Recent results of zebra patterns in solar radio bursts

This review covers the most recent experimental results and theoretical research on zebra patterns (ZPs) in solar radio bursts. The basic attention is given to events with new peculiar elements of zebra patterns received over the last few years. All new properties are considered in light of both what was known earlier and new theoretical models. Large-scale ZPs consisting of small-scale fiber bursts could be explained by simultaneous inclusion of two mechanisms when whistler waves "highlight" the levels of double plasma resonance (DPR). A unique fine structure was observed in the event on 2006 December 13: spikes in absorption formed dark ZP stripes against the absorptive type III-like bursts. The spikes in absorption can appear in accordance with well known mechanisms of absorptive bursts. The additional injection of fast particles filled the loss-cone (breaking the loss-cone distribution), and the generation of the continuum was quenched at these moments. The maximum absorptive effect occurs at the DPR levels. The parameters of millisecond spikes are determined by small dimensions of the particle beams and local scale heights in the radio source. Thus, the DPR model helps to understand several aspects of unusual elements of ZPs. However, the simultaneous existence of several tens of the DPR levels in the corona is impossible for any realistic profile of the plasma density and magnetic field. Three new theories of ZPs are examined. The formation of eigenmodes of transparency and opacity during the propagation of radio waves through regular coronal inhomogeneities is the most natural and promising mechanism. Two other models (nonlinear periodic space – charge waves and scattering of fast protons on ion-sound harmonics) could happen in large radio bursts.