Coriolis effect
The Coriolis effect is an apparent acceleration of moving objects observed in a rotating system, such as the Earth. This phenomenon occurs because the Earth is constantly rotating, creating an illusion that affects the motion of objects. According to Newton's First Law of Motion, objects in motion will remain in motion unless acted upon by an external force; however, this law applies only to inertial frames of reference, which do not include rotating systems like the Earth's surface. As a result, objects moving across the globe, such as air and water currents, are deflected: to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
This effect significantly influences climate patterns, as it contributes to the formation of large-scale circulation systems in the atmosphere and oceans. For instance, winds and ocean currents exhibit distinct rotational patterns, leading to the development of weather systems such as hurricanes. The Coriolis effect plays a crucial role in transporting thermal energy from warmer regions near the equator to cooler polar areas, thereby moderating global temperatures. Additionally, climate change may impact the dynamics of these currents, potentially altering weather patterns and the frequency and intensity of storms. Understanding the Coriolis effect is vital for grasping its implications for weather systems and climate dynamics.
Coriolis effect
Definition
The is an apparent acceleration of a moving object as seen in a rotating system. The acceleration is not a true change in velocity, but an illusion caused by the rotation of the system beneath the moving object.
An unconscious tendency to regard Earth as a fixed frame of reference generates an unrecognized expectation on the part of many people that objects free of forces will move with unchanging direction and speed. That is, they will be unaccelerated. This expectation is consistent with Sir Isaac Newton’s First Law of Motion, which states that a body in motion will remain in motion, in a constant direction, with constant speed, unless acted on by an outside force.
Newton’s First Law of Motion, however, applies only in frames of reference that are themselves not accelerating. These so-called inertial frames must be moving in a constant direction with constant speed. This condition is not met by rotating frames, such as Earth’s surface, where every point in the frame (though traveling at a constant speed) is constantly changing direction as it completes a circular path around the axis of rotation.
The farther an object is from the axis of rotation, the faster it will travel on its circular path. An object on the equator, for example, completes a path of 40,000 kilometers in one day, while an object at 60° north latitude travels only half that distance in the same time. Thus, the object at 60° north latitude travels at half the speed of the object on the equator.
Wind and water that leave the equator headed due north carry their equatorial speed with them. As they move north, they pass over territory that is traveling eastward more slowly than they are. As a result, the wind and water move eastward relative to the ground or the seafloor. Conversely, wind and water starting at northern latitudes and moving due south will cross ground that is moving eastward faster than they are; they will move westward relative to the ground or seafloor. This deflection from the original direction of motion is the Coriolis effect.
Significance for Climate Change
Convection-driven currents carry warm water and air poleward from the equator and carry cool air and water from the polar regions toward the tropics. Both the tropical and the polar currents are deflected to the right, relative to their direction of motion, in the Northern Hemisphere and to the left, relative to their direction of motion, in the Southern Hemisphere. In regions where the currents converge, the deflections merge into circular rotations about the point of convergence. In the Northern Hemisphere, these rotations move counterclockwise; in the Southern Hemisphere, they move clockwise.
A low-pressure weather system in the Northern Hemisphere, for example, draws in air from the surrounding terrain in all directions. The wind flowing in from the north is deflected to the west. The wind from the west is deflected to the south, the wind from the south is deflected to the east, and the wind from the east is deflected to the north. In combination, the winds form a vortex rotating counterclockwise about the center of the low-pressure area. A high-pressure system, by contrast, repels winds, creating a clockwise vortex. In the Southern Hemisphere, these directions are reversed. Similar effects occur in ocean currents.
The magnitude of the deflection caused by the Coriolis effect is proportional to the distance from the point of deflection to the rotation axis. For that reason, the Coriolis effect is most prominent at the equator. It is also proportional to the speed of the currents involved. High winds associated with hurricanes readily display the effect, generating the characteristic circular wind pattern with a calm eye at the center.
The Coriolis effect establishes the circulation pattern of major storms, trade winds, jet streams, and large-scale ocean currents. All of these convection currents transport thermal energy from the warm tropics to the temperate and polar regions, moderating the global difference in temperatures. The Gulf Stream, for example, keeps Great Britain, Ireland, and the North Atlantic coast of Europe substantially warmer than other regions of the Northern Hemisphere that are located at the same latitude. Air currents also transport large amounts of water evaporated from tropical oceans to temperate and polar regions, where the water precipitates as rain and snow.
The rate at which convection currents transport mass and heat poleward from the tropics is a function of the temperature difference between the two regions. If climate change raises average temperatures in the tropics more than it raises them at the poles, it will create more energetic and powerful currents. If climate change raises polar temperatures more than it raises equatorial temperatures, it will dampen these currents. The resulting effects on the number, type, and destructive power of storms in either case would be complex and difficult to model.
Bibliography
"The Coriolis Effect: Earth's Rotation and Its Effect on Weather." National Geographic, 19 Oct. 2023, education.nationalgeographic.org/resource/coriolis-effect. Accessed 11 Dec. 2024.
Cossu, Remo, and Matthew G. Wells. “The Evolution of Submarine Channels under the Influence of Coriolis Forces: Experimental Observations of Flow Structures.” Terra Nova, vol. 25, no. 1, 2013, pp. 65–71.
Goh, Gahyun, and Y. Noh. “Influence of Coriolis Force on the Formation of a Seasonal Thermocline.” Ocean Dynamics, vol. 63, no. 9/10, 2013, pp. 1083–1092.
Mayes, Julian, and Karel Hughes. Understanding Weather: A Visual Approach. Oxford UP, 2004.
Stommel, Henry, and Dennis Moore. An Introduction to the Coriolis Force. Columbia UP, 1989.
Walker, Gabrielle. An Ocean of Air: Why the Wind Blows and Other Mysteries of the Atmosphere. Harcourt, 2007.