1(Space Climate School, Saariselka, March, 2009) I. OUR OWN SUN(Space Climate School, Saariselka, March, 2009)Eric Priest (St Andrews)
2space physics/astronomy 1. Why Study the Sun ?1. Of great scientific interest in own right2. Influence on Earth3. Important for Astronomy-- fundamental cosmic processes4. Many misconceptions…..Many basic properties still mystery (astrony) - interior, dynamo, corona, wind, flaresSo Sun is 1 of liveliest branches ofspace physics/astronomy
3Another Theme: Many surprises caused by magnetic field (B) Sun is NOT a normal gasSun is in 4th state of matter("PLASMA")behaves differently fromnormal gas:B and plasma -- coupled (intimate, subtle)B exerts force on plasma -- stores energy
42. The SUNVital Statistics? Chemical compositionRadiusAge --
5Overall Structure Interior: Core Convection zone Atmosphere: Photosphere, Chromosphere, Corona
6Covered with turbulent convection cells: “Granulation” (1 Mm) 3. PhotosphereTemperature KCovered with turbulent convection cells: “Granulation” (1 Mm)“Supergranulation”( Mm)
7In close-up: points, flowers, ribbons (created by magnetic fields)
8Dark because cool But why cool ? SUNSPOTSPhotosphere --> SunspotsHarriot discovered (1610) w. telescopeDark because cool But why cool ?
9New Model (Thomas & Weiss) Mixture:Dark filaments-(low)Bright filaments-(high)
10Map of Photospheric Magnetic Field White -- towards you;Black -- away from youRegions around sunspots --bipolar"Active Regions"
11SURPRISES: -- B carried to edges of convection cells 1. Intense magnetic fields over whole SunB carried to edges of convection cells2. Patterns of sunspots/act. regs-- large flux tube--> dynamo …
13But - atmosphere is inhomogeneous Many temperatures in same region
144. Chromosphere is dynamic (2D Simulation) [Hansteen & Carlsson]CoronaChromo-spherePhoto-sphere(light/dense)
15Dynamic nature s. atmosphere Swedish Solar Telescope Quiet active regionH-alpha0.1 arcsecContinually-changing threads
165. CORONA Heating caused by magnetic field ("crown") -- See at ECLIPSE of Sun5. CORONAAlong open structures: -- fast solar windSURPRISE (1940) -- Temperature is million degreesStudents in St Andrews imaginative:Heating caused by magnetic fieldStructure outlines magnetic field
17Total Eclipse - March 29, 2006 - Motion of Moon’s shadow
20In last 10 minutes: Light level and temperature decrease more quickly WindStart to see planetsJust before totality (when Moon covers Sun) --Baily beadsRed chromosphereProminencesCorona - glowing against jet black disc !
21Just before totality2nd ContactMagnetic tubes “prominences”
276. SOHO (Solar & Heliospheric Observatory) Launched Orbiting Sun at point in phase with EarthObserving Sun continuously for 1st time (ESA/NASA)--> 1st comprehensive view of SunMANY NEW SURPRISES
28QN. -- ? Earth Influenced by Solar Variability Number of Sunspots Oscillates w. 11-year Cycle
29Solar Cycle Sunspots - two zones between -35o and +35o latitude Leading spots have opposite polarities in 2 hemispheres [Hale]Leading polarity is closer to equator [Joy]Magnetic field reverses every 11 years
30Solar cycle (ii) Spots emerge at high latitudes w. opposite polarity Sunspot minm -- no spots -- polar fieldsSpots emerge at high latitudes w. opposite polarity[later at lower latitudes]90% active region flux cancels --10 % migrates --following flux reaches polesreduces & reverses polar field-- new minmGlobal coronal magnetic field goes thro’ complex set of 17 topologies(Maclean & Priest, 2007)[Polar Fields:* maximum extent at s. minimum * change polarity 1-2 years after s. maximum]
31Whole atmosphere varies with cycle Max MinChromosphereCorona(Intensity Changes by 100)Schematic --> eq. streamers/polar holes
32Solar wind velocity [polar plot, ULYSSES] Sunspot minimum [ ]FAST Solar Wind(700 km/s) in coronal holesSLOW Solar Wind(300 km/s) in equatorial streamers[Red = inward field Blue = outward field]
33SURPRISE (1976) Realised NO sunspots in most of 17th centy "Maunder Minimum" -- Little Ice AgeSo B on Sun affects climate of Earth !!But mechanism not known !
34SOHO --> Total Emission (t) 1996-2000 Emission varies by 0.2% -- passage sunspotsIncrease by 0.1% from sunspot min to maxMuch too small to produce global warming?? Real & ?? cause
35Solar cycle variations further back to: 1980 from severalspacecraft [irradiance]1400 from 10Be in ice cores30, 000 yrs BP from 14C in tree rings (J Beer)
36amazing observations from space CONCLUSIONSSolar Physics - golden age - observationsMagnetic theory playing a key roleSense of vitality will continueamazing observations from space(SOHO, TRACE, RHESSI,Hinode, Stereo,SDO, Orbiter)- bright new young students