Cold and warm winds

[g.foster]

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