Tag: wind

Buys Ballot’s law

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I honestly thought* when I saw this that it was how Trump “won” the election, but as probably all my readers already know, Buys Ballot’s law is:

the relation of wind direction with the horizontal pressure distribution named for the Dutch meteorologist C.H.D. (Christophorus Henricus Diedericus**) Buys Ballot, who first stated it in 1857.

It’s a rudimentary method of estimating the position of varying centres of local atmospheric pressure from the prevailing wind direction.

Obvs.

Basically, it works around the relationship that (theoretically) states that the angle between the wind and the pressure gradient is a right angle. That means that in the Northern Hemisphere a person who stands facing away from the wind has high pressure on the right and low pressure on the left; in the Southern Hemisphere, the reverse is true.

We’re in the Southern Hemisphere [checks quickly… yep], so that means that if I stand with my back to the wind, then the low pressure area will be on my left (to be more accurate, it’s actually just slightly forward of my left), and the high pressure area on my right.

But why would I need to know this? Well, I probably wouldn’t, because I’m not a seafarer, miles out in the oceans. And if I did need to know it, then I’d just look at the nearest computer and it would show me where everything was. But in 1857 and for a long time before and afterwards, that wasn’t an option, because the internet was still dial up and that meant that you had to be attached to a really long cable.

Not possible in the middle of the South Atlantic (I am reliably informed).

So this law allowed sailors to estimate where the storm centre was, and thus allowed them to try to avoid it. Of course, you might not have been able to avoid the storm completely, but you could avoid the most dangerous quadrant – that is, the section of the ocean in front of you where the chances of damage from the storm was highest (Northern Hemisphere – front right, Southern Hemisphere – front left).

Less damage in those days (and maybe still even these days) meant more chance of survival.

There are a lot of factors that can mess up the wind/pressure relationship – it doesn’t work near the Equator, for example. But we’re not [checks quickly… nope] near the Equator. And though technology has far outpaced Buys-Ballot and his work, his law obviously still holds true. We just do things differently now.

Next time it’s a bit windy, cancel a marathon give it a go, then impress your friends by comparing your estimates with your modern day synoptic chart.

.

* I didn’t, this was just for comedic value.
** Crazy name, crazy guy.

A great walk, ruined

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Yesterday was a wild one. The rain cleared out early in the morning, but the wind persisted all day, and I couldn’t resist an afternoon walk with the camera and some Norwegian deep house. I did just about 7km and saw several (or more) birds, including this Caspian Tern (Hydroprogne caspia)…

…the world’s largest tern, which apparently has “a subcosmopolitan but scattered distribution”. (i.e. It’s found all over the world, but only in patchy or isolated areas all over the world. Rasper Point was one of those areas yesterday afternoon.

All was going well, and I was really enjoying my time, when suddenly, I saw someone else on my beach.

Walk. Ruined.

Absolutely shocking.
How very dare they? Do they not know the rules of windy, weekday afternoons on the Agulhas coast?

That’s my time, on my beach, with my Caspian Terns and my Norwegian deep house music.

Go and find somewhere else to be. Honestly.

Pixie help in the wind

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I’m been an incredibly blowy day in Cape Town and the Western Cape. Sustained 60kph winds with gusts into the mid-80s. The Fire Danger Index was red for most everywhere, and that forecast has proven to be wholly accurate, with fires… well… most everywhere, as well.

I did see one guy “in the know” describe it as “a shit show”. Who am I to argue?

Of particular personal interest above, that one bottom right, which – although a long way from our little place at the Southern Tip – is threatening to head that way. [UPDATE: I’ve just heard that they’ve got it contained.] And also the big one right in the middle, just north-east of Paarl, which has been burning for 8 days now, right around the area where we stayed just before Christmas, including the Bains Kloof Pass, and has consumed an immense amount of land, and sadly, a good number of buildings.

I was trying to glue some stuff to some other stuff earlier, using volatile glue for gluing purposes, and some meths for cleaning purposes. Obviously, I tried to work outside: a well-ventilated area being important, but being on my own, and having no-one to hold the wood, the wind was actually ventilating too much, and playing havoc with my efforts. And so I had to go inside into my office. This was much better, because not only was everything not being blown around, but I was also suddenly joined by an army of helpful pixies who sang and danced as the work got done.

Wonderful stuff. And I really enjoyed the nap that inevitably followed, even if it was on the floor.

Anyway, the pixies might not have helped the firefighters, but the early arrival of the first rain in over two months might give them a hand. I’m back in my car park for the first time this year, and it’s actually rather wet. Ironically, they’re sprinkling water on the grass on the playing fields opposite me.

What’s coming from the sky is not exactly a deluge, but it’s certainly better than nothing, and it’s very welcome. Everywhere is… was… dirty and dusty. Cape Town needed a wash.

As I write, it’s raining heavily, the wind is still blowing and the sun is setting. Trash chickens being blown around in the bizarre sulphureous light, and… is that… is that another pixie?!?

Day 631 – Breeze

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It’s time to head home. Back to the hustle and bustle of Cape Town, the city just 6000 miles from civilisation…

It’s been a good break down in Agulhas. I could have been a bit less lazy, but sometimes a pre-nap nap is just what you need before your nap.

And the weather could have been better: several bouts of heavy rain throughout the week, and today – when the sun is shining and the skies are blue – a gale force wind. Not a metaphorical gale, either. This is actually fully 60kph and up from the east, and that actually puts it into Admiral Beaufort’s Force 8 category: quite literally a gale.

Doors have to be hooked back, the beagle’s ears are flapping wildly, the dirt roads are drifting into the sky and a plastic chair has escaped to the far side of the garden. It’s actually quite nice if you can get out of the it, temperature-wise at least. But it’s omnipresent: noisy, constant and wearing.

The tailwind should make for a quick and economical trip home, at least.