Context : Narrow-band bursts appear on dynamic spectra from microwave to decametric frequencies as fine structures with very small duration and bandwidth .
They are believed to be manifestations of small scale energy release through magnetic reconnection .

Aims : We analyzed 27 metric type IV events with embedded narrow-band bursts , which was observed by the ARTEMIS–IV radio spectrograph from 30 June 1999 to 1 August 2010 .
We examined the morphological characteristics of isolated narrow-band structures ( mostly spikes ) and groups or chains of structures .

Methods : The events were recorded with the SAO high resolution ( 10 ms cadence ) receiver of ARTEMIS-IV in the 270–450 MHz range .
We measured the duration , spectral width , and frequency drift of \sim 12 000 individual narrow-band bursts , groups , and chains .
Spike sources were imaged with the Nançay radioheliograph ( NRH ) for the event of 21 April 2003 .

Results : The mean duration of individual bursts at fixed frequency was \sim 100 ms , while the instantaneous relative bandwidth was \sim 2 \% .
Some bursts had measurable frequency drift , either positive or negative .
Quite often spikes appeared in chains , which were closely spaced in time ( column chains ) or in frequency ( row chains ) .
Column chains had frequency drifts similar to type-IIId bursts , while most of the row chains exhibited negative frequently drifts with a rate close to that of fiber bursts .
From the analysis of NRH data , we found that spikes were superimposed on a larger , slowly varying , background component .
They were polarized in the same sense as the background source , with a slightly higher degree of polarization of \sim 65 % , and their size was about 60 % of their size in total intensity .

Conclusions : The duration and bandwidth distributions did not show any clear separation in groups .
Some chains tended to assume the form of zebra , lace stripes , fiber bursts , or bursts of the type-III family , suggesting that such bursts might be resolved in spikes when viewed with high resolution .
The NRH data indicate that the spikes are not fluctuations of the background , but represent additional emission such as what would be expected from small-scale reconnection .