red sky at night, sailor's delight

I hope that doesn't apply to airplanes.

We'll be fine - it's NOLA we need to worry about.

Hello again, bhankiii

That same principle does apply to airplanes, because they rely on air density and airspeed.

Cold dense air = easy lift-off at lower speeds.

Hot thin air = harder to lift-off and then keep flying - requires more airspeed to remain aloft.

Kind Regards....

Hi Sparkstation,

I do not believe that pressure is causing this phenomenon.

The difference between high and low pressure may be maximum 10%!

Maybe other governing factors?:

slow air-transport replacing continental dusty air with maritime clean air?,

or: maybe high ion content near the tropical storm versus low ion content in dusty air?

(ions attach to dust and force the dust to the nearest neutral surface).

RHABE

Hello RHABE

It is NOT an air pressure cause.

It IS an air density cause. (But of course air density determines the local pressure.)

You are welcome to believe whatever you wish.

Please remember: Sincerity of belief is never a substitute for truth.

Kind Regards....

Hi Sparkstation,

why do you think that pressure or density will change the optical properties of air?

Which physical principle shall be involved?

Certainly there is a slight change in refractive index. Else?

RHABE

Hello again, RHABE

Pressure or density does change the "optical properties of the air".

Liquid air and solid air have very different Optical Properties from gaseous air.

The differences are easily seen.

The suspended particles situation:

Reason it from the basic principles.

Air is a fluid, A thin fluid, but a fluid nevertheless..

The denser a fluid is, determines how long any suspended particles stay in suspension.

If the fluid is denser: The particles do not fall through the fluid as quickly.

If the fluid becomes less dense, the suspended solids fall much more quickly.

This is easily proven by allowing a feather to fall in air, then fall in a vacuum.

Example:

The principle is easily proved, by having two fluid-filled containers, one filled with water and the other filled with molasses.

Drop some small metal particles into the fluid in each container, and see in which container they first fall out of suspension to the container bottom.

The demonstration fluids have been chosen so you may easily see the difference.

However, if the molasses is carefully heated, thus expanding slightly and consequently becoming less dense, the particles fall much faster through the hot molasses fluid.

The optical property

Alteration of the "Optical property of the gaseous air itself" has not changed very much with increased pressure/density. But as the numbers of suspended solids (micro-particles of dust) are changed, the optical property of the air + the suspended solids does alter, by diffusion, refraction, reflection = interaction between all those micro-particles.

The general principle is easily seen, if after a dusty morning, there is a sudden heavy shower, and then it becomes sunny once more - and you should notice the sun appears "brighter" than before, the air is much clearer, because many of the airborne solids have been washed out of suspension.

Kind Regards....

If that is how it works, and you have put it in such simple words:Admiration! I think I got it. Makes sense.

Hi Sparcstation, I can agree partially: "Pressure or density does change the "optical properties of the air". We have been talking about air at 900 to 1100mbar, so how much is the refractive index changing there? "The denser a fluid is, determines how long any suspended particles stay in suspension." We are talking about air of 1.2kg/m³ and particles of 1000 to 3000Kg/m³, so any 10% change in air density is not affecting sedimentation. VCiscosity of air might have some influence butsmall particles move in pure viscous flow and viscosity is independent of pressure in gases. Electric charge has a big influence on very small particles, so any charging mechanisms and any air resitivity has a big influence. In your example youcompare very different viscosities - so for this example ok (but not for air). "But as the numbers of suspended solids (micro-particles of dust) are changed, the optical property of the air + the suspended solids does alter, by diffusion, refraction, reflection = interaction between all those micro-particles." This I assume is the governing factor:A. stray light generated by the air itself (our blue atmosphere if very thick and related red colors at dawn and dusk when the sunlight travels long distances through the atmosphere until it reaches our eyes. The blue is going partially to space and ground the red is remaining.) B. Stray light generated by airborne particles. So with this explanation I fully agree. Kind greetings to NZ RHABE

In addition to air density changes, I'd also look at changes in the relative humidity, caused by decreasing pressure and elevated water evaporation, which can make the air less clear, very slightly "foggy", if you will. Look at the air clarity over a desert vs. in Asian islands when a typhoon is approaching. Moist air being less dense than dry air, and why barometers fall during rainy or stormy weather.

Probale more of an effect on how polluation is flowing in the atmosphere. Stopping the flow and allowing the sky to clear as the rain will wash the junk out of the air for a short time.

Remember when that Volcano in Washinton State when off. The skys from Tennessee North to Novia Scotia were grey for almost 2 years.

It was so depressing to drive up to the farm on weekend from Flordia. Little direct sunlight. But once you got to Jaxsonville the sun light hit you with a WHAM it was so nice and felt to good on the eyes and skin.

bhankiii

Red sky at night, sailors delight. Well I'm not sure about that. This painting was done in 2000 three days before cyclone Tessie. It was a sight to behold and only some locals here witnessed it. It was amazing and was probably caused by the burning of sugar cane over in Australia. It was completely wind still and very clear air. It is not a photo and is not an exaggeration of what it looked like. Sailing? No way!

Hope all goes well. Ky.

It looks very like a photo, its wonderful art work.

is it painted by you?

oh, you are a painter,

glad to know an artist here.

If you like go to

http://www.zazzle.com/kysley.

and find out more. I hope you can get to the site from were you are. It is some thing I do on the side. The arts are very much like engineering: if you get the right components for the right project, at right measurements and the right temperature and light with a bit of this and some of that combined with a team of people who will go it all the way it becomes an art-form to recognize the importance of being trained with the technique and having a critical view of the end result. Did that sentence have a German accent or what?

Have a great day and thank your Country for that opening and closing ceremony. I was truly mesmerized by the display and the technology involved. Enjoy, Ky.

In my own sight, China is not so such close realm. it becomes more and more open to the world, I have not difficult to browse your pages. your paiting is goood and something (your avator original) like to sight in a kaleidoscope which I like to play when I was a child. In fact there are many such painting in chinse folk, we call it cloud pattern. once you see the pictures from "Dun huang" rock cave (gratto) you must be mesmerized.

Many foreigners like ceremony for its significant and magnificent. Once you see chinese splendid national dances and music and familir film produce, you may think its just so so.

However, the creation is very excellent. creaters work hard.

oh, a great piles of art works can also be produced in trsnsport line. many famous classical painting were painted in our Davinch villiges. very like a factory.

In cases where the low is intensifying the amount of moisture in the atmosphere increases allowing light to reflect in multiple directions..in other words light becomes 'softer' on the eye...diffused. With diffused light certain optical properties of the colour spectrum come into play. The brighter colours become contained in the reflection ie....they slow down by bouncing off the denser atmosphere.. This allows the slower moving colours to intensify giving rise to a phenomenon called aural glow.

On rare occasions when there are two cloud layers the aural glow occurs when the sun has set below the horizon and is still illuminating the higher level clouds which in turn reflect on the lower level ones. Given that the densities of the clouds are just right this glow is often rather spectacular and for a few minutes one finds oneself bathed in coloured light.

http://www.loc.gov/rr/scitech/mysteries/weather-sailor.html

Red sky at night, sailors delight.
When we see a red sky at night, this means that the setting sun is sending its light through a high concentration of dust particles. This usually indicates high pressure and stable air coming in from the west. Basically good weather will follow.

Red sky in morning, sailor's warning.
A red sunrise reflects the dust particles of a system that has just passed from the west. This indicates that a storm system may be moving to the east. If the morning sky is a deep fiery red, it means a high water content in the atmosphere. So, rain is on its way.