Because of the strong statistical correlation between solar activity and weather, scientists have been looking for other mechanisms that would enable small changes in the Sun to effect measurable changes in Earth's climate. Any mechanism linking solar variability to changing weather and climate must involve influencing the distribution of the energy within Earth's weather system. One possible mechanism is Earth's electric field.
Around the globe, thunderstorms maintain the lowest reaches of the ionosphere at an electric potential of 250,000 volts (250 kV) with respect to the ground. This results in a very weak current flowing from the atmosphere to the ground in the fair-weather regions of the globe. Near the ground, this charge maintains a vertical electric field of around 100 volts per meter. Cosmic ray ionization, which is controlled by solar activity via the solar wind, modulates the resistance of this global electric circuit. In this system thunderstorms are the generators. By controlling the ease by which thunderstorms can dissipate current, solar activity may modulate the intensity of thunderstorm development, thus controlling the distribution of energy within the meteorological system.312
Researchers have found other links between climate and solar output. In Portugal, they report the influence of solar variability is strongest in low clouds, pointing to a mechanism involving aerosol formation enhanced by ionization due to cosmic rays.313 The relation between thunderstorm activity and solar variability was analyzed by using monthly data on regular electromagnetic very low frequency (VLF) radio noises detected at Yakutsk, Siberia. These noises are an indication of thunderstorm activity. In a study covering 1979-1993, it was found that local thunderstorm activity in eastern Siberia and in Africa are in antiphase with the solar activity. The more active the Sun, the lower the thunderstorm activity. This result can be interpreted as linking higher levels of cosmic rays to increased thunderstorm activity.314
Illustration 96: The space environment around Earth caused by the solar wind. not to scale. Source NOAA.
On longer time scales, going back in time before recorded human history, scientists rely on proxy data. A fairly complete record of solar activity is contained within carbon-14 (14C) and beryllium-10 (10Be) isotope deposits, found in tree rings and ice cores. After correction for other climatic effects, a clear correlation with the 11-year sunspot cycle has been found. On longer time scales, there are characteristic periods of 80, 150, 200 and 500 years and longer. There are even suggestions of cycles lasting millions of years. Clearly, there are influences affecting Earth's climate that do not originate on this planet.
When talking about the wonders of the universe, Carl Sagan was fond of saying that we are all made of “star stuff.” Science has shown that the varied elements that make up people and our entire planet were created deep within stars and by supernovae explosions. But the influence of the stars doesn't end there. Astrophysicists have come to suspect there is a direct, ongoing connection between supernovae and Earth's climate. Because exploding stars don't just create heavy elements—they create cosmic rays.
Cosmic Rays
“There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy”
— W. Shakespeare, Hamlet
Scientists have only recently come to suspect that cosmic rays have an important influence on Earth's climate. Cosmic rays are highly energetic charged particles that originate from various sources in outer space. They travel at speeds approaching the velocity of light and strike Earth from all directions. Unlike X-rays and gamma-rays, which are highly energetic forms of light, cosmic rays are actually particles of normal matter. Most cosmic rays are the nuclei of atoms, ranging from the lightest to the heaviest elements in the periodic table. But, cosmic rays also include high energy electrons, positrons, and other subatomic particles.
The term “cosmic rays” usually refers to galactic cosmic rays (GCR), which originate outside the solar system and are distributed throughout the Milky Way galaxy. However, the name cosmic ray is often used to refer to other classes of energetic particles from space. Among these are atomic nuclei and electrons accelerated by energetic events on the Sun—called solar energetic particles. Also included as cosmic rays are particles accelerated by magnetic fields in interplanetary space.
Cosmic rays were discovered, in 1912, by Austrian scientist Victor Hess. Like many scientific discoveries, Hess' discovery built on the work of many earlier scientists. In particular, the recent discovery of X-rays and natural radioactivity.
