Cold and warm winds

[Kerry Parker and Andy Price]

Graham's points are really interesting, as is the physics of weather.
I didn't know that N Taranaki was wetter than the West Coast.  How does that 
work then? Why N and not W?  How does that work then?  Is it a just a few km 
sq of Taranaki that is of concern here, or all the way from New Plymouth to 
the top of the mountain?

The pressure changes in winds are complex too and I have only just started 
to think about what happens in NZ.  How can a wind blow into a place where 
the pressure is higher (and hence heat up)?  My very simplistic thinking is 
that the atmosphere has a pressure gradient increasing from space down to 
sea level due to gravity.  Winds mostly run sideways from high to low 
pressure due to convection cells.

Kerry

---------------------------
Kerry Parker
Senior Physics Teacher
The Correspondence School


----- Original Message ----- 
From: "g.foster" <g.foster at clear.net.nz>
To: <phys-teach-talk at nzip.org.nz>
Sent: Friday, May 09, 2008 8:32 PM
Subject: Cold and warm winds


> Perhaps it is also relevant to remind ourselves of the
> special fohn winds we experience in the South Island and the
> reason why the West Coast area and Taranaki get so much
> rain.
> It is interesting that The northern slopes of Mt Taranaki
> actually is the wettest place in NZ, not the West Coast SI.
>
> When moist winds come across off the Tasman Sea they are
> forced upwards by the mountains.
> This causes the air to expand and there is a nett loss of
> kinetic energy of the particles as they spread out and slow
> down. This cooling causes the moisture to precipitate out as
> rain or snow or hail.
>
> When the drier air moves over the top of the Southern Alps
> it then descends and is compressed causing it to warm up
> since there is a gain of kinetic energy of the particles as
> they come closer together and speed up. This causes the hot
> dry Norwesters experienced in Canterbury.
>
> This is also the bais of a refrigerator which cools things
> down inside by compression of a gaseous substance, then
> allowing it to expand through a tiny hole. The rapid
> expansion causes the substance to cool down and this cooler
> substance then takes the heat from inside the fridge when
> heat flows from warmer substances to the cooling
> refrigerant.
> Then the whole sycle is repeated after the heat is
> transferred to the air in the vanes.
>
> Also heat pumps work in the reverse to a fridge.
>
> We 'experience' warm winds since the molecules have more
> random Ek and take less heat from our epidermal layer than
> if they are cool.
>
>
> Graham Foster
> Director of Science, EGGS
> AMI Learned Society
>
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