In this course you can learn about the mechanics of global weather, the foundations of ocean meteorology, predictive modeling and how sailors receive data via satellite and use high-performance navigation software. This course looks at oceanic meteorology and climatology through the lens of the sport of sailing. You will gain a basic knowledge of meteorology needed by sailors to take part in a regatta such as the Barcelona World Race, the only double-handed, round the world regatta with no stops. You will learn about the strategies employed during a round the world regatta and how these are put to use on board the latest ocean racing yachts.
Video 6.1.1 The Southern Indian Ocean
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De la lección
Climatology and meteorology in the Barcelona World Race: From the Indian Ocean to Gibraltar
In this module we are going to study the meteorology and strategy for the seas of the south of the planet. Down in the Southern Ocean is where the sailors go up against the toughest sailing conditions in the regatta and where they must also abide by safety restrictions due to the danger of floating ice. On the following pages, Marcel van Triest will analyse general strategy and also look at case studies from the Barcelona World Race 2010/11. In that edition, ice gates were used to restrict the fleet's descent south and to avoid boats heading into danger zones. For the 2014/15 edition, however, ice gates have been substituted by a “restriction zone”, a polygon with some 72 sides surrounding the Antarctic. In this video Marcel explains the general context of the passage through the Southern Ocean and reviews the routes taken in the 2010/11 edition of the race. They key difference in this edition is that the regatta does not take the boats through Cook Strait (New Zealand).
Impartido por:
Tomàs Molina
[MUSIC]
Okay, so in this subject, let's focus on the South Indian.
Here's India and here's the ocean, named after India, the Indian Ocean.
We're dealing with the South Indian.
Kerguelen Islands over here.
South Africa, Australia, and as we said before, the three capes to port.
Cape of Good Hope, Cape of Llewellyn, and
India's Cape Horn at the end of the South Pacific.
Here are the ice gates.
You can see that the blue boat has already cleared the first ice gate: one,
two, three, four, five, six.
At some stage, the boat has to be north of these imaginary lines.
Because, see there's lots of winds here down south.
Boat's can't get there.
They can't get there, because of the ice gates, actually,
because of the ice itself.
Right, so here you can already see the sort of problem this boat is facing now.
Little cell of high pressure over here, under South Africa.
This sometimes happens when the Santa Elena high squashes under South Africa.
It will break off and then, go into the Indian.
The normal situation here is, to have high pressure over here, and
high pressure over here, at mid latitudes.
As we have seen in the general climatology of the globe.
So high pressure over here, low pressure over here,
what the boats are trying to do is every time to get back down south.
It makes the route shorter.
The further south they go, the less distance they have to sail, and
the more wind they can get.
However, all the strategy is going to be about when do I come back up
to cross this line?
When do I touch my ice gate again?
And that's where the, actually, the big game is in this part of the race.
Let's have a look at this boat, deal with it.
So here, you can see the blue boat, it tries to go south, but
it has to respect the right ice gates.
Now they're touching the line and will no doubt, they will straight away jive,
and try to go south again.
You can see the do it now, there it goes South.
You can see the low pressure here, South Westerly winds here,
right and they will try to ride that for as long as possible.
Again, go through the south but there's always the issue of,
how do I get back up here?
I'll zoom in a little bit more, so we can have a look at the detail.
Okay, so here we've already zoomed in South Indian Ocean.
You can see high pressure over here, You can see high pressure over here.
And above all, you you can see nice low pressure over here.
Low pressure here.
See the front here?
All right?
That's the front. Put a few isobars there...
There... All right?
And you can see that the blue boat here is ahead of the front, north-northwest.
This is potentially a problem for them.
If they go too fast, or
the low goes too slow, they could end up being just northerly all the time.
At some stage, they have to come back up here.
It would be a lot quicker for them, actually better off...
They're also at a wider angle, and
go through the south, shorter route, faster, all good.
But they have to come back up to the ice gate, so
they have to decide to make a compromise.
Is this low pressure going to overtake us?
Which means, we'll get in the westerly winds behind it,
it will be really easy to come back up north.
Or are we too fast and low pressure to slow, relatively speaking.
