall.
The cause of eye formation is still not fully understood. One theory is that the Coriolis effect causes wind to be deflected from the center of the storm, creating the calm eye.
Scientists have also suggested that the eyewall itself plays a 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.
Most experts agree that the eye is probably related to the conservation of angular momentum combined with centrifugal force. In science speak, conservation of angular momentum means that objects will spin faster as they move toward the center of circulation. In other words, air increases its speed as it heads toward the center of a hurricane or tropical cyclone.
And while eyes are easy to spot using weather radar, the only way to investigate them properly is to fly, quite literally, into the "eye of the storm."
Hurricane hunters are aircrews that deliberately fly into hurricanes and tropical cyclones to collect data. The Lockheed WP-3D Orion (pictured) is the NOAA's primary hurricane research platform, capable of flying directly through the hurricane's eyewall and conducting various experiments requiring flight patterns in various parts of the storm.
The US Navy also deploy lighter, more maneuverable F9F-8P Grumman aircraft to gather photographic data by flying high above the eyes of hurricanes.
The NOAA also use a modified Gulfstream G-IV jet as a preliminary reconnaissance vehicle to survey storm patterns. In this 2005 image, the aircraft is passing the eyewall on the backside of Hurricane Rita.
This remarkable photograph shows the eyewall of Hurricane Katrina viewed from a highly modified P-3 Orion as it flew through the eye of one of the most destructive tropical cyclones ever to make landfall in the contiguous United States.
This similar view of Katrina's eyewall includes the aircraft's antenna, used for collecting weather information.
The P-3 Orion used by the NOAA bristles with high-tech radar and instrumentation and is uniquely designed to withstand the enormous forces of nature that pummel the fuselage. This is the view from the cockpit as a P-3 approaches daunting Hurricane Dorian in 2019.
Satellites use infrared imagery to help meteorologists identify the areas of the greatest intensity within large storm systems, such as the areas with the most intense convection, known as overshooting cloud tops (dark orange), surrounding the eye and along the outer bands.
As a hurricane begins to weaken, the lack of a tight spiral gyre sees the eye less well defined. In fact, as it closes the eye is often obscured by dense central cloud cover.
Hurricane Helene, which struck the Southeastern United States in late September 2024, is the latest in an increasingly catastrophic series of tropical storms to make landfall around the world. But how does climate change relate to this increase in hurricane strength?
The oceans are heating up, and, as warm water is needed to fuel a hurricane and nourish its growth, it's inevitable that bigger and more powerful storms will become commonplace. And that's something scientists are keeping an increasingly concerned eye on.
Sources: (NOAA) (BBC) (Hurricane Science)
The science behind the eye of a storm
Investigating the calm inside a hurricane
LIFESTYLE Meteorology
The recent devastation visited upon the Southeastern United States by Hurricane Helene is yet another example of how more powerful and destructive tropical cyclones have become. But even the most ferocious of storms have a soft spot, a region in the center of all that swirling cloud that remains calm and clear and free of the most severe weather. This is the eye of the storm, a phenomenon that still baffles scientists and has yet to be fully explained. But how does an eye occur, and why are some people prepared to fly an aircraft through the most extreme of weather conditions to reach it?
For an explanation, click through this gallery for some eye-popping facts.