PX282 - G3 - sunspots

image: NASA/BBSO

• note: sunspots are dark as they are relatively cooler that the surrounding, at a temperature of $3000-4500K$

• the cooler regions of enhanced magnetic field, revealed by zeeman splitting of absorption lines, supress convection and allow the spot to cool

image: NOAO

• note: the black line on the image on the left is the light passed to the spectrograph, shown on the right, which shows the zeeman splitting

• the global magnetic field is approximately a dipole with magnetic flux loops emerging with spots at active regions

• opposite polarity is seen at either side of the spots

• the polarity is reversed either side of the equator

image: NASA/SDO

• note: visible light image on the left, magnetogram determined from zeeman splitting on the right

image: carroll & ostile (2007)

• a large-scale dipole field is present with higher order flux loops associated with sunspot groups
• generated by magnetic dynamo, requires bulk shearing flow in a conducting medium (and speed magnetic field)
• connects the kinetic energy to the magnetic energy
• in the sun, shearing flows from differential rotation (equator rotates faster than the poles) at tachocline (the core rotates as a solid body) drives the solar dynamo

image: GONG/NSO