Wind at night

[Mac of Cygnet]

Where does the wind go at night? Yesterday was blowing a gale, but died down in the evening. I deliberately set off at 6.30AM, when there was hardly a whisper, in order to get somewhere before the wind got too intolerable. Sure enough, by the time I got here (Radcot, upper Thames), it had increased to uncomfortable levels.

 

So what happens at night? Any meteorologists out there? It's a well-known (but not infallible), phenomenon, utilised by balloonists among others.

 

Mac

[jim and pat dalton]

As simply as I can and by no means complete:

 

The wind is first created by:

 

During the day the "direct" rays (think straight lines)from the sun pass throught the air and are absorbed by solid objects like buildings or land and also water ( the land absorbs more of the sun's energy than water) depending on the reflective qualites of land and buildings these will all absorb the radiation at different rates and in turn radiate it as heat at different rates

.

As the land and also water heats up it "radiates" heat (think zig zag lines) and this radiation warms the airmass above it and in turn becomes less dense .Please note the sun only heats up objects it hits, not the air it passes thru!!! with the excetion of solids in the air.

 

This now warmer less dense air has to rise (think floating like a bubble), drawing in colder more dense air below it and you have wind!! an example: this creates a cool sea breeze on the coast from the ocean during the day because the air over the land rises more as its hotter. as it rises colder air from the sea floods in creating the breeze. Then at night the reverse happens as the land cools quicker than the sea, you get a warm evening wind flowing back out.

 

This goes on in multitude all over the world at a large zonal level and local level too. Combined with the turning of the earth it creates all sorts of wind as these differing pressure and air systems flow into and about each other. The slope of these pressure differences is called the pressure gradient( those lines on the map). The closer the lines, the steeper the gradient, the stronger the flow from one to the other and as the earth turns this causes what we call wind.

 

There are lots of other things that also contribute, but this is the main cause.

 

The answer to your question is:

 

So as the sun passes the midday point at a particular spot on the earth, generally the air will get cooler and as the evening comes in it gets cooler still.

 

This cooling will have the reverse effect and settle down air over land or sea mass but because over a land mass there is less differential than at the coast, the air quickly becomes more stable (it takes longer at the coast), therfore less wind. The still effecting turning of the earth will now appear to cause the wind to back off in direction (ie come from a more anti clockwise direction)as the pressure gradient becomes less.

 

Vintage aircraft, paragliders and balloonists will take to the air late evening and early morning because of this effect.

 

Caveat:

 

Having said all that, a stronger wind from a more active weather system may come in from elswhere and will of course over ride the above local effects if its active enough.

 

Waffling section:

 

If you ever experiance a blustry wind going all over the place (not just in one direction. My experiance suggests that the big cloud above you wants to go wee wee's any minute now!

 

Currently we are experiencing big winds that were created over the American land mass last week and have been travelling over the atlantic, picking up water in the air as it has risen during each day, next system is due Thursday. after that I believe we will get much more settle air heading our way from the Azores. Ive probably got it all wrong tho

 

 

did that help?

 

 

jim

PS: I blame all that cider I drunk this weekend for my grammatical lack of expertise

Edited May 23, 2011 by jim and pat dalton

[Proper Job]

It goes to sleep.....

 

It's had a hard day blowing and then it's tired....

 

Who can blame it

 

 

 

......... gets coat

[Tonka]

lots of people wrongley think that it is the wind that makes the trees bend but it is the tree's bending that makes the wind and seeing as the trees sleep at night there is no wind.

[nicknorman]

Where does the wind go at night? Yesterday was blowing a gale, but died down in the evening. I deliberately set off at 6.30AM, when there was hardly a whisper, in order to get somewhere before the wind got too intolerable. Sure enough, by the time I got here (Radcot, upper Thames), it had increased to uncomfortable levels.

 

So what happens at night? Any meteorologists out there? It's a well-known (but not infallible), phenomenon, utilised by balloonists among others.

 

Mac

Winds such as we have at the moment are created by pressure gradients - whose cause is pretty complex. Wind would like to flow from high pressure to low pressure but the spherical and rotating earth means that in fact they tend to blow around the centres of low and high pressure. Anyway, ground features (trees, buildings, hills etc) and just the friction with the ground, act as mechanical "wind break" slowing the air movement down, so at night the wind near the surface tends to be light (air is surprisingly reluctant to mix, preferring instead to stratify, so its quite happy to have no wind near the surface whilst the wind at say 2000' is still strong). However when the sun starts to warm the ground, the ground then warms the air by conduction (not by radiation Jim!). Warmer air is lighter so tends to rise, cooler air around it tends to descend, in other words vertical air currents are set up that mix the fast-moving upper air at several thousand feet, with the slow moving air near the ground - result is windy and gusty conditions. As the sun loses its heating power in the late afternoon these vertical air current die out, the surface wind again reduces substantially.

 

Nick

[matty40s]

Google Butterfly effect, it will give you the answer.

 

Buterflies only come out when the sun is up, the combined wing movements make the wind happen, near sunset, the butterflies go to bed so the wind stops.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

moths only create wind around lights so don't count.

[Mac of Cygnet]

[jim and pat dalton]

oops used wrong word

 

conduction is quite right for heating the air

 

think i got th rest of it right

 

sorry

 

jim

[tillergirl]

We stood next to the canal tonight (Keadby) and watched the wind blowing through a field of barley. It was quite beautiful really.......all the different shapes its made across the top of the crop.

[Windfola]

I fink it might be my flatulence problem. I'm pretty sure that caused Hurricane Katrina.

 

Windy

[Grace and Favour]

I fink it might be my flatulence problem. I'm pretty sure that caused Hurricane Katrina.

 

Windy

 

Sorry - but your theory is all hot air!

[canaldrifter]

Sorry - but your theory is all hot air!

 

.... and it stinks.

 

Tone