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The Environment / Re: Do all hurricanes that form in the Atlantic spin anti-clockwise?
« on: 04/10/2020 23:49:08 »Quote from: evan_au on 09/09/2020 21:51:13I understand that hurricanes don't often originate right on the equator, as the Coriolis force is near zero there.
They spin the same direction when viewed from space (eg from the distance of the Moon).
But I've never seen a weather map take the external viewpoint, either.
Could you clarify that Evan please.
- Hurricanes tend to form somewhat away from the equator, where the Coriolis force is greater.
When looking at a weather map, looking down on the low-pressure region in the center of a hurricane as if from Low-Earth Orbit...
- When originating in the Northern Hemisphere, hurricanes spin counterclockwise
- When originating in the Southern Hemisphere, hurricanes spin clockwise
Now take a step back, as far as the Moon (even geosynchronous orbit would be fine, provided it showed a whole-Earth view)
- You see a hurricane at mid-Northern latitudes, spinning counterclockwise
- You see a hurricane at mid-Southern latitudes, spinning clockwise
- Due to the curvature of the Earth, you will discover that as a point near the hurricane rotates around the central low-pressure region:
- This point will be most distant from you when one in the Northern hemisphere is farthest North, and when the one in the Southern hemisphere is farthest South
- After its most distant point, they will both then move to the left
- This point will be closest to you when one in the Northern hemisphere is farthest South, and when the one in the Southern hemisphere is farthest North
- After its most distant point, they will both then move to the right
- So it is like looking at the spiral of a rolled-up newspaper, rotating in a single direction (parallel to Earth's axis of rotation).
- The image of rotating in opposite directions comes from looking at opposite ends of the newspaper in a traditional weather map (LEO)
- But when you take an external view, you can see that they rotate in the same direction.
Of course, you are highly unlikely to see a single image with a hurricane in both the Northern and Southern hemispheres, since hurricanes are driven by high sea surface temperatures, and these occur 6 months out of phase in Northern and Southern hemispheres
- But with continued ocean warming, who knows what is possible?
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