Posts Tagged ‘gerography’

Rain

It’s my regular guest blogger with something very topical right now in England… Rain! Enjoy.

 

Let me start with the answer to last week’s (27.9.12) puzzle question. No-one was brave enough to give it a go so here it is. You remember the tank for the boats to go in weighed 252 tons and I asked what it would weigh if two boats weighing 24 tons each were put into it. So that means what does 252 + 24 + 24 equal. Well the answer is 252. Why?

Simply because when you put the 48 tons of the two boats in, an amount of water overflows the tank and that amount of water if you caught it and weighed it would be 48 tons. (So 252+24+24 really does =252!).

Ok now on to this week’s subject: RAIN

I suppose after the bad summer the UK has had and just last week the almost 3 continuous days of rain it was inevitable my thoughts would turn in its direction. Why did it happen? Was there something special going on in the weather sphere?

I think we can all probably remember a time when there seemed to be (and possibly was) rain for days on end. The world has had incredible blips in the rain making cycle which are totally off the scale of normal weather. You may remember, in 2004, the village of Boscastle in Cornwall being badly damaged by flooding caused by just 8 hours of rain.

Rain affects all sorts of things, some for good some for bad. It gets our food crops growing and waters the natural landscape & woodlands. It can stop sporting events, cause rivers to overflow and make you and me wet in varying degrees. Sometimes it seems that every time we go out it is raining. In the paper last week big reductions of UK-produced honey were reported. The reason: wet weather from April to August meant honey bees had far less time to get out and about to do their job of pollinating. (Scotland’s ‘crop’ of honey was down by two-thirds because of the rain; a Derbyshire farmer said he was down 90%!).
Let’s start, as they say, at the beginning. How does rain start? What happens to make it?

Well, first off, it’s back to schooldays geography: heat acts on water on the Earth’s surface, as water droplets increase in heat they become less dense and therefore rise up into the atmosphere where they form clouds. All clouds are simply water droplets hanging up in the sky. They won’t fall down until other things take place. I’m sure you’ve quite happily looked up at those pretty, fluffy, rounded white ones and thought you were ok as they wouldn’t rain on you. I’m also sure you’ve looked up at increasingly darker ones and thought, “It looks like rain”. We do that don’t we? The fluffy rounded white ones are called cumulus and they pass through 3 stages before they get to the state when rain is likely: they start with cumulus humilis which grow into cumulus mediocris and then to the rain-bearing cumulus congestus. One stage further and congestus will grow into Cumulonimbus and this is the baddie as far as the weather goes. It’s the fatal motorway pile up of the weather world. It brings the extremes: hail, snow, lightning, hurricanes and, sadly, sometimes death. I wonder if you imagine what clouds would look like if you were up there alongside them. We tend to look up and think a bit two-dimensionally: we can see their length and we can see their width or so we think. How many of us think of their height (depth)? Think of when you’re on a plane flight: you look out of the window and when coming in to land you see the plane go into the cloud layer and then come out underneath. It’s hard to imagine that depth from the ground looking up because we can’t really see it. Well, the Cumulonimbus is big, massive in fact in physical size, starting at a height above ground of about 6,000 ft (1828 metres) and going up to about 45,000 (13,716 m). That means it can easily be taller than Mount Everest (29,029 ft, 8840 m).
Now let’s stop there for a mo’. How and more importantly where will the ‘heating’ process begin that results in these cloud formations? Think about it. Obvious really isn’t it? It has to be in the areas where the Earth’s temperature is at its greatest. That means the equatorial & tropical regions around the middle of the Earth. Gavin Pretor-Pinney gives an easy to understand example in his book The Cloudspotter’s Guide:

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He uses the lava lamp. You’ve probably all seen one and some will have owned one; my family had one when I was growing up and it was amazing how long you could look at it just waiting to see what the next shape it formed would look like. The ‘lava’ is in the bottom of the glass container when the lamp is switched on. It then heats up causing parts of the lava to become less dense and therefore to rise up in the liquid. Finally when it gets far enough away from the heat at the bottom it becomes more dense, increases in weight and falls back down to begin the whole process again.

