Wednesday, 28 October 2009

The Atmosphere

The aurora borealis seen high in the Earth’s ionosphere (credit: NASA)

The Earth’s atmosphere is layered. From the surface traveling upward the first layer one would encounter is the troposphere. This layer rests on the surface of the planet. Above the troposphere is the calm, stable stratosphere. About 90% of the ozone in our atmosphere is contained in the stratosphere. Ozone concentrations are greatest between about 20 and 40 km. This higher concentration of ozone, called the ozone layer, is said to "absorb" most of the harmful ultraviolet light from the Sun. If all of the ozone were compressed to the pressure of the air at sea level, it would be only a few millimeters thick.

We are taught that the ozone layer exists because it is routinely created from oxygen by solar ultraviolet light. But I don't believe that singular oxygen is floating about our atmosphere. I think that the common air is water vapour. So, I'm going to suggest that the ozone layer might have something to do with the release of oxygen from the breakdown of water vapour by solar energy. I'm reminded that pure hydrogen-oxygen flames burn in the UV colour range and the only combustion product is water.

I think the ozone layer is describing an interface where common air directly confronts energy from the Sun. Obviously, the energy which arrives from the Sun contains a lot of whallop. We are taught that the Sun sends energy to Earth in every frequency of the electromagnetic radiation (EMR) spectrum. I don't think this is true. For one, the space between the Sun and the Earth should be full of light and colour - but it's not - it's black.

I'm apprehensive about describing what form the energy from the Sun takes, I'm not even sure the energy has a frequency, but I think that when it strikes the Earth's atmosphere it is transformed into something far less punchy. It's as if the atmosphere works like a step-down transformer in-which high energy from the Sun is transformed into lower energy.

I notice that when a UV picture is taken of the Sun, the Sun looks like a burning blue ball - but I don't see UV light streaming across space. The Universe is not lit up in UV light. The Universe is bathed in more-or-less uniform infrared (IR) radiation, termed the infrared background. I wanted to thank Stanford U Solar Center for their UV image of the Sun, which I've included below:

It is said that the ozone layer absorbs the high energy UVC rays, but allows the lower frequency UVB and UVA rays to pass through. But I think of it more as the ozone layer transforming high energy UVC into UVB and UVA.

"UVA wavelengths (320-400 nm) are only slightly affected by ozone levels. Most UVA radiation is able to reach the earth's surface and can contribute to tanning, skin aging, eye damage, and immune suppresion.

UVB wavelengths(280-320 nm) are strongly affected by ozone levels. Decreases in stratospheric ozone mean that more UVB radiation can reach the earth's surface, causing sunburns, snow blindness, immune suppression, and a variety of skin problems including skin cancer and premature aging.

UVC wavelengths (100-280 nm) are very strongly affected by ozone levels, so that the levels of UVC radiation reaching the earth's surface are relatively small. "

There are higher UV energies to be found which surpass those of UVC, but these do not make it as far as the ozone layer, as apparently, they are stopped in the higher layers of the atmosphere. Extreme UV (EUV) is very high energy UV, with corresponding wavelengths in vacuum extending from about 5nm to 40nm. Few substances are transparent to extreme ultraviolet, and even air stops it within a fairly short distance. At the highest frequencies of the EUV range it starts to merge with soft X-rays (SXR) at 1nm in the EMR range. At 0.1nm, we then find the hard X-rays, which are associated with dental and medical X-rays. With even smaller wavelengths, at around 0.3 to 0.003nm, the highest energies are possessed by Gamma rays.

Balloon flights can carry instruments to altitudes of 35 kilometers above sea level, where they are above the bulk of the Earth's atmosphere. However, even at such altitudes, there aren't any obvious signs of X-rays, therefore satellites are necessary to measure X-rays in the upper atmosphere.

