Talk:Wind gradient

message: >>During climb into increasing wind, the airspeed increases, allowing the plane to gain energy and climb faster.<<
That's not strictly true, but I'm not sure I can correct it without it confusing the hell out of everyone. It's one of those cases where if you know what's going on, you don't need the explanation, but if you don't, then a simple explanation will not help much. So I'll offer this explanation for comments. BTW, most people don't realise that you control the speed of a plane with the elevators, not the engine, the engine controls the rate of energy input into the system (otherwise how would a sailplane fly fast?) If you don't get that, then don't bother with the rest of this comment.
The energy of a sailplane is dependant on groundspeed, not airspeed, so a 1000kg plane travelling at 20m/s groundspeed has a kinetic energy of 0.5mv2 due to its motion, and a potential energy of mgh due to its height. An increase in wind speed affects neither of those things. 
There is a lower airspeed limit called the stall speed below which the aircraft cannot fly, a pilot who flys below stall speed near the ground is called a dead pilot. This is fairly automatic on take-off, the plane remains a wheeled vehicle when below stall speed. 
Once the plane has taken off with groundspeed=airspeed (assuming zero wind near the ground), and climbed through the wind gradient a little, the wind speed adds to the ground speed to increase the effective airspeed, and the pilot suddenly finds himself with an excess of airspeed over stall speed margin. He can then choose to slow the aircraft down by climbing, converting kinetic energy into potential energy in the process.
The energy remains constant, but the height and speed have changed in that manouvre.
To put it another way, a height has been reached at a safe airspeed on a windy day that could not have been reached on a still day with the same engine power, but the aircraft is covering the ground more slowly as a result.
I have not yet found a way to extract energy continuously from a wind gradient, by turning/climbing/diving repetatively. Am I being thick? Sailplanes and birds extract energy from updraughts, especially slope soaring on the windward sides of waves and hills. AFAIKS, dynamic soaring allows a little extra height to be gained for a given energy input, and nothing more.
Do we want to be that pedantic with energy? Speaking as a physicist, I say yes, but we could obscure the reasonable with the accurate NeilUK 07:31, 4 May 2006 (UTC)
thread_title:  "climb into increasing wind" 

message: `AFAIKS, dynamic soaring allows a little extra height to be gained for a given energy input, and nothing more.' ... actually, it can do a lot more than that.  R/C sailplanes have been able to reach speeds of 300 mph using dynamic soaring, which could be converted into 3000 feet of altitude if you could ignore air resistance.  (Of course, you can't, but a 2000 feet gain seems attainable in the sort of plane (sleek, low drag) that could reach 300 mph via dynamic soaring.)
As for the `During climb into increasing wind, the airspeed increases, allowing the plane to gain energy and climb faster' claim, it's accurate enough.  Your airplane knows nothing of it's groundspeed -- all that matters is it's airspeed, and anything that increases it's airspeed gives it more energy.  It's all a matter of perspective ...
dougmc 02:06, 10 May 2006 (UTC)
thread_title:  Dynamic soaring 

message: Should this article on wind gradient be merged with wind shear?  It looks like the articles define it identically. Thegreatdr 14:47, 28 November 2006 (UTC)
replies: text: As said elsewhere, I'm not averse to merging this with wind shear, as long as gradient goes into shear and not vice versa. Evolauxia 23:49, 28 November 2006 (UTC)

text: I am for merging.  I understand that in aviation the terms may have separate meanings, but mathematically/meteorologically (and, as far as I can tell, these definition are the most common), the terms are interchangable.  I'm not saying to remove the separate definition for wind shear vs. wind gradient aeronautically, but instead put a subsection for the different meaning groupings in the overall article.JeopardyTempest 09:25, 22 March 2007 (UTC)

