Does the wind stop when the sun goes down? - RC Groups
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Jul 03, 2011, 01:35 AM
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Does the wind stop when the sun goes down?

I live in Australia close to the sea.

It's often windy but I notice it is always better in the early morning or evening.

Is this true? Does wind decease in the morning and evening?

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Jul 03, 2011, 01:40 AM
Registered User
The wind can pick up when you live by the sea, as the sun heats up the inland area air, causing it to rise and drawing in air to replace it.
Jul 03, 2011, 01:56 AM
Registered User
I live near the coast in California. The wind is calm all night and the early morning, picking up as it approaches noon, peaking at about 3pm then slowly dying or maybe handing on till about 6pm then dies out as it gets dark. It is definately cause by the heating of the landmass area.

On top of that there is the on shore wind off the ocean and the wandering H and L pressure areas that turn things around randomly. But yes, there is, in absence of other more severe weather, a daily wind cycle that is pretty consistant and driven but the sun heating the landmass during the day.
Jul 03, 2011, 04:00 AM
Registered User
Hot land and cool sea (relative to the land temperature) generate wind as the heavier cool air from the sea moves to displace the lighter hot air over the land. As the land cools down in the evening, the wind drops because the temperature difference between sea and land is less.
Jul 03, 2011, 07:06 AM
Will fly for food
Near the water/land transition, the wind switches direction twice each day.

During the day, the wind blows from sea to land, since the land heats up faster, causing the air to rise and the wind to bring air from the sea. At night, the sea cools slower, so the wind blows the other direction.

In the morning and evening there is a period of light to no wind as the temperatures are about the same.

Of course, other weather may over ride this wind.
Jul 03, 2011, 08:22 AM
Boogie_'s Avatar
Does the wind stop when the sun goes down?
The weather is directly related to my work schedule.
It stops blowing when I'm at work and gets windy on the weekends.

Same can be said about rain.
Jul 03, 2011, 08:31 AM
Registered User
Originally Posted by Boogie_
The weather is directly related to my work schedule.
It stops blowing when I'm at work and gets windy on the weekends.

Same can be said about rain.
Well, with the winds we have have had in this area so far this year, you must not be working much.
Jul 03, 2011, 08:42 AM
Boogie_'s Avatar
Well, with the winds we have have had in this area so far this year, you must not be working much.
hehehe, for real.
Jul 03, 2011, 09:30 AM
Shelter Kitty "Orange Death"
bartricky's Avatar
Sailors call it "sea breeze".
Jul 03, 2011, 10:11 AM
Registered User
I understand that it takes lots of heat energy to raise the temp of water. Thats why living near a big body of water has more consistent outside temps.
But even in the middle of the desert the wind picks up during the day. Would think the land would heat more evenly and not have that "sea breeze" effect since there is not an abrupt change in what the ground is made of. So why the heck are deserts more windy than the beach??
p.s. the wind picks up here the second a lipo touches my hands. There are great stories told of this effect in Greek Lipology. The wind gods are angry and demand virgins. But kids these days are all on pills and messing around at young ages so its hard to satisfy them gods
Jul 03, 2011, 10:16 AM
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ausf's Avatar
Flying micros my kids and I have been paying close attention to wind lately. When 8mph or below is forecast, it might be still blowing at 6:00, but drops off and is usually dead calm by 7. If we are at the field by then, we have a solid hour or more flying time almost every night.

It's the reverse in the AM. Might be dead calm early at home, but by the time we get moving it's picking up.
Jul 03, 2011, 10:42 AM
Registered User
The wind will be lightest some time around dawn and around sunset. Sailors know this well. RC flyers probably figure it out sooner or later.

Whether that's a universal truth everywhere on the planet, I don't know.
Jul 03, 2011, 03:01 PM
Registered User
I originally wrote this article for our club newsletter.

