Solar-Terrestrial Relations The sun can influence the Earth in several ways: 1. Evolutionary changes 2. Luminosity variations (spots, plage) 3. Particles (flares, solar wind) 1 Occurs on timescales of ~109 years, so only 2 and 3 are important for humans I. Solar Activity and Climate Changes The solar irradiance change by no more than 0.1–0.3% during the sunspot cycle. What is the corresponding temperature change at the Earth? 0.07 % Let„s take the solar irradiance changes of the last 30 years which gives DL = 0.00073 Intercepted flux, Fin = radiated flux, Fout L RE = radius of Earth Fin = pRE 2 (1– A) A = Albedo of Earth 4pd2 d = distance to sun Fout = sT4 · 4pRE2 s = Stefan-Boltzmann constant L(1 – A) = sT4 16pd2 DT = constants x (1/4) L–3/4 DL DT DL = T 4L T ≈ 300 K DT = 0.05 !!! Naively we would expect that solar activity has little influence on the Earth„s climate. But the real story is different. Evidence for the influence of Solar Activity on Climate: 1 The Maunder minimum coincided with the “Little Ice Age” in Europe. Baliunas and Jastrow estimate that the solar irradiance during the Maunder minimum was about 0.4% less than it is now (based on studies of solar-type stars). This could account for the climate change observed during the Maunder minimum During the Little Ice Age: 1. Glaciers in Switzerland advanced crushing villages 2. The Thames River and Canals in The Netherlands often froze 3. New York Harbor froze allowing people to walk from Manhattan to Staten Island 2. S. Bjorck of Lund University looked at tree rings and ice drillings in Greenland and found that there was a 200-year cold spell 10.300 years ago. This coincided with a large increase in the amount of 10Be in the Greenland ice sheet. 10Be is produced via cosmic rays colliding with nitrogen and oxygen in the atmosphere. During high levels of solar activity the Earth's magnetic field is stronger so less cosmic rays can penetrate. 3. Abnormally high solar activity during 1100–1250 coincided with a period of warming in Europe. During this time: a) Viking settled in Northern Europe, traveling to Greenland and America over seas usually filled with dangerous ice b) Grapevines grew as far north as England c) Higher tree lines in the Alps The Modern Maximum is comparable to the Medieval Maxium in strength Temperatures seem to be correlated with sunspot maximum Wilson claimed in 1997 that the level of solar activity is increasing from one cycle to the next and that this can account for 0.7–1.4 deg warming over the next 100 years. Higher levels of solar activity increases the amount of ozone in the upper atmosphere. Schindell argued that this warms the upper atmosphere and the warm air affects winds from the stratosphere to the surface. Postmentier, Soon, and Baliunas have claimed that there is a correlation with the size of coronal holes and the Earth's temperature. Large coronal holes allow more charged particles to strick the Earth. Presumably these affect the properties of clouds. Coronal Holes are „open“ field lines on the Sun where the X-ray emission is less It is clear that solar activity has some influence on climate. Since 1950 the sun has been in an enhanced maximum similar to the Grand Maximum that caused the Medieval Warm Period in the 9th to 13th centuries. So, can solar activity account for the observed „global warming“? Keep in mind that carbon dioxide in the atmosphere has increased by more than 25% in the last century. Is it the sun or is it humans? To answer this Solanki & Krivova at MPS did a study. • The created a model which reconstructs the solar irradiance. This is a four component model which including quiet sun, umbra, penumbra, and faculae • Assumed that all terrestrial temperature changes prior to 1970 were due entirely to the sun Krivova & Solanki reconstruction of Solar irradiance Global Temperatures Measured irradiance Reconstructed curve Conclusion: • Less than 30% of the Earth„s temperature rise can be attributed to the sun • A large part of the global warming may be due to CO2 There have been many attempts to try to