CSI 769-001/PHYS 590-001 Solar Atmosphere Fall 2004 Lecture 05 Sep. 29, 2004

Lower Solar Atmosphere:Photosphere andChromospherehttp://science.nasa.gov/ssl/pad/solar/

Layered Structure of the SunInside the SunVisible Solar Atmosphere(3) Convection Zone

(2) Radiative Zone

(1) Core(4) Corona(3) Transition Region between Corona and Chromosphere(2) Chromosphere(1) Photospheresurface

Inside the SunCoredepth: 0 0.25 RsTemperature: 20 Million KelvinDensity: 150 g/cm3Energy creation region of the Sun, through nuclear fusion process that converts H He and releases the nuclear energy (mass of 4H < 1He, and E=MC2

(2) Radiative Zonedepth: 0.25 0.70 RsTemperature: 7 MK to 2 MKDensity: 20 g/cm3 to 0.2 g/cm3 Energy transport region purely through radiation, or photon diffusion; no convection and conduction is negligible

Inside the Sun(3) Convection ZoneDepth: 0.70 1.00 RsTemperature: 2 MK to 0.06 MKDensity: 0.2 g/cm3 10-7 g/cm3Opacity increase: at 2 MK, opacity increases as heavy ions (e.g., C, N, O, Ca, Fe) starts to hold electrons from fully ionized state. As a result, energy transfer through radiation is less efficient, and temperature gradient increasesConvection occurs: when the temperature gradient becomes sufficient large, and larger than that in the adiabatic condition; unstable as boiling water in a panOvershooting: the rising bubble overshoots at the top of the convection zone because of kinematic momentumTachocline: the Suns magnetic field is possibly generated in the thin interface, called Tachocline, between convection zone and radiative zone

Inside the Sun: Temperature Dist.

Inside the Sun: Density Dist.

Granual

Sunspot (ctnl.)A phenomenological description of something we see

Been noticed in ancient time

Since 1700, systematic record of sunspot number

Sunspot was found to be a magnetic feature in 1930

Sunspot is half the brightness. L ~ Te4 ,Or Te ~ L 1/4Tspot/Tsun=(Lspot/Lsun)1/4=(0.5)1/4 = 0.84Tsun = 5700 KTspot = 5700 * 0.84 = 4788 K

Sunspot is about 1000 K cooler than surrounding

Sunspot: balancing (ctnl.) Pext = Pint + Pmag

Pext: external thermal pressurePext = Next * K *TextN: particle densityK: Boltzmann;s constantT: temperature

Pint: internal thermal pressurePint= Nint * K * Tint

Pmag: magnetic pressure inside sunspotPmag = B2/8B: magnetic field strength in the sunspot

Pext > P int, because Text > T int, but B helps the balance

Sunspot: structure (ctnl.)Sunspots show two main structures:

Umbra: a central dark region,Penumbra: surrounding region of a less darker and filamentary zoneSOHO/MDI 2004/10/24

Mangetic Field of SunspotObserved by a magnetogram

Magnetic Field: Measurement (ctnl.) Zeeman effectThe splitting of a spectral line because the presence of magnetic field. The electrons moving along different magnetic direction may have different energy

Magnetic Field: Measurement (ctnl.) A magnetograph measures the wavelength shift of certain spectral lines; the shift is proportional to the wavelength as

= 4.7 x 10-13 g 2 H

: wavelengthg: Lande factorH: magnetic field strengthReference: Zirin (1966), P. 368