Advanced Solar Theory (MT5810) OUTLINE 1.Observational properties of the Sun 2.MHD equations (revision) 3.Induction equation - solutions when R m >1 4.Magnetic equilibria 5.Waves 6.Solar wind 7.Reconnection 8.Instabilities Books:Solar MHD -- ER Priest Camb. Encyc. of the Sun -- K Lang Nearest Star -- L Golub & J Pasachoff

1. Observations 1.1 History Ancient observations - sunspots (chinese, greeks) - forgotten Galileo (1610) rediscovered sunspots first photograph of corona (eclipse) first solar flare observed sunspots have strong B foundations of MHD (Cowling) satellite observations of interplanetary medium 1980’s & 90’s -- development of MHD -- space observations (Skylab 73-74, Yohkoh 91-05, SOHO 95 - …, TRACE 98 - …, RHESSI 02 - …

Future Space Missions STEREO (NASA) April 2006 * Two satellites * _ _ _ _ _ _ _ _ _ _ _ _ _* Solar Orbiter (ESA) 2012 * _ _ _ _ _ _ _ _ _ _ _ _ * Solar Dynamics Observatory 2008 * _ _ _ _ _ _ _ _ _ _ _ _* Solar B (Japan-US-UK) Sept 2006 * Connections surface/corona

Ball of gas held together by gravity ? Chemical composition _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1.2 Properties of the SUN ? Radius _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ? Age _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ? T surface _ _ _ _ _ ? Mass/ s. system _ _ _ _ _

Some other properties ? Mean distance from Earth 93 million miles = 150 million km _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ? Rotation period = 25 days (equator), 37 days (poles) ? Mean density = 1.4 x 10 3 kg m -3 _ _ _ _ _ _ _ _ _ _ ? Surface gravity = 274 m s -2 _ _ _ _ _ _ _ _ _ _ ? Escape velocity at surface = 618 km s -1 _ _ _ _ _

Interior --> Core, Convection zone Atmosphere --> Photosphere, Chromosphere, Corona Overall Structure _ _ _ _ _

Covered with turbulent convection cells: * _ _ _ _ _ _ _ _ _ _ * (1 Mm) * _ _ _ _ _ _ _ _ _ _ * (15 Mm) Photosphere Temperature 6000 K ?? why

Amazing images [70 km] from La Palma (Canaries)

In close- up: points, flowers, ribbons (created by magnetic fields)

Photosphere --> Sunspots Galileo discovered (1610) w. telescope Dark because cool But why cool ? *_ _ _ _ _ _ _ _ _ _ _ _ _ _* 1.3 SUNSPOTS ??? why

Stunning Image from La Palma Penumbral structure created by B

Map of Photospheric Magnetic Field White -- towards you; Black -- away from you Regions around sunspots -- bipolar * _ _ _ _ _ _ _ *

2. Patterns of sunspots/active regions ?? why 1. Intense magnetic fields over whole Sun SURPRISES: -- _ _ _ _ _ _ _ _ _* ?? why

1.4 CORONA (Turkey, 1999) Magnetic tubes “prominences” Next: Egypt, March 2006 SURPRISE (1940) *_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _* Fine structure ??why

* Picture with X-ray telescope:

A magnetic world Yohkoh Amazingly rich variety of MHD phenomena

TRACE (Active region) - from above

Magnetic field dominates plasma creates intricate structure/ heats From side: *_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ * ?? how

1.5 Solar Activity On top of the “Quiet Sun” (ie the background photosphere, chromo sphere & corona), there are several types of transient phenomena : (i) _ _ _ _ _ _ _ _ _ (ii) _ _ _ _ _ _ _ _ _ (iii) _ _ _ _ _ _ _ _ _ (iv) _ _ _ _ _ _ _ _ _

(ii) Prominences On disc in chromosphere, see as long, thin structures Dark - cutting out light from below * _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _* ???

Sometimes erupt - [look like twisted tube] why ??

(iii) Solar Flare Sudden brightening in chromosphere & corona near sunspots *_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ * How ??

(iv) Coronal Mass Ejections SOHO Coronagraph -- Artificial eclipse Can reach Earth - communications / satellites Discovered huge ejections of plasma ?? *_ _ _ _ _ _ _*

1.6 SOHO(Solar & Heliospheric Observatory) Observing Sun continuously for 1st time (ESA/NASA) Launched Orbiting Sun at point in phase with Earth MANY NEW SURPRISES --> 1st comprehensive view of Sun