correlate solar activity with other things. Some might not be too crazy… Solar activity might incluence climate so you can argue there should be a correlation Others are total „rubbish“ Like the claim that solar activity influences world events There has been claims that Solar activity (maxima) has caused political and economic crises. The End of the Century was written by Francois Masson in 1979-1980. A publisher was never found (for good reason) but it was transcribed into English and published on the internet Dates of Maximum Solar Activity corresponding to revolts, famine, depressions and other catastrophes. Below are the events chronicled by Masson with additions by me in boldface: 1702: Protestant Revolts in France, general wars in Europe 1715: Scottish rebellion, depression and famine in Europe. Death of Louis XIV and big political changes 1725: Revolt in Scotland, Peter the Great dies. Russia enters 50 years of strife 1738: Workers revolt in England. Wesley founds the first Methodist Society 1729: Tax Revolt in England 1760: Founding of Freemasonry. Condemnation of the Encyclopedists in France. 1776-77: Declaration of Independence, American War of Independence 1787-88: True beginning of the French Revolution. Rioting in Paris. Economic Crisis in French State. 1803: French economic crisis. Napoleon renews wars with England 1814-15: Liberal rebellions in France and other European countries. Uprising in France in favor of Napoleon on his return from Elba. Waterloo. 1827: Serious depression in Europe 1836: Riots in France. TEXANS DEFEATED AT ALAMO. TEXANS GAIN INDEPENDENCE AT BATTLE OF SAN JACINTO 1848: Revolution and depression in Europe 1860-61: Revolutions in Italy, South Carolina secedes, Civil War begins in USA. 1870-71: Franco Prussian War 1882: Major Depression 1892-93: European Tariff war. Stock Market crash in U.S. 1905-06: Russo-Japanese War. Imporant revolts in Russia. Einstein 1917-18: Revolution and total change in Russia. Rebellion in French and Italian armies. Mutiny of the German fleet. Sun Yat-Sen„s revolution in China. 1928-29: Great Depression begins. Peasant revolts in Russia against collectization of land. Famin, bloody purges. Revolts in Serbia, Yugoslavia 1936-37: Franco„s rebellion in Spain, civil war. General strikes in France. Start of ideological wars Fascism vs. Communism 1947-48: Revolts in Eastern satellite nations, revolts in Indo-China, revolt of Chinese communists against Chiang Kai-Shek. 1957-58: First uprising of French colonists in Algeria, Castro„s revolt in Cuba. A. HATZES BORN: SPUTNIK LAUNCHED. TV DINNERS INTRODUCED 1968-69: World youth revolt. The Prague Spring. Height of Vietnam war. Gold crisis. MAN LANDS ON MOON: BEATLES RELEASE LAST ALBUM FOLLOWED BY BREAKUP 1979-80?: New economic crisis. Numerous localized wars. First sign of new religion in USSR. REAGAN ELECTED PRESIDENT: HATZES STARTS GRADUATE SCHOOL: JOHN LENNON ASSASINATED. 1990-91: End of USSR. Berlin wall falls (1989) 2000-2001: HATZES BECOMES DIRECTOR OF TLS: BUSH GETS ELECTED. TERRORISTS ATTACKS ON U.S. GEORGE HARRISON DIES. Conclusions. Solar Activity has been 1. bad for The Beatles 2. good for A. Hatzes 3. Mostly affects events in France and England 1865: Lincoln assassinated 1914: Assassination of Archduke Ferdinand. Start of WWI 1939-40: Start of WWII 1963: Kennedy assassinated 1986: Challenger shuttle disaster 2003: Iraq war starts, Columbia shuttle disaster 2004: Bush gets re-elected. Madrid train bombings 2005: London terrorist bombings 2007: G8 Protests Lessons: 1. With so many historical events one can always find correlations between these and solar maxima or minima 2. Don„t believe everything you read on the internet. II. The Solar Wind Spacecraft moving outside of the Earth„s magnetic field have demonstrated that a continuous flux of charged particles streams outwards from the sun Composition: 95% (by number) protons and electrons, the rest are a particles Density: 3–20 particles cm–3 (mean = 10) Plasma Temperature (velocity dispersion): 100.000 – 150.000 K. a particles 4–5 times higher