Strange Particles from Outer Space
On December 22, 1895, Wilhelm Roentgen315 created a photographic image of his wife's hand, but this was no ordinary photograph. The ghostly image revealed the unmistakable image of his wife's skeleton fingers, complete with wedding ring. Roentgen's discovery of these “mysterious” X-rays, capable of peering through living flesh and producing an image on a photographic plate, greatly excited scientists of his day. His was the first in a series of discoveries that would lead scientists to realize that the Universe was a much more complicated place than they had imagined.
Illustration 97: Wilhelm Roentgen ca. 1895. Inset photo: Photograph of Frau Roentgen's hand.
The discovery of X-rays led to a flurry of activity involving some of the most famous names in science: Marie Sklodowska Curie, Ernest Rutherford and Antoine Henri Becquerel. Antoine Becquerel,316 who was studying the related phenomena of fluorescence and phosphorescence, was among those who noticed Roentgen's discovery. After learning how Roentgen discovered X-rays from the fluorescence they produced, Becquerel decided to pursue his own investigations of these mysterious rays. Quite by accident, in the course of his investigations, Becquerel made a remarkable discovery.
While fluorescence and phosphorescence had many similarities to each other and to X-rays, they also had important differences. Fluorescence and X-rays stopped when the initiating energy source was cut off, but phosphorescence continued to emit rays for a time after the energy source was removed. In all three cases, the energy was derived initially from an outside source—or so it was thought.
Becquerel was working with a substance called potassium uranyl sulfate, K2UO2(SO4)2. He exposed the uranium crystals to sunlight and placed them on photographic plates wrapped in black paper. When developed, the plates revealed images of the crystals. At the time, it was believed that absorbing the Sun's energy caused uranium to emit X-rays. In March 1896, during a time of overcast weather in Paris, Becquerel was unable to use the Sun as an energy source for his experiments. He wrapped up his photographic plates and stored them in a dark drawer, awaiting the Sun's return. In one of those fortunate accidents that have so often advanced the development of science, Becquerel also placed some of his crystals in the drawer on top of the wrapped plates.
Much to Becquerel's surprise, when the plates were removed and developed, he found they were strongly exposed. During storage, invisible emanations from the uranium—emanations that did not require the presence of an initiating energy source—had left clear images on the plates. Later, Becquerel demonstrated that the radiation emitted by uranium, unlike X-rays, could be deflected by a magnetic field and, therefore, must consist of charged particles. This discovery that some natural substances spontaneously emit radiation—that they were radioactive—changed science dramatically. For his discovery of radioactivity, Becquerel was awarded the 1903 Nobel Prize for physics.
After the discovery of radioactivity, scientists began building devices specifically to detect radiation. As their devices became more sensitive, several researchers notice that radiation was detected even when the devices were not in the presence of a known radiation source. This led to speculation that radiation was being created in the upper atmosphere or entered the atmosphere from space above, but no one was sure. Whatever the source, the radiation was partially blocked by the thicker atmosphere at lower altitudes. An Austrian physicist, Victor Hess, decided to solve this mystery by going up in a balloon.
Illustration 98: Victor F. Hess. Source: Nobelpriz
e.org.
Victor Franz Hess was born on the 24th of June, 1883, in Waldstein Castle, near Peggau in Steiermark, Austria. His father, Vinzens Hess, was chief forester in the service of Prince Öttingen-Wallerstein. His mother was Serafine Edle von Grossbauer-Waldstätt, a member of the local aristocracy. He received his entire education in Graz. He attended Gymnasium (1893-1901), and then attended Graz University (1901-1905), where he took his doctorate degree in 1910.317
He worked, for a short time, at the Physical Institute in Vienna, where Professor von Schweidler acquainted him with the recent discoveries in the field of radioactivity. From 1910 through 1920, he worked under Stephan Meyer at the Institute of Radium Research of the Viennese Academy of Sciences.