And do we have to get to the ice case.
The boat's behind here, they're already behind the front.
They're in the west league at a much more down-wind angle, and
they'll be driving down.
They will drive south, try to find more pressure here, and
then try and come back up north again.
To respect get over here, okay so
you just saw this low pressure, this front, the northerly head of it.
What is this leading boat going to do?
They would like to ride this low pressure and go South.
They can't, they have to go back up to the ice skate.
There's something else here worthwhile paying attention to.
You can see a cyclonic movement over here, like a low pressure forming here.
It's something to keep and eye on, because although,
there is high pressure here and high pressure here.
This bringing in warm and
humid air from India basically, Gulf of Bengal, the tropics.
And this bringing down, generally speaking, cold air from Antarctica.
This will create some low pressures over here, cyclogenesis.
Most come out of the Atlantic, but
some come out of the Madagascar cold front, as well.
This what's going to happen here.
You're going to see a little bit of cyclonic movement here.
A low pressure starting to build and this boat is faced with a big dilemma.
Ride this down, hope for this low pressure to keep this one over there for a while.
All right, and end up in westerlies, come back up, go into the transition zone.
With no winds over here, between those two systems.
That's slow, the boats behind will catch up.
Very difficult, let's see what they did.
Still riding northerly there, the northerly out of this low pressure.
Here the low pressure starts tracking down south getting into the main
flow over here.
They have to get back up to the ice cape.
Right now there are no winds and here,
you can see this low pressure starting to come down.
Starting to deepen.
Here we start to get an influence.
I'll stop here for a moment.
Here we start to get an influence of this low pressure system
coming out of the Madagascar cold front.
Right, very bad situation here because these are North Easterlies.
They're on the wind.
They have to get back up to the ice caps, right.
They haven't been able to follow down here.
I mean twenty years ago, when we did around the world races,
there were no ice gates.
There were no satellites,
there was no knowledge about the danger that was down here.
The danger of the icebergs and we just went south to sixty sixty one and
spent weeks down there without knowledge, basically.
Which was a lot easier, because it was all downwind.
Now, times have changed.
These boats have to go further note to stay away from the danger,
go to those ice gates.
And here, you can see a prime example of how
the leading boat here cannot follow the westerlies.
They have to go back up north.
Now, to get an influence of this small low pressure system here.
Coming down, this will deepen and then get into the main flow.
And here, is the high pressure system, the normal high pressure system over here.
So, very dear for them now to come back up to this ice gate.
You can see that course is over there, they're setting 90 degrees away from
course not getting any closer to the finish in Barcelona.
And meanwhile,
both boats behind them are setting a much straighter route gaining miles on them.
Here they finally clear the ice gate, and you can see just touch the line once.
And straightaway, they take and
get into a better course again, heading towards Cape Horn.
Heading towards Barcelona and making some miles to the finish but
they've lost quite a bit in this little loop they did here.
Then again, there was no alternative for them.
Okay let's go [INAUDIBLE].
Okay, so we've got this low pressure system coming down here now.
These boats have gained a lot, lots of wind here.
And here, you will see the boats ending up quite far north of the Kerguelen islands.
There's no reason at this moment to plunge down south, right?
And again, there's already an excise gate, keep in mind.
Because see the wind here is northerly, if it goes down too far south here.
Although the route is shorter, the angle will be quicker, you have to come back up.
You always have to come back up.
Which is a constant consideration for those boats.
Okay, let's play out a little bit here.
Again, even here, you see boats looping down south trying to find more pressure.
It's light over there.
There's more westerlies over here and some stage.
They have to come back up.
They don't want to, but they have to.
They have to respect this line at some stage but
see what's happening to our leading boat now.
Our leading boat has managed to clear the first highest gate.
You can see there's more breeze down here.
There's a big low there.
There's the remnants of that low.
High pressure generally over here to the north of them.
All the time, it's always better to be south.
And also, what's very important in this part of the world is,
all the weather comes from behind.
All the weather comes to the west, goes to the east.
There's always an opportunity for the boats behind to catch up to the leaders.
