Decameter solar spikes for coronal diagnostics

The study aims to give some clues on the relationship between solar activity, plasma dynamics, and the occurrence of spikes. A total of one thousand spikes, recorded with high temporal and spectral resolution by the NenuFAR radio instrument, were analyzed. These spikes occur concurrently to Type III storms or Type II. The strong circular polarization observed suggests that emissions are in the fundamental mode. Electron beam velocities deduced from spike time-frequency drifts are at least ten times lower than those driving Type III bursts. The spike’s duration shows a dependence with the type of solar activity and scales with frequency as approximately f^-0.73. The coronal temperature decreases with altitude, ranging from about 1 MK to 0.5 MK. Finally, fitting the distributions of duration and bandwidth with a Gamma function indicates that, in contrast to the striae of Type IIIb emissions, spikes are significantly more sensitive to stochastic plasma phenomena.