The extended Corona of the Sun as seen in X-ray by the Yohkoh Satellite. (Image courtesy Yohkoh)

More than 99% of the total atmospheric mass is concentrated in the first 40 km from Earth's surface. The upper boundary at which gases disperse into space lies at an altitude of approximately 1000 km above sea level. If the atmosphere is working as a step-down transformer, then I think it's going to pay to keep working our way up through the layers to find the source of the ultimate energy from the Sun. I've borrowed a rather good explanation of the outer regions of the atmosphere from an article I found in I would like to thank the author Dennis Holley for sharing with us. The full article can be viewed here:

"The mesosphere (literally “middle sphere”) is separated by the stratopause from stratosphere and below and by the mesopause from the thermosphere layer above. The mesosphere is located about 50 to 85 kilometers (30 to 50 miles) above the Earth's surface.

The thermosphere (literally “heat sphere”) is the outermost layer of the Earth’s atmosphere and it is situated above the mesopause. The thermosphere begins at about 90 km (56 mi) and extends on outward from there gradually blending into space. The outermost area of the thermosphere where the last vestiges of atmosphere give way to the nearly complete vacuum of space is often referred to as the exosphere.

The most commonly held demarcation of the beginning of space is 100 km (62 mi) above the Earth’s surface. Hence, satellites, the International Space Station and the space shuttle all operate within the outer regions of the thermosphere.

Temperatures rise sharply in the lower thermosphere and then level off at around 200 to 300 km (124 to 186 mi) above the Earth’s surface and hold fairly steady with increasing altitude above that height. Temperatures in the upper thermosphere can range from about 500°C (932°F) to 2,000°C (3,632°F) or higher when the Sun is very active than at other times.

These extremely high temperatures are caused by the fact that the thermosphere absorbs most of the X-ray radiation and a great deal of the ultraviolet radiation streaming in from the Sun. However, even though the temperature is so high, one would not feel warm in the thermosphere because it is so near the vacuum of deep space due to the low density (number) of gas atoms there. Hence, there could not be enough contact with these few widely space atoms of gas to transfer much heat.

The thermosphere is constantly bombarded by solar radiation and the solar wind. This intense solar energy tears apart atoms and molecules in the thermosphere creating electrically-charged ions. Areas of ions within the thermosphere are known as the ionosphere."

Graph: The Average Temperature Profile of Earth's Atmosphere

At an altitude of 100-200 km, the major atmospheric components are nitrogen and oxygen. I'm suspicious because I think it is nitrogen and oxygen, and not hydrogen and oxygen, which ultimately compose water. It is said that the lower portion of the thermosphere is composed mainly of nitrogen (N2) and oxygen in molecular (O2) and atomic (O) forms, whereas above 200km atomic oxygen predominates over nitrogen (N2 and N).

When exposed to radiation, water undergoes a breakdown sequence into hydrogen peroxide, hydrogen radicals and assorted oxygen compounds such as ozone which when converted back into oxygen releases great amounts of energy.

Rain combines with ozone in the upper atmosphere. When water and ozone mix, the ozone loses one oxygen molecule to the water and hydrogen peroxide is formed. Hydrogen peroxide is very unstable and breaks down readily into water and a single oxygen molecule.

Radiation of frequencies above 300nm are "absorbed" by the upper atmosphere causing photochemical reactions, producing photo-ionization and generally heating up the air. Wavelengths in the solar spectrum associated with X-rays and EUV are "absorbed" by the atmosphere above 80 km with relatively high efficiency.

I don't think of the thermosphere as absorbing Gamma rays, X-rays or EUV. I think the thermosphere transforms the high energy of Gamma rays into something else, and very likely EMR with a lower energy. Do I think solar energy is made up by Gamma rays? I'm not sure, but I suspect Gamma rays are formed in the atmosphere too. That's because, while I'm looking for the ultimate source of energy from the Sun, I'm also thinking of the ultimate source of energy found inside a Crookes tube.

The unadulterated energy found inside a Crookes tube, was once deemed by the early pioneers as "radiant energy". This energy was found to move through the vacuum of the tube from the cathode, and today, this energy is referred to as "cathode rays". If the vacuum of the tube was low, then the radiant energy would act on whichever gas was present, and the discharge would thus produce light. Radiant energy acting upon matter was called "radiant matter". I mention all this because I think all these frequencies of EMR that we percieve in the atmosphere come under the umbrella of "radiant matter". What I really want to get to grips with is the source of energy which comes previous to radiant matter. Is it possible that radiant energy is emitted by the Sun?

