Current scientific models of the solar dynamo can be adjusted to reproduce the 11-year solar cycle. Longer periodicities may be predicted by the models, but at this stage the models are not sufficient to reproduce all of the changes observed in the solar cycle. The solar dynamo generates the magnetic field that causes the solar cycle (also called the 22-year solar cycle, the 11-year sunspot cycle, or the magnetic cycle).

Some important questions about the source of irradiance variations:

• What changes in the Sun cause irradiance variations?
• What measurements and models are required to determine and predict irradiance variations (e.g., magnetic field measurements, solar interior models)?
• How does the spectral irradiance vary from one wavelength to another? (We need this information because irradiance variations at different wavelengths can have different impacts at Earth).
• Can we understand the variations in irradiance on all relevant timescales, from the seconds of solar flares to centuries?

A longitudinal magnetogram from the MDI instrument on SoHO on October 30, 2001. White regions have an outward (Northern) polarity while black regions are an inward (Southern) polarity. The tilts are due to the differential rotation of the Sun.

All of these changes in solar irradiance are linked to changes in the solar magnetic field. Even the smallest magnetic features can have an observable connection to the irradiance output. The magnetic field is generated in the solar interior. Therefore, to fully understand the mechanisms which cause irradiance variations, we require:

• Measurements of irradiance over a broad range of wavelengths representing a wide range of energies (EVE)
• Images of the variation in radiance among the different magnetic features (AIA)
• An understanding of how magnetic fields are created and change (AIA & HMI)
• Measurements of the origin of the energy (HMI)