THE SEARCH CONTINUES: The pinger locator being towed by Australian Defence Vessel Ocean Shield in the search for the missing flight data recorder and cockpit voice recorder of Malaysia Airlines flight MH370 in the southern Indian Ocean. 

 

By Steff Gaulter

 The search for the missing plane, flight MH370, has raised a lot of questions. Not only is it perplexing that a huge aircraft can simply disappear, but there also seems to be a lot of strange weather in the Indian Ocean and a staggering amount of debris floating there.

The search area has changed over time, but a significant period has been spent scouring the ocean many hundreds of miles to the west of Perth. In his book Down Under, Bill Bryson describes Perth as the most remote city on earth, and it’s this far-flung city that is now the closest point to the search area. The logistics of conducting a search in such a remote location are obvious, but the weather hasn’t been helping either.

For a time it looked as though parts of the plane had been spotted in a region of the world known as the “Roaring Forties”. This may sound like a period of history, but it’s actually referring to a geographical location; a latitude between 40 and 50 degrees south of the equator, which is known for its howling winds.

Historically, this was a part of the world which delighted sailors. The strong winds could be counted on to speed the passage from southern Africa to Australia, and across the Pacific from Australia to the southern tip of South America.

The only part of the world that has stronger winds than the Roaring Forties is just to the south of this, in the region known as the “Furious Fifties”. By now, some of you are probably thinking that I’m making up these names, but that’s honestly what they’re called!

One reason that this part of earth is prone to severe weather is that there is so little land at these latitudes, so there is precious little to slow the wind down. After all, the climate of the southern hemisphere is mirrored in the northern hemisphere, but there are no Roaring Forties or Furious Fifties in the northern hemisphere, thanks to the huge landmasses of Asia, Europe and North America.

In the southern hemisphere, with the absence of land, this latitude is conducive to strong winds thanks to the way in which the sun heats the earth. Parts of the world are heated more strongly than others, and wind and rain are generated by the atmosphere as it tries to even out the heating. Near the equator, the sun is directly overhead, and this warms the ground quickly, which in turn heats the air above it.

This causes the air to rise, and as it rises it cools and forms showers. If you look at a satellite picture of the globe, there is a line of thunderstorms that extends all the way round the world. There are a few breaks in it, and a few regions where the showers are more intense, but you can trace it around the globe. It’s called the ITCZ (as the inter-tropical convergence zone is a bit of a mouthful!) and it follows the sun north for the northern hemisphere’s summer, and southwards again for the winter.

 After producing thunderstorms, the air flows towards the poles, high up in the atmosphere. However, as it reaches the mid-latitudes, around thirty degrees north or south of the equator, it sinks back toward the surface.

It continues to flow towards the poles, but because the earth is rotating, it is deflected and forms the westerly winds which we know as the Roaring Forties. In the southern hemisphere, there are only small pieces of land which could slow down these westerlies, namely the tip of South America, New Zealand, and a sliver of Australia.

Whilst there may be only a few pieces of land in the forties, in the fifties there is only one, the far southern tip of South America. This is why the winds are usually even stronger than in the forties. As these winds hurtle around the globe, they generate plenty of clouds and storms, and it’s the frequency of these storms which is proving to be a real problem for people trying to scour the surface of the ocean.

 As well as causing storms, the fast flowing winds also push along the surface waters of the ocean. These cause huge circulations, or ocean gyres. There is a vast gyre in the Indian Ocean, and there are similar gyres in the north and south Pacific and Atlantic Oceans.

The circular motion of the gyres draws in debris, which eventually makes its way into the centre, where it becomes trapped. This can happen to any kind of material, but that which isn’t biodegradable simply remains in the gyre. This includes many plastics which do not wear down, but simply break into tinier and tinier pieces.

This doesn’t happen quickly. It’s estimated that rubbish from the coast of North America would take about six years to reach the centre of the gyre in the North Pacific. The trouble is that none of these huge gyres are near land, so no nation will take responsibility or provide the funding to clean them up.

Until this happens, there will always be spurious pieces of debris in our oceans, which will make searching for missing planes and loved ones that little bit more difficult.

 

 

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