The compression we spoken about in another subject.
Here we are starting to get under Australia.
You can see the first boat, blue boat here getting out of the Indian Ocean
when it reaches out of Cape Leewin longitude.
Again, same system more or less.
You can see high pressure, right?
With the circulation around it.
Like that, remember Southern Hemisphere,
the other way around to the Northern Hemisphere, all right.
High pressure over here as well.
High pressure over here, roughly and
here at the bottom, you can see the west winds.
Right, low pressure here, low pressure here, low pressure here, right and
all this strong west winds, so all this It's quick.
Pleased to see light airs here,
lights airs here contrarian winds there and here strong westerlies.
And here, we have all the ice gates.
All the ice gates the boats have respect,
because the leading boat here is just on the edge.
Between wind to the south and nice weather and no winds to the north.
They want to get South all they can.
Here, you can see back over here, for
instance, trying to escape from the claws of the high pressure.
Go further south, get into those westerlies but
they have to come back up, to respected ice gate.
Also, here in the Maceford Dung, this is not an ice gate.
This was the passage point of the last person on a world race.
They had to go through Cook Straight, right.
Which has tons of complications, because you leave the southern ocean.
You get into the Tasmanian Sea,
you get into a more a changeful weather system, anything can happen here.
And then, Cook's Straight itself, with its acceleration zones, traffic.
It's a big change,
because you leave the southern ocean where you don't see anything.
A few albatrosses, it's all gray, and you get into the moderate
weather system with traffic, fishing boats, coast and all that.
Big change to your system.
We've just seen as we've got high pressure to the north, stronger westerlies and
low pressure to the south.
Boats want to stay south.
These two ice gates are actually not really ice gates.
They are there at the request of Australian authorities.
So if anything bad happens, the Australian authorities can still reach the boat for
any search and rescue operation that might be needed.
Which has been needed in the past and other races, right.
So, this is there to keep the boats closer to Australia.
Again, we go to Cook's straight between the North Island of New Zealand and
the South island of New Zealand.
And both, as you start thinking about sort of change.
In English they say change of latitude, changes of attitudes, right.
So in here, there will be a change of latitudes, so
in they get into a different system.
And they will have to change gears and get more dynamic.
Okay, let's go forward.
Okay, these boats trying to stay close to the south, close to the pressure but
they have to go back up north.
Low pressure moving in, headed winds, north-westerly.
Okay, they've cleared the gate.
They've cleared the gate and now,
they're a little bit freer against the western wind.
All right, well let's move through.
You see low pressure moving through, always the same.
Wind to the south, high pressure here, head winds over there, all right.
In case you want to get into the Tasman straight or the Tasman Sea, I should say.
Because again, we know I'll stop this for a second.
We'll get up further north.
Australia is overheated continent, very warm.
Tropics are not too far away and here, you've got some big conflicts of cold
air masses to the south and warm land masses to the north.
So again, around New Zealand, and sort of to the east of Australia.
Things can happen.
Things can happen.
It's not that frequent there's cold front back in Atlantic.
Nor as frequent as in the Madagascar cold front but things can happen.
There are cases of tropical low pressure systems, cyclones if you will.
Coming down, sort of shifting down here south,
then they become extra tropical, they lose their intensity, their warm core.
Sometimes, they get regenerated again and become normal low pressure system.
And end out their life in the southern ocean.
Always something to keep an eye out for.
Move the map a little bit and move forward again.
So here you can see the change of latitude coming for the leading boat.
Leaving the westerlies as they get to the south points,
southwest latitude of New Zealand.
They left westerlies behind, so they're now in the Tasman Sea.
Much more variable weather, changes quickly.
All right, and notice a big train of westerlies down here.
Sailing terms, talk about the roaring 40s, the furious 50s,
and the screaming 60s, right?
They're well outside that.
They're getting back into civilized territory.
Okay, they see it's quite variable here, lighter,
high pressure system sitting in Tasman Sea.
These boats are now losing massive distance because there's no wind and
they have to go to this gate, if you will.
That's why it's designed like this, it's a gate, it's not an ice gate.
It's a gate put in by the organizer.
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