  Incoherent solar radio radiation comes from the free-free, gyroresonance, and
gyrosynchrotron emission mechanisms. Free-free is primarily produced from
Coulomb collisions between thermal electrons and ions. Gyroresonance and
gyrosynchrotron result from the acceleration of low-energy electrons and mildly
relativistic electrons, respectively, in the presence of a magnetic field. In
the non-flaring Sun, free-free is the dominant emission mechanism with the
exception of regions of strong magnetic fields which emit gyroresonance at
microwaves. Due to its ubiquitous presence, free-free emission can be used to
probe the non-flaring solar atmosphere above temperature minimum. Gyroresonance
opacity depends strongly on the magnetic field strength and orientation; hence
it provides a unique tool for the estimation of coronal magnetic fields.
Gyrosynchrotron is the primary emission mechanism in flares at frequencies
higher than 1-2 GHz and depends on the properties of both the magnetic field
and the accelerated electrons, as well as the properties of the ambient plasma.
In this paper we discuss in detail the above mechanisms and their diagnostic
potential.
