The primary cosmic rays incident upon the Earth's atmosphere (from all sources, extra-galactic, galactic and solar) comprise 98% protons, 2% electrons and 0.3% positrons. (The other 98% of the electrons are trapped within the Earth's Van Allen radiation belts and are responsible for the Aurora or Northern Lights). In cosmic rays, protons out-number anti-protons by 10,000 to 1. The particles range in energy up to 3×1020eV (equivalent to a tennis ball travelling at 300km/s). A few particles consist of ions of elements from helium up to iron, including lithium, beryllium and boron which are almost absent from the solar system abundance because they are consumed within stellar furnaces. Cosmic rays with energies above 5×1019eV are thought to be slowed down so much by their passage through the Universe by interactions with photons that they are not expected to be observed, so it was with great disbelief when they were in fact observed. This cut-off energy of 5×1019eV is known as the Greisen-Zatsepin-Kuzmin (or GZK) limit. Their existence above this limit is still a puzzle. The flux of cosmic rays whose energy exceeds 1020eV is one per square kilometre per century. They are pretty rare! The shock waves from supernova can only accelerate electrons and not protons, so exactly how these ultra-high energy protons are generated remains a mystery. [2018 edit - But now see 'Nucleosynthesis by Neutron Star Mergers']
It is thought that cosmic rays of energies of 1016eV or over could be involved in initiating lightning strikes on Earth. The breakdown voltage of air is 2.5MV/metre whilst the highest measured electric fields under thunderclouds is only 400kV/metre, and usually much less at only 100kV/m. It is thought that a high energy cosmic rays hits an air molecule producing an extremely energetic electron, which in the high electric fields within storm clouds is accelerated to greater speeds, close to the speed of light, and then hits more air molecules in a cascade reaction. The avalanche of electrons ionises the surrounding air allowing charge to flow. Electrons travelling near light-speed should emit X-rays and gamma rays, so detecting this radiation at the same time as lightning strikes should prove this theory.
The incidence of primary cosmic rays on the surface of the Earth is 25% higher when the sun's activity is at its' lowest, at sunspot minima. This higher incidence of cosmic rays causes an increase in the Earths' cloud cover of 3% at sunspot minima. It is thought that this is due to the cosmic rays producing showers of secondary particles, muons and anti-muons, in the upper atmosphere, which interact with molecules of sulphur dioxide, ozone and water vapour there to create fine droplets of sulphuric acid, which are the nuclei around which more water vapour condenses to produce clouds. Further experiments are underway to confirm this under the CLOUD project at CERN.
MUON FLUX Muons, the 200-fold heavier second generation member of the electron family, are formed in the upper atmosphere by the bombardment of cosmic rays on atmospheric atoms. The at-rest halflife of a muon is 2.2 microseconds, but because they are travelling very fast (at relativistic speeds), the time-dilation allows them sufficient time for some of them to reach the Earths surface before they decay. Indeed, Ii it wasn't for time dilation, almost none would reach the Earths surface. The flux of muons at on the Earths surface sea level is 1 muon per square centimetre per minute. When a muon encounters other atoms, they are deflected off course. A novel form of detector to detect hidden objects in lorries at Country entrance ports has a detector surrounding the lorry. The detectors behave like cloud chambers; any muons entering or leaving the detector leave vapour trails. the entry and exit trails are traced back by computer to the point at which they were deflected. After a short time a virtual image builds up of any heavy hidden object within the lorry, such as lead shielding, or plutonium itself.
It is also thought that cosmic rays could influence the weather here on Earth by somehow seeding the formation of clouds in the upper atmosphere, and thus affecting the temperature of the Earth globally. As the flux of cosmic rays decreases, the cloud cover decreases increasing the temperature. This might also explain why there is more cloud cover at the poles, but less at the equator - the Earths magnetic field protects the equator more effectively from cosmic rays, but less effectively at the poles where the magnetic field dips into the Earth. Indeed, it has now been established that a high flux of primary cosmic rays impinging on the upper atmosphere can increase the chances of an over-cast day by 20%. The cloud droplets are seeded by the shower of charged particles (the secondary particles resulting from the impact of primary cosmic rays on the ions of the upper atmosphere).
For a possible explanation of the extremely high energy primary cosmic rays, see Rotating Black Holes.
Solar Electromagnetic Radiation
The total radiated solar power from the sun (in the form of light and other electromagnetic waves) is 392×24 watts.
The proportion incident upon the Earth is about one part in 10-9 of this flux, but some of this energy is deflected by the magnetosphere such that only a portion of this power actually hits the Earths atmosphere, or 170 × 1015Watts.
The Earth reflects about 3% of this incident radiation, or 50 × 1015Watts so the total absorption of the Suns radiation by Earth amounts to 120 × 1015Watts.
