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Electron cyclotron maser emission (ECME) is regarded as a plausible sourcefor the coherent radio radiations from solar active regions (e.g., solar radiospikes). In this Letter, we present a 2D3V fully kinetic electromagneticparticle-in-cell (PIC) simulation to investigate the wave excitations andsubsequent nonlinear processes induced by the energetic electrons in theloss-cone distribution. The ratio of the plasma frequency to the electrongyrofrequency ${\omega}_{pe}/{\Omega}_{ce}$ is set to 0.25, adequate for solaractive region conditions. As a main result, we obtain strong emissions at thesecond-harmonic X mode (X2). While the fundamental X mode (X1) and the Z modeare amplified directly via the electron cyclotron maser instability, the X2emissions can be produced by the nonlinear coalescence between two Z modes andbetween Z and X1 modes. This represents a novel generation mechanism for theharmonic emissions in plasmas with a low value of${\omega}_{pe}/{\Omega}_{ce}$, which may resolve the escaping difficulty ofexplaining solar radio emissions with the ECME mechanism.

Harmonic maser emissions from electrons with loss-cone distribution in solar active regions