Naked Science Forum

Life Sciences => The Environment => Topic started by: ConfusedHermit on 19/06/2013 02:33:49

Title: If wind goes on forever, is today's wind the same there's always been?
Post by: ConfusedHermit on 19/06/2013 02:33:49

I was interested by the thread 'Why does the wind blow?' (http://www.thenakedscientists.com/forum/index.php?topic=47797.0) and some odd questions came to mind:

1.) If wind is powered by the sun and never really 'stops;' it just keeps going, then does that mean the breeze I feel outside has been around before there was even life on this planet?

2.) Are there ways humans and animals add new wind currents that also go on forever, or does an electric fan or beat of a wing only go so far before 'dying?'

3.) Do all small winds eventually become hurricanes and tornadoes? Is it an endless cycle of 'breeze to medium, to heavy, to extreme, back to heavy/medium/breeze again?'

Thank you for humoring me and random thoughts :{D~

Title: Re: If wind goes on forever, is today's wind the same there's always been?
Post by: evan_au on 19/06/2013 12:34:30

Eddies, whirlpools and tornadoes are examples of turbulent flow (http://en.wikipedia.org/wiki/Turbulence) which happens in fluids like air and water when sufficient energy is injected into a small enough volume. The turbulent flow tends to diffuse this energy rapidly throughout the medium, dissipating the energy.

3.) Despite the story about the flap of a butterfly's wings creating a tornado a thousand miles away... While theoretically possible, statistically it is more likely to work the other way - big eddies carrying lots of energy (think of a tornado) spawn smaller eddies, which create even smaller ones, right down to very small scales where the viscosity of the fluid turns the energy into heat.

1.) Energy is deposited into our atmosphere and oceans the form of differences in temperature - eg the difference in temperature between the tropics and temperate climates, and between there and the poles; this produces the prevailing winds (http://en.wikipedia.org/wiki/Prevailing_winds). Other winds can be produced by temperature diferences night and day or between sea and land. However, as soon as these temperature differences disappeared, the winds would slow and stop.
So rather than saying that the same breeze has been around for a long time (because it rapidly dissipates due to turbulence), I would rather say that the day/night/seasonal differences continually produce new breezes...

2.) While humans do produce some new winds (eg contrails from aeroplanes), they mostly die out rapidly. However, climate scientists suggest that if global warming heats oceans above around 26C, they expect an increase in the frequency & strength of tornadoes, as these rapidly dissipate the newly available source of energy above warm oceans.

One tornado which has been around for an extended period is Jupiter's great Red Spot (http://en.wikipedia.org/wiki/Jupiter#Great_Red_Spot_and_other_vortices), which is very distinctive because of its colouration.