While at the Academy, Hess and two assistants ascended in a balloon to 17,500 feet (5,400 m). During the ascent, they measured the amount of radiation increase. Hess used a simple detector called an electroscope, that consisted of a doubled-over strip of gold leaf. When given an electrical charge, the two flaps of gold leaf would repel each other, spreading apart in an inverted V shape. Radiation striking the strip caused the charge to be lost, allowing the flaps to come back together. So, the intensity of radiation could be measured by charging the strip and timing how long it took to discharge. Hess found the higher the balloon rose, the faster the electroscope discharged. In Hess' own words:
When, in 1912, I was able to demonstrate by means of a series of balloon ascents, that the ionization in a hermetically sealed vessel was reduced with increasing height from the earth (reduction in the effect of radioactive substances in the earth), but that it noticeably increased from 1,000 m onwards, and at 5 km height reached several times the observed value at earth level, I concluded that this ionization might be attributed to the penetration of the earth's atmosphere from outer space by hitherto unknown radiation of exceptionally high penetrating capacity, which was still able to ionize the air at the earth's surface noticeably. Already at that time I sought to clarify the origin of this radiation, for which purpose I undertook a balloon ascent at the time of a nearly complete solar eclipse on the 12th April 1912, and took measurements at heights of two to three kilometers. As I was able to observe no reduction in ionization during the eclipse I decided that, essentially, the sun could not be the source of cosmic rays, at least as far as undeflected rays were concerned.318
Hess received the Lieben Prize, in 1919, for his discovery of the “ultra-radiation.” The following year he became Extraordinary Professor of Experimental Physics at the Graz University. Despite Hess' work, there was still a dispute as to whether the radiation was coming from above or from below.
In 1925, Robert Millikan,319 of Caltech, introduced the term “cosmic rays” after concluding that the particles came from above, not below the cloud chamber he used to study them. For some time, it was believed that the radiation was electromagnetic in nature, resulting in the name cosmic “rays.” Millikan became embroiled in a debate with Arthur Compton320 over whether cosmic rays were composed of high-energy photons or charged particles.
Illustration 99: Hess and his balloon in 1912. Source CERN.
Millikan put forth the theory that cosmic rays were photons—the “birth cries” of atoms—and pursued the study of cosmic rays for many years, trying to prove his theory.321 However, by the 1930s, it was proven that cosmic rays were electrically charged. This was discovered by observing the affect of Earth's magnetic field on the incoming radiation.
Compton, an expert in X-rays and their behavior, believed that cosmic rays were charged particles and not a form of electromagnetic radiation. He was eventually proven correct. In 1929, a Russian scientist, D. V. Skobelzyn, discovered ghostly tracks made by cosmic rays in a cloud chamber. Also in 1929, Bothe and Kolhorster verified that the cloud chamber tracks were curved.322 Since such curved paths were only made by charged particles passing through a magnetic field, cosmic rays had to be particles, not electromagnetic radiation. Still, some older textbooks incorrectly included cosmic rays as part of the electromagnetic spectrum—science evolves.
Compton published his, “positive evidence that the primary cosmic rays consist of electrical particles,” in 1936.323 That same year, Hess was awarded the Nobel prize for his discovery.324 After a period as head of the Institute for Radiation Research at the University of Innsbruck, he returned to the University of Graz as Professor of Physics and director of the Physics Institute in 1937.
Two months after the Anschluss325 in March 1938, Hess was dismissed from his post because he had a Jewish wife. A sympathetic Gestapo officer warned Hess that he and his wife would be taken to a concentration camp if they remained in Austria. They made their escape to Switzerland four weeks before the order came for their arrest. Shortly thereafter, Hess and his wife settled in the United States. Hess taught at Fordham University in New York City until 1956. He became an American citizen in 1944, and lived in New York until his death in 1964.326
From the 1930s to the 1950s, cosmic rays served as a source of particles for high energy physics investigations, and led to the discovery of subatomic particles, including the positron, π meson, μ meson and K meson. Since that time, man-made particle accelerators have reached very high energies, supplanting the use of cosmic rays in basic particle physics. Nowadays, the main focus of cosmic ray research is in astrophysics: investigations of where cosmic rays originate, how they are accelerated to such high velocities, what role they play in the dynamics of the Galaxy, and what their composition tells us about matter from outside the solar system. To measure cosmic rays directly, research is carried out by instruments carried on spacecraft and high altitude balloons. This allows observations to be made before the cosmic rays slow down and break up in the atmosphere.
