Less wind at night...

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Mark
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Less wind at night...

Postby Mark » Thu Aug 20, 2009 10:27 pm

Frequently - too much to be co-incidence - wind seems to die off at night. (I'm not talking merely about thermal wind.)

So does the Sun add a load of energy to the system all day and increase even gradient wind?

Or is something else a play?

Or am I wrong to think that even gradient wind drops off at night.

TIA.

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Rowana
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Re: Less wind at night...

Postby Rowana » Fri Aug 21, 2009 1:13 pm

I find that there is sometimes more wind at night.
I think it may have something to do with beer & Curry!
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sahona
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Re: Less wind at night...

Postby sahona » Tue Aug 25, 2009 9:22 pm

Two reefs in the duvet please.
I agree about the generally quieter nights, and often sail v. early to take advantage.
Perhaps this should be directed at Simon ?
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aquaplane
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Re: Less wind at night...

Postby aquaplane » Tue Aug 25, 2009 10:16 pm

It seems to be comon that the wind drops off in the evening on Windermere, about 5 or 6 o-clock.

The boats seem to point towards the shore too, when there is no wind, funny that. At the coast it could be explained by land breeze, but on Windermere? And no perceptable wind?

I left my eldest and the Grandson on Chiron on Sunday evening for a few days. I had a phone call @ about 22:30, "there are white horses all over, should I be going and putting another rope on or somat"? I pointed out that if the substantial rope strop she had put on the cleat failed, the chain she had put round the other cleat probably wouldn't. They both slept well. So the wind doesn't always drop at night, but it usually does.
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DaveS
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Re: Less wind at night...

Postby DaveS » Wed Aug 26, 2009 4:39 pm

I would agree that Simon is the most likely to come up with the correct answer!

I have noticed this phenomenon for many years but never got a satisfactory explanation until reading something a year or so ago - I now can't remember where. IIRC it's to do with flow detachment: the high level wind continues to blow, but slides over a low level layer of still air. In the morning convection starts, there is an exchange of air between the layers, and the low level air is dragged along again. I'm sure there's more to it than that, but it seems a reasonably convincing starting point.
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Silkie
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Re: Less wind at night...

Postby Silkie » Wed Aug 26, 2009 5:07 pm

We had a wee discussion about this last year Diurnal weather patterns and Simon put his tuppence worth in. I like Dave's explanation too.
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alanf
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Re: Less wind at night...

Postby alanf » Tue Sep 22, 2009 2:14 pm

Dave has the principal right.

This is caused by temperature inversion. As the Sun goes down the air nearer the ground cools first, this creates a form of layer barrier which prevents the gradient wind comming all the way down.

[url]en.wikipedia.org/wiki/Inversion_(meteorology)[/url]

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Re: Less wind at night...

Postby weatherman » Wed Oct 07, 2009 10:50 pm

Hi Chaps,

All to dop with stability in the atmosphere. At night, the air stratifies and near the ground, as temperatures fall, an inversion often forms. This is a zone where temperatures rise sharply with height (instead of falling as they usually do). This forms a stable layer and it in this layer that the winds are light.

By day the heating of the sun produces termals which mix up the atmosphere this allows air currents to flow between layers, both horizontally and vertically, hence more wind.

Does that make sense?

Sorry it took so long to reply,
Simon
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Mark
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Re: Less wind at night...

Postby Mark » Thu Oct 08, 2009 7:32 pm

weatherman wrote:Hi Chaps,

All to dop with stability in the atmosphere. At night, the air stratifies and near the ground, as temperatures fall, an inversion often forms. This is a zone where temperatures rise sharply with height (instead of falling as they usually do). This forms a stable layer and it in this layer that the winds are light.

By day the heating of the sun produces termals which mix up the atmosphere this allows air currents to flow between layers, both horizontally and vertically, hence more wind.

Does that make sense?

Sorry it took so long to reply,
Simon


Any chance you'd fancy reworking that for a small sailing club newsletter and putting your name to it? You'd get a web link and the satisfaction of educating a few people.

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Re: Less wind at night...

Postby weatherman » Thu Oct 08, 2009 8:17 pm

Hi,

No problem, let me know what you'd like. A plug for The Pocket Weather Forecaster book and the Weather School would be all that is needed!

Ta,
Simon
Simon Keeling, PhD MSc, FRMetS
My new book The Pocket Weather Forecaster is out now. Read sample pages here.
http://www.weatherweb.net
http://www.weatherschool.co.uk

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Mark
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Re: Less wind at night...

Postby Mark » Thu Oct 08, 2009 8:41 pm

weatherman wrote:Hi,

No problem, let me know what you'd like. A plug for The Pocket Weather Forecaster book and the Weather School would be all that is needed!

Ta,
Simon


Well I was thinking of slightly reworking that two paragraph post to explain the 'quiet at night' pheonomenon. It would require very little tweaking.

A plug for The Pocket Weather Forecaster book and the Weather School would be fine!

Of course if you have a pet (but not too advanced) subject that you'd like to do an article on I'm sure our stressed out editor would be delighted with the material. :-) (Personally i'm just glad to understand quiet nights!)


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