ABSTRACT
Solar magnetic fields and their motion from the smallest observable scales to the global scales play important roles in determining the level of short term transient activities in active regions, stability and eruption of prominences, to the long term solar activity cycles. Most of the energetic solar tran-sients derive their energy from the stored magnetic energy in active regions, and filaments. There-fore, the measurement of magnetic fields from photosphere to the upper layers of solar atmosphere is one of the most important tasks in solar physics. This chapter discusses the variety of Doppler and magnetic field diagnostic tools based on Doppler effect, the Zeeman and Hanle polarizations, instrumental and atmospheric effects leading to degradation of polarization measurements, and the observational techniques. Some aspects of more difficult measurements of chromospheric and cor-onal magnetic fields are discussed. Salient features of the 11-year activity and the 22-year magnetic cycles are described. The large scale solar magnetic fields and their interaction with solar differential rotation clearly drive the giant dynamo operating inside the Sun in the convective region. Solar dynamo models, methodologies for prediction of solar cycles, and solar irradiance variation with solar cycles are briefly discussed.
