From what I’ve read its because there’s no landmass to impede current flow. But isn’t the same true for the world’s major oceans? Or is it like a venturi effect with currents?
In: Planetary Science
Roughly speaking, average windspeeds at a given location are a function of the *fetch*: that is, the distance that the prevailing winds travel over water from the last time they met a major obstruction (that is: large bits of land).
In, say, the Caribbean, the fetch is somewhere in the region of 5,000km. In the Phillippines, it’s more like 10,000 km. In the Drake Passage, it’s something like 20,000km if you only count one lap around the earth, but in reality is functionally infinite, as the Drake Passage is itself not such a massive impediment to the wind, being some thousand kilometers wide, with only small islands in between.
Additionally, the Drake Passage is something of a chokepoint – while 1,000km is pretty wide, the Antarctic Circumpolar Current’s narrowest other point is more than twice that width, and carries somewhere in the 100 million cubic meters of water per second range. All of that water gets funnelled into the gap between Cape Horn and the Antarctic Peninsula, and if you’ve got the same amount of water flowing through a narrower space, the only option is for it to accelerate, which results in faster currents flowing through the passage. Similar effects (though weaker due to the ability of air to escape upwards) happen in the atmosphere, leading to faster wind speeds through the passage. There’s actually a really good example of this going on right now, which you can watch live-ish [here](https://earth.nullschool.net/#2024/02/03/1000Z/wind/surface/level/orthographic=-71.71,-65.03,892/loc=-68.321,-60.487): at that timestamp (10am UTC on the 3rd), there’s a fairly typical Southern Ocean weather system sitting West of the passage, with wind speeds in the 50-60km/h range to its North, well Northwest of the passage. If you click forward from there, you’ll see that as it approaches the passage, those strong winds to the North start moving South towards the passage, and also accelerate – by 6pm UTC, the peak wind speeds in the North (though now less North than they were earlier) are up to 75 km/h. At 2am UTC on the 4th, those peak winds are up to 96km/h, and are almost down to the latitude of the passage, and then as you click forward from there, you’ll see the storm squeeze itself down through the passage (including a period around 6pm UTC on the 4th when it was pulling winds *Westward* through the passage at ~50km/h, giving a “wind against current” situation, which results in larger seas (as from the reference frame of the water, the winds are effectively stronger). By 5pm UTC on the 5th (with the centre of the system itself still West of the passage), there’s broadly 70km/h+ winds across the whole passage, having been funnelled in by the passage.
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