Author Topic: Wind.....Directional Change Cause??  (Read 1802 times)

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Offline gginnj

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Wind.....Directional Change Cause??
« on: August 15, 2016, 11:29:56 AM »
First off, I'm sure, this is showing my ignorance on meteorology....

I get wind is a product of air movement from temperature differences....

ok, why would the wind direction suddenly change direction, then again??
    Are there areas that are suddenly changing temperatures enough to cause the wind to change direction?

I have a feeling I'm looking at this in the "looking at the trees instead of the forest" kind of way.....


Offline Jáchym

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Re: Wind.....Directional Change Cause??
« Reply #1 on: August 15, 2016, 11:56:14 AM »
It is indirectly temperature changes because basically:

- different solar radiation -> different temperatures -> changes in pressure -> wind

wind is basically based on pressure gradient.

This is the so-called pressure gradient force (PGF)

next thing that you must take into account is Coriolis force due to rotation of the Earth

however, near the ground it is also frictional drag that slows it down.

now this is mostly the wind on macro scale

However, what you are talking about is microscale.

Here, you must also consider random motion of air particles (molecular viscosity) and turbulent flow (eddy viscosity). Then the friction again (roughness of the terrain etc.)

Offline gginnj

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Re: Wind.....Directional Change Cause??
« Reply #2 on: August 15, 2016, 12:33:58 PM »
Am still reading more on the subject - some of what your saying makes sense, other parts - not yet.....that's ok.
the more I'm reading, the more confusing it gets - which is half the struggle.

What confuses me the most, is when you have the direction changing multiple times with the same minute.
Is something changing that drastically that quickly that it's causing those directional changes?
As you stated, I'm talking on the micro scale - (the trees from the forest) - what is changing on the
micro scale?

obviously, this can't be answered in forum post, given all the variables - but which variable would be the one
that changes most frequently that would cause those frequent changes in direction?  Obviously the terrain is constant
I can understand the cloud cover allowing more/less solar heat through, but you also have wind shifts when the cloud
cover is the same or non-existant.

Or is it (tongue in cheek) a result of thousands of people going in and out of their homes, with the AC/heat escaping
or entering their homes - cause minute changes....




Offline miraculon

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Re: Wind.....Directional Change Cause??
« Reply #3 on: August 15, 2016, 01:06:22 PM »
We live close to Lake Huron in Northern Michigan. We get a predictable wind shift in the early afternoon if conditions are right. It will start from the SW or W, then shift suddenly 180° when the on-shore breeze begins. I believe that it is solar heating of the inland fields and farms that cause a local "Low" and the wind shifts to that direction from the cooler lake. It will change quite abruptly along with the temperature falling several degrees.

Greg H.


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Offline Jáchym

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Re: Wind.....Directional Change Cause??
« Reply #4 on: August 15, 2016, 01:14:12 PM »
When you get to the most "micro scale" there are local factors such as the turbulent flow and there is a factor of randomness at the very micro scale

Offline nincehelser

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Re: Wind.....Directional Change Cause??
« Reply #5 on: August 15, 2016, 01:16:59 PM »
It might help to think of how water flows in a river.  Note the swirls and eddies in the current as it passes by.  The wind has these, too.

The original cause of an eddy can be considerably upstream, and it is hard, if not impossible to predict what it will do over time.

We're starting to get into chaos theory, here. 

Offline gginnj

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Re: Wind.....Directional Change Cause??
« Reply #6 on: August 15, 2016, 01:28:09 PM »
It might help to think of how water flows in a river.  Note the swirls and eddies in the current as it passes by.  The wind has these, too.

Interesting analogy.

Of course, randomness is just cause and effect that we haven't been able to detect/measure yet!

also, without chaos, we wouldn't be able to tell normal!

Offline Jáchym

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Re: Wind.....Directional Change Cause??
« Reply #7 on: August 15, 2016, 01:30:17 PM »
Quote
that we haven't been able to detect/measure yet

and never will be, thats why it is called "random" :D In this case if it is a trully random event, it can never be predicted. Example is also for example radioactive decay.

Offline nincehelser

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Re: Wind.....Directional Change Cause??
« Reply #8 on: August 15, 2016, 01:36:43 PM »
It's those damn butterflies!  :evil:

https://en.wikipedia.org/wiki/Butterfly_effect

Offline gginnj

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Re: Wind.....Directional Change Cause??
« Reply #9 on: August 15, 2016, 01:37:59 PM »
and never will be, thats why it is called "random" :D In this case if it is a trully random event, it can never be predicted. Example is also for example radioactive decay.

Maybe Random really means...... Radioactive-Atoms-Not-Dectectable-Or-Measureable  (RANDOM)

Oh well, time to be done lunch and back to work!

Offline Jáchym

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Re: Wind.....Directional Change Cause??
« Reply #10 on: August 15, 2016, 01:44:15 PM »
I saw a documentary and they asked some experts the following question:

Assuming that one day in the future there is a super computer that theoretically has information about absolutely every aspect of the atmosphere and other factors over the whole world. Will it be able to predict the weather conditions for any place with absolute accuracy?
The answer is that even in such case - no.... because of the random effects, which are not large, but because even just small change can trigger big change (butterfly effect) the computer would probably be very accurate, but not completely and it would only be possible, if I remember correctly, approximately 10 days in advance, then it would become more or less similar to how accurate our forecasts are today :D

Offline Jáchym

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Re: Wind.....Directional Change Cause??
« Reply #11 on: August 15, 2016, 01:45:39 PM »
Overexaggerating it, you wave at someone and a hurricane hits somewhere on the other part of the globe 2 days later :D

Offline Jáchym

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Re: Wind.....Directional Change Cause??
« Reply #12 on: August 15, 2016, 01:48:02 PM »
Oh and one more very important aspect...

basically everything that happens in terms of the weather comes down to energy ballance and the amount of heat a particular place gets (that transforms to temperature gradients, pressure gradients -> winds etc etc). And we cannot accurately predict the exact variations in solar energy we get, obviously this fluctuates all the time and since it only takes 8 minutes for the light rays to hit the Earth, you basially dont know exactly what will be in 8 minutes time

Offline gginnj

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Re: Wind.....Directional Change Cause??
« Reply #13 on: August 15, 2016, 02:01:04 PM »
That "waving" theory - reminded me of an article I read a few years back on why it rains so much on weekends!

http://io9.gizmodo.com/this-is-why-it-always-rains-on-weekends-1540233798

Offline Jáchym

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Re: Wind.....Directional Change Cause??
« Reply #14 on: August 15, 2016, 02:11:10 PM »
Yes, that in fact is absolutely correct, there are several factors here, some of the most important ones are:

- different air and car traffic intensity
- different rate of production in factories -> variable emissions

Offline PaulMy

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Re: Wind.....Directional Change Cause??
« Reply #15 on: August 15, 2016, 10:28:43 PM »
Quote
That "waving" theory - reminded me of an article I read a few years back on why it rains so much on weekends!
But then Jachym's neat "weekday trends" plugin shows that Saturdays and Sundays are on average the lowest rainfall for my station ;)

Paul

Offline Jáchym

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Re: Wind.....Directional Change Cause??
« Reply #16 on: August 16, 2016, 05:13:56 AM »
Thats why we should all move to Canada :D

 

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