With a high vacuum, the dark space takes over the space inside the tube, and once it reaches the sides of the tube, the glass emits an eerie green glow and X-rays. From what I understand of X-rays, they are made at the glass of a Crookes tube, and not at the electrodes. It's like the glass of the tube acts as a step-down transformer for the radiant energy inside the tube. It's as if matter gives the radiant energy a frequency.

Another well-known source of an eerie green glow and X-rays are the Aurorae. The Aurorae form an oval centred about the magnetic poles of the Earth. During an aurora, vivid arcs, curls, waves and bands of green, red, and sometimes blue dance across the sky for minutes or hours, peaking near midnight — all between 60 and 600 miles above the ground. On occasion, however, the Aurorae may appear at heights upto 1000km.

Only after the spectral measurements of Angstrom in 1867 did it become clear that the Aurora was caused by optical emissions of the atmospheric gases themselves. The typical colours of the aurora are green (557.7 nm) and red (630 nm) from atomic oxygen (O) and blue (391.4 and 427.8 nm) from molecular nitrogen (N2)

This photograph of an aurora was taken in Alaska. (Credit: Jan Curtis of the Geophysical Institute at the University of Alaska)

Well, where to go next I wonder? I then found a wonderful article "What Is An Aurora," by Alexander McAdie, and published by The Century Magazine (Vol. 54, No. 6, Oct 1897). I think it offers a helpful nudge in the right direction. McAdie talks about the similarities of the workings of electricity and the effects created in the Aurorae. If you like, you can get to the site from here:

"One well-nigh forgotten experiment of the Faraday of America may be recalled. Joseph Henry in 1872 concentrated by a small concave mirror a beam of auroral light, and allowed it to fall upon a paper on which were written some letters with sulphate of quinine, and these became visible just as when illuminated by a discharge of electricity. He also noticed the effect upon a galvanometer needle during an aurora, observing that the needle was deflected, and that a like deflection was always observed "when a flash of lightning took place within the visible horizon of Washington."

The aurora gives a spectrum something like that given by lightning, or rather like several lightning spectra superposed. One bright line is always present, but as many as eleven lines had been seen up to 1883. The Cape Thordsen observers ran the number up to thirty-two. Sixteen of these lines nearly coincide with air-lines, eight with the positive-pole spectrum of nitrogen, four with the nitrogen negative pole, and three with hydrogen lines. From spectroscopic evidence we should say that the aurora was a discharge of electricity in rarefied air. Lockyer has built up a spectrum almost identical with that of the aurora by taking low-temperature spectra of manganese, magnesium, lead, and thallium. It is not the auroral spectrum, however.

Very recently Berthelot succeeded in condensing the new gas argon with benzine vapor, and obtained a magnificent green-and-yellow fluorescence under the influence of a gentle electrification. The spectrum was very much like that of the aurora, and it is suggested that through some combination of argon in the upper air under electrical influences an auroral appearance might result. This brings us to the views which have been put forward by Paulsen abroad and Bigelow at home. The former thinks that the aurora may be a luminous electrification of the upper air, brought about by the absorption of radiant energy of a certain character and alteration of the wavelength.

The auroral light, then, would be a kind of fluorescence. Bigelow, independently of Paulsen, had suggested a similar explanation. He regards the aurora as a phosphorescence due to the transformation of vibrating energy by the air. In other words, certain motions of the ether, which we have no way of recognizing, are altered just enough to convert them into light."

So far, I've largely ignored argon because there's only about 1% of the stuff in the atmosphere, so I felt it probably has little to do with anything really. It doesn't help that argon is an inert gas, so I imagine it in the atmosphere like its sitting in a corner minding its own business. Maybe its about time I took a closer look at argon, and hopefully I'll get the chance in the next post.

And many thanks:
Atmosphere, weather, and climate By Roger Graham Barry, Richard J. Chorley

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