NOAA-20 Sees Low-Pressure System Spinning Off the Coast of South America

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A mature low-pressure system spins clockwise off the coast of South America in this stunning view captured by the NOAA-20 polar-orbiting satellite. Low-pressure systems like the one above are essentially spinning currents of warm, moist air. In a low-pressure system, the air pressure around the center is lower than the areas around the system and that causes the warm air to rise up.

In the Northern Hemisphere, or areas of the Earth located north of the equator, a low-pressure system’s converging winds rotate counterclockwise—or the same direction as the planet. Low-pressure systems in the Southern Hemisphere, or areas located south of the equator, actually spin clockwise, according to the National Weather Service. What’s known as the Coriolis Effect, causes these systems to spin in opposite directions in different hemispheres.

The Coriolis Effect, named after French physicist Gaspard-Gustave de Coriolis, “makes things (like planes or currents of air) traveling long distances around the Earth appear to move at a curve as opposed to a straight line.”

As you’ve probably noticed, the Earth is much wider at the equator than it is at the poles, so as the planet rotates, areas along the equator have a faster forward speed than areas closer to the poles. So as air converges at the center of a low-pressure system, it gets deflected either to the right or left. The low-pressure system above is spinning clockwise because the Coriolis Effect is pulling the air that’s rushing to the center of the system to the left.

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