Naked Science Forum
Life Sciences => The Environment => Topic started by: Harvey Shaw on 11/08/2009 14:30:02
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Harvey Shaw asked the Naked Scientists:
Dear chris
Ever since the first time i heard of your show (http://www.thenakedscientists.com/HTML/podcasts/) ive been wanting to think of a question to ask you and now ive thought of one:
How does the wind change direction?
                                                  from harvey shaw
What do you think?
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Wind is the movement of air from regions of high atmospheric pressure to regions of low atmospheric pressure.
These regions of high and low pressure form as a result of heating by the Sun; different surfaces on the Earth, ranging from snow and ice to the water of the deep oceans, absorb or reflect different amounts of solar energy and this leads to differences in the temperature and humidity of the air above different areas of the Earth.
As these regions form, they are 'stirred up' by the Earth's rotation; because the Earth is a Spheroid, the linear rotational speed is greatest at the equator and reduces as you go north or south, and this means that anything that is large enough to straddle different rotational speeds will start to turn and spin up into a vortex. The spin of these vortices then further affects the path that the vortices take and because of the range of variation in the size, spin, humidity etc. of all the weather systems, the whole lots becomes chaotic and nearly impossible to predict.
The end result is that you get regions of high and low pressure more or less randomly wandering about over the surface of the planet and while one day the region of high pressure might be to the north of you and the region of low pressure to the south, so that the wind blows from north to south, the next day the relative positions of the regions might have moved, changing the direction of the wind.
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But wind is not just Geostropic (blowing parallel to the isobars because the Coriolis force)
Surface winds are influenced by friction, large wooded areas, sea conditions and built up areas. All of these act to speed up or slow down the local winds.
If you stand where you can see a weathervane take not of the direction it's pointing, this will actually be moving as the wind is not constant. Although it will not be moving too much depending upon the strength of the gusts. Now use the pointy top of the vane as a reference point and take note of the direction the higher clouds are moving in.
It is likely that those aloft are moving in a totally different direction. You can use this to predict the weather! You can also use the wind to find fronts
Some examples of how can be found here:
Finding Cold Fronts Using Wind Direction (http://bit.ly/dyP9G)
Finding Warm Fronts Using Wind Direction (http://bit.ly/sLDAK)
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I just heard that at the council meeting, they said something to the fact, that you dont have to pay these tickets, however, if you dont, they company can turn you over to collections. Would like to find out more about this.
WHAT???
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Harvey Shaw asked the Naked Scientists:
Dear chris
Ever since the first time i heard of your show (http://www.thenakedscientists.com/HTML/podcasts/) ive been wanting to think of a question to ask you and now ive thought of one:
How does the wind change direction?
from harvey shaw
What do you think?
I think the answer you're after is as follows.
The wind in the UK is dominated by depressions - areas of lower pressure than the surroundings - generatd by the fact that, at our latitude, there is warm air moving one way (W) and colder air, just to the north, moving the other way(E) . These act a bit like plugholes in the bath or like enormous mild tornados. The air spirals into them in an anticlockwise way (looking down). The direction of the wind will depend where you are relative to the centre. Imagine a depression moving West to East, with its centre moving in a path just North of your house (a very common situation in the UK). As it approaches you, the wind will be blowing from the SW, when it's just past you, the wind will be about from the West and when it has past you, it will be coming from the North West. For people living hundreds of miles North of you the wind will start off from the SE, through E and end up From the NE because it's passing South of them.
Actually, there are very few isolated depressions flowing across the UK and I described an ideal situation - but you've got to start somewhere.
btw, air flows out of a high pressure region (anticyclone) so the directions are the opposite to what is described above.
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Sophiecentaur does your example to in to account that the wind blows along isobars at an angle or the curvature of those isobars? Until the original poster replies I would assume that he is thinking of surface winds.. The ones he can see and see the influence of.