Cosmic rays include the nuclei of all the naturally occurring elements found in the periodic table. Hydrogen nuclei, which consist of a single proton, account for 89%, helium 10%, and heavier elements account for the remaining 1%. The common heavier elements, carbon, oxygen, magnesium, silicon, and iron, are present in about the same relative abundances as in the Universe. There are, however, important differences in the distribution of rare elements and isotopes. For example, there is a significant overabundance of the rare elements lithium (Li), beryllium (Be), and boron (B) produced when heavier cosmic rays fragment into lighter nuclei during collisions with the interstellar gas.
The existence of isotopes provide information about the origin and history of galactic cosmic rays. An overabundance of an isotope of neon (22Ne) indicates that the nucleosynthesis of cosmic rays and solar system material are different. Other particles are also present: electrons constitute about 1% of galactic cosmic rays and positrons a tenth of that.327
The energy of sub-atomic particles is usually measured in electron volts (eV). One eV is the energy gained when a single electron is accelerated through an electrical potential difference of 1 volt. This is equivalent to 4.45 × 10-26 kilowatt-hours, a very tiny value indeed. The energy of cosmic rays is usually measured in units of millions of electron volts (MeV), or billions of electron volts (GeV, for giga-electron volts).
Just as cosmic rays are deflected by the magnetic fields in interstellar space, they are also affected by the interplanetary magnetic field embedded in the solar wind. The wind from the Sun is a plasma of ions and electrons blowing from the solar corona at speeds of 250 miles/second (400 km/sec). The Sun regularly emits particles with energies in the 100 MeV range, but solar flares, on occasion, can produce particles with up to 20 GeV.
Another source of energetic particles inside the solar system is the planet Jupiter. Jupiter has a powerful, complex magnetic field of its own and, for reasons not fully understood, its magnetosphere emits floods of high-speed electrons. These electrons have energies ranging from 1 MeV to 20 MeV, and the intensity of particles varies in a 10 hour cycle, Jupiter's period of rotation.328
Much like its brood of planets, the Sun rotates on its axis, with one rotation taking around four weeks. Because of the r
otation, its magnetic field is twisted around forming a spiral pattern, though there are many irregularities caused by flares and eruptions. When Earth and Jupiter are aligned with one of the spirals in the Sun's magnetic field, the intensity of high-speed electrons reaches a maximum. Due to the orbits of both planets, this happens about every 13 months.
But electrons from Jupiter and other particles from the Sun do not reach the ultra-high energies observed in some cosmic rays. Most galactic cosmic rays have energies between 100 MeV, corresponding to a velocity for protons of 43% of the speed of light, and 10 GeV, corresponding to 99.6% of the speed of light. Single particles with energies as high as 100,000,000,000 GeV (1020 eV) have been observed, higher than any other form of natural radiation and far beyond the capabilities of human particle accelerators. A 1020 eV cosmic ray, a single atomic nucleus, has as much kinetic energy as a baseball traveling at 100 mph.329 Considering the incredibly tiny size of an atomic nucleus, the energy contained in these ersatz-baseballs is mind-boggling.
Supernovae and Cosmic Rays
Since most of the cosmic rays, that originate in the Sun or from other sources in the solar system, lack the energy to deeply penetrate Earth's atmosphere, there must be other sources. What sources produce these highly energetic (>100MeV) particles?
The Sun's magnetic field extends outwards as far as 100 astronomical units (AU),330 shielding the inner solar system from galactic cosmic rays. Cosmic rays from interstellar space beyond the solar system must penetrate the Sun's magnetic field and the deluge of particles in the solar wind. As a result, galactic cosmic rays with less than ~100 MeV cannot penetrate as far as Earth's orbit. The Sun, through this process of solar modulation, controls the flux of cosmic rays arriving at Earth.
The Resilient Earth: Science, Global Warming and the Fate of Humanity Page 20