That’s why rain doesn’t start in the polar regions; it starts in the middle degrees of latitude around 00 (+/- 23.5 degrees of the tropics) and then works its way either north or south when the cooling process begins. This is the crucial point in the life cycle of rain – its birth as it were. At some point the water droplets then become too heavy to remain up in the air as clouds and will begin to fall as rain. All the preceding states could be considered as foetal or ‘ante-natal’; it is growing from random rising water droplets into clouds and waiting for the ‘something’ to happen which will release the droplets from the cloud to fall on us down here.

In the Boscastle example earlier the ‘something’ was warm air picking up moisture from the Atlantic. It travelled to the Cornish Coast where steep cliffs forced the air upwards. As we said above, the droplets would then cool sticking together forming clouds and further cooling resulted in them falling back to Earth as rain, but because of the massive volume of moisture they were carrying it was very heavy rain. Many records were broken in the Boscastle disaster just because of the amount of rain that fell in such a short time. One fact that intrigues me is that in that one afternoon 7 inches (almost 178mm) of rain fell and yet 10 rain gauges all fairly close by recorded under 3mm! How bizarre is that? It’s like Boscastle had its very own village rain cloud with all the taps turned on – if ever you wanted a definition of a local phenomenon that has to be it. It is believed that it was an occurrence of what is known as The Brown Willy Effect. Now before you go thinking X-rated thoughts let me explain: it is a meteorological term meaning heavy showers developing over high ground but then moving quite a way from their place of origin. Brown Willy comes directly from the Cornish Bronn Wennili which means “hill of the swallows”. It is the highest point on Bodmin Moor (420 m). So now you know.
And here it is.

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(Thanks to Stephen Dawson for photo – re-used under Creative Commons licence)

The disastrous flood that occurred in 1953 along the East Coast of England affected Norfolk, Suffolk, Essex, Kent & parts of the Thames Estuary, killed 307 people, damaged 24,000 homes and caused 30,000 people to be evacuated. It was not caused by primarily by rain but by a storm surge of water and a high Spring Tide. (We’d probably call it a tsunami today.) What is interesting is that one of the villages affected by it was called Salthouse. Given recent posts about salt I couldn’t resist checking the place out on line to see what its origins might be. Sure enough there’s a history there of salt making going back to Saxon times and beyond from remains discovered in the area. Maybe that’s one to investigate next time I’m down that way. It’s on the ‘things to do next year’ list.
People write music about the rain, sing about the rain, paint pictures or take photos with rain in, write about the rain and even eulogise in poetry about it. We’ll look at some of those next week but for now I want to direct you to one of the most famous and most shown film clips.

Who can forget the words of that classic song about the pleasure of rain, “I’m singing in the rain”? Gene Kelly was “laughing at clouds, so dark up above” but I doubt we do; he also “walked down the lane with a happy refrain”. Do you? Now I’ve watched this video (http://www.youtube.com/watch?v=WttNlbaECDY) and I’ve made a few notes. This guy is such a bad example to kids. Here are a few things which troubled me:

1. He puts his brolly down after just 43 secs. Therefore he gets very wet. Why would you do that?
2. At 1m 21s he actually takes his hat off for a full 7 secs so his head gets soaking wet. It’s off again briefly at 1m 52s. Would you want your child copying this sort of behaviour?
3. At 2m 27s he does the “kick-the-point-of-the-brolly-with-your-foot” trick so it spins-round in the air and he catches it by the handle. He then does it spinning from his own hand and catching it again a bit later. All this time it is not covering him and so he continues to get even wetter.
4. At 3m 1s he stands under the gutter downspout and drops his brolly down so he can get his head soaked again.
5. From about 3m 10s he jumps in the puddles splashing all over the place and seems to think this is just jolly good fun.
6. Only at 3m 40s when a policeman arrives does he seem to think his behaviour is incredibly childish and he acts sort of embarrassed and towards the end bumps into a passer-by and actually gives his umbrella away!

Now come on, hands up any of you who are parents out there – would you want your child to behave this way? No, I’m sorry Mr Kelly this is just not good enough!

I couldn’t finish without telling you about a super video on the subject of rain. Here it is: http://www.youtube.com/watch?v=LPodpYu_Ruo&feature=related. How long is it? I kid you not – the timer shows 8 hrs 1 min 13 secs!!! There are a few picture changes and a few thunderclaps but it really is just the sound of rain falling. Check it out (for a minute or so) if you don’t believe me. I’m sorry but I’ve only managed to listen to the first 7 hrs 59 mins then I had to go out so I can’t tell you how it finishes!