The power in the sunlight on the Earths surface at equator at midday and normal incidence is 1.353 KW/m2 (1.940 calories per square centimetre per minute) - but it fluctuates by about 6.9% over the year due to the Earths distance from the sun varying on a yearly cycle. About 89,000 TW of solar energy reaches the Earth's surface. The reader may detect discrepancies in all these figures; measuring them is not an exact science. Your Author cannot sort out all the disparities from the various reports.
At Earths' distance, the radiation pressure of light from the sun is 50 × 10-9 grams/cm2, producing a total force on the Earth of 10 tons.
Solar Cycles and Sun-spots
It is well-known that the sun has a Solar Cycle, which lasts on average lasts 11 years but any one cycle varies between 8 and 15 years. This cycle visibly affect the number of sun-spots on the surface of the Sun being far fewer (sometimes zero sunspots) at solar minimum rising to a maximum at solar maximum. The Sun-spots are darker than the rest of the sun, and therefore less hot and are threaded by writhing and intense magnetic fields which have broken through from the interior to the surface. The greater the number of sun-spots the greater is the perceived activity of the sun. When the magnetic field lines have been wound up they can reach breaking point, where the lines break allowing a huge flux of high energy solar particles to be flung off into space at high velocities, this is a coronal mass ejection; a very large solar flare that travels so fast as to escape the gravitational pull of the Sun. If any coronal mass ejection hits the Earth it not only causes the Northern Lights (and their South-pole counterpart) to increase in activity. The Northern Lights or Aurora are due to electrical currents set up in the upper atmosphere exciting the molecules up there. Solar flares of any given size are 50 times more frequent at solar maximum than solar minimum. Sometimes a coronal mass ejection can induce such very high fluctuations in the Earths Magnetic Field and the generated circulating electrical currents that they can induce extremely large and damaging currents in terrestrial structures, particularly any long metal bits in the air such as electricity wires carried by pylons or telephone wires. These currents are so large as they can severely damage any transformers they are connected to, taking out electrical transmission from a huge region of a country covering many cities. One such enormous coronal mass ejections happened in the 1800's when there was not much electrical infrastructure on Earth. If a similar one happened today it could take out electrical power to whole regions, and with no prospect of restoring power anytime soon after (they would have to manufacture hundreds of very large transformers and generators and all the other destroyed infrastructure associated with power generation, which could not be done overnight).
It has since been discovered that this solar cycle corresponds to polarity reversals of the Suns magnetic field. And more recently (in 2018) that this nominally 11-year magnetic cycle causes the Suns diameter to change in sympathy by 2km, it being larger when the magnetic field is lowest and there are fewer sunspots. Researchers measured this small 2km variation by studying waves of plasmas they travel around the Suns surface. The frequency of these waves depend upon the Suns size, and this enabled the Suns size to be measured more precisely than ever before. The average radius of the Sun was determined to be 695,000 km and that it shrinks by 1 or 2km during solar maximum when the number of sunspots is highest. Moreover, because the frequency of the waves change as they penetrate the Suns surface deeper, they were also able to ascertain that most of this shrinkage occurs about 5000km below the surface. It is thought that the decrease in size is probably the result of the stronger magnetic field compressing the plasma beneath the Suns surface. But the creation of this magnetic field is little understood at present, as is its structure.
This solar cycle itself varies, on much longer time scales, measuring centuries. One such minimum of minima occurred at the so-called Maunder Minimum which started in 1645 and lasted until 1715. This cycle seems to have period of maybe about ~100 years, but it is complicated by several other both longer and shorter possible cycles that have tentatively been hypothesized from the relatively short period over sunspot observations. But there are geological radio-isotopic methods of measuring solar particles; they affect the abundance of carbon-14 and beryllium-10 which are Cosmogenic Nuclides.
Recently (2015) another solar cycle has been discovered. This one is of less amplitude and occurs every 660 days (about every 22 months). This cycle too affects the number and intensity of solar flares.
At Earth distance the solar wind (comprising mostly protons and electrons and even some heavier ions like phosphosus, nickel and titanium) produces a force 1000 to 100,000 times weaker than this, and travels at 450km/second (or up to 1000km/s in sun storms). It contains 5 protons/cm3 (and an equal number of electrons), a flow of 108 protons/cm2/second. The total solar wind flux from the sun is 300,000 tons/second (or 1 part in 10-14 parts of the total solar mass per year).
Most solar particles cannot penetrate Earths magnetoshere and are deflected away by this magnetic shield, but of those that do penetrate, the greater proportion are trapped by the lower Van Allen radiation belts. Only the most energetic solar particles are able to penetrate both magnetosphere and Van Allen belts.
Van Allen Radiation Belts
The Van Allen radiation belts consist of two torroidal shaped regions of radiation that encircle the equator. The two torroidal belts are at different heights. The upper belt at a height of 20,000 to 25,000 kilometres consists mostly of protons. The lower belt at between 3000 and 6000 kilometres contains mainly electrons. Because the charged particles are moving, there is a magnetic field associated with these two belts, the cusps of which enter the Earth at the north and south magnetic poles of the Earth. The gap between the two belts, previously thought to be free of radiation, is now known to contain high energy streams of ionized helium, hydrogen and oxygen atoms during solar storms, as well as high-speed electrons. It seems that during solar storms, the ionized atoms streaming from the sun distort the Earths protective magnetic field, allowing electrons from the lower Van Allen belt to enter the normally radiation-free zone between the two belts.