Velocity: 350 – 750 km/sec. Speed varies little between 1– 20 AU Magnetic field strength: 2 – 10 g (g = 10–5 Gauss) In 1958 Eugene Parker worked out the model for a continuously expanding corona The radial outflow of the solar wind would follow the magnetic field lines radially, except that the sun rotates. Streamlines are given by: 1 dr Vr Vr df = = r Vf –wr The solar radial component of the magnetic field switches polarity several times + - - + Note: „Solar Sails“ do not use the Solar Wind! Solar Sails use radiation pressure! The solar wind is very tenuous and does not exert much force on anything it hits. The solar wind has 1.000 – 10.000 less force that the radiation pressure of sunlight III. The Solar Wind – Earth Interaction Magnetosphere: The Earth has a weak dipole field that is inclined by 11o from the spin axis. Forcing by the solar wind modifies this field creating a cavity called the magnetosphere. Inner magnetosphere: extends from the “nose” to a distance of 8 RE on the night side. It does not include the poles. This is a stable region populated by the inner and outer radiation belt. Typical densities of ions is 1 per cubic cm. In outer radiation belt the energy of an ion is about 50 keV. The electrical current associated with the plasma is the ring current circling the Earth. Plasma Sheet: Thick layer of hot plasma centered on the tail's equator. Typical thickness is 3–7 RE, density 0.3–0.5 ions per cubic cm and an ion energy of 2–5 keV. Electrical currents flows across the plasma sheet and then closes along the magnetosphere boundary. In a substorm this current is diverted earthwards along the magnetic field lines. Tail Lobes: Regions of relatively smooth magnetic fields north and south of the plasma sheet. The region is a good vacuum with a density of 0.01 ion/cubic cm. It has strong magnetic fields and thus stores appreciable magnetic energy. Ionosphere: Region 70–500 km above the Earth containing free electrons and ions. Motion of a Charged Particle in the Earth„s Magnetic Field Cyclotron Motion: dv m = qv x B dt Take B to be in the z-direction dvx m = q Bvy dt dvy m = –q Bvx dt Motion of a Charged Particle in the Earth„s Magnetic Field Differentiate the equation for x: 2 d2vx q B dvy qB ( = – ( vx dt = m dt m This is the equation for a harmonic oscillator frequency: wc = |q| B = |q| BG Cyclotron Frequency m mc BG = magnetic field strength in Gauss Motion of a Charged Particle in the Earth„s Magnetic Field Lamor Radius: vx = v┴ e ±iwct v┴ is the velocity of the particle perpendicular to the vy = v┴ e ±iwct magnetic field vy = ± 1 dvx = ±iv┴ eiwct dy = dt wc dt Integrating: And the same for x: y – y0 = ± v┴ eiwct x – x0 = –i v┴ eiwct wc wc Motion of a Charged Particle in the Earth„s Magnetic Field Defining the Lamor Radius: v┴ mv┴ c rL = = wc |q| BG x – x0 = rL sin wct y – y0 = ± rL sin wct Where ± is due to the sign of the charge Motion of a Charged Particle in the Earth„s Magnetic Field Bz Charge particles cannot move across the field One charge lines, but are free to move along the magnetic field lines RL Opposite charge The Ring Current Gradients in the magnetic field causes a drift in the “guiding center” defined by the Lamor radius. This is because in regions of stronger magnetic field the Lamor radius is smaller. The guiding center drift velocity is given by: D vDB = ± 1 v┴ rL B x B 2 B2 Increasing magnetic field strength Lamor radius is smaller Lamor radius is larger where where the field strength is the field strength is smaller higher Center of motion shifts At the Earth‟s magnetic equator this causes one charge to drift eastward, the other westward creating a ring current. Reflection at the Poles: The magnetic moment of a gyrating particle is an invariant: 1 m v┴2 m= 2 B As a particle moves from weaker to stronger fields its v┴ increases.To keep the energy constant the motion parallel to the field must decrease. Eventually it comes to stop and gets reflected. The force causing this reflection is that on a diamagnetic particle: F = –m D ║ ║ B Motions of particles in the Earth„s magnetic