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wiggy
2011-Apr-25, 05:11 AM
Hi,
We're having a discussion over on the Skeptoid mailing group about planets and winds.

The original thread started off with renewable energy, then solar energy, then wind energy. Then someone said wind comes from solar.

So this is where the question lays.

Back in '89(?) when voyager got out past Neptune, much higher winds were observed than predicted, because it was thought wind was caused by the sun.

Then someone suggested that the wind was driven by the planet rotating. The wind would be at 90 degrees to the spin axis. The atmosphere is driven by the planets surface. Surface imperfections cause turbulance bringing in to play the coreolis effect.

When an external heat source (sun) was bough in to play, thermal differences caused density differences in the atmosphere causing more extreme turbulance in the normal wind flow.

The hypotheses was that planetary rotation caused wind. But to have a dead calm required an external energy source to give opposition to the terestrial wind.

So, is this true?

Does the planet drive the wind? Does solar activity just make it more irregular?

WayneFrancis
2011-Apr-27, 03:27 AM
Well if it was primarily do to rotation of the planet then you'd think that on a planet like Venus that the wind would not be much since it doesn't rotate very fast but its winds are ~300km/h. Winds are caused mostly by thermal differences in the atmosphere I believe. Now for different planets the star(s) of that system might provide differing amounts of energy into that system.

Basically here on Earth the wind is primarily powered by the sun but it isn't any universal law or anything.

korjik
2011-Apr-27, 03:45 AM
The winds of Neptune are probably caused by whatever is making the planet abnormally warm. That is the heat source.

John Jaksich
2011-Apr-27, 04:37 AM
The winds of Neptune are probably caused by whatever is making the planet abnormally warm. That is the heat source.

Tangentially speaking --- Jupiter and Saturn, also, have an anomalous wind dynamic--driven from the inside--->

Here is a post by Fraser (circa 2005)

http://www.universetoday.com/11096/jupiters-winds-come-from-inside/

Shaula
2011-Apr-27, 08:02 AM
The solar input creates thermal imbalances which lead to the formation of convection cells. That is the primary source of winds. Heating effects over land and sea generate local wind patterns as well. The rotation of the planet does have an effect but even without it you'd get north/south wind patterns appearing in bands. The rotation just adds the east/west components.

Strange
2011-Apr-27, 12:15 PM
The original thread started off with renewable energy, then solar energy, then wind energy. Then someone said wind comes from solar.

Ultimately it is all solar: wind power driven by solar heat; hydroelectrics depend on the water cycle driven by the Sun; coal and oil come from once living things that, directly or indirectly, depended on photosynthesis. Arguably, even nuclear is solar as the heavy elements all came from stars. And then there is fusion: a star in a jar.

John Jaksich
2011-Apr-27, 11:30 PM
One other way to look at the situation is to view wind patterns as a result of pressure gradient changes on a planet. For instance, (although bad example and true)---on the west coast we will get a cold north wind after a storm system has passed through from the Pacific . . .

The result of such a pattern stems from the fact that the previous cold front will bring with it a lower barometric pressure (from the rain) and once it has left CA there will result a "so-called vacuum" which must be filled either by another cold front or a change in pressure from a warmer (and sometimes clear or sunny weather) --but in between the cold and warm fronts---there will be a pressure gradient and it will result in wind blowing in the direction that a subsequent front will follow.

I hope this makes some sense---and yes this type of pattern is primarily driven by the Sun (on Earth).

profloater
2011-Apr-28, 11:55 PM
the topological hairy sphere concept shows that once there is any wind, there must be vortices (it is impossible to comb down a hairy sphere without having a discontinuity) Usually heat on a planet will not be uniform but greatest nearest its near point to the sun so that the air is heated non uniformly and the hot air will tend to rise bringing in colder air at ground level. However the planet is a sphere shape so any surface movement will also involve angular momentum effects such as increase in rate and coriolis effects (2.dr/dt. w) as a perpendicular vector so the whole system gets excited and the gentle rotation of a stationary atmosphere becomes a chaotic pattern of rotation of the air with some very extreme velocities. So wind is the result of heat energy and inertial forces.

John Jaksich
2011-Apr-29, 12:15 AM
the topological hairy sphere concept shows that once there is any wind, there must be vortices (it is impossible to comb down a hairy sphere without having a discontinuity) Usually heat on a planet will not be uniform but greatest nearest its near point to the sun so that the air is heated non uniformly and the hot air will tend to rise bringing in colder air at ground level. However the planet is a sphere shape so any surface movement will also involve angular momentum effects such as increase in rate and coriolis effects (2.dr/dt. w) as a perpendicular vector so the whole system gets excited and the gentle rotation of a stationary atmosphere becomes a chaotic pattern of rotation of the air with some very extreme velocities. So wind is the result of heat energy and inertial forces.


Very informative and interesting---

Would you have any references for it?

profloater
2011-Apr-29, 02:55 PM
Would you have any references for it? Well I must admit this was exactly how climate was explained to me in maths lectures at Bristol University nearly fifty years ago. It was the practical example of Corioli's which was the central point at the time. The topology intro was also just how the subject was introduced. As it happens I still have my uni notes (somewhere) if you want me to check further.

Jeff Root
2011-Apr-29, 03:58 PM
The solar input creates thermal imbalances which lead to the formation of
convection cells. That is the primary source of winds. Heating effects over
land and sea generate local wind patterns as well. The rotation of the planet
does have an effect but even without it you'd get north/south wind patterns
appearing in bands. The rotation just adds the east/west components.
I wonder what the overall patterns would be if the day/night alternation
were removed by making the sun a contiuous band around the planet's
equator instead of a small spot in the sky, providing the same total
energy input.