Why are the winds usually calm in the morning?
Ever get up early in the morning, look outside, and see the trees barely moving (except where a few rambunctious squirrels are chasing each other)? You eat breakfast, load up the car, and take a leisurely drive out to the field, only to see the wind sock straight out as you pull up to the pits? What happened to those calm winds?!
Well, the reason is often an inversion.
Great! Of course, it’s an inversion. That answers everything!....Uh, what’s an inversion?
Time for a little background. Let’s assume we’re talking about a day when the air is dry, and we’ll restrict ourselves to the atmosphere below about 30,000 ft. (not that any of us fly anywhere near that high!).
Air temperature and pressure drop pretty continuously with height. Under normal conditions, the temperature drop is around 3.5 degrees Fahrenheit per 1000 feet of elevation. So, if it’s 80F on the ground, it’s about 76.5F at 1000’ and 73F at 2000’.
So, if it’s hot on the ground, it’s cooler aloft. No big secret there.
(picture 1)
Normally, the temperature drops with height
During the daytime, the sun heats the land. No problem there, either. The more sun, the hotter the land gets. Then, when the ground is hot, it warms bubbles of air. These bubbles (thermals) rise until they are no longer warmer than the surrounding air. Remember the saying that “Nature abhors a vacuum?” Well, when a bubble of warmer air rises, a bubble of cooler air aloft sinks down and replaces it (Actually, warm air doesn’t rise; it’s the cooler, denser air that sinks and forces warmer air aloft, but that’s not for this discussion). Those rising and descending bubbles mix the air in the lower atmosphere, making the lower levels cooler and drier, whilst at the same time taking moisture, heat, bugs and odd trash aloft (I hear the thermals in out west will take small dogs up, too!).
During the evening and night, the land cools off by radiating the heat back out as infrared radiation. The problem with infrared is that it has a hard time making it through water vapour. That’s why it doesn’t cool off when the sky is overcast. The clouds trap the heat.
But, if the air is clear, the infrared makes it out and the ground cools. The drier the air, the more it cools.
However, air is a great insulator. That’s why the best insulators are just loose frameworks, containing air. You know how light Styrofoam is? That’s because it’s mostly air, contained in thin bubbles of plastic.
At night, when the ground cools, the air in touch with the ground isn’t warmed as much as it was during the daytime. But, that wonderful insulator “air” doesn’t cool off as quickly. As you go up, the air aloft remains warmer. Eventually, the air nearest the ground doesn’t get warm enough to create bubbles that can punch through the warmer air aloft. At that point, vertical motion ceases, and an inversion is said to exist.
(picture 2)
Late night, the surface has cooled and the inversion has formed
Once the inversion has set up, the air below the inversion can’t mix with the air above the inversion, and the air above the inversion can’t mix with the air below it. In meteorological parlance, the two areas are said to be “decoupled”.
A really good sign that an inversion has formed is when smoke plumes rise a short distance, and then flatten out.
Fog can be an indicator of an inversion, provided the skies above are clear and the air is calm. You can’t count on fog indicating an inversion, because you can also get fog when warm, moist air blows over colder ground. We used to see that happen frequently at Shemya AFB, in the Aleutians. There, it’s not unusual to get fog with 80+ mph winds!
Okay, what does an inversion have to do with it being too windy to fly?
Well, you all know about the “jet stream”, right? Did you know there are actually several jet streams around the world, at different levels and latitudes? Yup, the air around our planet is always in motion. All of that heat from the Sun makes our atmosphere move. What slows it down is friction between the atmosphere and the ground.
You see, when one of those thermals moves upwards, it carries with it the wind speed (momentum) of the air at the surface. Then, when it is replaced by a bubble of air from aloft, that bubble from upstairs brings down the wind speed ALOFT with it. So, when a warm bubble of calmer air, slowed by friction with trees, buildings, people, hills, and so on, is carried aloft, it’s replaced by a bubble of cooler air that has been blowing along, unhindered, for perhaps thousands of miles. For the atmosphere, the result is a slowing down of the winds aloft, and a speeding up of the winds on the surface. For us, it means the winds start blowing and gusting, so we pack up and go home.
Okay, how do I use this info? Does the inversion happen every night, so I should always plan on going flying in the morning and evening?
No, you have to consider a few “big picture” points before you put your gear on charge.
First, inversions are local phenomena. Don’t plan on one forming if there is a tropical storm in the area or a strong wind gradient is forecasted. For example, if you know a cold front is moving in, don’t count on clear skies meaning calm winds!
Second, if satellite imagery shows low clouds moving in, don’t expect an inversion to set up. Low clouds mean the ground can’t cool, meaning no inversion.
Third, if the forecast is for fog (really just a cloud on the ground), the inversion may still form, but your field may be obscured in fog. The heat needed to burn off the fog may also burn off the inversion, so by the time the fog dissipates, here come the winds!
Fourth, if the center of a big high-pressure system is moving over the area, the winds will PROBABLY be light pretty far up into the atmosphere. That means that those descending bubbles won’t be carrying a lot of wind down with them. If that’s the case, take your time and don’t rush to the field.
So, what do I suggest? Well, if you get up and look outside and see clear skies and calm winds, don’t waste time. Load up your car, and get to the field!
Jul 03, 2011, 03:40 PM
Suspended Account
Awesome post! I learned a lot.
Jul 04, 2011, 07:35 AM
Will fly for food
Originally Posted by bartricky
Sailors call it "sea breeze".
Sea breeze during the day, land breeze during the evening.

Use to race sailboats.

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