Cosmic Neutrino Flux
The sun creates and 1.8×1038 anti-neutrinos/second, which corresponds to 65×109/cm2/sec at the Earth. Although the sun can only create electron anti-neutrinos, by the time they have travelled the 92 Million miles to Earth, only a third of them are now electron-anti-neutrinos, the other two-thirds having phased themselves into mu- and tau-neutrinos, which cannot yet be detected. See Neutrinos. High energy neutrinos (those with sufficient energy to be detected by the Cerenkov radiation emitted when impinging on water at faster than the speed of light in water) account for a only small fraction of this flux, amounting to 5 million/cm2/s. Neutrinos out-number photons in the Universe by 2.5×109.
Neutrino Flux from Earth
The decay of radioactive isotopes within the Earths core produces an out-flowing flux of anti-neutrinos measured at 16.2 million for every square centimetre measured at Earths' Surface each second. The uranium, thorium and possibly plutonium isotopes that are radiaoctively decaying within the core do not directly generate anti-neutrinos, it is their beta-decaying fission products that generate the flux of anti-neutrinos. From that flux, it has been estimated that the heat generated by radioactive decay in the Earth is probably 24 TeraWatts (but it could be as much as 60 TW). Other non-nuclear processes, such as possible release of heat of crystallization of liquid iron and nickel in the outer core, may add to that heat output.
The average geothermal Heat Flux from the oceans of the Earth is just 101mW per square metre whilst that over continental crust is 65mW/2 and that from the Whole Earth about 87mW/m2. Compare this value with the 1.35kW/m2 for the heating produced by normal-incidence sunlight at the equator. Much of the geothermal flux is produced by the radioactive decay of the radioisotopes within the Earth. The total geothermal flux (at the present day) contributes less than 0.025% of the Earths surface temperature that absorb solar radiation, but that figure was 3 times greater 4 × 109 years ago. In figures, the amount of heat generated within the Earth is about 44TW, with more than half of that, 30TW being generated by the decay of radioactive isotopes such as Uranium and thorium. The total heat content of the Earth is 1031 Joules at any one time (it used to be greater in the distant past).
Between 45% and 90% of the heat escaping from the Earth is due to the decay of radioactive isotopes which decay at the rate of 30TW; the rest being made up by: (a) latent heat released from the liquid core as that crystallizes at inner core boundary (b) flexing of the Earth by tidal forces (c) as heavy metals gradually descend towards the core.
Cosmic Microwave Background Radiation
The Universe is 13.81×109 years old since it came into being at the Big Bang. The Big Bang was a cosmic explosion where both time and space were created seemingly out of nothing. Initially, the temperature was so high that not even quarks existed, this is the period when the strong force was exactly equivalent to the other three forces that we see today, electromagnetic force, the weak force and the gravitational force. The hot Universe expanded, creating space in which to expand into at the same time. Thus it was able to seemingly expand at faster than the speed of light and numerous large volumes of the Universe became causally separated from one another. Any initial and slight asymmetries in the early Universe were greatly exaggerated by this cosmic expansion. As it expanded, it cooled. As it cooled, the elementary particles that we know of were able to condense from the seething energetic mass; the electron family and quark family. The Universe was also permeated with ultra-high energy electromagnetic waves - gamma-ray photons, but they continually interacted with all the free electrons, so were continually absorbed and re-emitted: the Universe was completely opaque. The gamma ray photons were in thermal equilibrium with the electrons. As it cooled further the quarks were able to form protons and neutrons (and other baryons). When it was 379,000 years old, the Universe had cooled sufficiently for all the electrons to form atoms with the protons and neutrons. There were now no free electrons and the gamma ray photons were free to travel; the Universe had become transparent to photons, and the photons were no longer in thermal equilibrium with the electrons. This occurred when the temperature of the Universe had dropped to 3000 Kelvin. Over the next 13.81 Billion years the Universe continued expanding and cooling. The gamma-ray photons were expanding at the speed of light, but the Universe was expanding faster than this and the gamma ray photons experienced this stretching; losing energy, until now they are red-shifted so much as to now be in the microwave band, at the same characteristic temperature as that of a Black Body at 2.7251 Kelvin (average). This microwave background radiation permeates the Universe, and is almost exactly uniform in all directions. The only exceptions to this are the slight 3 milli Kelvin temperature asymmetry caused by Doppler Shift as the Earth and Sun move through the frame of reference. Superimposed on this unipolar asymmetry is the much smaller Microwave Anisotropy of 0.2 milli Kelvin, caused (it is thought) by the asymmetries in the Universe at its very inception mentioned above.