field Geomagnetic Storms The term “geomagnetic storm” (world-wide disturbance) was coined by Alexander von Humboldt. Humboldt convinced the Czar to set up a network of magnetic observations across Russian lands. Other sites in throughout the world established that the magnetic storms were the same all over the world. There is a steep increase in the field (50-300 nanotesla) out of a total intensity of 30-60.000 nT occurring over 12-24 hours, followed by a recovery lasting 1– 4 days. Magnetic storms are caused when high energy particles from solar flares collide with the particles in the ionosphere changing the level of ionization. These events are associated with • increased Aurora activity • fluctuations in compass needle • disruption of short wave radio communications • induced currents that blow fuses, damage power lines • disruption of communications • decay of satellite orbits In other words, solar flares can cause significant damage and cost a lot of money to humans. Aurora: Aurorae occur when the charged solar particles from the solar wind interact with the Earth's magnetic field. These particles can only spiral along the field lines and thus strike the polar regions in what is called “the ring of fire”. In times of solar flares this ring of fire expands and extends to much lower latitudes. The Aurora taken from Tautenburg by Christian Högner The colors of the aurora result when charged particles strike molecules in the upper atmosphere causing collisional excitation of emission lines. Most are due to oxygen and nitrogen: O2 emission occurs at 200 km this is due to the 6300 Å, and 6364 Å lines (Red) O2 emission occurs at 100 km and is due to the 5557 Å line (yellow green). N2+ causes the blue colors due to the emission line at 4652 Å N2 also causes some red colors Important historical events in the studies of Aurora: • 500 BC Hippocrates suggest it is reflected sunlight •1600 Gilbert discovers that the Earth is a magnet. •1620 Galileo terms expression Aurora Borealis. •1774 Dortous de Mairan relates auroral displays to solar activity. •1790 Cavendish measures height at 80-110 km. Important historical events in the studies of Aurora: . • Alexander von Humboldt notes auroral displays coincide with magnetic storms. •1817 Biot proves aurora is self luminous. •1868 Angstrom uses a prism to show that the aurora is different from sunlight. Finds auroral green line. • Störmer used triangulation to confirm a height of at least 100km for displays • 1912-23 Oxygen and nitrogen lines identified • 1939 Hydrogen lines discovered. Auroral displays exhibit kinks, curls, and spirals. These are due to the magnetic field produced by the moving charged particles interacting with the Earth's field. The Geocorona: The outermost part of the Earth's atmosphere consists of a huge cloud of hydrogen gas extending a distance of 4-5 Earth radii. Collisions with this cloud removes the ion particles added during a geomagnetic storm. Picture of the geocorona taken by the Apollo astronauts Solar Flare Effect or Magnetic Crochet: A magnetic crochet arises from increased ionisation in the D and E layers of the ionosphere caused by the massive increase in X-ray radiation flux generated by a solar flare. The ionisation changes the conductivity of the ionospheric layers causing the electrical currents to flow more easily. The magnetic field produced by these currents causes a jump in the Earth's field. These events are rare because they are only observed by large flares that rise to a peak quickly. Substorms These are much more frequent (hours apart) than magnetic storms. These last about 1 hour during which energy is rapidly released in the magnetospheric tail. These are observed mainly over the polar regions unlike the larger magnetic storms which are observed globally. They do not inject as many particles into the ring current. The first sign of a substorm is that increase in polar auroras in the midnight zone. In space synchronous orbit satellites in the midnight zone see the magnetic field drop by half and they detect the arrival of many