View Full Version : Wind
comedyjock
13th Mar 2011, 21:47
Can someone explain in laymans terms why windspeed is greater round a high than a low pressure? Happy with PGF and Coriolis but don't understand the centrifugal/centripetal bit!
Cheers
Try drawing the balance of forces which are required to keep the wind flowing parallel to the isobars (the 'gradient wind') around both a high and a low (doesn't matter which hemisphere) and see if the answer appears.
If it doesn't I'll send you a link.
PS DO try and think of Centripetal force rather than Centrifugal when you balance the forces. It avoids ulcers in physics teachers:)
EK4457
14th Mar 2011, 13:41
If you were to explain this in one phrase, you would probably say 'adverse pressure gradient'.
In more detail, as air circles around a high or low, centrifugal effect* tries to 'throw' the air outwards away from the centre.
Hopefully you can picture some air spiralling outwards from the centre of a high/low.
Now, here is the clever bit. With the high pressure system, the high pressure is pushing air outwards, working in the same direction as the centrifugal effect. So they 'add up' and result in a faster air velocity (wind).
However, with a low, the pressures are the other way around. The higher pressure around the low wants push the air inwards towards the low. The pressure gradient is acting against the centrifugal effect. This is known as an adverse pressure gradient. The result is a lower air velocity (wind).
* those who like their physics will know that there is no such thing as a centrifugal force, just as there is no such thing as a coriolis force. However, the effect of circular motion makes objects appear to be thrown outwards. It looks like there is a force when there is none there, hence I used the term centrifugal effect (not force).
As previously said, if you want a pictorial explaination, you will have to use the centrapetal force as this is a real force. You may also have to read up on a bit of A level physics.
comedyjock
14th Mar 2011, 19:47
Thanks, if you could post the link BOAC I would be grateful.
Beware - it talks of centri-spit-fugal and Cori-spit-olis force. However, despite the gross errors I'm sure it will help:)
Gradient Wind: non-geostrophic winds which blow parallel to isobars (http://ww2010.atmos.uiuc.edu/%28Gh%29/guides/mtr/fw/grad.rxml)
What EK said, really!
No doubt someone will be along with a 3 page solution using a Laplace transform soon, but hey, 'KISS' rules :ok: