Slide 1Terrestrial Weather and Space WeatherThe Boundary Between the Atmosphere and SpaceTerrestrial Weather and Space WeatherSlide 5A Little GreekThe AuroraeHistorical References to AuroraeSystematic Study of AuroraeEarly Ideas on the Cause of AuroraeThe Auroral OvalGeomagnetismWilliam Gilbert’s Magnetic FieldSlide 14SunspotsGalileo’s SunspotsMaking the ConnectionA Digression on UnitsA Digression on Scientific NotationAssignmentESS 7ESS 7Lecture 2Lecture 2September 29, 2008September 29, 2008A Little HistoryA Little HistoryTerrestrial Weather and Space Weather•Space weather is interested in the space environment around the Earth all of the way to the Sun.•Space physics is concerned with the physics of gases of charged particles called a plasma. •Its roots are in the Sun.•Difference 1–Terrestrial weather occurs in the troposphere.–Space weather starts in the thermosphere which is about 100km above the Earth.The Boundary Between the Atmosphere and Space•The sharp contrast between the atmosphere and space is at about 100km.Terrestrial Weather and Space Weather•Difference 2–The Sun emits two types of energy – electromagnetic and particle.–Visible light, radio waves, microwaves, infrared, ultraviolet, X-rays and gamma rays make up the electromagnetic radiation.–About 1400 watts/m2 hit the upper atmosphere –Heats the lower atmosphere unevenly driving winds.–The Sun also emits particles – charged atoms, protons, electrons – the stream of particles is the solar wind.–The solar wind is driven by temperature difference in the Sun’s upper atmosphere. –The solar wind changes continuously. Occasionally it erupts and sends a large part of its atmosphere our way.Coronal Mass Ejection1012 kg of material is ejected at 1000km/s (2.5 million miles/hr.A Little Greek•Spheres – concentric regions around planets.–Litho – stone – the rocky surface of the Earth–Hydro- water–Bio- life–Atmos – vapors•Boundaries between spheres are called pauses.•Tropo – mixing 0-10 km –weather•Strato – 10 – 50 km – ozone layer •Meso – 50-80 km – coldest layer•Thermo 100 km – space•Iono – 100 km – aurora – greatly influences space weather.The Aurorae• Aurorae probably are the longest studied space weather phenomenon – The have been observed for thousands of years even in Los Angeles.Historical References to Aurorae•Old Testament references to auroras.•Greek literature (Aristotle – 384BC -322BC) speaks of “moving accumulations of burning clouds”•Chinese literature has references to auroras prior to 2000BCSystematic Study of Aurorae•Systematic study of aurorae began in the 16th century primarily in northern Europe.Early Ideas on the Cause of Aurorae•Galileo theorized that aurora is caused by air rising out of the Earth’s shadow to where it could be illuminated by sunlight. (Note he also coined the name aurora borealis meaning “northern dawn”.)•Pierre Gassendi who was working with Galileo concluded that the aurorae had to occur at high altitude because they can be seen in widely separated locations.•Descartes thought they are reflections from ice crystals.•Halley suggested that auroral phenomena are ordered by the Earth’s magnetic field. •In 1731 the French philosopher de Mairan suggested they are connected to the solar atmosphere.•Cavendish in 1790 used triangulation to deduce that they occurred at 80km -112km – confirmed by Størmer in 1900.The Auroral Oval•Scientists began carrying out observational studies designed to determine where the aurorae were found.•Elias Loomis (1869) collected observations of aurora and published the first map of their occurrence. They are not found at the pole but is a ring around. •By the end of the 19th century scientists had sysmatically determined that they occur at high altitudes and in a ring around the pole – understanding was next.Geomagnetism•By the 11th century the Chinese had learned that a magnetic needle points north-south.•By the 12th century the European records mention the compass.•That there was a difference between magnetic north and the direction of the compass needle (declination) was known by the 16th century.•William Gilbert (1600) realized that the field was dipolar.•In 1698 Edmund Halley organized the first scientific expedition to map the field in the Atlantic Ocean.William Gilbert’s Magnetic FieldWilliam Gilbert’s Magnetic Field• The dipole is the simplest magnetic field you can have. Gauss (1839) showed that the magnetic field was divergenceless. This that the magnetic lines of force (everywhere tangent to the magnetic field vector) must close.Sunspots•In 1610 Galileo used his telescope to observe sunspots for the first time. Note he did not look at the Sun instead he focused the image on a piece of paper – like a pin hole camera.•There was debate over whether they were planets moving across the Sun or actual features on the Sun.•Schwabe systematically looked for a planet or planets that could account for sunspots but failed.•He discovered that the sunspots had an 11 year periodicity.Galileo’s SunspotsMaking the Connection•In 1859 Carrington noticed a white light flare was followed by geomagnetic activity on the Earth.•It was controversial – Lord Kelvin – solar magnetic field couldn’t possibly effect the Earth’s field – “connexion between magnetic storms and Sun-spots is unreal…”•Becquerel (Nobel laureate) in 1878 suggested the either magnetic fields or matter provided the connection.•Corpuscular radiation (Crookes) was responsible (Sir Oliver Lodge) (J. J. Thompson (Nobel laureate) showed that corpuscular radiation was electrons).•Marconi (Nobel laurate) showed that radio messages could go across the Atlantic prompting Kennelly and Heaviside to postulate the ionosphere. Appleton won a Nobel Prize for showing they were correct,A Digression on Units•SI units will be used in this class – mostly.•The four fundamental units are–Time – seconds–Length – meters–Mass – kilograms–Electrical charge – coulomb•All other units are combinations of these units – if you use the SI units exclusively you will get the correct answer.•It is convenient to depart from SI is a few areas.–1AU – 150,000,000 km (or 1.5X108 km) the mean distance from the Sun to the Earth–1RE – 6371 km – the radius of the Earth.A Digression on Scientific Notation•For really big