Magnetic field lines
Mass ejection from the sun often follow magnetic field loops.
Reversal of magnetic polarity
After 11 years, North/South order of leading/trailing sun spots is reversed
=> Total solar cycle = 22 years
After 11 years, the magnetic field pattern becomes so complex that the field structure is re-arranged.
→ New magnetic field structure is similar to the original one, but reversed!
→ New 11-year cycle starts with reversed magnetic-field orientation
The Solar Cycle (II)
Maunder Butterfly Diagram
Sun spot cycle starts out with spots at higher latitudes on the sun
Evolve to lower latitudes (towards the equator) throughout the cycle.
The sun spot number also fluctuates on much longer time scales:
Historical data indicate a very quiet phase of the sun, ~ 1650 Ė 1700: The Maunder Minimum
Looped Prominences: gas ejected from the sunís photosphere, flowing along magnetic loops
Extreme events, called coronal mass ejections (CMEs) and solar flares, can significantly influence Earthís magnetic field structure and cause northern lights (aurora borealis).
Sound waves produced by a solar flare
~ 5 minutes
Coronal mass ejections
Chromospheric structures visible in Ha emission
Region of sunís atmosphere just above the photosphere.
T: 4400 K → 25,000 K
n: 1011 cm-3 → 107 cm-3
Absorption and emission lines from singly ionized metals (He II, Fe II, Si II, Cr II, Ca II)
The Chromosphere (II)
Spicules = filaments of hot gas, visible in Ha emission.
Streams extend up to ~ 10,000 km above photosphere