Warning: this post may be disorienting. If you think about the following concepts too hard and find yourself dizzy or with a headache, take a break and pat yourself on the back for thinking so hard about something sciency. Later, you can dwell on and research the topic in smaller pieces--I've needed to do that with this topic myself on more than one occasion!
If a plane attempted to fly straight from Anchorage, Alaska to Baja, California, the crew and passengers would find themselves somewhere over the Pacific ocean instead by the time they intended to arrive to Baja. Why is this? As the plane flew south over the course of a few hours, the earth rotated--and Baja, California moved east of where the plane was flying to! Alternatively, from the perspective of a satellite rotating along with the earth, the plane would have appeared to curve to the right (or west).
It's a well-known fact that the earth rotates in space. The sun doesn't revolve around the earth to cause the days and nights; instead, the earth is spinning in place to make the sun appear to cycle around the earth. We know easily from experience that the earth makes one full revolution, or spin, in about 24 hours--that's the length of time it takes for the sun to reach the same point on the horizon two times in a row. But while it may not seem so to us, the earth actually spins incredibly fast in some regions--roughly 1,000 miles per hour around the equator, in fact. Why did I only say "incredibly fast in some regions"? Can you figure it out yourself if you take a minute?
Here's the answer: if you stand on the northernmost or southernmost point on the earth for an entire day, you won't be moved at all--well, other than being spun around in a full circle. The difference in rotation speeds from the equator to the poles can have dramatic effects on everything that travels long distances north or south. This applies to air currents, ocean currents, and plane flights, to name a few notable examples. This prevailing pattern we experience is called the Coriolis effect or Coriolis force. Here's the consequences it generally has for any object moving north or south, such as if you shot a cannonball to test this out:
1A. When it starts at the equator and travels north, it curves to the right (the east).
1B. When it starts from the north and travels towards the equator, it curves to the right again (this time to the west).
2A. When it starts at the equator and travels south, it curves to the left (the east).
2B. When it starts from the south and travels towards the equator, it curves the the left again (this time to the west).
I highlighted the "rights" and "lefts" because that will be the easiest frame of reference for us to use. There's a pattern here: when things travel north or south, they always deviate to the right while north of the equator and to the left while south of the equator. Here's an explanation for the occurrences going FROM the equator:
Because an object that travels away from the equator is passing from a faster-moving area to a slower-moving area (remember the example of standing on the equator versus the poles), the object will continue moving east at a similar speed to the equator where it started at. If the object is traveling north, it will deflect to the right where its eastern velocity takes it. If it's traveling south instead, it will deflect to the left where its eastern velocity takes it.
Here's some real-life, pictured examples to help you see how this all works.
Dr. Michael Pidwirny, Public domain, via Wikimedia Commons
In the above photo, focus on the major oceanic gyres, or cyclical currents that are depicted by arrows. You'll notice that the cyclical arrows north of the equator always rotate to the right from their starting points, while the cyclical arrows south of the equator always rotate to the left from their starting points.
NASA, Public domain, via Wikimedia Commons
In the above photo, you're looking at Earth's major air patterns. The major wind currents, known most generally as the "Easterlies" and "Westerlies," are named for always blowing to the east or the west. What's really going on here--and you might be catching on by now--is that the wind currents north of the equator curve to the right of where they started, while south of the equator, they curve to the left of where they started. Depending on whether the wind currents travel north or south, they'll also consistently blow to the east or the west.
Even hurricanes are affected by the Coriolis effect! Hurricanes north of the equator always rotate counterclockwise because the right-deflected winds spin them in that direction. Oppositely, hurricanes south of the equator always rotate clockwise because the left-deflected winds spin them in that direction.
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