-- Jeff, in Minnneapolis

John Jaksich
2011-Apr-30, 12:44 AM
Well I must admit this was exactly how climate was explained to me in maths lectures at Bristol University nearly fifty years ago. It was the practical example of Corioli's which was the central point at the time. The topology intro was also just how the subject was introduced. As it happens I still have my uni notes (somewhere) if you want me to check further.

I thought the explanation was rather good---my maths is only up to University Calculus sequence--my real background is in chemistry. If it is no trouble to you----I am interested in whatever could be found on the internet.

gratefully---John

profloater
2011-Apr-30, 03:09 PM
-I am interested in whatever could be found on the internet.

gratefully---John
I can go into it a bit more and your mention of the internet raises a chuckle because the ubiquitous Wikipedia is very confusing about these inertial forces. Generally the atmosphere is heated by the earth surface. An important exception is a cloud which can be directly heated and then can get energy from surface water being sucked up as vapour and then delivering latent heat as it condenses higher up. However the hot air and the cloud both rise because their density decreases so they float up in bubbles of hot air. We can assume that on average the low atmosphere is dragged around by the earth surface so that any area being sucked into the low pressure hotter area will have angular momentum and as its radius decreases it will start to spin faster. If the hot air is at the equator, the incoming air also has to increase its overall radius of rotation, so it has both a surface speed and an enforced radial speed as it has to move from a lattitude towards the equator. The latter part is where the coriolis acceleration comes in as it has both a rotation (actually two rotations, one local as a declining pancake of air and one as rotation around the earth's axis) and a radial rate as it changes from its lattitude toward the equator. The corioilis acceleration is 2 dr/dt. w where w is the angular rate and it acts at right angles to the radial vector and the spin vector using vector mutiplication.
The whole effect is the conservation of the angular momentum of the area of air involved, and it results in anticyclones in the northern hemisphere. The local conditions especially if water is sucked in, can cause tornados and very big rotating systems which then drift from the origin. The spin also reduces pressure in the centre exaggerating the initial effect. The lift forces inside clouds can rip aircraft wings off and the air supply for these basically comes form inward rushing surface air from a wide area. Seen from above the north pole the cold northern air is moving radially outward, following the surface, and the coriolis acceleration as it moves toward the equator will make it spin eastwards, giving the general eastward rotation of weather systems in the northern hemisphere. The distribution of the land masses and oceans then causes major local variations. Sea temperature is very important to seeding energy into the rising air streams as latent heat. while equatorial land masses cause the most direct heating of the equatorial air. That is why the climate was very different when all the land was in one place. I think if you check WP it calls coriolis a fictional acceleration seen only in a rotating frame of reference. But it is an inertial effect directly generated by messing with a rotating mass!

profloater
2011-Apr-30, 03:11 PM
I wonder what the overall patterns would be if the day/night alternation
were removed by making the sun a contiuous band around the planet's
equator instead of a small spot in the sky, providing the same total
energy input.

-- Jeff, in Minnneapolis
Because the earth spins under the sun I don't think it would make that much difference globally although of course the day night local temperature changes would disappear along with the onshoe offshore winds of morning and night. The big anticyclones would still dominate the weather.

eburacum45
2011-May-02, 09:48 AM
The 'Hairy Ball Theorem' is described on Wiki here
http://en.wikipedia.org/wiki/Hairy_ball_theorem

I note that laminar flow is in fact possible on a torus, which should make wind patterns on an artificial torus planet (like this one (http://www.orionsarm.com/eg-article/49142c044cba7)) interesting.

Ivan Viehoff
2011-May-06, 02:20 PM
When one says "heat drives winds", one might conclude that warm places on earth should be windy places, but we all know it is mostly the other way around. The very strongest winds on earth are in tornadoes, but they tend to be fairly localised and brief, and peak in spring at latitudes just outside the tropics. Hurricanes are more long-lived, but likewise tend to be relatively brief and localised intermissions in weather in places that are normally not very windy. They peak in late summer around higher tropical to lower temperate latitudes, but stay away from the equator. For the highest average windspeeds, you have to go to cold places like Antarctica, especially in the winter. So in summary, warm places have violent passing storms, but on the whole they aren't very windy. On average, its the cooler places on earth that are the windiest

The reason is that winds are not caused not by high temperatures, but by high temperature differences, or more accurately heat imbalances. Thus a lot of heat, if evenly distributed, results in low winds. But cold places can be really windy if they are contrasted with warmer places. Thus Venus is probably not very windy, because its surface temperatures are relatively uniform because of the effect of the dense clouds.

On earth the equator maintains a relatively even temperature year round. The temperature differences from the equator to the pole are largest when that pole has winter. And the temperature gradients are steeper further away from the equator. That's why the winter hemisphere is on average windier than the summer hemisphere. Violent summer weather phenomena at lower latitudes, such as hurricanes and tornadoes, are driven by an increase in the heat imbalance between the ocean or land surface and the atmosphere above it, as the surface is heated by the sun.

profloater
2011-May-06, 06:34 PM
When one says "heat drives winds", one might conclude that warm places on earth should be windy places,
In my description I made it clear that inertial forces cause the spiralling of the winds from poles onwards and also that land masses and warm water masses affect it considerably. Any heat bubble effect on a spinning planet will invite the angular momentum and coriolis forces, it is not just adjacent cold and warm air. The whole is also chaotic in the sense of being unpredictable in the short to medium term because for one thing of variable cloud cover. Cloud initiation and formation/ evaporation, is still mysterious.