ions in the 5–50 keV range. Energy of the substorms: Substorms are believed to be due to a form of magnetic reconnection in the magnetospheric tail: •The cusp of the magnetosphere, where the field lines part between those pulled to the equator and those pulled to the tail, moves closer to the equator. Fewer field lines go sunward and more into the tail. •The shift in the cusp weakens the Earth's magnetic field near the noon side •More energy is drawn to the tail and the tail lobes of the magnetosphere expand. •The ``stretched'' magnetic field lines in the tail reconnect causing the tail to ``rebound'' like a slingshot. •A plasma bubble known as a ``plasmoid'' moves down the tail. A Magnetic Plasmoid Source of the substorms: • In 1904 Maunder proposed that substorms tended to occur in intervals of 27 days. Searches for features on the sun that could have been responsible for such storms yielded only bland and featureless regions, so called “M- regions” • In 1962 Mariner 2 on its way to Venus established that the solar wind contained recurrent fast streams whose sources rotated with the sun. The arrival of such streams triggered moderate substorms. • When X-ray observations of the sun began (starting with Skylab) it was established that the the elusive “M- regions” coincided with coronal holes. Coronal holes are regions where the magnetic field lines of the sun are open, not closed, allowing the particles comprising the solar wind to escape along the field lines. IV. Space Weather Example: Solar wind: 300.6 km/s, density = 3 protons per cubic cm X-ray flares: One C2 class and one M2 class: X-class: big, large radio blackouts and radiation storms M-class: medium, brief radio blackouts C-class small: few noticeable affects Active Regions: Region 9802 harbors energy for a class X-flare. There is a 10% chance of a class X flare, and a 50% chance for class M-flare in the next 24 hours. Sunspot 9821 is rapidly growing and poses a threat for Earth-directed flares (12.2.2002) Interplanetary magnetic field: 6.0 nT Coronal Holes: A substantial coronal hole is crossing the Earth- facing side. Expect strong gusts in the Solar wind. 11.2.2002: Solar wind gusts buffeted the Earth's magnetosphere last week. The encounter triggered mild geomagnetic storms and Nothern Lights. Geomagnetic storms. Measured via a K index. Ranges from 0--9 (minor storm has K=5, Severe storm has K > 6). The probability for a severe storm is 0.01 The study of space weather and the sun are important because: • Induced currents from large geostorms can cause massive blackouts (1989 Quebec) 1. March 24, 1940: Storm disrupted power service in New England, New York, Pennsylvania, Minnesota, Quebec, and Ontario 2. Feb 9-10, 1958: Power transformer failed in British, Columbia 3. Aug, 1972: Reclamation power station experienced swings of power line voltages of 25.000 volts. A 230.000 volt transformer exploded. Manitoba Hydro recorded power drops of 164 – 44 megawatts in minutes. 4. 1989: 9 hour power blackout in Quebec 5. Costs: $100 Million damage to power transformer of Minnesota Power and Electric. Estimated cost of a storm slightly more severe than the 1989 storm: $9 Billion! • Radiation dosages lethal to astronauts • Magnetic storms can interfere with GPS, compasses • Currents in pipelines enhance the rate of corrosion In June 1989 a powerful pipline explosion demolished part of the Trans-Siberian Railroad engulfing two trains. 800 people died. Alaskan pipeline has safeguards against geomagnetic storms. • Magnetic storms can damage satellites 1. 1982: GOES-4 Weather satellite has radiometer disabled for 45 min. 2. 1989: GOES-7 loses half its solar cells to proton release from flare. 3. Two Canadian satellites disabled due to activity 4. 1997: Telstar 401 experienced massive power failure Shorten the lifetime of low orbit satellites (e.g. Hubble Telescope) Bad news: Predictive abilities poor, only up to 1 hour in advance can we geta reliable prediction. Good news: It takes particles 2-4 days to get here.
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