text: If it gets merged, then we still need an article on gradient wind, which incorrectly redirects here. Gradient wind is all about the flow around high and low pressure systems. For example the wind speeds around a low pressure system are often less than those around a high pressure system for the same isobar spacing. Do not redirect gradient wind to wind shear which is a more localised phenomenon. JMcC 10:21, 3 April 2007 (UTC)
replies: text: It is now merged.  You are correct, gradient wind should not redirect here.  Thegreatdr 13:24, 28 May 2007 (UTC)
replies: text: I have restored this page. Wind gradient (at least in the aviation sense) has nothing to do with tropical cyclones. Dhaluza 21:12, 28 May 2007 (UTC)
replies: text: Wind shear has a variety of effects...which can all be added to wind shear.  It sounded like we had a consensus.  Expect your additions to this article to also appear in that article soon. Thegreatdr 00:38, 29 May 2007 (UTC)
replies: text: WP:CCC. Wind gradient has a common usage in many fields usually relating to vertical change in wind speed due to surface friction. And windshear (not wind shear) is an aviation term mostly associated with downbursts. Wind shear may be a more encompassing term, but that does not mean that everything needs to be subsumed under that heading. Let's see what else I find on wind gradient, and then see what fits where. This article had been a turned into useless redirect anyway, so what's the hurry? Dhaluza 02:46, 29 May 2007 (UTC)
replies: text: The merger was proposed months ago, so there obviously is no hurry.  You yourself just said that wind shear is more encompassing, and a simple check of a search engine will prove it is the more common term.  Wind shear is only abrupt when moving at high rates of speed, since it acts over hundreds to thousands of feet, whether it is horizontal or vertical.  Two no's does not change the consensus, since people both within this talk page and wind shear favored merger.  Thegreatdr 10:20, 29 May 2007 (UTC)
replies: text:  Wind shear is a much broader term in aviation than only to microbursts, the usage is similar to meteorology, the term is heavily used for changing winds in clear air as well as around convection.  Wind gradient is almost never used in meteorology, while they may be interchangeable in some aviation circles, wind shear is still used there too (and predominately in my experience).  A discussion of the aviation aspects along with the meteorological in the wind shear article makes sense.  There is no entry in the Glossary of Meteorology (or probably any other professional glossary) for wind gradient; a Google Scholar search returns 22,500 returns for "wind shear" vs. 888 for "wind gradient".  Wind gradient should be merged into wind shear. Evolauxia 06:22, 3 June 2007 (UTC)
replies: text:  This article now has over 30 references, and most of them use the terminology "wind gradient" although some use "wind speed gradient." The latter term is more specific and descriptive, but the first is more common in this specific case. Since wind shear is a more general term, it naturally has more GShits. Wind gradient is not specifically a meteorological phenomenon, although it is a function of wind. It is used in relation to the wind's effects on things on the ground, and sound propagation, which are engineering applications. It is also used specifically in gliding, in both American and British English, by the authors of the primary flight training references in both countries. Dhaluza 10:38, 8 June 2007 (UTC)
replies: text:  I'm still in favor of merging this article, with effects near the surface going into planetary boundary layer or Ekman layer rather than wind shear since that is how you define wind gradient.  Aviation effects would go into wind shear.  As bad as this sounds, when you ask the common person about wind shear, it has to do with crashing planes moreso than meteorology. Thegreatdr 14:43, 8 June 2007 (UTC)
replies: text:  strongly oppose merger.  These are both vast topics and have distinct places in the encyclopaedia... obviously there is some common ground, but that doesnt justify merger.  There is common ground with air and atmosphere, but they shouldnt be merged, for example. Cuvette 14:28, 30 August 2007 (UTC)
thread_title:  Merger? 

message: In case this article, by some miracle, remains separate, your lead appears too long and has unique information not found elsewhere down the article.  Remember that the lead is meant to be a summation of the article, and should not be the only place where a certain piece of information resides. Thegreatdr 14:52, 8 June 2007 (UTC)
thread_title: Lead problem

message: :\ v_w(h) = v_{10} \cdot \left(  \frac {h} {h_{10}} \right)^ a
where:
:\ v_w(h) = velocity of the wind at height,  h  [m/s]
:\ v_{10} = velocity of the wind at height,  h_{10}  = 10 meters  [m/s]
:\ a = Hellman exponent
Could someone who knows explain why :\ a is called the Hellman exponent.  I have never seen this exponent referred to as Hellman.  Neither "Air Pollution" by J. Colls nor H. Perkins refers to it as Hellman.   —Preceding unsigned comment added by 70.53.124.11 (talk) 00:43, 6 January 2008 (UTC)
replies: text: Have a look at the book here Dhaluza (talk) 00:54, 6 January 2008 (UTC)
thread_title: Hellman Exponent

message: If this article had more images, I'd think it would make GA class.  Since its survival as an independent article has now been determined, and it is throughly referenced, I don't see any other obstacles on its path to GA.  Thegreatdr (talk) 20:54, 4 July 2008 (UTC)
replies: text: The lead needs to be expanded as well before GA submission is attempted.  I'm tempted to drop the article back to C class due to the lead's shortness/non-comprehensiveness.  Thegreatdr (talk) 17:54, 19 February 2009 (UTC)
thread_title: Close to GA

message: I've removed comments:
"According to one source[38], the wind gradient is not sigificant for sailboats when the wind is over 6 knots (because a wind speed of 10 knots at the surface corresponds to 15 knots at 300 meters, so the change in speed is negligible over the hight of a sailboat's mast). According to the same source, the wind increases steadily with height up to about 10 meters in 5 knot winds but less if there is less wind."
:Since you have the book, you can check that the citation correctly reflects what the book says.  Your claim below is that the citation was incomplete, because it didn't deal with taller masts.  This is not quite correct, because in the case of winds greater than 6 knots, Bethwaite states that the change in speed is confined entirely to the one to two meters closest to the surface (p. 11).  I have no objections to amplyfing the citation to provide additional information.  But I cannot understand why you think it should be deleted.  So I will restore it, together with additional text and additional citations.  See also below.--Gautier lebon (talk) 13:08, 10 March 2010 (UTC)
replies: text: It appears to me that you misinterpret Fig 3.8.  It shows asypmtotic increase for wind speeds greater than 6 knots, which is consistent with what the book says on p. 11 and also with the citation that you yourself provided, see .  Please note that the paragraph at the end of that citation assumes a mast height of 1.8 meters, so indeed the wind speed changes significantly from the top of the mast to the water surface.  But that says nothing about how the gradient changes higher up.--Gautier lebon (talk) 13:08, 10 March 2010 (UTC)
thread_title: Gradient in Sailing - > 6 knots

message: With my basic understanding of tensors, wouldn't the wind gradient, as the total spatial derivative of a vector field, be a tensor field of type (0, 2)? Then wouldn't I then just get a directional derivative if we talk about vertical wind gradient? Is this correct?--Jasper Deng (talk) 02:19, 29 November 2015 (UTC)
thread_title:  Wind gradient as a tensor quantity